Geotechnical Properties of Cemented Soils in Kuwait

Australian Road Research 16(2), June 1986, pp. 94-104

Geotechnical Properties of Cemented Soils in Kuwait

N.F. ISMAEL

Civil Engineering Department, Kuwait University,

P.O. Box 5969, Kuwait

M.A. MOLLAH

0. AL-KHALIDI

Government Laboratories and Testing Station, Ministry of Public Works, Kuwait

ABSTRACT

The properties and behaviour of cemented soils in Kuwait were examined by a laboratory testing program on undisturbed block samples taken from three local sites. The program included physical and index properties, direct shear and consolidation tests. The test samples were obtained from two deposits — a windblown calcareous dune sand, and a marine deposited calcareous silty sand known locally as `gatch'. The effect of varying degrees of cementation on the strength and compressibility was examined. The effect of saturation on the cemented soil properties was evaluated by tests on pre-saturated samples. The results indicated that saturation or soaking results in a loss of the cementation component of strength. Modest collapse of soil structure also occurred in the occasionally cemented windblown dune sand deposit after saturation for 24 hours. The influence of cementation on the stress-strain behaviour of the test soils is assessed, and the peak and residual strength parameters are compared for soaked and unsoaked samples.

Introduction

Cemented soils exist in many places of the world where arid or semi-arid conditions prevail. These include the Arabian Peninsula (Fookes and Higginbottom 1980; Oweis and Bowman 1981), the South-Western United States and Mexico (Beckwith and Hansen 1982), the Indian continental shelf (Datta, Gulhati and Rao 1982), South and South West Africa (Netterberg 1982), and Western Australia (Beringen, Kolk and Windle 1982). Among the principal cementing agents are carbonates, hydrous silicates, iron oxides, and gypsum. They are deposited at the points of contact between the particles (Krynine and Judd 1957) at a rate depending on local conditions and the geologic history of the deposit. As a result, various degrees of cementation are produced at different locations, and at different elevations at the same location. The degree of cementation can range from weakly-cemented to very-strongly cemented. Some attempts were recently made to provide a cementation classification or description system (Beckwith and Hansen 1982; Beringen et al. 1982; Datta et al. 1982) to be used in conjunction with the Unified Soil Classification System.

With development and major construction in desert areas, particularly the Arabian Peninsula, and with the increasing number of offshore platforms being founded by the oil industry (Beringen et aL 1982), interest has grown in the properties and behaviour of cemented soils. Cemented soils possess distinctive geotechnical properties

94

quite different from other soils. A good understanding of the behaviour of these soils is necessary for foundation design, slope stability analysis, earthworks, and highway construction. Recently, the strength characteristics of two naturally-cemented sands were examined by Clough et al. (1981) using drained triaxial loading tests, and the results were compared with those for uncemented, and artificially-cemented samples. These workers showed that cementation results in a slight increase in friction and cohesion intercept, and that the residential angle of friction was the same for cemented and uncemented sands. Saxena and Lastrico (1978) and Clough et aL (1981) have shown that cementation bonds in sands are broken at small strain levels. The geotechnical properties, behaviour, and performance of calcareous soils was the subject of a symposium held in Florida in 1982 where basic properties of these soils were presented and discussed. However, much work remains to be done before a clear understanding of the behaviour of these soils is reached.

This paper presents the results of a laboratory testing program carried out to determine the geotechnical properties of cemented soils in Kuwait. For this purpose, three test sites were chosen which were known to have varying degrees of cementation. The test sites included two different deposits. Testing included classification properties, strength, and compressibility characteristics as determined by direct shear, and consolidation tests. The effect of saturation on the properties and parameters of these soils

Australian Road Research, 16(2), June 1986

CEMENTED SOILS IN KUWAIT

was also examined. Emphasis is placed on the effect of cementation on the stress displacement curves, and deformation under load.

Local Conditions and Geology

The State of Kuwait occupies the north-east corner of the Arabian Peninsula. It is bordered by Iraq to the north and west, by Saudi Arabia to the south and south-west, and by the Arabian Gulf to the east. The ground is in general a flat, gently undulating desert plain with occasional low hills, escarpments, and depressions (Al-Saleh and Khalaf 1982). Sediments ranging in age from Eocene to Recent make up the bulk of the surface and near surface formations of Kuwait. The soil profile typically consists of a surface layer of wind-blown fine dune sand with silt content often near 10 per cent. The wind-blown layer usually extends from the surface to a depth of 6 m. It is underlain by a dense to very dense marine deposit of silty sand, containing between 5 and 35 per cent silt and clay, which is usually cemented. It is known locally as `gatch' and extends to limestone bedrock, which occurs at great depth.

The climate of Kuwait is characterised by extremely hot and dry summers, with an average daily temperature of about 45° C, and mild to cold winters. The mean annual rainfall is about 100 mm, with virtually no rain from May to October (Al-Saleh and Khalaf 1982). The rate of evaporation is high throughout the year. The excess of evaporation over rainfall leads to upward movement, or leaching of groundwater and a concentration of soluble materials at or near the surface, enriching the top layers with gypsum and carbonates and leading to the formation of crusts of cemented soils (Fookes and Higginbottom 1980). The carbonate material enclosing or cementing the mainly quartz soil particles consists of calcite (calcium carbonate) and/or dolomite (calcium-magnesium carbonates). In some cases gypsum (calcium sulphate) acts as a cementing agent, replacing the carbonates in the soil. Gypsum dehydrates in the sun temperature reached at the desert surface, rehydrating with expansion when exposed to moisture (Fookes and Higginbottom 1980).

Soil Conditions, Sampling, and Testing Program

Three sites as shown in Fig. 1 were chosen for testing. Sites 1 and 2, named Subhan and Bayan respectively, represent weakly-cemented and strongly-cemented silty sand extending almost to the ground surface. Borings at both sites indicated very dense conditions with the Standard Penetration Test (SPT) values exceeding 50 at all depths. Site 3, located in Salmiya, has different soil conditions. The soil profile includes an upper layer of calcareous compact to dense wind-blown dune sand with little silt to a depth of 3 m over the very dense cemented silty sand deposit. The wind-blown sand, which is usually uncemented, was found to contain large very weakly-cemented lumps at this location. Hence it was decided to test cemented samples from this deposit. Fig. 2 shows the soil profile at the three sites, together with the SPT values and the level of sampling.


Cubed block samples of approximate size 0.3 m to 0.5 m were taken from the bottom of just-opened excavations. Moisture loss from these blocks was prevented by wrapping them with plastic bags before transportation to the laboratory. Undisturbed samples were trimmed to fit the sample holder of the test apparatus by sawing and rubbing with sandpaper for final refinement. The sample preparation process is time consuming and, on average, 50 per cent of the samples had to be discarded for failing to be of the proper size. However, this is the only way good undisturbed samples can be taken in cemented sands.

The testing program consisted of first determining the basic and classification properties of each soil, followed by direct shear and consolidation tests. The effect of saturation on the strength and compressibility was examined by testing pre-soaked samples. The test results are presented and compared herein for the three soils possessing varying degrees of cementation.

Physical and Index Properties

The samples for classification tests were prepared by breaking the block samples, first by mortaring with a rubber pestle, followed by treatment with 4 per cent Sodium Hexametaphosphate solution for 24 hours. However, the latter was not necessary for samples from Salmiya which crushed easily under light hand pressure. Atterberg limit tests were conducted on fractions passing the No. 40 U.S. (approx. 0.5 mm) sieve. Grain size distribution curves are shown in Fig. 3. Table (summarises the test results including natural moisture content, dry density, grain size distribution, Atterberg limits, shrinkage limit, specific gravity, and classification. The latter is based on the Unified Soil Classification system and on `AASHTO' M145 (AASHTO 1970).

An examination of Table I reveals that the natural moisture content was well below the shrinkage limit at all locations, indicating moisture deficiency and possible sensitivity to saturation. The per cent fines appears to be related to the degree of cementation as it increased from 8 per cent for the very weakly-cemented Salmiya dune sand to 15.5 per cent and 25.8 per cent for the weakly- and strongly-cemented samples taken from the same `gatch' formation at Subhan and Bayan.

A summary of the chemical tests is given in Table II It indicates that quartz was the predominant mineral in all samples. The principal cementing agents at all sites were the same, namely carbonates and sulphates, which usually exist in the form of gypsum. The amount of carbonates was limited to about 5 per cent or less for Subhan and Bayan which agreed with other findings (Riedel and Simon 1973) on similar soils. For Salmiya, however, the amount of carbonates was 15.5 per cent which indicated that the degree of cementation is not solely proportional to the amount of carbonates in the soil, and that other factors such as density, gradation, origin, and composition affect the degree of cementation.

Falling head permeability tests carried out on samples from Subhan indicated a coefficient of permeability of 1.7 x 10-3 mm/s. Other tests performed in boreholes on similar local soils (Electrowatt Engineering Services Ltd 1984) indicated values in the same range increasing to the 10-2 mm/s range for the upper dune sands.

95

Entertainment City

Kuwait Univ.

ARABIAN GULF

O..

c. 0 cla

c. ?.... `6 .s.

0.)

'-';s 'f----.. Ln ,.5.• ARABIAN GULF

en

• Bayan

a. Sixth Ring Road 4.

Scale 1 200000

Subhan 0

Kuwait Intl Airport

mm 500/150

500/170

500/160

500/150

500/150

500/170

500/120

500/110

500/80

500/90

Grey Calcareous

Slightly Plastic

Weakly Cemented

Fine to Medium

Silty Sand (SC)

mm 500/180

500/200

500/150

500/180

500/160

500/280

500/170

500/180

500/140

500/100

500/100

Grey Calcareous

Strongly Cemented

Fine to Coarse

Silty Sand with

a Trace of Fine

Gravel (SM)

mm 120

230

370

Brown Calcareous Fine Windblown Sand with a Trace of Silt and Cemented Lumps (SP)

500/220 Grey Calcareous

520/220 Fine to Coarse

500/200 Silty Sand, Occasionally

Cemented (SM—SC) 550/200

570/200

550/200

600/200

600/150

0

1

2

3

4

5

6

7

8

9

10

11

12


Fig. 1 — Location plan showing test sites

Depth SPT Soil Description SPT Soil Description

SPT Soil Description

(m) (Blows/0.3 m)

(Blows/0.3 m)

(Blows/0.3 m)

SITE 1 — SUBHAN

SITE 2 — BAYAN

SITE 3 — SALMIYA

NOTE: BLOCK SAMPLES DEPTH:

Subhan 8.5 m Bayan 2.0 m Salmiya 2.0 m

Fig. 2 — Soil conditions at test sites

96 Australian Road Research, 16(2), June 1986

5 1 05 Diameter (mm)

0.1 0.05

AS Sieve Sizes (mm) 1009.5 6.7 4.75 2.36 1.18 0.600 0.300 0.150 0.075

90

80

70

60

% Passing 50

40

30

20

10

Fig. 3 - Grain size distribution curves

0 10


Strength Characteristics

Unconfined compression tests conducted on samples from Subhan and Bayan indicated an unconfined compressive strength of 83 kPa and 2900 kPa respectively. For Salmiya, attempts to trim an undisturbed sample failed due to the very weak cementation. However, its magnitude was judged to be less than the measured value for Subhan.

Drained direct shear tests indicated that peak strength increased with increasing normal pressure with volume expansion (dilation) occurring during shear. A comparison of the stress displacement curves and the volume change during shear is shown in Fig. 4 for the three soils tested at a normal pressure of 100 kPa. A brittle failure occurred for the strongly-cemented Bayan soil compared with a ductile failure of the weakly-cemented soils of the other two sites. This mode of failure was the same under the normal pressures employed herein, which varied between 50 and 200 kPa.

Table I

Summary of Physical and Index Properties

Site Depth (m)

Natural Moisture Content

(%)

Dry Density (IcN/m3)

ASTM Grain Size Distribution (%)

A nerberg Limits (%)

Shrinkage Limit (%)

Specific Gravity

Classification

Fine Gravel

Coarse Sand

Medium Sand

Fine Sand

Passing US. #200 Sieve

Liquid Limit

Plastic Limit

Unified Soil

System

Group* Index

Subhan 8.5 10.0 17.1 0.2 3.5 37.9 42.9 15.5 26.4 19.1 16.7 2.66 SC A-24

Bayan 2 6.8 17.5 0.3 26.1 47.8 25.8 41.0 35.0 19.3 2.68 SM A-2-5

Salmiya 2 1.0 17.2 8.8 8.0 75.2 8.0 NP NP None 2.66 SP A-3

• AASHTO M145

Table II

Chemical Analysis of Soil Samples

Components Content (%)

Subhan Bayan Salmiya

Si02 85.64 84.69 69.20

Fe203 0.76 0.58 0.88

A1203 3.52 3.94 7.30

CaO 3.40 0.22 9.96

MgO 2.45 * 2.07

Organic Matter 0.78 2.58 0.89

CO2 2.62 2.05 6.83

MgCO3 0.73 1.69 *

CaCO3 4.71 0.51 15.52

Cl (ppm) 250 160 710

SO3 (ppm) 2670 1230 250

pH Value 8.30 9.95 8.71

* Not measured


An examination of Fig. 4 reveals that the residual strength was nearly the same for the three soils. As previously noted by Clough et al. (1981) the effect of increased cementation resulted in an increase in peak strength, and a decrease in the corresponding strain. Moreover, the volume increase during shear occurred over a small range of displacement.

A summary of the strength parameters based on the peak and the residual strengths is given in Table III Cementation resulted in a cohesion intercept, and an angle of friction greater than the residual values. One of the interesting aspects of these data is the similarity of the residual friction angles of all the soils. Since the resistance to failure is due to friction and cementation, when cementation is broken at peak strength the remaining component due to friction would be nearly the same for all soils. The difference between the peak and residual angles of frictions was not significant except for the strongly cemented soil of Bayan.

Because of the moisture deficiency of the local soils having their natural moisture content below the shrinkage limit, it was decided to examine the effect of saturation on

97

on = 100 kPa

Shear Stress

(kPa)

I_

1

2

3

4

5

Bayan

1 2

3

4

5

6

7

Shear Displacement


6 7

V/V* (%)

Exp.

Cont.

= AH/H

Fig. 4 — Stress displacement curves for cemented soils

Table III

Summary of Direct Shear Strength Parameters for Cemented Soils

Site Thy Unit Unit

(kN/m3)

Unconfined Strength

(kPa)

Peak Cohesion Intercept in

(kPa)

Peak 0 (0)

Residual Cohesion Intercept

(kPa)

Residual 0 (0)

Peak Sat. Cohesion Intercept

(kPa)

Peak Osa,

Subhan 17.1 83 10 40 0 36 5 37

Sayan 17.5 2900 50 54 0 36 10 38

Salmiya 17.2 20 40 0 33 0 35

* Not measured; samples crushed under light finger pressure.

the strength parameters. This was prompted by the fact that some contractors occasionally use flooding to facilitate excavation in strongly-cemented soils. For this purpose, specimens were subjected to the desired normal pressure, followed by flooding of the shear box with water for 24 h. Subsequently, the specimens were sheared at a very slow rate to ensure dissipation of excess pore water pressure.

A comparison of the strength parameters for natural moisture and saturated conditions (Sr = 100 per cent) is shown in Table III. Comparing the peak parameters in both conditions, it is evident that both the cohesion intercept and the angle of friction decreased after soaking. This is shown in Fig. 5 where the shear stresses v. normal stresses are plotted and the Mohr Coulomb envelopes are determined for the three test soils. In fact, the residual angles of friction from tests at natural moisture content were similar to the peak values under saturated conditions. This implies loss of all or most of the cementation component of strength upon saturation. To examine this aspect of behaviour, the stress-displacement curves for the natural and saturated moisture conditions are compared in Fig. 6 at a normal pressure of 100 kPa. The centre curves

98

for Bayan demonstrate clearly the change from brittle to ductile failure mode after saturation and the associated loss of cementation. For the other two sites, the curves for the saturated condition lie below and nearly parallel to the natural moisture condition curves.

To provide a clear understanding of the effect of saturation, the stress displacement curves for the saturated samples were subtracted from the stress-displacement curves of samples tested at natural moisture content. The net curves shown in Fig. 7 represent nearly, but not entirely, all of the effect of cementation. The basis for this assumption is the similarity of the residual parameters of Table III with the peak saturated parameters provided that the peak saturated cohesion intercept is small and can be neglected. An examination of Fig. 7 indicates that the net curves peak at a small displacement of 1 mm or less, and then decline and approach a small stable value at large displacement. The peak in these curves corresponds to the mobilisation of cementation bonds which are usually broken at small displacement levels (Clough et al. 1981; Saxena and Lastrico 1978).


L

(1) (deg)

40

37

c (kPa)

10

5

Unsoaked

Soaked

80 160 240 320

0 (deg)

54

38

c (kPa)

50

10

Unsoaked

Soaked

0 80 160 240 320

c (kPa) ¢ (deg)

20 40

0 35

Unsoaked

Soaked vc\

240

0

320

80

0

240

160 Shear Stress

(kPa)

80

240

Shear Stress

(kPa)

160

160 Shear Stress

(kPa)

80

Site : Subhan r

Site : Bayan

I I

Site : Salmiya


0 80 160 240 320

Normal Stress (kPa)

Fig. 5 — Mohr-Coulomb envelopes for unsoaked and soaked conditions

Consolidation Tests

Compressibility characteristics were determined by con-solidation tests on 63.5 mm diameter undisturbed samples. Initially the effect of saturation and the possible collapse potential was examined in a manner similar to that suggested by Knight (1963). A sample was loaded in the consolidation apparatus at its natural moisture content until a pressure of 200 kPa was reached. At the end of this loading, the specimen was flooded with water and left for a day, and the test was then continued to its maximum


loading limit. The resulting curves for the test soils are shown in Fig. 8. The collapse potential 'CP' is defined as:

e OH c CP =

1 + e O

where Ae, change in voids ratio upon wetting, natural voids ratio,

change in height upon wetting, and

initial height.

99

e, =

AHc =

H, =

Site : Bayan Depth : 2.0 m an = 100 kPa

Unsoaked

11 1 1 1 1 1 1 1

Soaked


160

Shear Stress

(kPa) 80

240

160 Shear Stress (kPa)

80

0

11 11 1 1 1 1 1

Site : Subhan Depth : 8.5 m on = 100 kPa

0 1 2

3

4

5

6

7

0

2

3

4 5

6 7

Shear Stress

(kPa)

160

Site : Salmiya Depth : 2.0 m an = 100 kPa

80

Unsoaked

Soaked

1 2

3

4 5

6 7

Shear Displacement (mm)

Fig. 6 — Comparison of stress displacement curves for soaked and unsoaked conditions

Difference between Unsoaked & Soaked Shear Stress

(kPa)

240

160 an = 100 kPa

80

0

2

3

4 5

6 7

Shear Displacement (mm)

Fig. 7 — Difference between stress displacement curves at unsoaked and soaked conditions

Jennings and Knight (1975) have suggested some severity ratings for different values of the collapse potential as shown in Table IV

From Fig. 8 the collapse potential was calculated to be 0.5 and 0.4 for Subhan and Bayan, respectively, and 3.6 for Salmiya. Comparing these values with the ratings on Table IV, the Salmiya soils would be considered to have moderate trouble with collapse. This can be explained by the fact that the Salmiya sample was taken from the

100

wind-blown dune sand — an aeolian deposit which is known to collapse upon saturation (Clemence and Finbarr 1981; Lobdell 1981). Generally the soil deposit is not cemented but it occasionally contains very weak calcareous cemented lumps which lose strength upon wetting. The Subhan and Bayan soils have a more competent and stable matrix, resulting from stronger cementations and larger percentage of fines, and are not collapsible. The possibility of collapse apparently increases substantially when very


0.56 1 I Hill

50 100

O3? 10

I I 1 ILI 1 d 500 1000 5000

200 kPa 0.52

0.48

Void Ratio, e

0.44

Site NMC Dry eo CP % Density (%)

(kN/m2 )

Subhan 10.8 17.1 0.526 0.5

Bayan 6.8 17.5 0.522 0.4

Salmiya 1.0 17.2 0.527 3.6

0.40

0.36


Table IV

Collapse Potential Values (after Jennings and Knight (1975))

CP (%) Severity of Problem

0-1

No problem

1-5

Moderate trouble

5-10

Trouble

10-20

Severe trouble

> 20

Very severe trouble

weak cementations or calcareous bonds are present when the percentage of fines is limited to 10 per cent or less.

In order to investigate the effect of saturation on the compressibility characteristics and settlement under load, double consolidation tests were performed on the three soils (Peck, Hanson and Thornburn 1974) using the method proposed by Jennings and Knight (1975) and employed by Clemence and Finbarr (1981). Two identical undisturbed samples were placed in consolidmeters under a 1 kPa load for 24 h. At the end of this period, one sample was saturated by flooding with water, while the other sample was kept at its natural water content. Both samples were left for a further 24 h. The test is then completed in the ordinary manner as per ASTM D2435 for one-dimensional consolidation testing. The results of the present tests are shown in Fig. 9. It can be seen that the two curves do not start from the same point, with the curve for the saturated samples (Sr = 100 per cent) usually

below the other. Interestingly, however, samples from the Bayan site exhibited swelling (0.9 per cent) during the initial saturation (Slater 1983) under a pressure of 1 kPa.

In order to calculate the settlement, the total overburden pressure Po, at the depth of the sample is calculated and plotted on the e logp curves obtained from the two tests. The pre-consolidation pressure Pc, is found from the soaked curve employing the Casagrande empirical method, and compared with Po. For the case of normally-consolidated soil in which PC/PO = 0.8 to 1.5, compression is considered to occur along the virgin curve and the natural moisture content curve is adjusted to the (eo, Po) point by drawing a curve parallel to the natural moisture consolidation curve, as shown in Fig. 9.

If the load is increased by 4, then the settlement will consist of two components as follows:

Li e A e

S C

1 + e 1 + e 0

With reference to Fig. 9 the first term is the unit settlement due to an increase in pressure Ap without change in the moisture content, and the second term is the additional unit settlement due to saturation. A comparison of the second term of eqn (2) for the test soils, under the same pressure increment Ap = 300 kPa, is evident from Fig. 9. It indicates that the largest value of the second term is for the Salmiya soils, decreasing sharply and approaching zero for Subhan and Bayan soils. For the latter, if the initial swelling due to saturation is considered, the resultant effect will be a net heave of volume increase. The initial swelling is possibly due to the presence of gypsum.

Consolidation Pressure (kPa)

Fig. 8 — Collapse potential test results


Po Pc

Po

Pc P

AP

Te es

Salmiya Depth = 2.0 m Soaked

Pc

Subhan :Depth 8.5 m Soaked

Po

* Soil at natural moisture content

0 Soil soaked after 24 hour bedding at 1 kPa

• •

Sayan Depth = 2.0 m Soaked



10 100 500 1000 3000

0.48

Void Ratio,

0.44

0.40 10

100

500 1000

3000


Fig. 9 - Double consolidation test results and adjustment for settlement

calculations

A summary of the consolidation test data is given in Table V. Indicated are site location, depth, overburden pressure, consolidation pressure, initial voids ratio, compression index cc, swelling index Cs, Cc/1-i-e0' the coefficient of consolidation cv at a pressure of 200 kPa,

Table V

and the number of tests performed. A comparison of these results with consolidation tests performed on samples from the New Telecommunications Center Building and Antenna Tower (Electrowatt Engineering Services Ltd 1984) in Kuwait City reveals similar trends. The compression index Cc was smaller than 0.10 and Cc/l+e, ranges up to 0.05 (see Table V).

Foundation Design and Construction in Cement Soils

The preceding test results indicate that saturation of cemented soils leads to some loss of shear strength and a reduction in bearing capacity. Increased settlement is also expected, leading to differential settlement, particularly when saturation occurs over a portion of the site rather than over the entire site. It is therefore necessary to use saturated or soaked strength parameters in the design of foundations and earth retaining structures in cemented soils. The design of pavements requires subgrade par-ameters such as the California Bearing Ratio (CBR) and the subgrade modulus which should be also based on soaked conditions. The additional settlement due to saturation should be calculated from the results of double consolidation tests, and accounted for in design.

Foundations in cemented soils should be placed on the virgin ground to avoid loss of strength due to the breaking of cementation bonds. Proper drainage system should be provided to facilitate quick drainage of rain and other water away from the site and prevent prolonged saturation. If this soil is used for backfilling, then field supervision should ensure proper placement to achieve the highest possible relative compaction. Several incidents of ground floor slabs settlement and cracking of building walls have occurred recently in Kuwait due to improper compaction and subsequent soaking and the effects were clearly visible after heavy rain occurred in the winter season.

Of the local layers examined in this work the more permeable upper wind-blown layer is sensitive to saturation compared with the lower `gatch' layer. The latter is more competent and is less affected by saturation. The upper layer, however, displayed moderate collapse and additional in situ tests such as the plate bearing tests and cone tests are recommended and will be carried out to fully assess the effects of saturation by means of field tests. The results of these tests will be presented in a follow-up paper.

0.50

0.46

Void Ratio, e

0.42

0.38

0.54

0.50

0.46

Void Ratio, e

0.42

0.38

0.52

Summary of Consolidation Test Results

Site Depth (m)

Overburden Pressure, Pp (kPa)

Preconsolidation Pressure Pc (kPa)

Initial Void

Ratio, eo

Compression Index,

Co

Swelling Index,

Cs

Co/Cs Coa eo Coefficient of Consolidation

c,, m2/year at 200 kPa

No. of

Tests

Subhan 8.5 150 110 0.509 0.083 0.011 7.5 0.055 10.6 2

Bayan 2.0 30 150 0.519 0.079 0.022 3.6 0.052 16.8 2

Salmiya 2.0 36 50 0.492 0.050 0.011 4.5 0.034 10.0 2

Kuwait City 4-59 70-700 63' 0.436' 0.048' 0.013' 3.8' 0.033* 44.8* 20

* Average of 20 Tests

102



Conclusions and Recommendations

Based on the test results presented in this paper the following conclusions and recommendations are made.

(1) Cemented sandy soils in Kuwait are moisture deficient. The behaviour of these soils depends on the degree of cementation which varies from very weak to strong. Also, density, gradation, and mineral composition affect the behaviour of these soils.

(2) Strongly-cemented soils show brittle failure during shear while weakly-cemented soils show ductile failure under low to moderate normal pressures. Volumetric strain occurs during shear for all soils at a small displacement.

(3) Cementation results in a cohesion intercept and an increase in the angle of friction over uncemented soils. The residual parameters are nearly the same for all cemented soils.

(4) Long-term saturation results in the loss of all or most of the cementation component of strength. The peak parameters for the saturated condition compared well with the residual parameters from tests at natural moisture content.

(5) In view of the effect of saturation on strength, it is recommended that the saturated parameters be employed in foundation design and slope stability analysis.

(6) The amount of consolidation settlement expected in cemented sands and silty sands is small. However, the upper deposit of wind-blown dune sand, which is usually uncemented, is sensitive to saturation. It displayed modest collapse upon wetting. The amount of fines in this deposit and others suspect to collapse is usually limited to 10 per cent. The lower deposit of cemented silty sand locally known as `gatch' is more competent, denser, and contains a larger percentage of fines and slight plasticity. It shows nearly no collapse upon wetting. On the contrary, it might swell upon saturation.

(7) The added settlement due to saturation of cemented soils should be calculated from double consolidation tests and accounted for in design.

(8) The effect of saturation on cemented soils should be assessed by additional in situ tests such as the plate bearing and static cone tests and the results compared with laboratory tests.

References

AL-SALEH, S. and KHALAF, F.I. (1982). Surface texture of quartz grains from various recent sedimentary environments in Kuwait. J. Sedimentary Petrology 52(1), March, pp. 215-25.

AMERICAN ASSOCIATION OF STATE HIGHWAY AND TRANSPORTATION OFFICIALS (1970). Standard specification for highway materials and methods of sampling and testing. 10th Ed. (AASHTO: Washington.)

AMERICAN SOCIETY FOR TESTING AND MATERIALS (1982). Annual book of standards. Part 19, 'Soil and Rock; Building Stones'. (ASTM: Philadelphia, Pa.), pp. 380-86.


BECKWITH, G.H. and HANSEN, L.A. (1982). Calcareous soils of the Southwestern United States. Symp. on Geotechnical Properties, Behaviour, and Performance of Calcareous Soils. ASTM STP 777, pp. 16-35.

BERINGEN, F.L., KOLK, H.J. and WINDLE, D. (1982). Cone penetration and laboratory teting in marine calcareous sediments. Symp. on Geotechnical Properties, Behaviour, and Performance of Calcareous Soils. ASTM STP 777, pp. 179-209.

CLEMENCE, S.P. and FINBARR, A.O. (1981). Design considerations for collapsible soils. J. Geotech. Eng. Div., ASCE 107(GT3), Proc. Paper 16106, pp. 305-17.

CLOUGH, G.W., SITAR, N., BACHUS, R.C. and RAD, N.S. (1981). Cemented sands under static loading. J Geotech. Eng. Div., ASCE 107(GT6), Proc. Paper 16319, pp. 799-817.

DATTA, M., GULHATI, S. and RAO, G. (1982). Engineering behaviour of carbonate soils in India and some observations on classification of such soils. Symp. on Geotechnical Properties, Behaviour, and Performance of Calcareous Soils, ASTM STP 777, pp. 113-40.

ELECTROWATT ENGINEERING SERVICES LIMITED (1984). Site investigation engineering report. New Telecommunications Centre Building and New Antenna Tower, Kuwait. Electrowatt Engineering Services Ltd, Zurich, Switzerland.

FOOKES, P.G. and HIGGINBOTTOM, I.E. (1980). Some problems of construction aggregates in desert areas, with particular reference to the Arabian Peninsula. 1: Occurrence and special characteristics. 2: Investigation, production and quality control. Proc. Inst. Civ. Eng. 68(1), London, pp. 39-90.

JENNINGS, J.E. and KNIGHT, K. (1975). A guide to construction on or with materials exhibiting additional settlement due to 'collapse' of grain structure. Sixth Reg. Conf. for Africa on Soil Mechanics and Foundation Eng., pp. 99-105.

KNIGHT, K. (1963). The origin and occurrence of collapsing soils. Proc. Third Reg. Conf. for Africa on Soil Mechanics and Foundation Eng. 1, pp. 127-30.

KRYNINE, D.P. and JUDD, W.R. (1957). Principles of Engineering Geology and Geotechnics. (McGraw-Hill: New York.)

LOBDELL, G.T. (1981). Hydroconsolidation potential of polouse loess. J. Geotech. Eng. Div. ASCE 107(GT6), Proc. Paper 16309, pp. 733-42.

NETTERBERG, F. (1982). Geotechnical properties and behaviour of calcretes in South and South-West Africa. Symp. on Geotechnical Properties, Behaviour and Performance of Calcareous Soils, ASTM STP 777, pp. 296-309.

OWEIS, I. and BOWMAN, J. (1981). Geotechnical con-siderations for construction in Saudi Arabia. J. Geotech. Eng. Div., ASCE 107(GT3), Proc. Paper 16092, pp. 319-38.

PECK, R.B., HANSON, W.E. and THORNBURN, T.H. (1974). Foundation Engineering. 2nd Ed., pp. 333-46. (Wiley: New York.)

RIEDEL, G. and SIMON, A.B. (1973). Geotechnical properties of Kuwaiti `gatch' and their improvement. Eng. Geol. 7, pp. 153-65.

SAXENA, S.K. and LASTRICO, R.M. (1978). Static properties of lightly cemented sand. J Geotech. Eng. Div., ASCE 104(GT12), Proc. Paper 14259, pp. 1449-64.

SLATER, D.E. (1983). Potential expansive soils in Arabian Peninsula. Technical Note. J. Geotech. Eng. Div., ASCE 109(5), pp. 744-46.

103


Dr Nabil F. Ismael obtained his Bachelor's degree in 1966 from Cairo University, Egypt, and his M.Sc. and Ph.D. in 1970 and 1974 from Duke University, North Carolina, U.S.A. From 1966-68 he served as an instructor at Cairo Univrsity. Between 1969 and 1972 he was a graduate student at Duke University. In 1972 Dr Ismael joined the Port Authority of New York and New Jersey in New York as a Civil Engineer. Beween 1974 and 1978 he was a Research Engineer at Ontario Hydro in Toronto, Canada. In 1978 Dr Ismael joined Kuwait University as an Assistant Professor where he is currently an Associate Professor of Civil Engineering. He has published a number of papers and research reports in the area of soil properties, foundation testing and design.

Mohammad A. Mollah received his B.Sc. in Civil Engineering in 1968 from Bangladesh University, and M.S. in Soil Engineering in 1977 from the Asian Institute of Technology, Bangkok. From 1968 to 1977 he has been a structural engineer on a multi-storey building project in Bangladesh. In 1977 he took a job as a Soil Engineer in Iraq. In 1980 he joined the Ministry of Public Works, Government Laboratories and Testing Station, Kuwait as a Soils Engineer. During his professional career he acquired wide ranging experience with the soil properties and behaviour of Eastern and Middle Eastern countries.

N.F. ISMAEL, M.Sc., Ph.D.

M.A. MOLLAH, B.Sc., M.S.

Mr Omayya AI-Khalidi received a Diploma from the International Correspondence Schools (London) in Civil Engineering in 1967. Hejointed the Government Laboratories and Testing Station, Ministry of Public Works, Kuwait in 1957 as a laboratory technician where he became a chief laboratory technician in 1979. He has nearly 30 years experience in materials and soil testing.

0. AL-KHALIDI, Dip.C.E.

104 Australian Road Research, 16(2), June 1986

Documents

Geotechnical Properties of Cemented Soils in Kuwait