Geology Department Electronic Thesisweb.pdx.edu/~i1kc/geolinq/thesis/texts/155-Bednarz-2002.pdf · Toutle River Sediment Retention Structure ... Oahu, Hawaii ... Vicinity map showing

THESIS APPROVAL

The abstract and thesis of Susan L. Bednarz for the Master of Science in

Geology were presented May 29, 2002, and accepted by the thesis committee

and the department.

COMMITTEE APPROVALS: ____________________________________ Michael L. Cummings, Chair

____________________________________ Georg H. Grathoff

____________________________________ Scott F. Burns

____________________________________ Trevor D. Smith Representative of the Office of Graduate Studies

DEPARTMENTAL APPROVAL: ____________________________________ Michael L. Cummings, Chair Department of Geology

ABSTRACT

An abstract of the thesis of Susan L. Bednarz for the Master of Science in

Geology presented May 29, 2002.

Title: Influence of Halloysite on the Engineering Behavior of Basaltic Saprolites

in Northwestern Oregon and Southwestern Washington.

Saprolite is commonly developed on Tertiary basalt in northwestern

Oregon and southwestern Washington. Basalt saprolites are often sensitive, in

that they release water and lose shear strength when disturbed. Non-sensitive,

featureless residual soil mantles sensitive basalt saprolites.

Borehole samples of extrusive basalt and intrusive basalt (diabase)

saprolites from six study sites in northwestern Oregon were analyzed using X-

ray diffraction and scanning electron microscopy (SEM). Clay mineral zonation,

observed in borehole samples obtained on Mt. Scott in southeast Portland,

Oregon, show that 10Å halloysite is most abundant near the bedrock contact,

7Å halloysite is most abundant toward the middle to upper portions of the

saprolite, and kaolinite is most abundant in the residual soil. Zonation of

smectite is unclear. Interlayered halloysite/expandable clay is identified in

almost all saprolite samples analyzed but not in the overlying residual soil

samples.

Laboratory and field testing can be used to identify sensitive saprolites

prior to construction. Sensitive saprolites have high natural water contents

(generally >50%), low dry densities (5.7 to 6.4 kN/m3), Atterberg limits

and moisture/density relationships that vary with drying and remolding, and

release water when compressed.

Engineers have linked soil sensitivity in saprolites to the presence of

water-filled, hydrated (10Å) halloysite tubes that are crushed during

construction, adversely affecting stripping, placement, and compaction.

Although 7Å halloysite is found in all sensitive saprolites analyzed within the

study sites, 10Å halloysite is not ubiquitous to these soils. The water released

during compression of sensitive soils is stored in boxwork voids (identified by

SEM analysis) and not inside individual halloysite tubes. The loss of sensitivity

in surficial residual soil is due to the breakdown and collapse of the boxwork

voids within the saprolite due to pedogenic processes.

INFLUENCE OF HALLOYSITE ON THE ENGINEERING BEHAVIOR OF

BASALTIC SAPROLITES IN NORTHWESTERN OREGON AND

SOUTHWESTERN WASHINGTON

by

SUSAN L. BEDNARZ

A thesis submitted in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE in

GEOLOGY

Portland State University 2002

i

ACKNOWLEDGMENTS

Many thanks to the following individuals who provided information,

assistance, and advice towards the completion of this research: Michael

Cummings, Georg Grathoff, Scott Burns, and Sherry Cady, Portland State

University; Jim Maitland and Tim Pfeiffer of Foundation Engineering, Inc.; Derek

Cornforth, Charlie Hammond, and Brent Black of Cornforth Consulting; Jim

Griffith of the US Army Corps of Engineers; Reka Gabor, Portland, Oregon;

Reed Glasmann of Oregon State University; David Rogers of University of

Missouri, Rolla; Michael Williams of the Washington Department of

Transportation; Clackamas County Department of Transportation and

Development; Wayne Isphording, University of South Alabama. I would also

like to thank the Clay Minerals Society for providing a grant to fund this

research.

ii

TABLE OF CONTENTS

ACKNOWLEDGMENTS ........................................................................................ i

TABLE OF CONTENTS ........................................................................................ ii

LIST OF FIGURES ............................................................................................... vi

LIST OF TABLES ................................................................................................ vii

INTRODUCTION .................................................................................................. 1

BACKGROUND .................................................................................................... 3

GEOLOGIC SETTING .......................................................................................... 9

LOCAL ENGINEERING CASE HISTORIES ...................................................... 17

Mud Mountain Dam ....................................................................................... 17

Toutle River Sediment Retention Structure .................................................. 18

Trask River Dam Raise ................................................................................. 19

Hills Creek Dam ............................................................................................ 21

Spirit Lake Memorial Highway ...................................................................... 22

H3 Tunnel, Oahu, Hawaii .............................................................................. 23

STUDY SITES .................................................................................................... 24

Monterey Avenue Overcrossing, Southeast Portland, Oregon .................... 24

West Salem Site 1, Oregon .......................................................................... 25

West Salem Site 2, Oregon .......................................................................... 25

Carlton, Oregon............................................................................................. 26

Silverton, Oregon .......................................................................................... 26

South Salem, Oregon ................................................................................... 27

iii

METHODS .......................................................................................................... 28

Field Sampling Methods ............................................................................... 29

Field Soil Sensitivity Testing ......................................................................... 30

X-Ray Diffraction Analysis ............................................................................ 30

X-ray Diffraction Analysis of -2μm Material ............................................. 31

X-ray Diffraction Analysis of Bulk Samples ............................................. 33

Toluidine Blue Treatment .............................................................................. 33

Magnetism ..................................................................................................... 34

Scanning Electron Microscopy ..................................................................... 35

Engineering Index Testing ............................................................................ 36

RESULTS ........................................................................................................... 37

X-Ray Diffraction Analysis Overview ............................................................ 37

X-Ray Diffraction Sample Data Summary .................................................... 39

Monterey Overcrossing Borehole BH-3 .................................................. 39

Monterey Overcrossing Borehole BH-7 .................................................. 41

Monterey Overcrossing Borehole BH-10 ................................................ 43




West Salem Site 1 Borehole BH-1 .......................................................... 47

West Salem Site 2 Borehole BH-1 .......................................................... 48

Carlton Boreholes BH-1 and BH-2 .......................................................... 48

iv

Silverton Borehole BH-1 .......................................................................... 49

South Salem Borehole BH-2 ................................................................... 49

Magnetism Observations .............................................................................. 50

Field Sensitivity Testing Results ................................................................... 51

Testing for Amorphous Clay (Allophane and Imogolite) ............................... 52

Scanning Electron Microscopy (SEM) Results ............................................. 52

Engineering Index Testing Results ............................................................... 62

DISCUSSION ..................................................................................................... 64

Clay Mineralogy in Basaltic Saprolites and Residual Soil ............................ 64

Clay Zonation .......................................................................................... 64

Mixed-Layered Halloysite/Expandable Clay ........................................... 67

Desiccation of 10Å Halloysite .................................................................. 70

Development of Sensitivity in Basaltic Saprolites ......................................... 70

Occurrence of Sensitive Saprolites in Other Volcanic Rocks ....................... 74

Identification of Sensitive Volcanic Saprolites .............................................. 75

Field Index Testing .................................................................................. 75

Engineering Index Testing ....................................................................... 76

X-Ray Diffraction Analysis ....................................................................... 78

Mitigation of Sensitive Volcanic Saprolites ................................................... 78

CONCLUSIONS ................................................................................................. 80

FUTURE WORK ................................................................................................. 84

LITERATURE CITED ......................................................................................... 85

v

vi

APPENDICES

A Oregon and Washington Case Histories of construction in Sensitive Volcanic Saprolites…………………………………………………………94

B Engineering Test Procedures and Data…………………………………113

C Study Area Sample Descriptions………………………………………...119

D X-ray Diffraction Analysis…………………………………………………139

vii

LIST OF TABLES

TABLE PAGE

1. Volcanic Saprolites in Northwestern Oregon and Southwestern Washington ....................................................................................... 10

2. Overview of Laboratory Testing ......................................................... 29

3. Significant XRD Peaks for Study Area Clay Minerals ....................... 38

4. X-ray Diffraction Peak Parameters for Clay Minerals in Monterey Overcrossing Samples ....................................................................... 42

5. Monterey Overcrossing Borehole BH-10 XRD Mineralogy ............... 44

6. Magnetic Properties of Soil Samples ................................................. 51

7. Summary of Engineering Index Data ................................................. 63

viii

LIST OF FIGURES

FIGURE PAGE

1. Undisturbed sensitive volcanic breccia saprolite ....................................... 6

2. Disturbed sensitive volcanic breccia saprolite ........................................... 6

3. Basalt exposures in northwestern Oregon and southwestern Washington ....................................................................... 12

4. Ferruginous bauxite deposits in western Oregon and southwestern Washington .............................................................................................. 14

5. Basaltic saprolite developed from Columbia River Basalt bedrock ........ 15

6. Residual clastic texture in Boring Lava breccia saprolite ........................ 16

7. Vicinity map showing the location of study sites and engineering case history sites .............................................................................................. 20

8. Example of kaolinite-poor saprolite ......................................................... 40

9. Example of kaolinite-rich saprolite ........................................................... 40

10. Residual texture visible in volcanic breccia saprolite sample SH-43-6 prior to SEM analysis............................................................................... 55

11. SEM microphotograph of sample SH-43-6 at 10X magnification ........... 56

12. SEM microphotograph of sample SH-43-6 at 50X magnification .......... 57

13. SEM microphotograph of sample SH-43-6 at 390X magnification (Box B) ............................................................................. 58

14. SEM microphotograph of sample SH-43-6 at 390X magnification (Box A1) ........................................................................... 59



ix

LIST OF FIGURES (continued)

FIGURE PAGE 17. Air-dried XRD trace of crystalline, well-ordered low cristobalite ............. 69

18. XRD trace showing expansion of halloysite peaks with glycolation ........ 72

1

INTRODUCTION

Saprolites form where bedrock has been exposed to prolonged tropical

or wet temperate climates (Prudencio et al., 1990; Schwarz, 1997). Volcanic

saprolites are commonly used as foundation and embankment soils throughout

the world (Terzaghi, 1958; Sherard et al., 1963; Wesley, 1974; Hammond and

Vessely, 1998). Characteristics of volcanic saprolites affect their engineering

properties and suitability as foundation soils. Engineers have previously

identified clay mineralogy, specifically halloysite content, as a contributing factor

to adverse engineering properties (Mitchell, 1989; Cornforth Consulting Inc.,

1991; Hammond and Vessely, 1998).

Volcanic saprolites are common in the Pacific Northwest due to climate

conditions that have deeply weathered Tertiary-age basalt and andesite units.

Local engineering projects have experienced difficulties in sensitive volcanic

saprolites, which release water and lose shear strength when disturbed. These

difficulties have resulted in expensive “change of conditions” construction

claims. Although hydrated halloysite (in conjunction with smectite) has been

suspected as the cause of sensitivity in volcanic saprolites, no systematic study

has confirmed this relationship.

This study examines clay mineral zonation with depth in selected

northwestern Oregon basaltic saprolites, compares changes in clay mineralogy

with soil sensitivity, develops a mechanism by which soils become sensitive,

and addresses the correlation between halloysite and sensitive basalt and

2

andesite saprolites. Laboratory and filed testing methods are provided to

identify sensitive soils. Mitigation techniques are developed based on case

history information.

3

BACKGROUND

Saprolite is defined as “a residual regolith developed isovolumetrically on

crystalline rocks, in which some or all of the primary minerals have been

extensively transformed in situ to weathering products” (Velbel, 1990). Saprolite

is much weaker than weathered rock but maintains the original volume,

structure, and fabric of the parent rock (Pavich, 1996). During the formation of

saprolites in igneous rocks, individual minerals are dissolved (leached) and

weathering products (clay minerals and iron and aluminum oxides) are

reprecipitated in crystal fractures along cleavage planes and around the

perimeter of the mineral (Velbel, 1989). As weathering progresses, clay- and

oxide-bounded, porous “negative pseudomorphs” of the original minerals form

micro-boxwork structures in the saprolite (Velbel, 1989). These micro-boxworks

can trap isolated pockets of water within the saprolite.

Mineralogical studies have identified both hydrated (10Å) and

dehydrated (7Å) halloysite in volcanic saprolites (Glasmann and Simonson,

1985; Prudencio et al., 1990). 7Å halloysite (Al2Si2O5(OH)4) consists of a

combined octahedral and tetrahedral sheet (1:1) structure, while 10Å halloysite

(Al2Si2O5(OH)4⋅2H2O) contains a 2.9Å layer of water between the combined 1:1

sheets (Moore and Reynolds, 1997). The nature of the relationship between 7Å

and 10Å halloysite has not been determined. They may represent two separate

phases of the same mineral or two separate minerals (Moore and Reynolds,

1997).

4

Halloysite forms as an intermediate weathering product in volcanic

material (especially plagioclase) which later transforms to kaolinite with

continued weathering (Romero et al., 1992; Jeong, 1999). Repeated alternating

wet and dry cycles and a high water content of the soil in a warm humid climate

favors the formation of halloysite in the soil and cause laterization (Wang et al.,

1998). Detecting abundant halloysite in lateritic paleosols facilitates the

identification of paleoclimates (Wang et al., 1998).

Numerous halloysite morphologies have been identified including tubes

(Kirkman, 1981; Singh, 1996; Wang et al., 1998), plates (Mitchell, 1993),

crumpled sheets (Wada and Mizota, 1982), spheroids (Prudencio et al., 1990),

and ellipsoids (Jeong, 1999). Halloysite morphology is related to aluminum

oxide (Al2O3) and iron oxide (Fe2O3) content (Bailey, 1989). Long tubes indicate

high aluminum substitution in the tetrahedral sheet, while spheroids and plates

indicate high iron substitution in the octahedral sheet (Bailey, 1989). Tubular

halloysite, which is commonly found in basalt saprolites in Oregon (R.

Glasmann, personal communication, February 2001), may store free water

internally within the tube.

Studies of halloysite in basalt saprolites have been conducted in many

parts of the world, including Spain (Prudencio et al., 1990), Kenya (Terzaghi,

1958), Indonesia (Terzaghi, 1958), Philippines (Terzaghi, 1958), Australia

(Terzaghi, 1958; Eggleton et al., 1987) and Japan (Wada and Mizota, 1982).

Numerous articles and reports discuss halloysite in basalt and andesite

5

saprolites in western Oregon and southwestern Washington (Istok, 1981; Thrall,

1981; Glasmann, 1982; Gabor et al., 1987; Gabor and Cummings, 1988;

Mitchell, 1989; Hammond and Vessely, 1998). Additionally, studies have been

conducted on halloysite in soils derived from other types of igneous rocks,

predominantly silicic lava and ash deposits (Kirkman, 1981; Theng et al., 1982;

Wada and Mizota, 1982; Romero et al., 1992; Jeong and Kim, 1993; Wang et

al., 1998; Jeong, 1999). These studies can be divided into two groups that

show little or no overlap:

• The mineralogy, morphology, formation, and presence of halloysite based on laboratory studies and theoretical modeling conducted by mineralogists and soil scientists (e.g. Glasmann, 1982; Wada and Mizota, 1982).

• Geotechnical investigations and case histories that discuss construction problems related to sensitive soils where halloysite has been identified. These documents discuss the engineering properties and performance of project soils (e.g. Terzaghi, 1958; Hammond and Vessely, 1998).

Sensitivity is defined as the ratio of the peak undisturbed (in situ)

strength to the remolded strength as determined by unconfined compression

testing (Mitchell, 1993). A soil with a ration greater than 4:1 is considered

sensitive (McCarthy, 1998). Sensitive soils experience a significant loss of

shear strength and release water when disturbed or remolded. Figures 1 and 2

show an undisturbed and remolded sensitive volcanic breccia. Although

volcanic saprolites represent only one category of sensitive soils, they are

particularly problematic in northwest Oregon and southwest Washington as a

result of the abundance of deeply weathered volcanic material.

6

Figure 1. Undisturbed sensitive volcanic breccia saprolite. Note moist appearance prior to compression under hand pressure.

Figure 2. Disturbed sensitive volcanic breccia saprolite. Note wet appearance of Figure 1 sample following compression under hand pressure.

7

Geotechnical engineers label saprolites as “residual soil”; however, the

term “residual soil” is used in this thesis to identify the featureless, highly

weathered soil that overlies and is derived from the saprolite (Pavich, 1996).

The residual soil discussed below is located in the pedogenic A and B horizons

and has lost all original rock texture and a portion of its original volume due to

collapse of the saprolite structure (Pavich, 1996). Since engineers consider

saprolites soil, the term saprolite and soil are used interchangeably.

Dr. Karl Terzaghi, who is credited with establishing the profession of

geotechnical engineering, may have been the first to describe the properties

and problems associated with sensitive volcanic soils. In the 1950’s, during the

construction of the Sasumua Dam in Nairobi, Kenya, he observed and identified

the engineering properties of sensitive volcanic saprolites used for the dam core

(Terzaghi, 1958). Additionally, geotechnical engineers have since tested

sensitive volcanic saprolites during their site investigations for dams, roads, and

other engineering structures (U.S. Army Crops of Engineers Portland Engineer

District, 1966; Hammond and Vessely, 1998). The engineering properties of

these soils include low dry density, high natural water content, significant loss of

shear strength when disturbed, and Atterberg limits values which show a

reduction in the liquid limit and plasticity index between oven dried and air dried

samples (Deere and Thornburn, 1955; Terzaghi, 1958; Pope and Anderson,

1960; Thrall, 1981). Terzaghi (1958) explained these anomalous and

8

contradictory engineering properties by theorizing that the halloysite clay forms

spongy aggregates that clump together but break apart when compressed,

thereby losing strength and releasing water.

Other mechanisms have been postulated as a cause for sensitivity in

volcanic saprolites. Water stored in hydrated halloysite tubes may be released

if these tubes are compressed and broken during construction (Hammond and

Vessely, 1998). Velbel (1990) postulates that cavities form in saprolites during

isovolumetric weathering. These cavities are bounded by clay and iron oxides

that form a rigid "boxwork" around these water-filled cavities. When these

boxworks are compressed, the interstitial water is released. Lastly, blocked soil

pores have been identified in weathered volcanic ash deposits that contain

allophane, imogolite, and halloysite (Thrall, 1981). Water stored within and

released from these pores may produce soil sensitivity. Although several

theories to explain sensitivity in volcanic saprolites have been proposed, no

absolute mechanism has been established to explain sensitivity in basaltic and

andesitic flow rock and breccia.

9

GEOLOGIC SETTING

Significant portions of northwestern Oregon and southwestern

Washington are underlain by Tertiary and Quaternary mafic and intermediate

volcanic rocks that are weathered to saprolites. Basaltic, andesitic, and dacitic

units mapped in the study area include Boring Lavas, Sardine Formation,

Columbia River Basalt, Little Butte Volcanics, Goble Volcanics, Hatchet

Mountain Volcanics, Tillamook Volcanics, Siletz River Volcanics, and various

undivided Quaternary and Tertiary units in both Oregon and Washington.

These units range in age from early Eocene to Pleistocene. Table 1 identifies

the location and lithology of Quaternary and Tertiary volcanics and their

combined exposure is shown in Figure 3. These units included flows, breccias,

tuffs, associated volcaniclastic sediments, and scattered dikes and sills.

Volcanic deposits and intrusions have been grouped together for the purpose of

this study.

Tertiary and Quaternary volcanic saprolites are common in Western

Oregon and Southwestern Washington. Although volcanic units range in age

from Eocene to Pleistocene, a temperate climate with alternating wet and dry

cycles that was present during the late Miocene through early Pliocene (Wilson,

1997) deeply weathered these rocks. Weathering since the late Miocene has

formed ferruginous bauxites on Columbia River Basalt exposures in specific

areas (Corcoran and Libbey, 1956; Livingston, 1966; Hook, 1976; Cummings

and Fassio, 1990). Figure 4 shows the distribution of ferruginous bauxite within

10

Table 1. Volcanic Saprolites in Northwestern Oregon and Southwestern Washington

Formation Age Lithology Locations of Abundant Exposures Reference

Boring Lavas Pliocene to Pleistocene

Basalt and basaltic andesite flows and interflow breccia

Western Cascades, Multnomah and Clackamas Counties,

Oregon

(Trimble, 1963; Walker and MacLeod, 1991; Madin, 1994)

Various undivided volcanic units

Pliocene to Pleistocene

Basalt, andesite, and dacite flows, breccia, tuff, and volcaniclastic sediments

Southern Washington Cascade Range

(Hammond, 1980; Phillips, 1987b; Phillips, 1987a; Walsh et

al., 1987)

Sardine Formation Upper Miocene Andesite flows, tuff breccia, and lapilli tuff, and tuff

Western Cascade Range in northern Oregon

(Thayer, 1939; Peck et al., 1964)

Columbia River Basalt Group Miocene Basalt flows

Willamette Valley north of Albany, Columbia County, Clatsop County, Oregon,

southwest Washington (west of Interstate I-5)

(Hampton, 1972; Beeson and Moran, 1979; Korosec, 1987;

Phillips, 1987b; Phillips, 1987a; Walker and Duncan, 1989;

Walker and MacLeod, 1991; Yeats et al., 1996; Tolan and Beeson, 1999; Tolan et al.,

2000) Various undivided

volcanic units (including Hatchet

Mountain volcanics)

Upper Eocene to Miocene

Andesite and basaltic andesite flows, and

andesite and dacite breccia, and tuff

Southern Washington Cascade Range

(Hammond, 1980; Phillips, 1987b; Phillips, 1987a; Walsh et al., 1987; Cummings, In Press)

Little Butte Volcanics

Oligocene to lower Miocene

Basalt and andesite flows; and andesite, dacite, and

rhyolite tuff, lapilli tuff, domes, and flows of andesite, dacite, and

rhyolite

Western Cascade Range in northern Oregon

(Thayer, 1939; Peck et al., 1964; Hammond et al., 1982; Sherrod

and Smith, 1989)

11

Table 1. Volcanic Saprolites in Northwestern Oregon and Southwestern Washington (continued)

Formation Age Lithology Locations of Abundant Exposures Reference

Goble Volcanics Upper Eocene

to lower Oligocene

Basaltic andesite flows, flow breccia, and interbedded

tuff, sandstone, and siltstone

Columbia County, Oregon and Cowlitz County, Washington.

(Phillips, 1987b; Phillips, 1987a; Walsh et al., 1987) (Walker and

MacLeod, 1991)

Tillamook Volcanics Upper to middle Eocene

Subaerial basalt flows, pillow lava, and interbedded


Northern Oregon Coast Range (Wells et al., 1983; Walker and MacLeod, 1991; Wells et al.,

1994)

Siletz River Volcanics

Lower to Middle Eocene

Subaerial basalt flows, pillow lava, and interbedded


Oregon Coast Range (Bela, 1979; Wells et al., 1983; Walker and MacLeod, 1991;

Wells et al., 1994)

Tertiary Intrusives Eocene to Pliocene Basalt/Diabase/Gabbro

Scattered across northwestern Oregon and southwestern

Washington highlands.

(Schlicker and Deacon, 1967; Sherrod and Smith, 1989;

Walker and MacLeod, 1991; Yeats et al., 1996)

12

Figure 3. Basalt exposures in northwestern Oregon and southwestern Washington (Walsh et al., 1987; Walker and MacLeod, 1991).

SCALE: 1 cm = 15 km

13

the study area. Flows of Boring Lava extruded during the Pleistocene also

show significant weathering.

Within northwestern Oregon, saprolites are commonly very thick with a

very narrow interface between the saprolite and fresh bedrock. Boreholes

conducted at Mt. Scott in southeast Portland penetrated up to 11.3 m (37 feet)

of decomposed basalt flows and interflow breccia before encountering

competent bedrock. Figure 5 shows a saprolite that has developed on Grande

Ronde Basalt of the Columbia River Basalt Group in the south Salem Hills.

These saprolites have the consistency of soil, but preserve the original rock

structure. Figure 6 shows a sample of Boring Lava volcanic breccia from the

Monterey Overcrossing study area in southeast Portland in which the relict rock

structure is clearly visible.

14

Figure 4. Ferruginous bauxite deposits in western Oregon and southwestern Washington (after Livingston, 1966).

15

Figure 5. Basalt saprolite (red-brown) developed from Columbia River Basalt bedrock. Quarry is located on the east side of I-5, directly south of Willamette Vineyards (T.9 S., R. 3 W., SW ¼ of Section 2). Note sharp contact between saprolite (orange) and bedrock (gray).

16

Figure 6. Residual clastic texture visible in sample of Boring Lava breccia saprolite from Monterey Avenue Overcrossing project in southeast Portland. Pointer identifies outline of ash-sized clast surrounded by secondary orange clay. (Sample diameter is approximately 1.2 inches).

17

LOCAL ENGINEERING CASE HISTORIES

Numerous engineering projects in northwestern Oregon and

southwestern Washington have experienced construction difficulties in areas

underlain by sensitive volcanic saprolites. A sampling of these projects include

the following:

• Mud Mountain Dam, Pierce County, Washington; • Toutle River Sediment Retention Structure, Cowlitz County, Washington; • Trask River Dam Raise, Tillamook County, Oregon; • Hills Creek Dam, Lane County, Oregon; and • Spirit Lake Memorial Highway, Cowlitz and Skamania Counties,

Washington.

Additionally, a case history evaluating in situ soil strength in sensitive

saprolites during the design of the H3 Tunnel in Hawaii is included to further

characterize the engineering properties of this material. Appendix A contains a

detailed description of each of the study area projects (with references). Figure

7 shows the approximate location of each of these sites, with the exception of

Mud Mountain Dam which is to the north. Appendix B.1 includes a discussion

of engineering testing methods. The key aspects of each case history are

summarized below.

Mud Mountain Dam

Mud Mountain Dam, constructed in 1941, is one of the earliest cases of

construction problems related to excessively wet volcanic soils that were used

for the dam core. Earth embankment soils were kiln-dried and covered with a

gigantic, canvas tent to reduce the water content enough to reach compaction.

18

A small amount of colloidal clay was blamed for preventing soil drying or

drainage (Anonymous, 1941a; Anonymous, 1941b).

Toutle River Sediment Retention Structure

Change of conditions claims were filed by the contractor shortly after

construction began for the Toutle River Sediment Retention Structure (SRS).

Flow top breccia and Pleistocene-age debris flow saprolites, selected for the

impervious dam core, became excessively wet and lost shear strength when

disturbed. These soils appeared to be stable, silty to sandy gravels at optimum

water content in outcrop but quickly broke down to a wet, sticky mass that

caused heavy equipment to bog down in deep ruts. The contractor claimed that

the presence of halloysite and smectite in the saprolites was responsible for the

sensitivity of the embankment soils, although 10Å halloysite was not ubiquitous

to problematic soils (Gabor and Cummings, 1988; Cornforth Consulting Inc.,

1991). They contended that excess water was trapped in the “soil grains” by

halloysite, which released this water to the soil pores when disturbed. Gabor

and Cummings (1988) observed that halloysite was not present in all sensitive

soils and concluded that soil sensitivity was caused by microtextures within the

saprolite becoming crushed during handling and releasing water trapped within

micropores. Loss of shear strength due to rapid hydration of smectite was

dismissed due to the low permeability of smectite-rich soils.

19

Trask River Dam Raise

Based on knowledge of construction difficulties in sensitive soils experienced at

the Toutle River SRS, sensitive soils were anticipated in saprolites developed

on Eocene-age basalt at the Trask River Dam site. During the geotechnical

investigation for the dam raise, sensitive soils were encountered locally. Natural

water contents ranged from 68 to 89 percent in foundation areas, but

embankment fill materials were selected to reduce the in situ moisture content

to between 30 and 43 percent and avoid sensitive soils (Cornforth Consultants

Inc., 1995). Foundation soils consisted of high plasticity (elastic) silt (MH) with a

natural water content that usually exceeded the liquid limit. Atterberg limits

tests conducted on air-dried samples produced lower liquid limits and plasticity

indexes than samples that had never been dried, indicating that an irreversible

change had occurred during drying (Hammond and Vessely, 1998).

As with the Toutle River SRS, the presence of halloysite and

montmorillonite (smectite) was thought to cause problematic saprolite soils.

Halloysite was claimed to break down with handling and release water that was

absorbed by smectite, thereby changing the character of the soil from

apparently granular to cohesive. Significant 10Å halloysite was detected in the

two borrow area samples that were tested for clay content and one of these

samples contained significant smectite (Cornforth Consultants Inc., 1995).

Even though sensitive soils were anticipated and avoided where

possible, construction equipment still became bogged down in wet weather.

20

Figure 7. Vicinity map showing the location of study sites ( ) and engineering case history sites ( ). (Mud Mountain Dam is north of map area.

South Salem

West Salem 1 & 2

Monterey Overcrossing

Silverton

Carlton

Toutle River SRS

Trask River Dam

Hills Creek Dam

Spirit Lake Memorial Highway

Scale: 1 cm = 15 km

21

Thus, stripping and placing of impervious core materials was limited to the dry

summer months.

Hills Creek Dam

Hills Creek Dam, constructed in 1961 in south-central Oregon, was one

of the first Oregon dams to experience construction difficulties related to

sensitive soils (U.S. Army Corps of Engineers Portland Engineer District, 1959).

The impervious core of the dam was partially constructed of highly weathered

alluvial gravel that contained colloidal clay. Although this in situ material

appeared near optimum moisture content when excavated, it became wetter

after handling and developed ruts. The soil’s sensitivity was attributed to small

pockets of highly plastic colloidal clay mixing with lower plasticity fines during

handling and an increase in the plasticity of halloysite-bearing soils as hydrated

(10Å) halloysite altered to highly plastic intermediate halloysite during drying

(U.S. Army Crops of Engineers Portland Engineer District, 1966). Clay

analyses conducted by Ralph Grim for the U.S. Corps of Engineers (1966)

showed 10Å, 7Å, and intermediate forms of halloysite and lesser smectite. The

highly plastic intermediate halloysite was thought to be responsible for

compaction problems. As with the Trask River Dam, Atterberg limits tests

showed a progressive decrease in the plastic limit and the plasticity index with

air and oven drying.

To mitigate against the effects of sensitive embankment soils, aggregate

was added to improve drainage, roller weight was reduced, and lift thickness

22

was reduced to 0.2 m (8 inches) (U.S. Army Crops of Engineers Portland

Engineer District, 1966).

Spirit Lake Memorial Highway

During the construction of the Spirit Lake Memorial Highway in the

Western Cascades of Washington, the performance of embankments soils was

assessed using test fills and laboratory testing. The natural water content of

these soils was significantly above the optimum moisture content for standard

compaction (Golder Associates, 1987b). In-place density measurements in

hydrothermally altered tuff test fills showed an increase in dry density with two

tractor passes, followed by either no further increase or a significant decrease in

the dry density (and compaction) with additional passes. The in situ moisture

content of test fills decreased with two tractor passes and then increased as the

dry density decreased. Concurrently, deep rutting (0.5 m or 18 inches) occurred

on the third and fourth tractor pass. Dry densities measured within these test

fills were significantly less than the maximum dry densities established during

laboratory Proctor compaction tests. The hydrothermally altered tuff was

designated as waste due to its performance in test fills and high natural water

content. Deposits of Holocene and Quaternary volcanic ash produced similar

problems in test fills and were designated as waste.

The hydrothermally altered tuff was determined by the design engineers

to have similar properties to saprolites, including poor compaction

characteristics, high natural moisture content (commonly above the liquid limit),

23

low in situ densities (unit weight), anomalous Atterberg limits and Proctor test

values, and low remolded strength. These properties were attributed to the

presence of halloysite and the release of water held in the relict structure of the

soil during construction, although the clay mineralogy was not analyzed (Golder

Associates, 1988b).

H3 Tunnel, Oahu, Hawaii

The in situ soil strength in sensitive saprolites is not accurately

determined by laboratory strength testing methods. Dr. Glenn Boyce (personal

communication, October 2000) observed that laboratory testing of remolded

standard penetration test (SPT) samples of sensitive basalt saprolite for the H3

Highway Tunnel on Oahu, Hawaii, produced low strength values. Pile design

for approach piers was based on these low strength values. Over design and

waste occurred when piles could only be driven a few feet before refusal.

Similar anomalously low strength values were previously recorded during

laboratory testing of relatively undisturbed tube samples for the Wilson Tunnel 4

km (2.5 miles) southeast of the H3 Highway Tunnels (Boyce and Abramson,

1991a). Due to the recognition that the basalt saprolite had structure, in situ

testing was initiated for the design of the H3 Tunnels (Boyce and Abramson,

1991b). This testing included pressuremeter testing and plate load testing

(using a 460 mm diameter steel plate, attached to a load frame as per ASTM D-

4394-84) to determine accurate strength values for the design of the tunnel

(Boyce and Abramson, 1991a).

24

STUDY SITES

Although the study area included sites in both northwest Oregon and

southwest Washington (Figure 7), laboratory analysis was conducted on

samples collected by me (or under my supervision) during routine geotechnical

investigations in northwestern Oregon. Most borings extended into bedrock.

Study sites for this thesis were selected based on the presence of basalt

saprolites and the availability of samples. These sites include the following:

Monterey Avenue Overcrossing, Southeast Portland, Oregon

Over 50 borings were drilled for this project, which is located in southeast

Portland on the western slopes of Mount Scott, a Pleistocene-age volcano

composed of Boring Lavas (Schlicker and Finlayson, 1979). Lava flows from

Mount Scott yield a 1.26±0.39 Ma age based on K-Ar age dating (Conrey et al.,

1996). All but one boring was logged in the field by me. Borings were

conducted along both sides of I-205 between SE Sunnyside Road and SE

Johnson Creek Road. Figure C.4.1, Appendix C.4 shows the location of the

study area in T. 1 S., R. 2 E., Section 33, SW ¼. Deeply weathered Boring

Lava including interbedded basalt flows and breccias are commonly mantled by

Quaternary-age fine-grained Missoula flood deposits (Willamette Silt). In most

borings conducted at the site, featureless residual soil overlies the basalt

saprolite that ranges up to 18.9 m (62 feet) thick. Gravel to boulder corestones

developed from the Boring Lavas are common in the residual soil. Within the

saprolite, alternating layers of flow rock and interflow volcanic breccia were

25

identified based on their relic textures. Saprolites are thickest in areas

predominantly underlain by breccia due to higher initial permeability.

West Salem Site 1, Oregon

Six borings were drilled near the intersection of Doaks Ferry Road and

Orchard Heights Road in West Salem, Oregon, to provide geotechnical design

data for a new building. The site is located in T. 7 S., R. 3 W., Section 17, SE ¼

of the SW 1/4 and is shown in Figure C.4.2, Appendix C.4. The site is located

on the gently rolling Eola Hills, which are locally underlain by deeply weathered

middle Miocene Grande Ronde Basalt of the Columbia River Basalt Group

(Crenna and Yeats, 1994; Yeats et al., 1996). The depth to fresh basalt varies

from 2.4 to greater than 12.2 m (8 feet to 40 feet) across the site. The deep

borings encountered flow rock saprolite mantled by residual soil. No interflow

breccia zones were observed within the borehole samples. Saprolite excavated

in test pits resembled highly weathered rock, but low Standard Penetration

Testing (SPT) N-values of 7 to 19 blows per foot indicated medium stiff to very

stiff clayey silt soil.

West Salem Site 2, Oregon

One boring was drilled to a depth of 10.6 m (35 feet) for the design of a

water reservoir in West Salem, Oregon. The site is located approximately 1.21

km (0.75 miles) northwest of the West Salem building site described above and

is shown on Figure C.4.2, Appendix C.4. The site is underlain by deeply

weathered middle Miocene Grande Ronde Basalt (Crenna and Yeats, 1994;

26

Yeats et al., 1996). The boring encountered 1.5 m (5 feet) of featureless

residual soil and 7.2 m (23.5 feet) of saprolite above the basalt bedrock

Carlton, Oregon

Two borings were drilled for the design of a water reservoir on a hillside

directly west of Carlton, Oregon. The site is located in T. 3 S., R. 4 W., Section

19, SE 1/4 and is shown in Figure C.4.3, Appendix C.4. The hillside is underlain

by a deeply weathered Tertiary diabase intrusion, which cuts Eocene submarine

volcanic and sedimentary rocks (Schlicker and Deacon, 1967). The borings

encountered 2.7 m (9 feet) of residual soil over 6.2 m (20.5 feet) of saprolite

with core stones. Fresh diabase bedrock was encountered at a depth of 9.0 m

(29.5 feet) below the ground surface.

Silverton, Oregon

One boring was drilled for the design of a water reservoir on a hillside on

the east side of Silverton, Oregon. The site is located in T. 6 S., R.1 W.,

Section 35, SE ¼ of the NE ¼ and is shown in Figure C.4.4, Appendix C.4. The

hillside is underlain by deeply weathered flows of the middle Miocene

Frenchman Springs Member of the Wanapum Basalt of the Columbia River

Basalt Group (Tolan and Beeson, 1999). The boring encountered 2.1 m (7 feet)

of residual soil and at least 13.1 m (43 feet) of saprolite. The depth to bedrock

was not defined during drilling.

27

South Salem, Oregon

Four borings were drilled for the design of a road in the gently rolling

Salem Hills of south Salem, Oregon. The site is located along SW Robins Lane

in T. 8 S., R 3 W., Section 23, NW 1/4 and is shown in Figure C.4.5, Appendix

C.4. The site is underlain by deeply weathered, middle Miocene Grande Ronde

Basalt flows (Walker and Duncan, 1989). Borehole BH-2, which was sampled

for this study, penetrated 6.4 m (21 feet) of decomposed basalt without

encountering bedrock.

28

METHODS

Soil samples were collected from geotechnical borings drilled in SE

Portland (Monterey Overcrossing), West Salem (Sites 1 and 2), Silverton, and

Carlton, Oregon. Two different approaches to analysis were used on samples

from these sites. At Monterey Avenue Overcrossing and West Salem Site 1,

samples from three different borings were analyzed with XRD to observe

changes in clay mineralogy with depth, soil texture, and sensitivity. At West

Salem Site 2, Silverton, and Carlton, two samples from each site were analyzed

using XRD to compare variations in clay mineralogy. At South Salem, one

sample of sensitive soil was analyzed using XRD for clay content. All sites were

tested for magnetic minerals. One sample (Monterey Overcrossing SH-43-6)

was examined to evaluate the microscopic soil texture using a scanning

electron microscope (SEM). Secondary orange clay observed at Monterey

Overcrossing was evaluated for mineralogy and the presence of amorphous

clays (allophane and imogolite) using Toluidine Blue and XRD. Table 2

identifies the type of laboratory testing conducted for samples from each site.

Due to the sample size collected, soil sensitivity is defined in this thesis

based on the amount of water released when a soil sample is compressed

under strong finger pressure. Extremely sensitive samples release abundant

water, moderately sensitive samples release less water, and samples with

minor sensitivity release only enough water to be barely visible without

29

magnification. Samples with no sensitivity did not release water when

compressed.

Table 2. Overview of Laboratory Testing

Study Site Borehole Number

Number of Samples Tested

Type of Test and/or Preparation1

Monterey Avenue Overcrossing

BH-3 1 Bulk2, E3

BH-7 9 A, G, H, D, E, T4 (One bulk sample= A, G, H)

BH-10 7 A, E

(One bulk sample=A, G, H) (One sample=A, G, H, D)

BH-18 3 A, G, H, D, E BH-27 1 A BH-43 1 A, SEM5

West Salem, Oregon Site 1 BH-1 9 A, G, H, E

(One sample=A, G, H, D) West Salem, Oregon Site 2 BH-1 2 A, G, H, E

Carlton, Oregon BH-1 1 A, G, H, E BH-2 1 A, G, H, D, E

Silverton, Oregon BH-1 2 A, G, H, D, E South Salem,

Oregon BH-2 2 A, G, H, E

1 Tests performed on one or more samples. XRD treatments include the following: A=air dried, G=ethylene glycol, H=heat, D=DMSO. 2 Bulk analyses consisted of air-dried random powder mounts of a representative portion of the entire sample. All other XRD samples consist of clay sized (-2μ) material. 3 E = Engineering index tests 4 T=Toluidine Blue 5 SEM = scanning electron microscope Field Sampling Methods

During drilling, disturbed 381 mm (1.5 inch) diameter samples were

obtained at 0.76 to 1.52 m (2.5 to 5 ft) intervals in conjunction with Standard

Penetration Testing (SPT). Several relatively undisturbed, 700 mm (2.75-inch)

diameter samples were also obtained in the Monterey Overcrossing borings.

Although bentonite drilling mud was used during drilling, care was taken to

30

remove the mud, if present, from the samples prior to storage. Samples were

stored in airtight plastic bags and were kept moist or wet prior to analysis,

except where noted.

Field Soil Sensitivity Testing

Each soil sample was field tested for sensitivity either during drilling or

within a week following drilling. Samples were stored in sealed plastic bags to

maintain the natural moisture content of the soil. An indication of sensitivity was

determined based on the soil’s ability to release water when compressed under

strong finger pressure. Non-sensitive soils did not appear to change in moisture

content or “wetness” under compression, while sensitive soils became visibly

wet, released water, and left a film on the skin surface (Figures 1 and 2).

X-Ray Diffraction Analysis

X-ray diffraction (XRD) analyses were conducted on soil samples to

evaluate the variation in clay mineralogy between sensitive and non-sensitive

soils. Clay zonation with depth was studied within two borings at the Monterey

Avenue site and one boring within the West Salem site. Two or three samples

were selected at the other four sites to evaluate variations in clay mineralogy

between sensitive (saprolite) and non-sensitive (residual soil) samples. Clay

zonation analyses were conducted on both less than 2 micrometer (-2μm)

material and the entire sample (bulk analysis). Sample treatments used during

XRD analysis of -2μm material included ethylene glycol, heating to 250° for two

hours, dimethyl sulfoxide (DMSO), and toluidine blue dye. Sample treatments

31

were required to more accurately identify the various clay minerals present in

the soils. Table 2 includes a summary of XRD analyses at each site. Table D-1

(Appendix D) provides a detailed listing of XRD analyses and sample

treatments applied to each sample. XRD traces for each sample are included in

Appendix D.3 through D.14.

X-ray Diffraction Analysis of -2μm Material

The soil samples were soaked in a solution of deionized water for

between five minutes and 24 hours (as necessary to suspend the sample) and

rinsed through a #230 sieve. The resultant minus #230 suspension initially

flocculated in many of the samples and had to be dispersed by adding 10 to 30

grains of sodium hexametaphosphate. After settling 45 minutes, the -2μm

fraction in the upper 1 cm of fluid was siphoned off, vacuumed through a

Millipore® filter, and applied as a transfer to a glass slide. This preparation

limited analysis to clay-sized particles and enhanced preferred orientation of

individual clay crystallites. Samples were then analyzed between 3° and 35° 2θ

using Copper K-α X-radiation and a 20 mm incident beam mask. An

acceleration of 40 kV and a current of 30 milliamps were used to generate X-

radiation. All air-dried samples were analyzed once without treatment. The

following treatments were used on selected samples and are discussed below.

Air Dried Preparation

Samples were prepared as discussed above and were analyzed

immediately after application to the glass slide to minimize dehydration. Sample

32

slides were visibly moist when placed in the sample holder of the X-ray

diffractometer.

Ethylene Glycol Treatment

Sample slides were placed in a covered glass jar containing ethylene

glycol for seven days prior to XRD analysis to allow time for absorption and

intercalation (Moore and Reynolds, 1997). Ethylene glycol treatment facilitates

the identification of smectite by inducing a shift in the 001 reflection from 15Å to

17Å. Peaks between 14.5 Å and 15 Å that shift to 17 Å with glycolation are

identified as smectite.

Heat Treatment

Sample slides were heated in a 250° C oven for two hours and then

cooled in a desiccator prior to XRD analysis. Heat treatment causes the

collapse of hydrated clays such as smectite and 10Å halloysite (Moore and

Reynolds, 1997).

DMSO Treatment

Sample slides were lightly sprayed with DMSO and placed in a sealed

container for 2 days prior to XRD analysis. Treatment with DMSO causes

halloysite peaks between 7.4 Å and 10.0 Å (001 reflections) and 3.6 Å (002

reflection) to shift to 11.3Å and 3.7Å, respectively (Jackson and Abdel-Kader,

1978; Gabor, 1981). Kaolinite peaks are not affected by DMSO treatment

(Gabor, 1981).

33

Kaolinite and 7Å halloysite are difficult to identify and separate based

solely on peak position. Within this paper, 7Å halloysite and kaolinite are

distinguished by the location of the 001 peak (7.15Å vs. 7.2 to 7.4Å) and based

on the magnitude of 7Å peak shift measured after DMSO treatment and

intercalation. Although intercalation of DMSO into the kaolinite structure has

been reported (Franco and Ruiz Cruz, 2002), analyses conducted for this

investigation suggest that kaolinite shows only minimal intercalation in basalt

saprolites over a time period of 48 hours. Jackson and Abdel-Kader (1978)

suggest the degree of kaolinite intercalation with DMSO is significantly reduced

with a decrease in crystal size and iron content.

X-ray Diffraction Analysis of Bulk Samples

Bulk XRD analyses of the entire sample were conducted on two samples

(one non-sensitive and one sensitive) from Monterey Avenue Borehole BH-7

and BH-10. Bulk samples were air dried and ground with a morter and pestal

to <#230 mesh and back-loaded into an aluminum sample holder to minimize

orientation. Samples were scanned from 3 to 65° 2θ at a speed of 1°/min

during bulk analysis of a randomly oriented powdered sample.

Toluidine Blue Treatment

The toluidine blue spot test was developed by Wada and Kakuto (1985)

to identify amorphous clays such as allophane and imogolite in soils. The

authors contend that toluidine blue, (CH3)2N+C6H3NSC6H2(CH3)NH2, changes

color from blue to purplish red (metachromasis) in the presence of negatively

34

charged colloids found in soils derived from granite, andesite, and sedimentary

rocks. During their testing, volcanic soils containing allophane and imogolite

remain blue when tested and do not show metachromasis.

Both a sensitive and a non-sensitive soil were tested. Additionally, one

sample of orange clay from the Monterey Avenue Overcrossing site was tested

for allophane and imogolite. The presence of amorphous clay was suspected in

this secondary clay as it appears to have been deposited by groundwater in the

voids between clasts in interflow breccias. The clay is very plastic and is

susceptible to severe cracking during desiccation.

Using the procedure outlined in Wada and Kakuto (1985), 0.4 g of a

0.02% solution of Toluidine blue was mixed with 0.04 g of the three soil samples

and one clay sample. A control sample of decayed wood replaced by abundant

allophane remained blue when tested with the above solution (G. H. Grathoff,

personal communication, March 2001).

Magnetism

During sample preparation for XRD analysis, the remaining >#230 mesh

material from 14 samples was tested for magnetism. Testing was conducted by

adding the coarser soil fraction to a beaker full of water and then stirring the

soil-water mixture with a pencil magnet. The relative abundance of magnetic

grains adhering to the magnet was observed to identify soils with magnetic

minerals and evaluate the presence of magnetic material with soil texture type.

35

Magnetic mineralogy was investigated by conducting a bulk random powder

XRD analysis of a Monterey Avenue Overcrossing sample (Sample SS-10-10).

Scanning Electron Microscopy

Scanning electron microscopy (SEM) was conducted on a relatively

undistrubed sample of a sensitive decomposed volcanic breccia (SH-43-6)

obtained from Monterey Avenue Overcrossing Borehole BH-43. The analysis

was conducted to determine the microscopic fabric of the rock and look for

boxwork structures.

In preparation for SEM analysis, the sample was broken into small clods

and air dried until apparently completely desiccated. Each desiccated clod was

broken in half to expose a fresh surface and several were selected that typified

the decomposed breccia clasts. Samples were mounted using a five-minute

epoxy and the sides of the samples were painted with colloidal graphite to

facilitate electrical grounding as per Portland State University SEM laboratory

procedure. The mounted samples were placed in a vacuum and sputter-coated

with gold-palladium. The sample was analyzed using a JEOL Model JSM-35C

scanning electron microscope operated at 15kV accelerating voltage with a

working distance of 39 mm.

A series of SEM photographs of the sample were taken at magnifications

of 10X, 50X, 390X, and 2000X. Scale bars are shown on the lower right corner

of each photograph (Figures 11 through 16). A photograph of the sample prior

to desiccation is included to show megascopic saprolite structure.

36

Engineering Index Testing

Index tests, including natural water content, Atterberg limits, bulk density,

and grain size analyses, were conducted on borehole samples for foundation

design at each of the study areas. A description of each of the index tests is

included in Appendix B.1. Index tests conducted during the geotechnical

investigation for a project are extremely useful in identifying problematic

sensitive soils before construction begins. Engineering index test data for the

borehole samples analyzed in this research are provided in Table B.2.1.

Engineering index properties for samples analyzed in this investigation are

summarized in Appendix B.2. Table E.2 includes engineering index testing data

for Monterey Avenue Overcrossing samples that are similar to those analyzed

in this research.

37

RESULTS

X-Ray Diffraction Analysis Overview

Clay minerals identified by XRD analysis include 7Å and 10Å halloysite,

kaolinite, smectite, and potentially mixed-layered 7Å halloysite/expandable and

10Å halloysite/expandable. The expandable clay may be smectite or a similar

mineral. Non-clay minerals identified in both random bulk analyses and

oriented -2μm material analyses included goethite, quartz, low cristobalite,

feldspar, maghemite, chlorite, and mica. Although gibbsite commonly is present

in bauxites, none was clearly identified in the bulk or -2μm samples. X-ray

diffraction traces for all samples are included in Appendix D.3 to D.14. A

summary table (Table D.1.1) showing samples analyzed and sample treatments

is included in Appendix D.1. Diagnostic peaks for clay minerals with and

without sample treatment are listed in Table 3.

Based on analyses conducted on study area samples, DMSO appeared

to intercalate within the 7Å and the 10Å halloysite structures and caused the

001 peak for both types of halloysite to expand to 11.2Å. Kaolinite, however,

did not appear to expand with DMSO. Figure 8 shows the almost complete shift

of the broad 7.5Å peak between 7.2Å and 9Å and the 10Å peak to 11.2Å. This

saprolite sample was located at a depth of 25 to 26.5 feet. Figure 9 shows a

partial expansion of the 7Å peak to 11.2Å (halloysite), with the remaining 001

peak showing a d-spacing of 7.14Å (kaolinite). This residual soil sample was

38

Table 3. Significant XRD Peaks for Study Area Clay Minerals

Clay Mineral Location of Diagnostic Peak With Treatment1

Air Dried Ethylene Glycol 250° Heat DMSO

7Å Halloysite 7.2Å – 7.4Å2 7.2Å – 7.4Å2 7.2Å – 7.4Å2 11.2Å3

10Å Halloysite 10Å2 10Å2 7.2Å2 11.2Å3

Kaolinite 7.15Å2 7.15Å2 7.15Å2 7.15Å3,4

Smectite 14Å – 15Å2 17Å2 9.4Å2 18Å – 19Å4

Interlayered 10Å halloysite/expandable 10Å4 10.3Å - 11Å4 7.2Å4 11.2Å4

Interlayered 7Å halloysite/expandable 7.3Å – 9Å4 10.3Å - 11Å4 7.2Å4 11.2Å4

1 Sample treatments described in Methods section 2 Peak locations identified in Chen (1977) 3 Peak locations identified in Gabor (1981) 4 Peak locations identified in this paper

shallow (10 to 11.5 feet deep) and showed more weathering as indicated by a

lack of relic rock texture. A higher percentage of kaolinite is expected in this

sample (Delvaux et al., 1990; Romero et al., 1992) and the resultant significant

7.14Å peak supports the conclusion that DMSO does not intercalate with

kaolinite in basalt saprolite soils over a period of 48 hours at room temperature.

Kaolinite-rich samples were characterized by intense and symmetrical

d001 peaks that were located between 7.2 and 7.3Å. Heat treatment had no

effect on the location and intensity of the 7Å kaolinite peak. 7Å halloysite-rich

samples were characterized by broad, asymmetrical peaks that gradually

decreased toward the lower diffraction angles. Maximum peak height for 7Å

halloysite was generally located between 7.3 and 8.0Å, with the 001 peak d-

39

spacing increasing with depth. Heat treatment caused the collapse of the 7.3 to

8.0Å halloysite peak to between 7.22 to 7.3Å.

X-Ray Diffraction Sample Data Summary

The following interpretations summarize the XRD analyses conducted on

borehole samples at each of the study sites. All Monterey Overcrossing borings

penetrated Boring Lavas saprolites. Geologic units penetrated at other study

areas are identified below and are listed in Table 1.

Monterey Overcrossing Borehole BH-3

Orange, secondary clay collected from infilled primary void spaces in a

breccia sample was analyzed from sample SS-3-9 to identify clay mineralogy

and degree of crystallinity. Due to the highly plastic, “slimy” nature of this clay

the presence of allophane, imogolite, or significant smectite was suspected.

Additionally, poorly-crystalline minerals that produce broad, poorly-defined XRD

peaks were anticipated. A random orientation bulk sample that was analyzed

from 3° to 65° 2θ contained well-crystalline 7Å halloysite, with only a trace

amount of 10Å halloysite and hematite (using the 2.69Å peak). The random

orientation of the sample appeared to intensify the 020 peak above the 001

peak. The 001 7Å halloysite peak in oriented samples generally showed the

highest intensity in all samples analyzed for this research. The XRD trace for

this sample is located in Appendix D.3.

40

41


A detailed study of clay zonation with depth was conducted using nine

samples collected in Borehole BH-7 between depths of 2.1 m (7 ft) and 13.7 m

(45 ft). Each sample was analyzed using XRD with the following treatments:

air-dried, ethylene glycol, heat, and DMSO. The XRD traces are included in

Appendix D.4.

Borehole BH-7 penetrated 4.3 m (14 ft) of silt and clayey silt residual soil,

over volcanic breccia saprolite (silt) to a depth of 6.1 m (20 ft). Flow rock

saprolite (silty sand to sandy silt) was encountered to 9.6 m (31.5 ft) followed by

breccia (sandy silt with clay) to 13.7 m (45 feet). Fresh basalt was encountered

below 13.4 m. The borehole log for Borehole BH-7 is included in Appendix C.3.

Peak parameters were calculated for clay minerals in each of the

samples analyzed. Appendix D.2 includes a discussion of peak parameter

calculation from XRD traces. Tables D.2.1 through D.2.4 (Appendix D.2) list the

peak parameters for 7Å halloysite, 10Å halloysite, kaolinite, and smectite. A

summary of the net area of the diagnostic peak for each of the clay minerals is

shown in Table 4 below. Net area is proportional to the abundance of a clay

mineral in the soil (Moore and Reynolds, 1997).

42

Table 4. X-ray Diffraction Peak Parameters for Clay Minerals in Monterey Overcrossing Samples

Sample Depth (m) Corrected Net Area of Diagnostic Peak (°counts/sec)1 Original

Rock Morphology

Soil Texture Sensitivity 7Å Halloysite

10Å Halloysite Kaolinite Smectite

SS-7-2 2.1 – 2.6 60 0 315 810 Unknown Residual soil None

SS-7-3 3.0 – 3.5 522 229 424 230 Unknown Residual soil None

SS-7-4 4.6 – 5.0 520 41 186 101 Flow rock Saprolite Minor

SS-7-6 6.7 – 7.2 131 113 33 19 Flow rock Saprolite Moderate



SS-7-9 10.7 – 11.1 463 205 22 57 Interflow breccia Saprolite Moderate


SS-7-12 13.7 122 1965 18 25 Flow rock Weathered rock None

SS-18-6 4.6 – 5.0 958 0 145 41 Flow rock Saprolite None


SS-18-9 9.1 – 9.6 553 316 59 30 Flow rock Saprolite None

1 Discussed in Appendix D.2.

43

The following trends in clay mineralogy were identified based on XRD analysis:

• 10Å halloysite generally increases with depth and this increase is not related to original basalt morphology.

• 7Å halloysite increases with depth, and then decreases below 7.6 m (25 ft).

• The 001 peak for 7Å halloysite generally becomes broader, less distinct, and more asymmetrical toward the lower diffraction angles with depth.

• Kaolinite decreases with depth and is significantly more abundant in residual soil.

• Smectite decreases with depth. • Trace amounts of illite and or quartz occur in residual soil samples (SS-

7-2 and SS-7-3) and are scattered within the saprolite samples (SS-7-4 and SS-7-11).

Both 7Å and 10Å halloysite in Borehole BH-7 samples expanded to

11.3Å with glycolation indicating the presence of interlayered

halloysite/expandable clay. Heat treatment caused all halloysite to collapse to

7.2 to 7.2Å. Both the intensity of the peak and the degree of

ordering/crystallinity of the 7Å peak increased with heat treatment.


Seven air-dried samples were analyzed from Borehole BH-10 to

corroborate trends in clay mineral zonation identified in Borehole BH-7. Sample

SS-7-10 was evaluated for kaolinite using DMSO. A bulk, randomly oriented

sample of SS-10-10 was analyzed for total mineralogy, and an oriented sample

of –2μm material was prepared for each of the sample treatments listed in Table

D.1.1. Table 5 summarizes the clay mineralogy for each random and oriented

44

sample based predominantly on air-dried analyses and comparison with

analyses conducted on other Monterey Overcrossing samples.

Table 5. Monterey Overcrossing Borehole BH-10 XRD Mineralogy

Sample Depth (m)

7Å Halloysite1

10Å Halloysite Kaolinite1 Smectite Other

Minerals

SS-10-4 4.9 – 5.3 Some2 Trace2 Some Abundant2 Not detectable

SS-10-5 6.1 – 6.6 Some Trace Some Trace Trace goethite

SS-10-7 8.2 – 8.7 Abundant Some Trace Trace Trace goethite

SS-10-8 9.1 – 9.6 Abundant Trace Trace Some Trace goethite

SS-10-9 10.7 – 11.1 Abundant Trace Trace Trace Not detectable

SS-10-10 12.2 – 12.6 Trace Abundant3 None Trace

Abundant maghemite,

some hematite

SS-10-11 13.7 Some Trace None Some Trace feldspar

1 The amount of 7Å halloysite vs. kaolinite is only confirmed using DMSO in Sample SS-10-7. All intermediate halloysite between 7Å and 9Å is identified as 7Å halloysite. 2 Abundance of clay mineral based on XRD peak area. 3 10Å halloysite peak in Sample SS-10-10 is located at 10.88Å

Borehole BH-10 penetrated 4.6 m (15 ft) of Willamette Silt over volcanic

breccia saprolite (stiff silt with some clay) to a depth of 12.2 m (40 ft). Flow rock

saprolite was encountered to 12.8 m (42 ft) followed by fresh basalt flow rock.

The borehole log for Borehole BH-10 is included in Appendix C.3. Unlike

Borehole BH-7, BH-10 may only penetrate two feet of residual soil (not sampled

and not recorded in the borehole log). Thus, all samples show sensitivity,

ranging from minor (SS-10-4) to extreme (SS-10-10).

Borehole BH-10 confirms many of the trends identified in Borehole BH-7.

These trends include:

45

• 10Å halloysite generally increases with depth and this increase is not related to original rock morphology. Sample SS-10-11 shows only trace 10Å halloysite, but this sample consists of the weathering rind on jointed basalt bedrock and did not contain abundant clay-size material.

• 7Å halloysite increases with depth and then decreases below 10.7 m (35 ft) with the exception of Sample SS-10-11.

• The 001 peak for 7Å halloysite generally becomes broader, less distinct, and more asymmetrical toward the lower diffraction angles with depth.

• Only trace kaolinite is found in Sample SS-10-7 at 8.2 to 8.7 m (27 to 28.5 feet).

• Smectite decreases with depth but is more abundant at the bottom of the boring within the weathering rind of the jointed basalt bedrock.

Similar to Borehole BH-7, the nature of the 7Å halloysite 001 peak

changes with depth, becoming broader toward the lower diffraction angles, less

intense, and less distinct. This broadening indicates a decrease in the degree

of crystallinity and an increase in the amount of halloysite intermediate between

7Å and 9Å.


Samples from Borehole BH-18 were selected to evaluate clay

mineralogy variation between sensitive and non-sensitive saprolites within a

single borehole. Three sequential samples collected at depths ranging from 4.6

to 9.6 m (15 to 31.5 ft) were analyzed. The upper and lower samples are non-

sensitive decomposed flow rock, while the center sample at 7.6 m (25 ft)

consists of moderately sensitive decomposed volcanic breccia. The peak

parameters calculated for Borehole BH-18 samples (SS-18-6, SS-18-8, and SS-

18-9) are listed in Table 4.

46

Based on XRD analyses, clay mineralogy does not appear to vary

significantly between sensitive and non-sensitive saprolites. Trends in clay

variation observed in Borehole BH-7 that are replicated in these three samples

include:

• Kaolinite content decreases with depth. • 10Å halloysite increases with depth. • 7Å halloysite is most abundant in the middle sample and becomes less

abundant and poorly crystalline in the deepest sample.

Smectite is more common in the central, sensitive sample. Both

Boreholes BH-7 and BH-18 do not show any clear association between

sensitivity and smectite content.

Interlayering of an expandable clay with both 7Å and 10Å halloysite is

present in all three samples. Both the 10Å peak and the broad, asymmetrical

peak between 7Å and 9Å shift to 10.6 to 10.7Å with glycolation (Figure 18).


Similar to sample SS-3-9 discussed above, the orange, secondary clay

from saprolite sample SS-27-7 was evaluated using XRD for mineralogy and

degree of crystallinity. The air-dried, oriented sample of less than 2 micrometer

sized (-2μm) material contained predominantly 7Å halloysite, with lesser

amounts of smectite and 10Å halloysite, and a trace amount of hematite, illite,

and quartz. Each mineral, with the exception of hematite, showed distinct

peaks indicating an ordered, crystalline structure. The XRD trace for this

sample is located in Appendix D.7.

47


Sample SH-43-6 was photographed using SEM to evaluate the

microtexture of this extremely sensitive volcanic breccia saprolite. An air-dried,

oriented sample of –2μm material was analyzed by XRD to determine the clay

mineralogy present in the photomicrographs of the sample. The majority of the

sample consisted of 10Å halloysite, with lesser amounts of poorly crystalline 7Å

halloysite, and only a trace amount of smectite. The XRD trace for this sample

is located in Appendix D.7.

West Salem Site 1 Borehole BH-1

Clay zonation in Borehole BH-1 was analyzed in ten samples using XRD

and the following samples treatments: air-dried, ethylene glycol, and heat.

Sample SS-1-4 was analyzed after treatment with DMSO to determine the

amount of kaolinite in the saprolite. The XRD traces for these samples are

included in Appendix D.9.

Borehole BH-1 penetrated 1.4 m (4.5 ft) of clay residual soil over flow

rock saprolite consisting of silt with some (15 to 30%) clay and trace to some

sand to the bottom of the boring 12.6 m (41.5 ft). The entire borehole appeared

to remain within a single Grande Ronde Basalt flow.

7Å halloysite, kaolinite, and minor smectite was detected in all samples.

No 10Å halloysite was observed within the borehole. The -2μm fraction of the

soil was not as well crystalline as the Monterey Overcrossing samples. Peaks

were generally low and poorly defined. Similar to the Monterey Overcrossing

48

samples, the 7Å halloysite peak shifted to between 10.9Å and 11.1Å with

glycolation indicating the presence of interlayered expandable clay.

In addition to clay minerals, significant low cristobalite and trace goethite

were detected in XRD traces. The well-crystalline low cristobalite was most

abundant between 4.6 m to 7.6 m (15 to 25 feet) and was characterized by

sharp, distinct peaks.

West Salem Site 2 Borehole BH-1

Two samples were analyzed from Borehole BH-1 at West Salem Site 2

to evaluate the variation in clay mineralogy between non-sensitive residual soil

(SS-1-1) and sensitive saprolite (SS-1-6). 7Å halloysite/kaolinite, smectite, and

trace low cristobalite, goethite, and 10Å halloysite were observed in both

samples. The residual soil sample showed well-crystalline 7Å

halloysite/kaolinite and some smectite. The sharpness, symmetry, and d-

spacing of the residual soil 7Å peak indicates that significant kaolinite is present.

The sensitive saprolite sample contained abundant smectite and some 7Å

halloysite/kaolinite. Portions of the broad 7Å peak shift to 10.7Å with glycolation

indicating interlayering with expandable clay. XRD traces for Borehole BH-1 are


Carlton Boreholes BH-1 and BH-2

Unlike the sample areas above, the Carlton sample area is underlain by

a diabase intrusion. Although clay mineralogy is very similar to that observed in

the Monterey Overcrossing samples, smectite is more abundant and only trace

49

10Å halloysite is present. Smectite is present in all three samples analyzed, but

is most abundant in sensitive saprolite Sample SS-2-6 at 4.6 to 5.0 m (15 to

16.5 ft). Abundant kaolinite and trace quartz and mica were observed in the

residual soil sample (SS-2-2). Only sensitive saprolite Sample SS-1-8 showed

evidence of interlayered 7Å halloysite/expandable clay. XRD traces for

Boreholes BH-1 and BH-2 are included in Appendix D.11 and D.12,

respectively.

Silverton Borehole BH-1

Borehole BH-1 penetrated Columbia River Basalt Group flow rock

saprolite but a different unit (Frenchman Springs Member of the Wanapum

Basalt) than was encountered at West Salem Sites 1 and 2 and South Salem.

Two samples were analyzed for variation in clay content with soil type and

sensitivity. The non-sensitive residual soil sample (SS-1-2) showed abundant

kaolinite, with some 7Å halloysite and trace amounts of smectite, cristobalite,

quartz, and goethite. The sensitive saprolite sample (SS-1-4) showed 7Å

halloysite and trace amounts of smectite and goethite. Portions of the broad,

asymmetrical 7Å peak in the saprolite sample expanded to 11Å after glycolation

which indicated the presence of interlayered halloysite/expandable clay. XRD

traces for Borehole BH-1 are included in Appendix D.13.

South Salem Borehole BH-2

Borehole BH-2 penetrated Grande Ronde Basalt saprolite. One

moderately sensitive saprolite sample (SS-2-6) was analyzed to evaluate clay

50

mineralogy. The sample contained 7Å halloysite/kaolinite with trace amounts of

smectite and goethite. Similar to West Salem Sites 1 and 2 saprolite samples,

Sample SS-2-6 did not contain 10Å halloysite and the peaks were broad and

poorly-defined. Portions of the broad, asymmetrical 7Å peak in the saprolite

sample expanded to 10.8Å after glycolation, indicating the presence of

interlayered halloysite/expandable clay. XRD traces for Borehole BH-2 are


Magnetism Observations

Thirteen samples from a variety of sites were tested for magnetism using

a hand-held pencil magnet placed in a soil-water suspension. Abundant

magnetic material was retained on the magnet in strongly magnetic samples.

Testing of weakly magnetic samples produced only minor magnetic material.

The results of this testing are shown in Table 6. Except for one example,

saprolite samples contained magnetic material and residual soil samples were

not magnetic.

To evaluate the magnetic mineralogy of a bulk sample, Monterey

Overcrossing Sample SS-10-10 was analyzed using random powder XRD

analysis between 3° and 65° 2θ (Appendix D.5). This analysis showed the

presence of reddish-brown maghemite, the ferromagnetic form of Fe2O3 that

forms in soils and is isostructural with magnetite (Schwertmann and Taylor,

1989). Maghemite was identified using the 2.52 and 2.96Å peaks.

51

Table 6. Magnetic Properties of Soil Samples

Site Sample Depth (m) Soil Texture Magnetism


SS-7-9 10.7 – 11.1 Saprolite Strong





SH-43-6 6.6 – 7.2 Saprolite Strong

West Salem Site 1 SS-1-4 3.0 – 3.5 Saprolite Weak

West Salem Site 2 SS-1-1 8.0 – 1.2 Residual soil None

SS-1-6 4.6 – 5.0 Saprolite Weak

Carlton


SS-2-2 1.4 – 1.8 Residual soil None


Silverton SS-1-2 1.5 – 2.0 Residual soil Strong

South Salem SS-2-6 4.6 – 5.0 Saprolite None

Soils containing exclusively silt and clay-sized material were generally

not magnetic. Saprolite samples that contained abundant >#230 mesh grains

were generally more magnetic. Magnetism is attributed to the presence of

secondary maghemite based on XRD analysis of Monterey Overcrossing

Sample SS-10-10.

Field Sensitivity Testing Results

Field sensitivity testing on all the study site samples identified the

following trends:

• Soil sensitivity generally increases with depth. • Saprolite soils are generally sensitive.

52

• Residual soils are not sensitive. • Volcanic breccia saprolites are more sensitive than flow rock or intrusive

rock saprolites.

Although soil sensitivity appears generally to increase with depth, one

sample of flow rock saprolite (Monterey SS-18-8) did not appear sensitive, even

though it was beneath a sensitive volcanic breccia. Table C.1.1 (Appendix C.1)

identifies the field sensitivity of each sample.

Testing for Amorphous Clay (Allophane and Imogolite)

Samples of a non-sensitive residual soil, sensitive saprolite, and a

secondary orange clay were tested for allophane and imogolite using the

toluidine blue spot test (Wada and Kakuto, 1985). These samples included

Monterey Overcrossing samples SS-7-2, SS-7-9, and SS-7-4 (orange clay

portion). The soil – solution mixture created for each sample turned purple,

indicating that neither allophane nor imogolite were present.

Scanning Electron Microscopy (SEM) Results

A series of SEM photos were taken of Monterey Overcrossing Sample

SH-43-6 using resolutions of 10X, 50X, 390X, and 2000X to identify the nature

of primary and secondary porosity within a volcanic breccia saprolite. Figure 10

shows a slightly enlarged (1.7X) photograph of the sample prior to analysis.

Secondary orange and white clay has precipitated in relict rock joints and inter-

clast voids. A white clay has replaced the plagioclase phenocrysts.

Sample SH-43-6 was obtained at a depth of 6.6 to 6.7 m (21.5 to 22 ft),

directly above the weathered rock interface. Basalt bedrock was sampled (rock

53

core) below a depth of 7.0 m (23.5 feet). Sample SH-43-6 is best described as

a soft, dark brown mottled orange, damp to moist low plasticity silt with trace

(<15%) fine sand. The consistency of the sample is based on a SPT N-value of

3 blows per foot obtained at 6.1 to 6.6 m (20 to 21.5 feet). Although the sample

can be crushed under moderate finger pressure, it is only in the early stage of

saprolite formation and still retains much of the original rock texture and greater

than 50 percent original minerals (R. Glasmann, personal communication,

February 2001). Even though the sample is not completely weathered, it is

sensitive and freely releases water when compressed under finger pressure.

XRD analysis of the -2μm fraction identified significant amounts of 10Å

halloysite in this sample, with lesser amounts poorly crystalline 7Å halloysite,

and only trace amounts of smectite.

At 10X magnification (Figure 11), primary porosity consists of large (0.5

to 4 mm) voids within and surrounding the breccia clast. The voids appear to be

partially or completely infilled with a secondary mineral. In addition to the

primary porosity, secondary micro-voids are visible on a portion of a volcanic

breccia clast that has been outlined (Box A).

At 50X sample magnification (Figure 12), Box A1 shows enlarged micro-

voids or boxworks as defined by Velbel (1990) that are visible in the breccia

clast (Box A, Figure 11). A smooth, secondary, white, clay-like mineral is visible

in the upper right hand corner (Box B).

54

At 390X sample magnification (Figure 13), the secondary mineral in Box

B appears extremely smooth with conchoidal fractures cutting surfaces. This

material shows desiccation cracking. At 390X sample magnification (Figure

14), the portion of the breccia clast within Box A1 clearly shows a boxwork

structure of angular dissolution voids bounded by clay septa. Boxes A2 and A3

enclose the two different textural morphologies present within Box A1 (Figure

12).

At 2000X sample magnification (Figure 15), the boxwork morphology

within Box A2 (Figure 14) consists of 10 to 40μm voids. These voids form

isolated, pockets within the in situ soil structure. At the same magnification,

apparent iron oxides are visible as rounded clusters in Box A3 shown in Figure

16 (R. Glasmann, personal communication, November 2001)

55

Figure 10. Residual texture visible in volcanic breccia saprolite sample SH-43-6 from Monterey Avenue Overcrossing. Sample is approximately 70 mm (2.75 inches) in diameter (thumb tack for scale). Note orange clay infilling a relict rock joint and white clay replacing relict plagioclase phenocrysts.

56 Figure 11. SEM photomicrograph of Sample SH-43-6 at 10X magnification. Note the primary porosity in decomposed volcanic breccia.

A

57

Figure 12. SEM photomicrograph of Box A from Sample SH-43-6 at 50X magnification. Box A1 encloses portion of decomposed basaltic breccia clast. Box B encloses secondary white clay-like precipitate in a primary void or vesicle.

B

A1

58

Figure 13. SEM photomicrograph of Box B from Sample SH-43-6 at 390X magnification showing close-up of white secondary clay-like precipitate filling a void or vesicle in a decomposed basaltic breccia clast.

59

Figure 14. SEM photomicrograph of Box A1 from sample SH-43-6 at 390X magnification showing boxwork structure in decomposed basaltic breccia clast. Box A2 shows dissolution voids bounded by clay septa. Box A3 contains apparent iron oxide material.

A3

A2

60

Figure 15. SEM photomicrograph of Box A2 from Sample SH-43-6 at 2000X magnification showing close-up view of boxwork structure. Note the extremely thin clay septa dividing the dissolution void near the center of the picture (Banding on photograph caused by charging artifacts.)

61

Figure 16. SEM photomicrograph of Box A3 from Sample SH-43-6 at 2000X magnification showing close-up of apparent iron oxides.

62

Engineering Index Testing Results

Index testing of study area samples included natural water content and

Atterberg limits. Laboratory testing results are shown in Table B.2.1, Appendix

B.2. Natural water content tests were conducted on all but two of the samples.

Atterberg limits tests were conducted on West Salem Site 2, Sample SS-1-6

(saprolite) and Silverton, Sample SS-1-2 (residual soil). In addition to index

testing of samples analyzed for this project, index testing on similar samples

from Monterey Avenue Overcrossing are shown in Table B.3.1, Appendix B.3.

These tests included natural water content, Atterberg limits, percent <#200

mesh, and wet and dry unit weight. Table 7 includes a summary of the average

engineering index testing data for both sensitive and non-sensitive samples

(and similar samples) tested at each study site.

Engineering index test results show that volcanic saprolites generally

consist of high plasticity silts (MH) while residual soil generally consisted of high

plasticity clay (CH). The moisture content of the saprolite soils is extremely high

(59% average) and their dry unit weight is very low (5.6 to 6.4 kN/m3 or 36 to 41

lb/ft3 for volcanic breccia saprolite). Residual soil samples are characterized by

a lower water content (generally between 20% to 30%) and higher unit weight

(13.8 kN/m3 or 88 lb/ft3).

The moisture content of study area samples generally increase with

depth and then decrease just before the rock interface. The most sensitive soils

generally show the highest natural water content and there is a dramatic

63

difference in water content between residual and saprolite soils. Three samples

obtained from Monterey Avenue Overcrossing boreholes show moisture

contents near or above their liquid limits indicating that these soils will lose all

shear strength when disturbed.

Table 7. Summary of Engineering Index Testing Data

Site Sensitivity

Average Natural Water

Content (%)

Atterberg Limits

(LL/PI/USCS)1

Wet/Dry Unit Weight

in kN/m3 (lb/ft3)

Percent<#200 mesh


Not sensitive 41 57/26/MH2 19/14

(120/88) N/A3

Sensitive 63 86/32/MH 16/6.0 (101/39) 65

West Salem Site 1

Not sensitive 39 N/A N/A N/A

Sensitive 57 N/A N/A N/A

West Salem Site 2


Sensitive 55 51/6/MH N/A N/A

Carlton



Silverton

Not sensitive 37 57/36/CH N/A N/A


South Salem Sensitive 63 N/A N/A N/A

1 LL = Liquid limit, PI = Plastic index, USCS = Unified Soil Classification System symbol 2 Residual soil classification at Monterey Avenue Overcrossing included a CH, CL, and MH. An average value is not representative of these soils. 3 Not determined

64

DISCUSSION

Clay Mineralogy in Basaltic Saprolites and Residual Soil

Laboratory research conducted for this paper investigates the

characteristics of individual clay minerals or mixtures and clay mineral zonation

in basalt saprolites and residual soil. The following discussions compare this

research with research conducted by others.

Clay Zonation

Zonation in clay mineralogy was observed in detail in Boreholes BH-7

and BH-10 at Monterey Overcrossing in southeast Portland and in Borehole

BH-1 at West Salem Site 1. Selected borehole samples from the other study

sites were used to evaluate and confirm trends in clay mineralogy zonation

observed in the Monterey Overcrossing borings. Based on the XRD analyses,

vertical clay zonation did not appear to be significantly affected by original rock

texture (i.e. flow verses interflow zones). 7Å halloysite is present in all zones

and appears interlayered with expandable clay only within the saprolite. 10Å

halloysite is rarely observed in the residual soil and is also commonly

interlayered with expandable clay in the saprolite. Basaltic saprolites analyzed

within the study area showed the following vertical zonation of the 1:1 clay

minerals:

10Å halloysite (deep saprolite)→ 7Å halloysite (intermediate saprolite) →

kaolinite (shallow residual soil)

65

Smectite is most abundant near the rock interface; no clear zonation

within the borehole samples was observed. Previous research has shown the

highest smectite concentration in the lower portions of the saprolite or closest to

the rock interface (Glasmann and Simonson, 1985; Eggleton et al., 1987;

Watanabe et al., 1992; Righi et al., 1999), no clear trend in smectite zonation is

observed in the study site samples. Abundant smectite is observed in the

residual soil (Monterey Sample SS-7-2, Appendix D.4) and also near the rock

interface (Carlton Sample SS-1-8, Appendix D.11). High smectite

concentrations in the residual soil may be partially attributed to contamination

from overlying soils or be due to clay enrichment in the B soil horizon. Even

though the formation of smectite usually requires low leaching rates and poorly

drained soils, the formation of smectite and halloysite in well-drained soils may

be controlled by the microenvironment developed in isolated, fluid-filled

microboxworks. Glasmann and Simmson (1985) postulated that it might be

possible for reducing conditions to exist in these water-filed voids even in an

aerated soil.

Zonation in the clay mineral crystallinity was also observed within study

site samples. The 7Å halloysite 001 peak appeared sharp and distinct in

shallow samples, but became broad and poorly defined with depth. The 001

peak became asymmetrical toward the low diffraction angles with depth. These

peak characteristics may indicate decrease in crystallinity with depth, the

66

presence of intermediate halloysite varieties, interlayering with expandable clay,

or all three.

Allophane and imogolite, which have been associated with sensitive

saprolites (Thrall, 1981), are composed of a solid solution between silica,

alumina, and water (Wada, 1989). Both minerals are x-ray amorphous and are

commonly associated with halloysite (Wada, 1989). They are most common in

saprolites formed in volcanic ash but have been found in soils derived from

basalts in warm, tropical environments (Moore and Reynolds, 1997). Allophane

forms hollow spherules (35 to 50Å in diameter), while imogolite forms tubes (18

to 20Å in diameter) (Moore and Reynolds, 1997). Both minerals form gels that

are thought to contain water in their structure and block water-filled pores

(Thrall, 1981). Since no allophane or imogolite were detected in any of the

samples tested, soil sensitivity observed in saprolites at the study area sites

cannot be attributed to these minerals.

In addition to systematic variations in clay mineralogy and crystallinity,

zonation in the abundance of well crystalline low cristobalite or opal C (SiO2) is

present in the -2μm size soil material is present at the West Salem Site 1. This

mineral is formed during the laterization process as dissolved SiO2 is carried

downward by groundwater and precipitated as metastable layered cristobalite

(Jones and Segnit, 1972). Laterization is a de-silication process in which silica,

alkalies, and alkaline earths are leached from the soil (Corcoran and Libbey,

1956). Due to the low energy environment, the stable SiO2 polymorph, quartz,

67

is unable to form (Jones and Segnit, 1972). Tridymite also precipitates in low

energy environments, but the sharpness and location of the low cristobalite

peaks in the West Salem Site 1 samples indicate limited tridymite.

Low cristobalite, although rare in soils, is characterized by sharp,

symmetric XRD peaks and is usually associated with pyroclastic rocks (Drees et

al., 1989). At West Salem Site 1, low cristobalite is most abundant between 4.6

m and 8.1 m (15.0 and 26.5 feet), based on peak height. Physical and chemical

conditions at this depth interval appear to favor the precipitation of well-ordered

cristobalite and may be related to current or ancient fluctuations in groundwater

levels. Figure 17 shows crystalline, well-ordered low cristobalite in the air-dried

XRD trace for Sample SS-1-7 at 7.6 to 8.1 m (25 to 26.5 feet) at West Salem

Site 1.

Mixed-Layered Halloysite/Expandable Clay

Mixed-layered halloysite/expandable clay was identified in study site

samples of sensitive saprolite. Previous research indicates that pure halloysite

doesn’t expand with glycolation (Glasmann and Simonson, 1985; Delvaux et al.,

1990; Moore and Reynolds, 1997). However, in interlayered halloysite/smectite

clays, Delvaux and others (1990; 1992) observe a shift in the 10Å halloysite

peak to 10.5Å, with a broadening towards the low diffraction angles, after

exposure to ethylene glycol.

Interlayered halloysite/expandable clay was observed in at least one saprolite

sample from each of the six study sites. In Monterey Avenue Overcrossing

68

Sample SS-18-8, the low diffraction angle portion of the broad(7.3Å - 9Å) peak

shifts to 10.5Å (Figure 18). The 10Å halloysite 001 peak in this sample also

shifts to 10.5Å after glycolation. This shift of the lower diffraction angle portion

of a broad 7Å halloysite peak (7.4Å<d001<10.0Å) and the entire 10Å halloysite

peak to between 10.3Å and 11Å occurs in almost all of the saprolite samples,

but does not occur in the residual soil samples with ethylene glycol sample

treatment. Monterey Overcrossing Sample SS-10-10 (a saprolite near the rock

interface) did not show a shift in the 10Å halloysite 001 peak, but that peak is

located at 10.8Å in both air-dried and glycolated analyses.

Research conducted for this thesis does not identify if the interlayered

clay is smectite, and thus it is only identified as expandable clay. Interlayering

may only include a small amount of expandable clay (10%) with R0 ordering

(Reichweite) (Moore and Reynolds, 1997). Additionally, interlayered 10Å

halloysite may separate into smectite and 7Å halloysite with glycolation-based

peak shifts observed in Monterey Overcrossing Sample SS-10-10 (Appendix

D.5). Interlayering does not appear to be present in residual soils containing

abundant kaolinite, indicating that the interlayered halloysite/expandable clay is

destroyed and converted to 7Å halloysite and kaolinite (Monterey Overcrossing

Sample SS-7-2, Appendix D.4).

69

Figure 17. Air-dried XRD trace of crystalline, well-ordered low cristobalite in West Salem Site 1 sample SS-1-7 (25 to 26.5 feet deep).

70

Desiccation of 10Å Halloysite

Previous research has indicated that 10Å halloysite converts to 7Å

halloysite if desiccated (Churchman et al., 1972; Gillott, 1987) and that

dehydration of 10Å halloysite is irreversible (Bailey, 1989). Costanzo and Giese

(1985) suggest that 10Å halloysite is unstable under ambient conditions (room

temperature and less than 90% relative humidity) and rapidly dehydrates if not

immersed in water. Although subjected to desiccation at room temperature,

conversion of 10Å halloysite to 7Å halloysite does not appear to have occurred

in Monterey Overcrossing samples at any depth. XRD analysis of an air-dried

and pulverized sample (Monterey Overcrossing sample SS-10-10) showed a

distinct 001 halloysite peak at 10Å. Similarly, Monterey Overcrossing Sample

SS-7-12 was completely desiccated during storage, but still contains abundant

10Å halloysite (Appendix D.4). However, based on the higher d-spacing of the

10Å halloysite peak (10.88Å) in sample SS-10-10 and the shift with glycolation

from 10.04Å to 10.43Å, this sample contains interlayered 10Å

halloysite/expandable clay. This clay mixture may be more resistant to

desiccation than pure 10Å halloysite. The data obtained from XRD analyses of

study site samples indicate that the conversion from 10Å halloysite to 7Å

halloysite in saprolites is complex and not exclusively related to soil desiccation.

Development of Sensitivity in Basaltic Saprolites

Previous engineering hypotheses have attributed sensitivity in volcanic

saprolites to the presence of hydrated (10Å) halloysite (Mitchell, 1989) or the

71

combined presence of halloysite and smectite (Cornforth Consulting Inc., 1991).

This hypothesis contends that water-filled 10Å halloysite tubes crush when

compacted releasing the water into the soil and causing moist soil to become

wet and lose shear strength (Mitchell, 1989). Additionally, water released by the

halloysite is absorbed by smectite, further lowering the shear strength of the soil

(Cornforth Consulting Inc., 1991). However, even if both 7Å and 10Å halloysite

form tubes (Singh and Gilkes, 1992), the energy required to rupture these small

tubes would be excessive. Furthermore, the amount of stored water within the

interior of the tubes would be inadequate to produce the effects observed in

sensitive soils. The average outside diameter of a halloysite tube is 0.07μm, the

inner diameter is 0.03μm, and tubes may be several microns in length (Grim,

1962). The volume of an individual tube is 1.4 X 10-3 μm. Conversely, a 10μm

boxwork void can store 1000μm3 of water, or 710,000 times the amount of

water stored in a halloysite tube. Cummings (In Press) summarizes the source

of water in sensitive saprolites in the following manner:

“The crystallization of halloysite, smectite, and other clay minerals and development of bonding between particles at the same time primary minerals are dissolving and the porosity is evolving provides an opportunity for water to be trapped in the saprolite and bedded sediments. Mechanical working progressively disrupts the bonds and releases pore water.”

Based on XRD clay data and SEM photographs included in this paper,

sensitivity is not a function of the formation of any specific clay mineral or clay

mineral association, but the development of clay-bounded boxwork voids that

trap and isolate water in the saprolite structure. Sensitive saprolites form in

72

Figure 18. Expansion of 10Å halloysite peak, half of the 7Å halloysite peak, and the broad peak between 7Å and 10Å to 10.5Å with glycolation. This expansion indicates that the halloysite has interlayered with an expandable clay. (Sample Monterey SS-18-8, the blue trace is air-dried, the green trace is glycolated, and the red trace is heated).

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flow rocks, interflow breccias, tuffs, and well crystalline intrusive rock (diabase)

and are not related to the formation of clay minerals in weathered volcanic

glass.

Both 7Å and 10Å halloysite are stable in environments that form saprolite

boxworks. XRD data obtained from Monterey Avenue Overcrossing samples in

Borehole BH-18 indicate that clay mineralogy doesn’t vary significantly within a

saprolite between sensitive and non-sensitive soils, and 10Å halloysite is not

ubiquitous to sensitive soils. This observation supports the conclusion that soil

microstructure, and not clay mineralogy, is the controlling factor in the

development of sensitive soils.

Sensitivity in volcanic soils is found only in saprolites and is not observed

in residual soils where physical movement, desiccation, and pedogenic

processes have destroyed the original soil texture. Saprolites form

isovolumetrically, while the formation of residual soil is not isovolumetric and

involves the collapse the saprolite (boxwork) structure (Pavich, 1996). Causes

for in situ mineralogic and morphologic changes that destroy sensitivity include

the following:

• Soil creep on slopes. • Pedogenic processes within the A and B soil horizons. • Pedoturbation (soil mixing) by roots and burrowing animals. • Shrinking and swelling of expandable clays (smectite) in the vadose

zone with seasonal wetting and desiccation.

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Each of the above processes works incrementally to break down the

saprolite boxwork structure, destroying the clay bounded voids and releasing

trapped water. Once the boxwork texture is destroyed, it cannot be recreated.

Occurrence of Sensitive Saprolites in Other Volcanic Rocks

Sensitive basalt saprolites are found in the study sites and at The Trask

River Dam Raise project site. Laboratory testing of Trask River Dam Raise

project soils identified properties similar to those found in study site samples.

Halloysite was encountered in all samples tested for this project, but the clay

mineralogy varied in each sample.

Sensitive saprolites do not form exclusively on basalt. Case history

information (Appendix A) identifies sensitive saprolites forming on flows and

tuffs composed of andesite (Toutle River SRS and Spirit Lake Memorial

Highway) and dacite (Toutle River SRS and Hills Creek Dam). Clay mineralogy

studies conducted for the Toutle River SRS identified variable clay mineralogy

including 7Å and 10Å halloysite, smectite, kaolinite, vermiculite, and expandable

mixed layer clay (Cummings, In Press). These clays were detected in sensitive

flow rock, breccia (debris flow), and volcaniclastic saprolites. Only a minor

amount of halloysite is present in portions of one sensitive unit (Hatchet

Mountain volcanics) (Cummings, In Press). X-ray diffraction analyses

conducted for the construction of Hills Creek Dam identified similar variation in

clay mineralogy in sensitive weathered terrace gravel, although halloysite was

present in each sample tested (U.S. Army Crops of Engineers Portland

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Engineer District, 1966). Although the clay mineralogy was not consistent in

sensitive saprolites tested for these projects, similar construction difficulties

were experienced at each site.

Based on study site and case history data, sensitive soils should be

suspected within any volcanic saprolite. The presence of sensitive saprolites

does not appear to be related to original igneous rock type or texture or any

specific clay mineral, but the isovolumetric leaching of silica and other elements

to form microscopic water-filled boxwork voids bounded by aluminum and iron-

based secondary minerals. Basically, the conditions that lead to boxwork

formation in volcanic saprolites are similar to those that favor the formation of

halloysite.

Identification of Sensitive Volcanic Saprolites

Based on engineering case history information and techniques

developed for this research, field, index, and laboratory tests can be conducted

to identify sensitive volcanic saprolites prior to construction.

Field Index Testing

Field index testing during the geotechnical investigation can alert the

designers to the presence of sensitive volcanic saprolites in the project area and

can identify the need for additional laboratory testing. Sensitive volcanic

saprolites can commonly be identified by crushing a clod of soil with strong

finger pressure (Figures 1 and 2) and observing if the soil becomes wet. If the

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soil shows no discernable increase in moisture content after crushing, it is most

likely not sensitive.

Sensitive volcanic saprolites also feel cold to the touch. During test pit

excavations, stick your hand into the pile of soil in a backhoe bucket. If the soil

feels abnormally cold, then it is sensitive (with a high water content) and should

not be used for embankment material without further testing. This technique

was used successfully by Brent Black of Cornforth Consulting (personal

communication, April 2000) during the geotechnical exploration for the Trask

River Dam raise.

Prior to construction, build test embankment fills to assess potential

compaction difficulties. Make numerous passes with the type and size (weight)

of earth moving equipment to be used during construction.

Engineering Index Testing

Once field sensitivity testing has indicated the presence of sensitive soils,

additional index testing can be conducted to determine the engineering

properties of these soils and estimate their performance during construction.

The following index tests should be conducted on soils identified for foundation

and embankment materials:

Natural Water Content

Sensitive soils have high natural moisture contents and are usually

greater than 50% water, by weight. These soils may appear only moist in

exposures.

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Unit Weight (Dry Density)

Due to the abundant void space in sensitive saprolites, they have low dry

densities. Samples of volcanic breccia saprolite form Monterey Avenue

Overcrossing have low dry unit weights of 5.7 to 6.4 kN/m3 (36 to 41 lbs/ft3). A

non-sensitive residual soil at the same site had a unit weight of 13.8 kN/m3 (88

lbs/ft3).

Atterberg Limits Test

Atterberg limits tests are extremely helpful in identifying sensitive

volcanic saprolites. Sensitive soils are generally high plasticity silts (MH) and

often have natural moisture contents equal to or greater than the liquid limit of

the soil. Atterberg limits change between moist, air-dried, and oven dried

samples. Both the liquid limit and the plastic index decrease with increased

drying.

Proctor (Moisture-Density) Tests

Conduct Proctor tests on all materials to be used for embankment fills to

identify sensitive soils. Since the maximum dry density and optimum moisture

content become higher and drier, respectively, with working, pulverize soils prior

to Proctor testing to obtain accurate maximum dry density and optimum water

content of soils under actual construction conditions (Cornforth Consulting Inc.,

1991). Conduct Proctor density tests on samples obtained from test fills to

more accurately identify compaction parameters prior to construction (Cornforth

Consulting Inc., 1991). Additionally, Harvard miniature compaction testing may

78

provide more accurate compaction parameters than can be obtained with

Proctor testing (T. Smith, personal communication, May 2002)

X-Ray Diffraction Analysis

If index test results for project area soils are similar to values typical for

sensitive soils, XRD analysis can be helpful identifying the presence of

halloysite and smectite. Even though halloysite crystals may not store

significant water, both 7Å and 10Å halloysite (along with smectite) are

commonly associated with sensitive saprolites based on XRD analyses

conducted for this research and other engineering projects. Additionally, the

presence of intermediate halloysite, which may increase the plasticity of the soil

(U.S. Army Crops of Engineers Portland Engineer District, 1966), should be

evaluated. This intermediate halloysite shows either intermediate degrees of

hydration (U.S. Army Crops of Engineers Portland Engineer District, 1966) or

interlayered 7Å and 10Å halloysite.

Mitigation of Sensitive Volcanic Saprolites

If sensitive volcanic saprolites have been identified by field and

laboratory testing, and these soils must be worked during construction, mitigate

against adverse effects by manipulating the soil as little as possible. Use light

compaction equipment, limiting scraper size to 20 tons (D. H. Cornforth,

personal communication, April 2000). Less manipulation and lighter

compaction will limit the crushing of water-filled saprolite boxworks and reduce

the amount of soil drying required.

79

During fill placement, don’t try to dry back the soil too much with disking

or spreading. Increased manipulation will cause the soil to release more water

and become wetter. Place soil only during dry weather and grade

embankments to facilitate drainage. Limit lift thickness to enhance the soil’s

ability to dry.

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CONCLUSIONS

Halloysite is an abundant clay mineral in sensitive basaltic and andesitic

saprolites in northwestern Oregon and southwestern Washington. These soils

release water and lose shear strength when compressed. 7Å halloysite was

detected in all sensitive soils analyzed. 10Å halloysite was abundant in only a

few of the sensitive samples analyzed, and was absent or present in trace

amounts in most samples. Both 7Å and 10Å halloysite appear to be stable in

the soil environment that forms sensitive saprolites and 10Å halloysite was

stable after desiccation at room temperature.

The significant amount of water released during compression of sensitive

soils is stored in boxwork voids, and not inside individual halloysite tubes or

spheres as has been previously suggested. These voids form by selective

crystal dissolution and precipitation along crystal perimeters and cleavage

planes. Both the small size and the amount of energy required breaking

individual halloysite crystals make them unlikely sources of stored water. Clay-

bounded boxwork voids, identified during SEM analysis, seem the most viable

source of adequate water to cause soil sensitivity. Thus, soil microstructure, hot

halloysite, is critical in the formation of sensitive soils.

Soils lacking relict texture (residual soils) are not sensitive. The loss of

sensitivity in surficial residual soils is due to a breakdown and collapse of the

boxwork voids within the saprolite. This collapse is caused by near surface soil

81

creep, shrinking and swelling of expandable clays (smectite) with seasonal

wetting and desiccation, and pedoturbation by roots and burrowing animals.

Clay mineral zonation was observed in borehole samples obtained on

Mt. Scott in southeast Portland (Monterey Overcrossing). 10Å halloysite was

most abundant toward the base of the saprolite (near the bedrock contact). 7Å

halloysite was most abundant toward the middle to upper portions of the

saprolite, and kaolinite was most abundant in the overlying, featureless residual

soil. Clay zonation was not significantly influenced by original rock type (flow

rock vs. breccia) in the basalts. Although smectite was more abundant near the

rock interface, no clear zonation was identified for smectite in these samples.

Selected samples from five other sites in northwestern Oregon confirmed this

zonation. Testing for allophane and imogolite confirmed the lack of amorphous

clay in these samples.

Interlayered halloysite/expandable clay which expands with glycolation

was identified in almost all saprolite samples analyzed, but not in the residual

soil samples. The disappearance of clay interlayering may be related to

collapse of the saprolite structure and/or the chemical conditions (including

hydration) present near the surface in the residual soil.

In addition to clay zonation, one site in the Eola Hills of West Salem

(West Salem Site 1) showed variation in the abundance of low cristobalite with

depth caused by silica dissolution and reprecipitation lower in the soil profile.

82

Maximum concentrations of well-crystalline low cristobalite occurred between

4.6 m and 8.1 m (15.0 and 26.5 ft).

Construction problems related to sensitive volcanic saprolites have been

documented in northwestern Oregon and southwestern Washington since the

1940’s and include Mud Mountain Dam, Hills Creek Dam, the Toutle River

Sediment Retention Structure, the Trask River Dam raise, and the Spirit Lake

Highway. Difficulties experienced during the construction of these structures

include excessive rutting during stripping and placing of embankment materials,

soils that are wet of optimum, and difficulty in achieving compaction.

Laboratory and field testing are invaluable tools in identifying sensitive

saprolites during the geotechnical investigation phase of design. These tests

include natural water content, dry unit weight, Atterberg limits, X-ray diffraction,

and field sensitivity measurements. Sensitive saprolites are generally high

plasticity silts (MH) that have anomalously high natural water contents (>50%),

low dry unit weight (5.7 to 6.4 kN/m3), Atterberg limits that decrease with drying,

generally contain halloysite but little or no kaolinite, and possess the ability to

release water and become wet when compressed under strong finger pressure.

Proctor density test maximum densities and optimum water contents vary with

the amount of soil working. Residual soils, however, are generally high

plasticity clays (CH), have lower natural water contents (20 to 40%), and have

higher dry unit weights (14 kN/m3)

83

Methods to mitigate the impact of sensitive saprolites include

manipulating the soils as little as possible with light weight equipment, placing

thin embankment lifts to allow the soil to dry, and grading fills to enhance

drainage.

84

FUTURE WORK

Since microstructure is the controlling mechanism in the formation of

sensitive volcanic saprolites, additional SEM analysis should be conducted to

investigate the following:

• Determine the microstructure of residual soils to confirm that boxwork voids have been destroyed or filled.

• Evaluate the microstructure of more silicic volcanic saprolites including andesites through rhyolites to see if sensitivity is related to boxwork structures in these rocks.

• Compare the microstructure of sensitive ash deposits that contain allophane and imogolite to see if boxworks are present or if water is stored within these clay minerals. Additional investigation is necessary to evaluate the relationship between

7Å and 10Å halloysite in a soil environment. The mechanism that causes 10Å

halloysite to lose its water layer and convert to 7Å halloysite is undetermined.

Furthermore, the role (if any) of interlayered expandable clay in this process

should be investigated.

85

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U.S. Army Corps of Engineers Portland Engineer District, June 1959, Embankment Design Review: Hills Creek Reservoir, Middle Fork Willamette River, Oregon: Report to U.S. Army Corps of Engineers.

U.S. Army Crops of Engineers Portland Engineer District, June 1966, Hills Creek Reservoir, Middle Fork Willamette River, Oregon: Design Memorandum No. 4, Embankment Design, Addendum B, Completion Report: Report to U.S. Army Corps of Engineers.

Velbel, M. A., 1989, Weathering of hornblende to ferruginous products by a dissolution-repreciptiation mechanism: Petrography and stoichiometry: Clays and Clay Minerals, v. 37, no. 6, p. 515-524.

Velbel, M. A., 1990, Mechanisms of saprolitization, isovolumetric weathering, and pseudomorphous replacement during rock weathering--A review: Extended Abstract, 2nd International Symposium on the Geochemistry of the Earth's Surface and of Mineral Formation, Aix-en-Provence, France, July 2-8, 1990, Chemical Geology, v. 84, p. 17-18.

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Wada, K., and Kakuto, Y., 1985, A spot test with toluidine blue for allophane and imogolite: Soil Science Society of America Journal, v. 49, p. 276-278.

Wada, S. I., and Mizota, C., 1982, Iron-rich halloysite(10A) with crumpled lamellar morphology from Hokkaido, Japan: Clays and Clay Minerals, v. 30, no. 4, p. 315-317.

Walker, G. W., and Duncan, R. A., 1989, Geologic map of the Salem 1° by 2° quadrangle, western Oregon: U. S. Geological Survey Miscellaneous Investigations Series Map I-1893

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Walker, G. W., and MacLeod, N. S., 1991, Geologic Map of Oregon: U.S. Geological Society

Walsh, T. J., Korosec, M. A., Phillips, W. M., Logan, R. L., and Schasse, H. W., 1987, Geologic map of Washington--southwest quadrant: Washington Division of Geology and Earth Resources Geologic Map GM-34, 28 pp.

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Watanabe, T., Sawada, Y., Russell, J. D., McHardy, W. J., and Wilson, M. J., 1992, The conversion of montmorillonite to interstratified halloysite-smectite by weathering in the Omi acid clay deposit, Japan: Clay Minerals, v. 27, p. 159-173.

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Wells, R. E., Snavely, P. D., Jr., MacLeod, N. S., Kelly, M. M., and Parker, M. J., 1994, Geologic map of the Tillamook Highlands, northwest Oregon Coast Range (Tillamook, Nehalem, Enright, Timber, Fairdale, and Blaine 15 minute quadrangles: U. S. Geological Survey Open File Report 94-21, 24 pp.

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APPENDIX A OREGON AND WASHINGTON

CASE HISTORIES OF CONSTRUCTION IN SENSITIVE VOLCANIC SAPROLITES

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Appendix A.1 Mud Mountain Dam, Pierce County, Washington

One of the earliest records of construction problems in the Pacific

Northwest related to excessively wet volcanic soils was observed in 1941 at the

Mud Mountain Dam, located in Pierce County 76 km (47 miles) southeast of

Seattle, Washington. The design of the earth and rock-fill embankment had to

be modified to include more rock when embankment soils could not be dried

back to optimum moisture content for compaction (Anonymous, 1941c). The

presence of a small amount of colloidal clay was blamed for preventing the soil

from adequately drying or draining (Anonymous, 1941c). To allow for

construction during wet weather, a huge canvas tent was suspended over the

earth-fill core to prevent rainwater infiltration (Anonymous, 1941b). Additionally,

construction of the impervious core was completed using oil-burning kilns to

reduce the moisture content of embankment soils by 2.5% to 5% (Anonymous,

1941a).

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Appendix A.2 Toutle River Sediment Retention Structure, Cowlitz County, Washington

The Toutle River Sediment Retention Structure (SRS) was constructed

by the US Corps of Engineers (COE) to impound volcaniclastic debris deposited

during the 1980 eruption of Mount St. Helens. The Toutle River valley, which is

located in the Cascade Range of southwest Washington, was partially infilled

with debris flows and lahars during the 1980 eruption of Mount St. Helens. The

location of the SRS was selected to prevent upstream eruptive material from

washing downstream during flooding and impacting shipping on the Columbia

River.

Shortly after dam construction began, Granite Construction claimed a

change of conditions and initiated litigation (Cornforth Consulting Inc., 1991;

Cummings, In Press). Problematic soil and rock was encountered in several

geologic units, including Tertiary-age decomposed andesitic and basaltic flow

rock and flow top breccia (Hatchet Mountain volcanics), Pleistocene-age debris

flow material (saprolitic diamicton), layered clay-rich deposits (“the slimes”), and

pre-eruption river alluvium. Although these materials appeared stable in situ,

once disturbed they became excessively wet and slippery, extremely difficult to

compact, and unstable in the dam core and waste piles.

Heavy equipment used to place and compact impervious core material

routinely created deep ruts and bogged-down. The decomposed flow-top

breccia of the Hachet Mountian volcanics and the debris flow material were

selected for the impervious core (Cornforth Consulting Inc., 1991). According to

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Granite, “The Impervious Material was very deceiving. When viewed in a cut

slope, it appeared to be gravelly in nature, fairly dry and stiff, very stable and

almost at optimum water content. As it was disturbed by construction

equipment, the water inside the structure of the clay and relic rock clasts was

freed, and material that had appeared to have good bearing capacity was

reduced to a wet, sticky mass that scrapers could not operate efficiently

upon…The more manipulation by construction equipment, the more excess

water and instability was realized” (Cornforth Consulting Inc., 1991). The

layered clay-rich deposits and pre-eruption river alluvium, designated as waste

material, were difficult to strip due to rutting and flowed when placed in spoils

piles (M. L. Cummings, personal communication, April 2000).

Granite Construction claimed that the presence of halloysite and smectite

in volcaniclastic soils created water sensitive soils that were responsible for the

construction problems at the SRS. They claimed that halloysite held water “in

the soil grain” and resisted drying. During stripping and placing of borrow

materials, the halloysite “grains” broke apart, releasing water into the soil pores.

This additional water has to be removed before adequate compaction can be

attained. The optimum moisture content of the in situ borrow soil was ±4%

lower than the optimum moisture content of the fill soils. Extensive disking,

used by Granite to aerate and dry the fill soils, exacerbated the problem by

increasing the maximum dry density of the soil, decreasing its optimum moisture

content, and further lowering its shear strength.

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To support Granite’s claim, clay mineral analyses were conducted on

sensitive soils. Gabor and Cummings (1988) identified smectite and 7Å

halloysite (with minor kaolinite and vermiculite) in the Hachet Mountain

volcanics flow top breccia. Total clay content ranged between 31% and 100%.

The debris flow material contained 37% to 64% clay minerals including

predominantly 7Å halloysite, with generally lesser amounts of 10Å halloysite,

smectite, and vermiculite. Kaolinite was detected near the upper contact of the

debris flow saprolite at the approximate location of a paleosurface (Cummings,

In Press). Layered clay-rich deposits contained 18% to 43% clay minerals,

including 7Å halloysite, 10Å halloysite, chlorite, smectite, vermiculite, kaolinite,

and mixed-layer clays. Significant 10Å halloysite was found in three out of the

seven samples. The matrix of pre-eruption alluvial deposits contained 18% to

46% total clay minerals, predominantly 7Å halloysite, chlorite, smectite,

vermiculite, and lesser kaolinite (one sample) and mixed-layer clays. 10Å

halloysite is present in two of the six samples. Gabor and Cummings (1988)

and Cummings (In Press) concluded that soil sensitivity was caused when

microtextures in saprolites were crushed during handling and water trapped

within micropore spaces was released. Cummings (In Press) observes that

volcaniclastic deposits have become bonded by precipitated clay minerals and

silica as weathering progresses within local deposits from the 1980 eruption.

Due to this bonding, micropores form isovolumetrically in the saprolite during

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leaching (Cummings, In Press). 10Å halloysite was not ubiquitous to the

problem soils.

Swelling in smectite-rich soils was dismissed by Warkentin (1988) as a

cause of the rutting problems experienced during SRS construction. He

discounted rapid swelling and loss of shear strength in these soils due to their

low hydraulic conductivity and contended that a 0.9 m (3-foot) thick layer of soil

would require months to reach an expanded condition. He did acknowledge

that decomposed volcanic rock can be crushed by heavy equipment,

“…releasing clay minerals, amorphous minerals, halloysite, or smectite, and the

water associated with them” and creating a “…smeary clay with excess water.”

Gabor and Cummings (1988), however, hypothesized that water freed from

crushed micropores was absorbed by adjacent smectite crystallites. Based on

the ubiquitous presence of water within the saprolitic soil structure, low hydraulic

conductivity would not inhibit swelling of smectite minerals.

In addition to swelling from pore-derived water, slaking within smectite-

rich flow rock and flow breccia caused by repeated wetting and drying

transformed apparently hard rock into soil when exposed to the air. Such

degradation occurred along haul roads constructed out of hard blocks of flow

breccia (D. H. Cornforth, personal communication, April 2000).

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Appendix A.3 Trask River Dam Raise, Tillamook County, Oregon

The Trask River Dam impounds Barney Reservoir in the Coast Range of

northwestern Oregon (Figure 3). The dam site is located on a deeply

weathered uplifted erosional surface that forms the core of the northern Oregon

Coast Range. The dam area is underlain by Eocene-age Siletz River Volcanics

composed of submarine basalt flows, pillow lavas, flow breccias, and siltstone

and shale interbeds (Wells et al., 1983; Wells et al., 1994). Bedrock is mantled

by an average of 50 feet of saprolite soil (Hammond and Vessely, 1998).

In 1995, construction for the enlargement of the dam was initiated and

anticipated sensitive soils were encountered in selected areas (C. M.

Hammond, personal communication, May 2000). Cornforth Consultants, Inc.

(1993) identified these soils as sandy silts and silty sands with lesser clay-sized

material. The natural water content of the soils encountered during the

geotechnical investigation for the dam raise averaged 60%, but ranged up to

100%. Cornforth Consultants, Inc. (1995) found that natural water contents in

the foundation area of the expanded dam averaged 68%, but ranged up to 89%.

In situ water contents for the existing embankment fill ranged between 30% and

43%. Atterberg limits testing on foundation soils identified high plasticity silts

with relatively high liquid limits (46% to 80%) and low plastic indexes (<27%).

The natural moisture content of the majority of the foundation soils exceeded

their liquid limits.

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Borrow areas were selected to attempt to avoid sensitive saprolites.

Atterberg limits testing on borrow soils identified high plasticity silts with

relatively high liquid limits (50% to 75 %) and low plastic indexes (<20%). In the

borrow areas, the liquid limit did not exceed the natural water content of the soil.

Atterberg limits varied for moist and air-dried samples. Even after rehydrating

prior to testing, the air-dried samples showed lower liquid limits and plastic

indexes than samples that had never been dried, indicating an irreversible

change had occurred during drying.

Compaction testing (standard Proctor—ASTM D698) was conducted on

test fills composed of borrow soils (Cornforth Consultants Inc., 1995). Maximum

dry densities ranged from 11.3 to 13.2 kN/m3 (72 to 84 lb/ft3), with optimum

moisture contents of 32% to 42%. Although these values showed a slight

seasonal variation between July and October, in every case the optimum

moisture content ranged from 6% to 15% less than the natural moisture content.

The problematic soils had relict rock texture (saprolite) and were “…very

sensitive to handling and moisture due to the presence of halloysite and

montmorillonite clay minerals” (Hammond and Vessely, 1998). “Upon handling,

halloysites frequently break down and release water trapped in the soil grain.

Smectites, and to a lesser degree vermiculites, readily accept free water and

may expand and soften when additional free water is available.” (Cornforth

Consultants Inc., 1995). This absorption of water by expandable clay minerals

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supposedly changes the texture of the soil from granular to cohesive (Cornforth

Consultants Inc., 1995).

Clay analyses conducted on two borrow area samples with natural

moisture contents greater than 45% identified 66% hydrated (10Å) halloysite

(with an additional 34% possible 7Å halloysite) in one sample, and 42%

hydrated halloysite (with 53% smectite) in the second. These samples were

collected at depths of 1.5 to 2.0 m (5 to 6.5 feet). The four other borrow

samples tested had natural moisture contents 24% to 44% and contained

chloritized vermiculite, 7Å halloysite, and possibly mixed layered kaolinite and

halloysite.

Since the geotechnical engineering for the Trask River Dam raise was

conducted after the SRS change of conditions claim, sensitive soils were

anticipated and avoided, where possible. However, anticipation of adverse soil

conditions did not eliminate all construction problems. Construction equipment

still became bogged-down in wet weather limiting stripping and placing of

impervious core materials to the dry summer months (Hammond and Vessely,

1998). Lighter equipment was used to compact the fill in the dam core. The

weight of the scrappers was limited to 178 kN (20 tons), instead of 445 kN (50

tons) (D. H. Cornforth, personal communication, April 2000).

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Appendix A.4 Hills Creek Dam, Lane County, Oregon

Hills Creek Dam was one of the first Oregon dams to experience

construction difficulties related to sensitive volcanic saprolites. The dam, which

was completed in 1961 by the Army Corps of Engineers, impounds the Middle

Fork of the Willamette River. It is located approximately 8 km (5 miles)

southeast of Oakridge in the Western Cascades of central western Oregon.

The dam site is underlain by massive lapilli tuff and hydrothermally altered,

highly fractured dacite of the Oligocene to lower Miocene-age Little Butte

Volcanics (U.S. Army Corps of Engineers Portland Engineer District, 1954;

Peck et al., 1964). The lapilli tuff bedrock has been deeply weathered and

fractured and joints are either open or partially infilled with secondary colloidal

clay (U.S. Army Corps of Engineers Portland Engineer District, 1954). Within

the river channel, the bedrock is overlain by “older” (Pliocene or Pleistocene)

valley fill consisting of highly weathered, gravel in a cemented matrix of silt and

clay (decomposed volcanic ash) (U.S. Army Corps of Engineers Portland

Engineer District, 1954). Colloidal clay coats sand and gravel clasts and fills

voids in the older valley fill. The upper 10 to 15 feet of the older valley fill had

been reworked by the river. More recent alluvium flood plain deposits of silty

sand, fresh valley boulder gravel mantle the older valley fill.

The impervious core of the dam was constructed of both reworked and in

situ older valley fill gravel deposits, but only the in situ gravel was difficult to

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place and compact (U.S. Army Corps of Engineers Portland Engineer District,

1959). Although the valley fill gravel appeared near the optimum moisture

content when excavated from the borrow area, it appear wetter after spreading.

Core fill consisting of the sensitive in situ gravel rutted, became more plastic,

and caused 50-ton rollers to become stuck. The sensitive fill could not be

compacted properly even when spread and allowed to dry for 24 hours. The

COE attributed soil sensitivity to small pockets of highly plastic colloidal clay

mixing with lower plasticity fines during remolding and an increase in the

plasticity of halloysite-bearing soils as hydrated halloysite is altered to highly

plastic intermediate halloysite during drying.

An Atterberg limits test run on a sample from the impervious core

material showed a progressive reduction in the plastic limit and plasticity index

with air drying followed by oven drying. This trend is similar to that observed

within sensitive soils at the Trask River Dam.

Soft colloidal clay that filled voids and coats gravel and sand grains in the

in situ older alluvium is blamed for these construction problems even though

grain size analyses identified the older gravel deposits as well graded with 2%

to 4% silt and clay size material (U.S. Army Crops of Engineers Portland

Engineer District, 1966). Clay analyses conducted by Dr. Ralph Grim on the silt

and clay sized matrix material identified predominantly of 10Å, 7Å, and

intermediate forms of halloysite, with lesser smectite (U.S. Army Crops of

Engineers Portland Engineer District, 1966). Dr. Grim advanced the following

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hypothesis regarding the unusual properties of soils that contain partially

hydrated halloysite:

“…2H2O [dehydrated] or 4H2O [hydrated] form [of halloysite] has very low plasticity. Its

[Atterberg] limits are very low and sometimes it appears to be substantially nonplastic.

In an intermediate state of hydration with a moisture content between the 2 and 4 H2O

form the mineral has very different properties – it may be and usually is quite plastic

and very difficult to compact. When the molecular layer is complete (4H2O) or when it

is absent (2 H2O), the silicate layers are held together rigidly. When the water layer is

partially present, the silicate layers are easily split apart and very different properties

develop” (U.S. Army Crops of Engineers Portland Engineer District, 1966).

To improve compaction within the sensitive older valley fill, each lift was

covered by a 0.76 m (2.5 foot) lift of “random” rock (U.S. Army Crops of

Engineers Portland Engineer District, 1966). This more permeable aggregate

created a layered fill that allowed the excessively wet sensitive alluvium to drain.

Additionally, the weight of the roller was reduced to 178 kN (20 tons) which

produced only 12 inch ruts. A D-9 tractor was required to pull the lighter roller

across the fill. Eventually, Dr. Arthur Casagrande recommended minimizing

rutting by reducing the lift thickness to 0.2 m (8 inches), compacting each lift

with two passes of the tractor treads after spreading, and sloping the core of the

dam to promote drainage (U.S. Army Crops of Engineers Portland Engineer

District, 1966). Following implementation of these modifications, construction of

the dam core was completed.

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Appendix A.5 Spirit Lake Memorial Highway,

Cowlitz and Skamania Counties, Washington

Spirit Lake Memorial Highway (SR 504) is located in Cowlitz and

Skamania Counties in southwest Washington. Damage caused by debris

torrents along the Toutle River during the 1980 eruption of Mount St. Helens

required 32 km (20 miles) of the existing SR 504 to be rebuilt and an additional

40 km (25 miles) of road was built to reach the Coldwater Lake observation

area near the mountain (Golder Associates, 1988a). Construction of the new

road was completed in six segments.

The project area is located in the Washington Western Cascades and is

underlain by Tertiary-age volcanic rocks consisting of andesite and basalt flows,

agglomerates, and tuffs (including lahar deposits). These volcanic rocks have

subsequently been intruded and hydrothermally altered by andesite, basalt, and

gabbro dikes and sills. Bedrock is mantled by Pleistocene and Holocene ash

deposits, glacial drift, colluvium, and alluvium (Golder Associates, 1988a).

Performance of the construction materials, including embankment soil,

was assessed during the geotechnical investigation for Segment 3 of the new

road (Golder Associates, 1987b). The field test procedure consisted of placing

a 1.0 to 1.5 foot layer of soil in a loose condition and then measuring the density

change after successive passes of a D8 or D7G track-type tractor. Prior to field

testing, laboratory testing was conducted on embankment soils to determine

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Atterberg limits, dry density, natural moisture content and standard Proctor

values for maximum dry density and optimum moisture content.

Five test fills were constructed in Segment 3. Two of these test fills were

used to evaluate the workability of the hydrothermally altered tuff (Golder

Associates, 1987b). Both test fills were composed of soils with significant fines

(48% and 50% <#200 mesh) that consisted of low plasticity silts (ML) with very

low plastic indexes (5% and 9%). In both cases, the natural moisture content of

the soil was significantly (6% and 11%) above the optimum moisture content for

standard compaction. Maximum dry densities and optimum moisture contents

established during standard Proctor compaction tests (ASTM D698) averaged

16 kN/m3 (99 lb/ft3) and 22%, respectively.

In-place density measurements on the hydrothermally altered tuff test fills

showed an increase in dry density with two tractor passes, followed by either no

further increase or a significant decrease in the dry density with additional

passes (Figure A.5.1) (Golder Associates, 1987b). Dry densities measured

within these test fills were significantly less than the maximum dry densities as

established by standard Proctor moisture/density testing (ASTM D698). The in

situ moisture content of the test fills decreased with two tractor passes and then

increased as the dry density decreased (Golder Associates, 1987b).

Concurrently, pumping and deep rutting occurred on the third tractor pass in

one test fill and on the fourth in the other. Ruts ranged from 0.2 to 0.5 m (8 to

18 inches) deep (Figure A.5.2). Based on the results of these test fills and the

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above optimum natural water content and high silt content of this material, the

altered tuff was identified as unworkable (Golder Associates, 1987b).

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FIGURE IS INCLUDED IN GEOLOGY DEPARTMENT AND LIBRARY THESIS COPY

Figure A.5.1. Effect of compaction on density on hydrothermally altered tuff test fill (Golder Associates, 1987b).

110

FIGURE IS INCLUDED IN GEOLOGY DEPARTMENT AND LIBRARY THESIS COPY

Figure A.5.2. Rutting in a sensitive hydrothermally altered tuff test fill during construction of the Spirit Lake Memorial Highway (Golder Associates, 1987b).

111

Portions of Segments 1, 2, 4, 5, and 6 are also underlain by

hydrothermally altered and weathered andesite and tuff (“Completely Altered

Rock”) (Golder Associates, 1987a; Golder Associates, 1988c; Golder

Associates, 1988d; Golder Associates, 1988a; Golder Associates, 1988b).

These units contain 30% corestones in a decomposed matrix of sand, gravel,

and low plasticity silt and clay (ML and CL). In each of these segments, the

optimum water contents in the altered andesite and tuff were significantly lower

than the natural water contents indicating that the soils would require extensive

drying prior to compaction. Thus, Golder classified “Completely Altered Rock”

in all six segments as waste material. Golder Associates (1988b) describe

andesite and tuff saprolites in the following manner:

“The Completely Altered Rocks appeared to exhibit some properties typical of

residual soils. Properties generally attributed to residual soils include poor

compaction characteristics, high natural moisture contents often above the

liquid limit, Atterberg Limit and compaction results sensitive to the method of

drying, low in situ unit weights, local zones of low in situ strengths, and low

remolded strengths. This behavior is generally attributed to the types of clay

minerals present, often including halloysite, and the retained structure of the

parent bedrock. The completely altered rocks encountered in Segment 4

exhibited many of these properties, including low in situ unit weights and high in

situ moisture contents, often exceeding the liquid limit and well above the

optimum Proctor compaction moisture contents…The Completely Altered Rock

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has a low in situ unit weight and a high water content attributed, at least in part,

to the relict structure of the formation. Once excavated, place, and

recompacted the structure will be destroyed and the resulting fill will be at a

water content in excess of optimum.”

Portions of Segment 1 of the Spirit Lake Memorial Highway are underlain

by Holocene and Quaternary volcanic ash (Golder Associates, 1988a). The

thickness of ash deposits range from 0.6 to 7.0 m (2 to 23 feet) thick and

Atterberg Limits testing identified both ash deposits as low plasticity silts (ML).

The dry unit weights of the Holocene and Quaternary volcanic ash are

approximately 9.4 to 14.1 kN/m3 (60 and 90 lb/ft3), respectively. The

anomalously low dry unit weight of the Holocene volcanic ash indicates a high

amount of porosity undoubtedly related to the mode of deposition. Natural

water contents for Holocene and Quaternary volcanic ash average 45% and

40%, respectively, but range from 22% to 83%. Natural moisture contents were

significantly higher (14%) than optimum moisture contents obtained for standard

Proctor compaction tests (ASTM D 698). The in situ strength of both ash

deposits is higher than that indicated by Standard Penetration Testing during

drilling. Effective angles of internal friction (φ) ranged from 32 to 35 degrees

with an effective cohesion of 4.8 to 14.3 kN/m2 (100 to 300 lb/ft2). Construction

difficulties were anticipated by Golder Associates in both ash deposits due to

their high natural water content, high silt content, and apparent cementation and

these materials were designated as waste.

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APPENDIX B ENGINERING TEST PROCEDURES AND DATA

114

Appendix B.1 Discussion of Engineering Test Procedures

Natural Moisture Content (ASTM D2216)

The natural or in situ soil moisture content is the ratio of the weight of

water in a given volume of soil to the weight of the solid particles within that

same volume and is reported as a percentage. The test requires placing a soil

sample in a 71°C degree oven for a period of 24 hours before calculating the

dry weight. Using this method, water trapped within soil voids is evaporated.

Atterberg Limits (ASTM D4318)

Atterberg limits discussed in this report include the plastic limit, liquid

limit, and plastic index and classify the amount of plasticity in cohesive soils.

These tests are conducted on material finer than #40 mesh including fine sand,

silt, and clay. Although the methods for determining the plastic and liquid limits

are somewhat arbitrary, these limits are widely used by engineers to classify

soils and predict their engineering properties. The plastic limit is defined as the

moisture content at which a thread of soil just begins to crack and crumble when

rolled to a diameter of 3 mm (1/8 inch). The liquid limit is defined as the

moisture content at which a 2 mm wide groove in a soil sample closes for a

distance of 13 mm (½ inch) when dropped 25 times in a standard brass cup.

The cup on the liquid limit device falls 10 mm each time at a rate of 2 drops per

second. The plasticity index is the difference in moisture content between the

liquid limit and the plastic limit. Accurate Atterberg limits are recorded on soil

115

samples that have never been desiccated. Air-drying or oven drying sensitive

soils changes their Atterberg limits.

Inorganic soils are classified into four categories based their plasticity as

identified by their liquid limit and plastic index. These categories include low

plasticity silt (ML), low plasticity or “lean” clay (CL), high plasticity or “elastic” silt

(MH), and high plasticity or “fat” clay (CH). Soils that are finer than #40 mesh,

but cannot be rolled into a 1/8 inch thread at any moisture content are identified

as nonplastic (NP).

Unit Weight

The unit weight or density of a soil sample is the ratio of the weight of the

soil to the total volume of the soil and is commonly reported in lb/ft3, kN/m3, or

g/cm3. Natural (moist), saturated, and dry unit weight are commonly calculated.

Dry density is used for moisture/density (Proctor) tests (see below).

Void Ratio

The void ratio of a soil sample is the ratio of the volume of the voids

contained in the soil to the volume of the soil solids, expressed as a decimal.

The void ratio is determined by consolidation testing.

Maximum Dry Density (ASTM D 698)

The maximum dry density of a soil is defined as the highest density (or

greatest compaction) that the soil can attained under a specific compactive

effort. Greater compaction can be obtained if larger (heavier) earthmoving

116

equipment is used. The maximum dry density is determined by conducting a

standard or modified Proctor or moisture-density test to measure the compacted

soil’s density at a variety of water contents. The water content of the soil is

critical to attaining maximum dry density. As water is added to the soil, it

facilitates compaction by allowing individual soil particles to move over one

another more easily. As even more water is added to the soil, the voids

between the particles begin to fill with water, further increasing the density of the

soil. However, when most of the voids become full, the water begins to push

the soil particles apart, lowering the soil dry density. The optimum water

content of the soil occurs when the majority of the soil voids are filled with water

and the maximum dry density is reached.

Percent –200 Mesh

To determine the percentage of silt and clay-sized material in a sample,

the sample is washed through a 200-mesh sieve and the remaining +200-mesh

material is oven dried at 110° and weighed. The natural water content of the

soil is measured to calculate the initial dry weight of the soil. The difference

between the initial and washed sample weight is the weight of the –200 mesh

material in the sample. The percent –200 mesh is the ratio of the weight of the

–200 mesh material over the initial dry weight, expressed as a percent.

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Appendix B.2 Engineering Index Test Data for Samples

Analyzed Using X-Ray Diffraction

Table B.2.1 Engineering Test Results for X-ray Samples1

Site Borehole Sample Natural Water Content (%)

Atterberg Limits

(LL/PI/USCS)2

Monterey Avenue BH-3 SS-3-9 40

Monterey Avenue BH-7

SS-7-2 32 SS-7-3 43 SS-7-4 58 SS-7-6 55 SS-7-7 52 SS-7-8 34 SS-7-9 68 SS-7-11 75 SS-7-12 333


SS-10-4 31 SS-10-5 66 SS-10-7 74 SS-10-8 83 SS-10-9 72 SS-10-10 69 SS-10-11 253

Monterey Avenue BH-18 SS-18-6 60 SS-18-8 74 SS-18-9 52

Monterey Avenue BH-27 SS-27-7 58

West Salem Site 1 BH-1

SS-1-1 26 SS-1-2 40 SS-1-3 51 SS-1-4 56 SS-1-5 61 SS-1-6 55

West Salem Site 2 BH-1 SS-1-1 17 SS-1-6 55 51/6/MH

Carlton BH-1 SS-1-8 50

BH-2 SS-2-2 39 SS-2-6 33

Silverton BH-1 SS-1-2 37 57/36/CH SS-1-4 56

South Salem BH-2 SS-2-6 63

1 Soil sensitivity for each sample is identified in Table C.1.1 (Appendix C.1) 2 LL = Liquid limit, PI = Plastic index, USCS = Unified Soil Classification System symbol

3 Samples contain abundant rock material

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Appendix B.3

Engineering Index Test Data for Monterey Avenue Similar Samples

Table B.3.1 Engineering Test Results for Similar Monterey Avenue Samples

Borehole/Test Pit Sample Depth

(m) Soil

Description Soil Texture Sensitivity

Natural Water

Content (%)

Atterberg Limits

(LL/PI/USCS)1

Wet/Dry Unit

Weight in kN/m3 (lb/ft3)

Percent –200 mesh

BH-17 SH-17-2 3.0 - 3.7 Silt with sand

Decomposed breccia

Moderate 59 90/45/MH 16/6.4 (101/41) 75

BH-28 SS-28-4 5.8 - 6.2 Silt with sand Extremely 69 68/27/MH --- 68

TP-4 S-4-3 2.9 - 3.0 Clayey silt Moderate 61 97/5/MH --- 73

BH-40 SH-40-3 3.8 - 4.4 Sandy clay with silt Moderate 65 87/50/CH 16/5.7

(101/36) 45

BH-46 SS-46-5 7.6 - 8.1 Sandy silt Decomposed basalt None 58 56/16/MH --- ---

TP-9 S-9-1 1.5 - 1.7 Clay Residual soil None

22 70/38/CH --- ---

BH-44 SH-44-4 5.3 - 5.9 Clay with silt 32 45/25/CL 19/14 (120/88) ---

1 LL = Liquid limit, PI = Plastic index, USCS = Unified Soil Classification System symbol

119

APPENDIX C STUDY AREA SAMPLE DESCRIPTIONS

AND STUDY SITE LOCATIONS

120

Appendix C.1 Geologic Properties of Study Area Samples

Table C.1.1. Geologic and Engineering Properties of Study Area Samples

Study Site Borehole Sample Depth

(m) Soil/Rock Description1 Sensitivity Original Lithology

Soil/Rock Texture

Description2

Monterey Avenue BH-3 SS-3-9 9.4 – 9.9 Medium dense silty sand Moderate

Basalt interflow breccia

Secondary orange clay in

void space


SS-7-2 2.1 – 2.6 Stiff clayey silt None Unknown Residual soil SS-7-3 3.0 – 3.5 Stiff clayey silt None SS-7-4 4.6 – 5.0 Stiff silt Minor

Basalt flow rock

Saprolite

SS-7-6 6.7 – 7.2 Very stiff sand silt Moderate SS-7-7 7.6 – 8.1 Medium dense silty sand

SS-7-8 9.1 – 9.6 Dense silty sand SS-7-9 10.7 – 11.1 Stiff sandy silt with some clay

Moderate Basalt

interflow breccia SS-7-11 12.8 – 13.3 Loose silty sand

SS-7-12 13.7 Extremely weak to very weak basalt N/A Basalt flow rock

Highly weathered flow rock


SS-10-4 4.9 – 5.3 Hard clayey silt with trace sand Minor

Basalt flow rock Saprolite

SS-10-5 6.1 – 6.6 Stiff silt Moderate SS-10-7 8.2 – 8.7 Stiff silt Moderate SS-10-8 9.1 – 9.6 Stiff silt with trace clay Moderate SS-10-9 10.7 – 11.1 Medium stiff silt Extreme SS-10-10 12.2 – 12.6 Medium stiff sandy silt Extreme

SS-10-11 13.7 Weak to very weak basalt N/A Basalt flow rock

Highly weathered flow rock

121



Soil/Rock Texture

Description2


SS-18-6 4.6 – 5.0 Loose silty sand None Basalt flow rock

Saprolite SS-18-8 7.6 – 8.1 Stiff silt with some sand Moderate Basalt

interflow breccia

SS-18-9 9.1 – 9.6 Medium dense sand with some silt None Basalt flow rock

Monterey Avenue BH-27 SS-27-7 10.7 – 11.1 Medium dense silty sand Moderate Basalt flow

rock

Secondary orange clay in

void space

Monterey Avenue BH-43 SH-43-6 6.6 – 7.2 Soft silt with some silt and sand Extreme

Basalt interflow breccia

Saprolite

West Salem, Site 1

BH-1

SS-1-1 0.8 – 1.2 Hard clay with some silt and trace sand None

Basalt flow rock

Residual soil

SS-1-2 1.5 – 2.0 Very stiff silt with some clay None

Saprolite

SS-1-3 2.3 – 2.7 Medium stiff silt with some clay None SS-1-4 3.0 – 3.5 Medium stiff silt with some clay Minor

SS-1-5 4.6 – 5.0 Medium stiff silt with some clay and trace fine sand Moderate

SS-1-6 6.1 – 6.6 Medium stiff silt with some clay and

trace fine sand and gravel-sized angular clasts

Moderate

SS-1-7 7.6 – 8.1 Stiff silt with trace clay and sand Moderate SS-1-8 9.1 – 9.6 Stiff silt with some sand Moderate SS-1-9 10.7 – 11.1 Stiff sandy silt Moderate

SS-1-10 12.2 – 12.6 Medium stiff silt with trace sand and clay Moderate

West Salem Site 2

BH-1 SS-1-1 0.8 – 1.2 Hard clayey silt None Basalt flow

rock

Residual soil

SS-1-6 4.6 – 5.0 Hard sandy silt with some clay and trace gravel-sized angular clasts Moderate Saprolite

122



Soil/Rock Texture

Description2

Carlton

BH-1 SS-1-8 7.6 – 8.1 Stiff silt with sand and gravel-sized angular clasts Moderate

Basaltic dike or sill

Saprolite

BH-2 SS-2-2 1.4 – 1.8 Very stiff clayey silt None Residual soil

SS-2-6 4.6 – 5.0 Stiff sandy silt with trace angular gravel-sized angular clasts Extremely Saprolite

Silverton BH-1 SS-1-2 1.5 – 2.0 Stiff clay with trace fine to coarse sand None Basalt flow

rock Residual soil

SS-1-4 3.0 – 3.5 Stiff sandy silt Moderate Saprolite South Salem BH-2 SS-2-6 4.6 – 5.0 Medium stiff clayey silt Moderate Basalt flow

rock Saprolite

1Key to soil and rock descriptions in Appendix C.2 2Residual soil shows no original rock texture and has been subjected to more sever weathering, desiccation, soil creep, and bioturbation. Saprolite, while classified as a soil, shows relict rock texture including phenocrysts, joints, and breccia clast boundaries.

123

REMAINING APPENDICES ARE INCLUDED IN THE GEOLOGY DEPARTMENT AND LIBRARY THESIS COPIES

Documents

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