6 Soils and Aggregates

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Week 3: Soils and Aggregates

CEE 363 Construction Materials

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Week 3: Soil and Aggregate Topics

SoilsSoil classification systemsSoil related tests

AggregatesAggregate ProductionAggregate Characterization

Soils

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Laterite Soil--Brazil

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Soil Classification

Two major soil classification systems used in the US

“AASHTO” Classification (ASTM D3282, AASHTO M145)Unified Soil Classification (USBR, 1973 and ASTM D2487)

Why classify a soil? (USBR)Identifies and groups soils of similar engineering characteristics.Provides a “common language” to describe soils.In a limited manner, soil classifications can provide approximate values of engineering characteristics.

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Soil Classification

How do classification systems work?Determine gradation

Is the dominant percentage of particles larger or “granular”Is the dominant percentage of particles “fine graded” (or silt-clay sizes).

Perform Atterberg Limit tests (more on these tests shortly).

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Soil Classification—Highway Oriented System—ASTM D3282, AASHTO M145

Actual title for ASTM D3282 and AASHTO M145: Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes.Classification Groups split into

Granular Materials: Contains 35% or less passing the No.200 sieve. These groups generally make good to excellent subgrades.Silt-Clay Materials: Contains more than 35% passing a No.200 sieve. These groups generally are fair to poor as subgrades.

Sieves used in ASTM D3282 and AASHTO M145

No.10 No.40 No.200

No. 10 Sieve—Close-up View No. 40 Sieve—Close-up View

No. 200 Sieve—Close-up View Soil Classification—Highway Oriented System—ASTM D3282, AASHTO M145

Clayey soils.A-6Clayey soils. Similar to A-6 except for high liquid limits. A-7

Silty soils. Similar to A-4. Can be highly elastic.A-5

Silty soils.A-4

Fine sand.A-3

Silty or clayey gravel and sand.A-2

Well-graded mixture of stone fragments, gravel, and/or sand.

A-1

Silt-Clay Materials

Granular Materials

Soil Group

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No.10No.40No.200

No.10No.40No.200

No.10No.40No.200

No.10No.40No.200

No.10No.40No.200

No.10No.40No.200

No.10No.40No.200

% Passing Sieve

A-7

A-6

A-5

A-4

A-3

A-2

A-1

Soil Group

----36% min

----36% min

----36% min

----36% min

--51% max10% max

----35% max

--50% max25% max

Silt-Clay Materials

Granular Materials

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Additional tests required to perform classification grouping.

Liquid Limit (AASHTO T89, ASTM D4318): “The water content, in percent, of a soil at the arbitrarily defined boundary between the liquid and plastic states.” See next image to view the device used to determine LL. The higher the LL, the poorer the soil.Plastic Limit (PL) and Plasticity Index (AASHTO T90, ASTM D4318): “The water content, in percent, of a soil at the boundary between the plastic and brittle states.” Plasticity Index (PI) is the “range of water content over which a soil behaves plastically.”PI = LL – PL. The higher the PI, the poorer the soil.

Liquid Limit Device

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Soil Classification—Unified Soil Classification System—ASTM D2487

Actual title for ASTM D2487: Classification of Soils for Engineering Purposes (Unified Soil Classification System)Classification Groups split into

Coarse-grained soils: More than 50% retained on a No.200 sieve.Fine-grained soils: 50% or more passes the No.200 sieve.

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Soil Classification—Unified Soil Classification System—ASTM D2487

Coarse-grained soils: More than 50% retained on a No.200 sieve.

Gravels: More than 50% of coarse fraction retained on No.4 sieve.Sands: 50% or more of coarse fraction passes No.4 sieve.

Fine-grained soils: 50% or more passes the No.200 sieve.

Silts and Clays: LL less than 50%.Silts and Clays: LL 50% or more.

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Unified Soil Classification System—ASTM D2487—Additional Terminology

Gravel: Particles of rock passing a 3 in. sieve but retained on a No.4 sieve.Sand: Particles of rock passing a No.4 but retained on a No.200.Clay: Soil passing a No.200 that exhibits plasticity (putty-like properties) within a range of water contents. Exhibits considerable strength when air dry.Silt: Soil passing a No.200 that is nonplastic or very slightly plastic and that exhibits little or no strength when air dry.

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No.4 Sieve—Close-up View

Unified Soil Classification System—ASTM D2487—Additional Terminology

Lean clayCL

Clayey sandSC

Silty sandSM

Poorly graded sandSP

Well-graded sandSW

Clayey gravelGC

PeatPt

Organic silt or clayOH

Elastic siltMH

Fat clayCH

Organic silt or clayOL

SiltML

Silty gravelGM

Poorly graded gravelGP

Well-graded gravelGW

Group NameSoil Group Symbol

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Unified Soil Classification System—ASTM D2487

As shown in the prior image, the primary goal of this classification system is to determine the group for a specific soil (such as CL, etc.). To fully describe how this is done is too detailed for this lesson—but the process is fully described in ASTM D2487. Basically, it is a combination of sieve analyses and Atterberg Limits (LL, PL, PI). The following table shows typical engineering characteristics associated with the Unified Soil Classification System (from USBR, 1973).

Unified Soil Classification SystemTypical Properties (Source: USBR)

0.314.7115SC

0.812.8119SM-SC

7.514.5114SM

>15.012.4110SP

--13.3119SW

>0.3<14.7>115GC

>0.3<14.5>114GM

64,000<12.4>110GP

27,000<13.3>119GW

Permeability (ft per year)

Optimum water content (%)

Maximum Dry Density (pcf)

Soil Group

Unified Soil Classification SystemTypical Properties (Source: USBR)

------OH

0.0525.594CH

0.1636.382MH

------OL

0.0817.3108CL

0.1316.8109ML-CL

0.5919.2103ML

Permeability (ft per year)

Optimum water content (%)

Maximum Dry Density (pcf)

Soil Group

Unified Soil Classification SystemTypical Properties (Source: FAA)

200-30010-20105-130SC

------SM-SC

200-30020-40120-135SM

200-30015-25105-120SP

200-30020-40110-130SW

200-30020-40120-140GC

300 or more40-80130-145GM

300 or more35-60120-130GP

300 or more60-80125-140GW

Subgrade k (psi/in)

Field CBR (%)Maximum Dry Density (pcf)

Soil Group

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50-1003-580-105OH

50-1003-590-110CH

100-2004-880-100MH

100-2004-890-105OL

100-2005-15100-125CL

------ML-CL

100-2005-15100-125ML

Subgrade k (psi/in)

Field CBR (%)Maximum Dry Density (pcf)

Soil Group


Slight to HighFair to GoodSC

----SM-SC

Slight to HighGoodSM

None to Very SlightFair to GoodSP

None to Very SlightGoodSW

Slight to MediumGoodGC

Slight to MediumGood to ExcellentGM

None to Very SlightGood to ExcellentGP

None to Very SlightExcellentGW

Potential Frost ActionValue as a Foundation When Not Subject to Frost Action

Soil Group


MediumPoor to Very PoorOH

MediumPoor to Very PoorCH

Medium to Very HighPoorMH

Medium to HighPoorOL

Medium to HighFair to PoorCL

----ML-CL

Medium to Very HighFair to PoorML

Potential Frost ActionValue as a Foundation When Not Subject to Frost Action

Soil Group

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Soil Related Tests

Soil compactionStrength or stiffness of soils

LaboratoryField

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Soil compaction

Soil compaction is the process of “artificially” increasing the density (unit weight) of a soil by compaction (by application of rolling, tamping, or vibration).Standards are needed so that the amount of increased density needed and achieved can be measured.Two compaction tests are commonly performed to achieve this information.

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Soil Compaction: Moisture-Density Tests

Moisture-density testing as practiced today was started by R.R. Proctor in 1933. His method became known as the “standard Proctor” test.This test (today described by ASTM D698 and AASHTO T99) applied a fixed amount of compaction energy to a soil at various water contents. Specifically, this involves dropping a 5.5 lb weight 12 inches and applying 25 “blows” per layer in 3 layers in a standard sized mold. Thus, 12,375 ft-lb per ft3 of compaction effort is applied.

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Soil Compaction: Moisture-Density Tests

US Army Corps of Engineers developed “Modified Proctor” or “Modified AASHTO” to accommodate compaction needs associated with heavier aircraft used in WW 2. ASTM D1557 and AASHTO T180: “Laboratory Compaction Characteristics of Soil Using Modified Effort (56,000 ft-lb/ft3)”Refer to relative location of compaction curves on the next image. The higher the compaction energy, the lower the optimum water content and the higher the dry density.

Water Content (%)

Dry Density (lb/ft3)

Typical Compaction Curves

Typical for Modified

Compaction

Typical for Standard

Compaction

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Soil Compaction—Typical Compaction Specification

Section 2-03.3(14)C, Method C: “Compacting Earth Embankments”

“Each layer of the entire embankment shall be compacted to 95 percent of the maximum densityas determined by the compaction control tests described in Section 2-03.3(14)D. In the top 2 feet, horizontal layers shall not exceed 4 inches in depth before compaction. No layer below the top 2 feet shall exceed 8 inches in depth before compaction.”….“Under Method C, the moisture content shall not vary more than 3 percent above or below optimum determined by the tests in described in Section 2-03.3(14)D.”….Go to next image.

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Soil Compaction—Typical Compaction Specification

Section 2-03.3(14)D: “Compaction and Moisture Control Tests”

“The maximum density and optimum moisture for materials with less than 30 percent, by mass, retained on the US No.4 sieve shall be determined …[by]…AASHTO T99.”The are many more requirements that relate to specifying soil compaction but these two images provide a quick but focused example.

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Strength or Stiffness of Soils

Typical tests of soil strength are:Shear strength testsIndex types of tests

California Bearing Ratio (CBR)Modulus of subgrade reaction (k)Stabilometer Test (Hveem method)Cone penetrometers

Resilient modulus testCBR, R-value, cone penetrometers, and resilient modulus tests will be briefly covered.

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California Bearing Ratio

The CBR test is a relative measure of shear strength for unstabilized materials and the results are stated as a percentage of a high quality crushed limestone—thus all results are shown as percentages. A CBR = 100% is near the maximum possible. CBRs of less than 10% are generally weak soils.The test was originally developed by O. J. Porter of the California Division of Highways in 1928. The widespread use of the CBR test was created by the US Corps of Engineers during WW 2.

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The CBR test can be reviewed in the WSDOT Pavement Guide, Module 4 (Design Parameters), Section 2 (Subgrade)--http://hotmix.ce.washington.edu/wsdot_web/index.htmThe CBR test is only conducted on unstabilized materials (soils or aggregates).The test is most always done in the laboratory; however, a field test is available but rarely conducted.

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Test apparatus and specimen. Photo by ELE International

Standard methods: ASTM D1883, AASHTO T193.

Correlations between CBR, AASHTO and Unified classification systems, the DCP, and k.

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R-value

This test was developed in California by Hveem and Carmany in the late 1940’s. In effect, it is a relative measure of stiffness since the test apparatus operates somewhat like a triaxial test.The test is mostly used by western states for highway base and subgrade characterization.Use of this test is likely declining a bit.ASTM D2844 and AASHTO T190: “Resistance R-Value and Expansion Pressure of Compacted Soils”

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Stabilometer Device (R-value)

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Dynamic Cone Penetrometer (DCP)

Originally developed in the Republic of South Africa (RSA). South Africans have used and developed related tools and analyses for over 25 years.Standard test method

ASTM D6951: “Use of the Dynamic Cone Penetrometer in Shallow Pavement Applications”

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Dynamic Cone Penetrometer

Rod

Reference

Mass

Engine

Data Recorder

Positioning System

DCP As Developed in the RSA

Semi-Automatic DCP

Photos of Florida DOT equipment (June 2004). This type of DCP saves time and labor.

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DCP

Examples of DCP use by the Minnesota DOT

Pavement rehabilitation strategy determination.Locate layers in pavement structures.Supplement foundation testing for design.Identify weak spots in constructed embankments.Use as an acceptance testing tool.Location of boundaries of required subcuts.

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DCP

Assumption: A correlation exists between the strength of a material and its resistance to penetration. Typical measure is DCP Penetration Index (DPI)Measured in mm/blow or inches/blowMaximum depth for the DCP ≈ 800 mmCorrelations follow

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DCP (if CBR > 10) Correlation

Correlation developed by the US Army Corps of Engineers (USACE)

1.12DPI

292CBR =

Where

CBR = California Bearing Ratio (if CBR > 10)

DPI = Penetration Index (mm/blow)

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DCP (if CBR < 10) Correlation

Correlation developed by the US Army Corps of Engineers (USACE)

Where

CBR = California Bearing Ratio (if CBR < 10)

DPI = Penetration Index (mm/blow)

2)(DPI)][(0.017019

1CBR =

CBR Examples (based on USACE Correlation)

1020

2210

485

CBR(%)

DPI(mm/blow)

DCP Values and Subgrade Improvement (Illinois DOT)

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DCP Correlation

CBR Correlation developed in South Africa (for values of DN>2 mm/blow)

1.27410(DN)CBR −=Where

DN = Penetration of the DCP through a specific pavement layer in mm/blow. The DN is a weighted average. DN is similar to DPI.

CBR Examples (based on RSA Correlation)

440

920

2210

535

CBR(%)

DN(mm/blow)

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DCP Correlation

Modulus Correlation developed in South Africa

(DN)1.06166log3.04758logEeff −=Where

R2 = 76% and n = 86 data points

Eeff = Effective elastic modulus for a 40 kN load.

DN = Weighted average DCP penetration rate in mm/blow.

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E-value Examples (based on RSA Correlation)

22 (3,000 psi)40

46 (7,000 psi)20

97 (14,000 psi)10

202 (29,000 psi)5

Eeff

MPa (psi)DN

(mm/blow)

Typical DCP Plot (from RSA)

RSA Design Curves

Note: MISA is the same as ESALs. 58

DCP Testing Frequency (based on RSA recommendations)

Existing paved road8 DCP tests randomly spaced over the length of the project in both the outer wheelpath and between the wheelpaths.

Gravel road5 DCP tests per kilometer with the tests staggered between the outer and between wheelpaths. Perform additional test at significant locations identified via visual distress survey.

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DCP—Supplemental Information

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Modulus Background

What is it?Nomenclature?What affects values?Typical values?

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Elastic Modulus

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Pavement Modulus Abbreviations

EAC = Asphalt Concrete

EPCC = Portland Cement Concrete

EBS = Base course

ESB = Subbase course

ESG or MR = Subgrade

Stress StiffeningStress Softening

Comparison of Moduli for Various Materials

1,200,000Diamond

200,000Steel

70,000Aluminum

7,000-14,000Wood

7Rubber

E (MPa)Material

Moduli for Various Materials Pavement Materials

20-40,000

Portland Cement Concrete

35-210Subgrade Soils

150-750Crushed Stone Base

350HMA (50°C)

3,500HMA (20°C)

21,000HMA (0°C)

E (MPa)Material

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Summary of National Pavement Practices

State DOT Flexible Pavement Design Subgrade Inputs

Summary of National Pavement Practices

State DOT Rigid Pavement Design Subgrade Inputs

Resilient Modulus (MR)

Measure: stress-strainUnits: psi, MPaTypical Values

Subgrade: 3,000 to 40,000 psiCrushed rock: 20,000 to 50,000 psiHMA: 200,000 to 500,000 psi at 70°F

Picture from University of Tokyo Geotechnical Engineering Lab

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Modulus CorrelationsUse with caution

MR = (1500) (CBR)

Fine-grained materials with soaked CBR ≤ 10

MR = 1,000 + (555)(R-value)

Fine-grained soils with R-Value ≤ 20

MR = (2555)CBR0.64

New AASHTO Design Guide

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Modulus—CBR Correlation

Modulus Correlation developed by TRRL

Where

E = Elastic modulus (MPa)

CBR = California Bearing Ratio

0.64(17.6)CBR E = Aggregates

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Aggregate Production

Aggregate production in the US is large—some annual production figures include:

Natural aggregatesSand and gravel: 1.13 billion metric tonsCrushed stone: 1.49 billion metric tons

Recycled aggregates: 200 million metric tons produced from demolition wastes (includes roads and buildings).

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Sand and gravel (estimated for 2003)1.13 billion metric tons of sand and gravel produced in the US in 2003.Value $5.8 billion Produced by 4,000 companies from 6,400 operations in all 50 states. Leading production states are: California, Texas, Michigan, Arizona, Ohio, Minnesota, Washington, Wisconsin, Nevada, and Colorado.How were these aggregates used?

53% unspecified20% concrete aggregates11% road bases and road stabilization7% construction fill6% HMA and other bituminous mixtures3% other applications

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Crushed stone (estimated for 2003)1.49 billion metric tons of crushed stone produced in the US in 2003.Value $8.6 billion Produced by 1,260 companies from 3,300 operations in 49 states. Leading production states are: Texas, Florida, Pennsylvania, Missouri, Illinois, Georgia, Ohio, North Carolina, Virginia, and California.How were these aggregates used? 35% was for unspecified uses followed by construction aggregates mostly for highway and road construction and maintenance, chemical and metallurgical uses (including cement and lime production), agricultural uses, etc.

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Crushed stone—cont.Of the crushed stone produced it was composed of these source rock types:

Limestone and dolomite: 71%Granite: 15%Traprock: 7%Sandstone, quartzite, marble, etc: 7%

View “Aggregate Production at Glacier NW”

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PerspectiveThe eruption of Mt. St. Helens in 1980 was estimated to produce 3.7 billion yd3

of debris. This amounts to about 5.6 billion metric tons of material (assuming a unit weight of 125 lb/ft3). The total annual production of sand and gravel, crushed stone, and recycled aggregates amounts to about 50% of the St. Helens debris.

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Recycled aggregates (1999)200 million metric tons of recycled aggregates produced (or generated) in the US in 2000.100 million metric tons of recycled asphalt paving materials recovered annually. 80% of this material is recycled with the other 20% going to landfills. Of the 80% that is recycled—2/3 used as aggregates for road base and 1/3 reused as aggregate for new HMA.

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Recycled aggregates (1999)—cont.100 million metric tons of recycled concrete is recovered annually.

68% of recycled concrete reused as road base.9% aggregate for HMA mixes6% aggregate for new PCC mixes3% riprap7% general fill7% other applications

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Recycled aggregates (1999)—cont.Only 15% of recycled aggregates reused in HMA or PCC mixes—why?—Due to quality issues (the lack thereof).Economics of recycling according to USGS (1999 data)

Capital investment for an aggregate recycling facility about $4.40 to $8.80 per metric ton of annual capacity.Processing costs: Range from $2.76 to $6.61 per metric ton. Average production of fixed site processing facilities is 150,000 ton/year.Prices best for aggregate-poor southern states.

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Aggregate Characterization

Aggregate Physical PropertiesMaximum Aggregate SizeGradationOther Aggregate Properties

Toughness and Abrasion ResistanceSpecific GravityParticle Shape and Surface TextureDurability and SoundnessCleanliness and Deleterious Materials

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Aggregate Characterization

Maximum Aggregate SizeMaximum sizeThe smallest sieve through which 100 percent

of the aggregate particles pass.

Nominal maximum sizeThe largest sieve that retains some of the

aggregate particles but generally not more than 10 percent by weight.

Aggregate Gradation

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0.45 Power Curves

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Calculation of the Max Density Curve

n

DdP ⎟⎠⎞

⎜⎝⎛=

where P = % finer than the sieve

d = aggregate size being considered

D = maximum aggregate size being used

n = parameter which equals 0.45—represents the

maximum particle packing

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Gradations and Permeability• Uniformly graded

- Few points of contact- Poor interlock (shape dependent)- High permeability

• Well graded- Good interlock- Low permeability

• Gap graded- Only limited sizes- Good interlock- Low permeability

Types of Gradations

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Other Aggregate Properties

Los Angeles AbrasionSoundnessSand Equivalent

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Los Angeles Abrasion TestStart with fraction retained on No. 12 sieve

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Sample submerged in magnesium or sodium sulfate—causes salt

crystals to form in the aggregate pores

Soundness Test

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Sand Equivalent

SE = (Height of Sand/Height of Clay)100

Photo Courtesy of Caltrans

This is a test to determine the amount of clay in fine aggregate.

Aggregate passing a No. 4 sieve is agitated in a water-filled transparent cylinder. Liquid is water and flocculating agent. After settling, the sand separates from the flocculated clay. Measure each.

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Week 3: References

USGS (2004), “Mineral Commodity Summaries,”US Geological Survey, January 2004.USGS (1999), “Natural Aggregates—Foundation of America’s Future,” USGS Fact Sheet—FS 144-97, Reprinted February 1999.WSDOT (2003),“WSDOT Pavement Guide Interactive,” Washington State Department of Transportation, URL: http://hotmix.ce.washington.edu/wsdot_web/index.htm

USBR (1973), “Design of Small Dams,” Second Edition, US Department of the Interior, Bureau of Reclamation.

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Week 3: References

FAA (1996), “Airport Pavement Design and Evaluation,” Advisory Circular 150/5320-6D, Federal Aviation Administration, January 30, 1996. http://www.faa.gov/arp/pdf/5320-6dp1.pdf

PCA (1992), “PCA Soil Primer,” Publication EB007.05S, Portland Cement Association, Skokie, Illinois.WSDOT (2004), “Standard Specifications for Road, Bridge, and Municipal Construction,” M41-10, Washington State Department of Transportation. http://www.wsdot.wa.gov/fasc/EngineeringPublications/Manuals/SS2004.PDF

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6 Soils and Aggregates