Geotechnical properties of calcrete soil (Gatch) in Kuwait

Engineering Geology, 28 (1990) 191-204

191

Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Technical Note

Geotechnical Properties of Calcrete Soil (Gatch) in Kuwait JAWAD S. AL-SULAIMI, MOHAMMAD A. MOLLAH and MUNEER A. MATTI Kuwait Institute for Scientific Research, P.O. Box 24885, 13109 - - Safat (Kuwait) Government Laboratories and Testing Station, Ministry of Public Works, P.O. Box 8, 13001 - Safat (Kuwait) Formerly, Engineering Department, Kuwait Institute for Scientific Research, P.O. box 24885, 13109- Safat (Kuwait)

(Received December 11, 1986; accepted after rewsion January 1, 1989)

ABSTRACT A1-Sulaimi, J.S., Mollah, M.A. and Matti, M.A., 1989. Geotechnical properties of calcrete soil (gatch) in Kuwait. Eng. Geol., 28: 191-204. This paper presents the results of a comprehensive laboratory testing program carried out to study the geotechnical properties of gatch (calcrete soil) samples. A total of 17 samples collected from 17 different sites in Kuwait City and its suburbs were used for the study. The testing program included determination of physical, index and engineering properties of gatch samples. The sensitivity of various geotechnical properties of compacted gatch was examined by testing specimens at various moisture contents and also at different soaking periods.

INTRODUCTION G a t c h is t h e local n a m e of a p a r t i a l l y c o n s o l i d a t e d s e d i m e n t o f a m a s s i v e c a l c r e t e t y p e f o u n d in m a n y p a r t s of K u w a i t a t v a r i a b l e d e p t h b u t g e n e r a l l y a b o u t 2 m b e l o w t h e surface. T h i s deposit w h i c h c a n a t t a i n t h i c k n e s s e s o f t e n s of m e t e r s , c o n s i s t s b a s i c a l l y of q u a r t z s a n d s c e m e n t e d p r e d o m i n a n t l y by c a r b o n a t e s (calcite a n d / o r dolomite). S i n c e 1950 a h u g e c o n s t r u c t i o n p r o g r a m h a s b e e n u n d e r w a y in K u w a i t , in w h i c h g a t c h h a s b e e n u s e d p r i n c i p a l l y as a sub-base m a t e r i a l for r o a d c o n s t r u c t i o n , for t h e f o r m a t i o n o f e m b a n k m e n t s a n d for fill m a t e r i a l . G a t c h is also t h e soil on w h i c h m o s t b u i l d i n g f o u n d a t i o n s rest. C o n s i d e r a b l e field a n d l a b o r a t o r y w o r k h a s b e e n c a r r i e d o u t in t h e p a s t by e n g i n e e r s e n g a g e d in specific projects, b u t so f a r n o a t t e m p t h a s b e e n m a d e to c o r r e l a t e t h e r e s u l t s of t h e s e studies so as to o b t a i n a g e n e r a l p i c t u r e o f g a t c h deposits. T h i s p a p e r presents the geotechnical properties and characteristics of gatch encountered in K u w a i t C i t y a n d its suburbs. A t o t a l o f 17 d i s t u r b e d g a t c h s a m p l e s w e r e r a n d o m l y c h o s e n f r o m d i f f e r e n t a r e a s for a n i n t e n s i v e l a b o r a t o r y g e o t e c h n i c a l testing. T h e p r o g r a m o f t e s t i n g i n c l u d e d t h e d e t e r m i n a t i o n of t h e b a s i c a n d 0013-7952/90/$03.50

© 1990 Elsewer Science Publishers B.V.

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strength properties. The effect of saturation of various degrees on soil properties was also examined. GEOLOGICALSETTINGAND CLIMATE Kuwait is a small country located in the northeastern edge of the Arabian peninsula, bordered by the Arabian Gulf in the east. The eastern part of the Arabian Peninsula, known as the Arabian Shelf, consists of a sedimentary succession in which the most common rock types are sandstone and carbonate rocks (Powers et al., 1963). The area of Kuwait constitutes a part of the interior homocline of the Arabian Peninsula. The rocks exposed range in age from Eocene to Recent. The Dammam Limestone Formation, of Eocene Age, crops out along the Ahmadi Ridge about 40 km south of Kuwait City and is the oldest rock exposed m Kuwait. The Dammam Limestone is overlain by a sequence of terrigenous sediments t h a t range in age from Miocene to Recent. These sediments are exposed in the Jal Az-Zor Escarpment northwest of Kuwait City. The rock sequence of Jal Az-Zor consists of three main formations named, from bottom to top, Ghar, Fars and Dibdibah (Fuchs et al., 1968). The Dibdibah Formation covers most of the northern area of Kuwait and consists mainly of a fluviatile sequence of cross-bedded sands and gravels usually cemented by gypsum and carbonates. The rest of Kuwait is covered by other Quaternary deposits. The climate of Kuwait is characterized by a typical desert environment, with prolonged hot dry summers and mild to cool, relatively wet winters. Annual pan evaporation is about 3500 mm per year which increases gradually from a minimum value of 2.1 mm/day in winter (January) to a maximum of 13 mm/day in summer (June and July). PETROGRAPHY OF THE GATCH A typical fully developed simple soil profile m the study area can be divided into five zones or horizons. In descending order these are: (1) aeolian soil 0.5 to 10 m thick, but commonly less t h a n 2 m; (2) up to 3 m thick of friable sand with powdery calcrete or tightly cemented calcrete lumps (nodules) up to 30 cm m diameters; (3) massive calcrete 0.2 to 2 m in thickness (gatch); (4) a mottled calcrete zone up to 2 m in thickness; and (5) unaltered parent material. Detailed accounts of the diagenesis and formtion of the different calcrete zones have been published by A1-Sulaimi (1988). The massive calcrete (gatch) is a white to light-yellowish, porcellaneous, carbonate rock. It consists of variably cemented and replaced sand particles. The carbonate in the massive calcrete (gatch) represents a substantial replacement of the original material. Mineral grains such as quartz and feldspar are etched and replaced to varying extents by carbonate. The dominant cementing material is largely low-magnesium calcite (1-4 mole ~/o MgCO3) and]or microcrystalline dolomite. Moderately coarse (up to 0.6 mm) dolomite usually occurs as subhedral or small euhedral rhombs whereas the low-magnesium

GEOTECHNICAL PROPERTIES OF CALCRETE SOIL (GATCH) IN KUWAIT

pp. 193-196

I

*

KUWAIT &SUBURBS

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Fig.I. Map of Kuwait City and its suburbs showing sampling locations.

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GEOTECHNICAL PROPERTIES OF CALCRETE SOIL (GATCH) IN KUWAIT

197

calcite often occurs as microsparite and sparite. The carbonte fraction in the massive calcrete averages 60% (range 15-90~/o) with the dolomite content averaging 40% (range 5-90%). Gypsum is also observed in a few gatch samples and in some cases it effectively cements the assemblage as a result of intensive replacement of the carbonate. The main effect of the diagenetic processes on this horizon is an overall decrease in porosity and effective permeability of the gatch zone due to cementation by carbonate (A1-Sulaimi, 1988). SAMPLING AND TESTING PROGRAM This study forms an integral part of the Kuwait Institute for Scientific Research project entitled "Study of the Gatch Deposits in Kuwait City and Suburbs" (A1-Sulaimi et al., 1984). Over 200 samples of gatch were collected from different locations of Kuwait City and its suburbs to study the geological characteristics. Out of these a total of seventeen massive gatch samples taken from various locations (Fig.l) were made available for geotechnical analysis. The samples were collected from depths ranging between 1.0 and 6.5 m from open test pits and also during visits to various construction sites. Upon receipt of the samples in the soil laboratory a visual classification was made followed by the determination of the natural moisture content. A systematic laboratory testing program was carried out in which firstly the basic and index properties of all the samples were determined. The compaction characteristics of gatch were determined employing both standard (2.5 kg rammer) and modified (4.5 kg rammer) energies. An intensive testing program was undertaken to study the strength parameters intended for foundation design analysis, as well as suitability of compacted gatch as a subgrade material using five selected samples. These tests included performing direct shear, California bearing ratio (CBR) and permeability tests using specimens compacted by both energies. The effect of soaking on strength characteristics was studied by performing tests at different soaking conditions. PRESENTATION AND DISCUSSIONSOF TEST RESULTS

Classification tests These tests were performed according to ASTM standards, and the results are summarized in Table I. The grain-size analysis indicates that sand size dominates the particle composition of the gatch, with gravel content varying between 0 nd 4%. The percentage of fine materials having the size of clay and silt particles varies between 8 and 33%. The mean grain-size diameter and specific gravity of soil solids vary from 0.15 to 0.8ram and 2.63 to 2.70, respectively. The plasticity of the gatch samples was determined on material fractions passing U.S. sieve size of 425 pro. Ten out of seventeen samples were found to be non-plastic (NP), and the remainder showed a low plasticity index (PI)

G-1 G-2 G-3 G-4 G-5 G-6 G-7 G-8 G-9 G-10 G-11 G-12 G-13 G-14 G-15 G-16 G-17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

16 05 1.5 03 15 4.1 14 27 19 15 05 03 19 6.7 2.0 38 41

(%)

Natural moisture content

11.9" 13 4 24.3 13 6 16 5 13 1 16.2 14.8 22.8 8 4*' 32.6 12.9 16 6 14 4 28 6 18.0 29 8

(%)

P a s s i n g no 200 US stove

*1Sample c o n t a i n s c e m e n t e d f r a g m e n t s (10 20%) *2Np = n o n - p l a s t i c

Locatmn

No

P h y s : c a l a n d i n d e x p r o p e r t i e s of g a t c h

TABLE I

0.70 0 23 0.18 0.20 0 20 0.30 0 23 0 51 0.27 0 60 0.16 0.34 0 20 0.30 0.17 0.20 0 17

Mean gram diameter, Ds0 (mm)

21.0 NP 20.3 NP NP NP 18.8 18 1 22 1 NP NP NP 23 2 NP NP NP 171

19.0 16 8 17 1 19 1 19 4 20.4 16 0 16.3 17.9 12.5 15.5 21 1 12.7 186 16.8 15 7 15 6

(%)

(%)

(%)

24.8 N P .2 28 7 NP NP NP 22 5 21.5 31 6 NP NP NP 25 0 NP NP NP 19 1

Shrinkage hmlt

Plastm hmlt

Llqu:d llm:t

2 65 2.66 2.69 266 2.68 2 63 2.65 2.60 2.70 2.58 2 72 266 2.65 2.63 2.70 2.67 2.70

(Vs)

Specific g r a v i t y of soil s o h d s

SM SM SC SM SM SM SM SM SC SM SM SM SM SM SM SM SM

U m f i e d soil classification system

Class:ficatlon

A-l-6(0) A-2-4(0) A-2-4(0) A-2-4(0) A-2-4(0) A-2-4(0) A-2-4(0) A-l-6(0) A-2-4(0) A-2-4(0) A-2-4(0) A-2-4(0) A-2.4(0) A-2-4(0) A-2-4(0) A-2-4(0) A-2-4(0)

Group index system

GEOTECHNICALPROPERTIESOF CALCRETESOIL(GATCH)IN KUWAIT

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between 2 and 10%. When plotted on the Casagrande chart, the gatch samples lie at or slightly above the A-line in the low plasticity region. Accordingly, the United Soil Classification System (USCS) designation of the gatch is SM-SC. For road works, the gatch belongs to a soil group of A-2-4. The results are in full agreement with those reported by Riedel and Simon (1973) on samples from three locations in Kuwait City, and by Ismael et al. (1984) on samples from the A1-Andalus area about 20 km southwest of Kuwait City. The shrinkage limit (SL) which is the moisture content of the soil below which little or no volume change is to take place is recorded to vary from 12.5 to 21.0% with an average of 17.0%. An examination of Table I reveals that the natural moisture content (NMC) is well below the shrinkage limit at all locations indicating a general moisture deficiency. Upon saturation, these soils are liable to swell; this explains why gatch soils at the surface crack once subjected to drying.

Compaction characteristics Test results summarized in Table II show the maximum dry density together with their corresponding optimum moisture content. The results obtained are similar to those reported by Riedel and Simon (1973). In constructions, TABLE II Summary of results of compaction tests No.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Average

Location

G-1 G-2 G-3 G-4 G-5 G-6 G-7 G-8 G-9 G-10 G-11 G-12 G-13 G-14 G-15 G-16 G-17

2.5 kg rammer and 305 mm drop

4.5 kg rammer and 457 mm drop

OMC (%)

~dm.x (kg/m a)

OMC (%)

?din., (kg/m 3)

11.0 11.0 13.0 13.0 13.0 12.5 10.5 13.0 15.0 8.5 12.5 12.0 13.0 9.5 12.0 12.5 13.0

1950 1915 1860 1880 1825 1870 1985 1895 1810 1880 1940 1850 1850 2000 1910 1880 1875

9.0 9.0 11.5 9.5 9.5 11.5 9.5 8.0 12.5 7.5 10.0 8.0 10.5 7.5 8.5 9.0 10.5

2060 1995 1970 2030 1940 1940 2040 2025 1965 1975 2040 1935 1970 2095 2065 2035 2025

12.1

1880

9.4

2005

OMC = optimum moisture content; ~dm.x= maximum dry density.

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compaction is deemed acceptable when in-situ dry density exceeds 95% of the density obtained in the laboratory for the standard of compaction applied. The in-situ dry density of gatch should be above 1900 kg/m 3 for the modified Proctor (4.5 kg rammer) and 1790kg/m 3 for the standard Proctor (2.5 kg rammer). The density of gatch is very sensitive to changes in moisture content. Once the optimum moisture content is exceeded, there is a sharp decrease in density, as the material becomes rather spongy and difficult to compact. Further increases in moisture content will cause the material to flow under compaction.

Strength characteristics The shear strength of a soil can be used to determine its ultimate bearing capacity. The test results of undrained samples (G-l, G-2, G-5, G-8 and G-14) compacted at optimum moisture content are given in Table III. Results showed that soaking for 24 and 96 h has little effect on shear strength. The angle of internal friction (~b) remained unchanged after soaking for samples compacted by 4.5 kg rammer and for samples compacted by 2.5 kg rammer it decreased by 1° only, which is insignificant in practical engineering work. Increasing the compaction effort caused an increase of 3 ° to 4 ° in the value of ¢, which indicates improvement in the shear strength of properly compacted soils. The cohesion (c) values were very small and ranged from 0 to 16 kN/m: for low compaction energy and from 0 to 28 kN/m 2 for higher compaction energy. It is interesting to note an increase in the value of c with soaking. This could be due to the wetting effect of the finer fractions of the gatch which also caused the material to swell.

Californm bearing ratio (CBR) The CBR tests were performed on five selected gatch samples (G-l, G-2, G-5, G-8 and G-14) prepared at optimum moisture content (OMC). The test results are summarized m Table IV. The average CBR value ranges from 4% to 32% for unsoaked specimens compacted with 2.5 kg rammer while the soaked CBR values for similar specimens ranged from 4% to 28%. This indicates that there is a slight decrease in strength due to soaking but not so significant. However, increasing the compactive effect resulted in 300% increase in CBR value and this explains why compaction has to be controlled. The swelling of the gatch was also investigated. It was found that the values ranged from 0 to 0.26%, and that swelling decreased with increasing compaction. This illustrates that if a satisfactory compaction cannot be guaranteed, the gatch is unsuitable unless its properties are improved by means other than compaction alone. The gatch is reported to be very sensitive to changes in the moisture content (Bissada and Qabazard, 1974). Accordingly, tests were carried out in which the molding moisture content at the time of compaction was varied from 4 to 16%.

c (kN/m 2)

peak

Unsoaked

10 0 6 14 0 12

43.3 42.8 45.0 41.7 42.8 43.2

38.7 40.4 40.5 38.7 40.0 39.7

0 0 0 0 0 0

0 0 0 0 0 0

~ c (degr.) (kN/m 2)

ultimate

*1Specimens compacted at OMC to y d . ~ .

U s i n g 4.5 kg rammer: G-1 8 G-2 10 G-5 12 G-8 10 (]-14 8 Average 9.6

G-1 G-2 G-5 G-8 G-14 Average

U s i n g 2.5 kg rammer:

Sample

S h e a r s t r e n g t h p a r a m e t e r s .1

TABLE III

33.7 34.3 34.0 32.7 33.7 33.7

32.6 31.8 32.0 32.0 33.3 32.3

~ (degr.)

12 10 8 12 10 10.5

10 16 8 16 8 12

c (kN/m 2)

peak

24 h s o a k e d

42.5 42.0 45.O 39.8 42.8 42.4

38.7 38.7 40.0 37.8 39.8 39.0

0 0 0 0 0 0

0 0 0 0 0 0

~ c (degr.) (kN/m 2)

ultimate

33.5 34.9 33.7 32.7 33.7 33.7

32.0 32.3 31.6 32.O 34.3 32.4

~ (degr.)

8 14 12 --16

8 8 12 16 -11

c (kN/m 2)

peak

96h soaked

42.8 42.0 44.4 40.9 -42.5

38.6 38.7 39.8 37.8 -38.7

33.7 33.7 33.7 33.7 33.7

--

32.0

32.6 32.0 32.0 31.3

(degr.)

0 0 0 0

0 0 0 0

~ c (degr.) (kN/m 2)

ultimate

t~

P~

O

.=

O ~0 t~

t~

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J S AL-SULAIM[ET ~L

T A B L E IV R e s u l t s of C B R t e s t s .1 Sample

Using standard G-1 G-2 G-5 G-8 G-14

Unsoaked, C B R (%, a v e r a g e of 2 tests)

r a m m e r (2 5 kg) 8 32 30 5 26

U s i n g h e a v m r r a m m e r (4 5 kg) G-1 58 G-2 57 G-5 66 G-8 93 G-14 56

24 h s o a k e d

96 h s o a k e d

C B R (%, a v e r a g e of 2 tests)

swelhng (%)

C B R (%, a v e r a g e of 2 tests)

swelling

6 28 25 5 19

0 0 0 0 0

11 02 04 11

6 28 25 6 20

0 0 0 0 0

15 07 04 07 11

25 61 52 50 51

0 0 0 0 0

02 03 09 11 07

22 62 54 43 41

0 0 0 0 0

0 0 16 20 02

(%)

*1Specimens c o m p a c t e d at o p t i m u m m o i s t u r e c o n t e n t to m a x i m u m dry d e n s i t y

These tests were carried out using 4.5 kg rammer on 2 selected samples (G-5 and G-8) only and the soaking conditions were varied as usual. The result of the test contains wholly the findings of Bissada and Qabazard (1974).

Permeability tests Permeability tests were conducted using five selected samples (G-l, G-2, G-5, G-8 and G-14). The specimens were prepared by compacting at OMC by both energies. The tests were conducted using the falling head method. The results are summarized in Table V. The permeability coefficient (k) TABLE V R e s u l t s of p e r m e a b l h t y t e s t s .1 Sample

G-1 G-2 G-5 G-8 G-14

P e r m e a b l h t y (m/s, × 10-1°) 2 5 kg rammer

4.5 k g r a m m e r

80 420 3400 46 34

22 305 740 06 6.30

*1Specimen c o m p a c t e d at O M C to ydmax

GEOTECHNICAL PROPERTIES OF CALCRETE SOIL (GATCH) IN KUWAIT

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varies between 4.6 and 3400"10 -1° m/s for specimens compacted by 2.5kg rammer, and 0.6 and 740"10 -1° m/s for specimens by 4.5kg rammer. This indicates a five-fold decrease in the permeability figures just by increasing the compactive effort. The average permeability coefficient of United States Bureau of Reclamation (USBR, 1977) for silty and clay sands varies from 720 to 480.10 -1° m/s and the soils are described as: (1) impervious when k is < 100.10 -1° m/s; (2) semi-impervious when k is 100 to < 1000"10 -1° m/s; (3) previous when k is > 1000-10-10 m]s. Accordingly, gatch soils are considered as impervious, comparing the figures with the exception of those from G-2 and G-5 areas where the gatch is semi-impervious. This implies that the use of gatch requires proper drainage arrangements when used as fill material. CONCLUSIONS

(1) Massive gatch is predominantly sandy with the percentage of material finer than 75 tan ranging from 8% to 3 3 ° . It is either non-plastic or has a low plasticity index, and can be classified as SM-SC in the Unified Classification or A-2(0) in the AASHTO classification. This makes it suitable for use in road subgrades. The average shrinkage limit is 17~/o, which is considerably abvoe the natural moisture content. This is critical, because it means that the soils are liable to swell when saturated and to crack when dry, and suitable drainage arrangements must be made to ensure their stability. (2) The average values of the California bearing ratio (CBR) for unsoaked samples ranged from 5~/o to 3 2 ~ when compacted at OMC using low energy; the same samples compacted at higher energy gave a CBR value between 56% and 93°/0. This indicates that certain types of massive gatch can be used as subbase or even as a base course for road construction. Soaking of gatch samples compacted at their optimum moisture content has little effect on the CBR value. The CBR value is very sensitive to the moisture content of the gatch at the time of compaction, and this will dictate the need for good quality control during compaction. (3) The cohesion of gatch is very low and at times negligible, while on the other hand the angle of friction has been found to improve considerably with proper compaction. The permeability is consistently low; the massive gatch in the study area is either impervious or semi-impervious. ACKNOWLEDGEMENTS

The authors express their gratitude to Dr. Abdulmajid Jeragh, Head of the Government Laboratories and Testing Station for allowing to use the soil laboratory. Thanks are also due to Dr. Hamed Saeedy of Kuwait Institute for Scientific Research for review and useful comments on the manuscript. The KISR project EES-46 staff are acknowledged for field and laboratory assistance.

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REFERENCES A1-Sulalml, J , 1988. Calcrete and near surface geology of Kuwait City and suburbs, Arabian Gulf Sediment. Geol., 54: 331-345. A1-Sulaimi, J., El-Sayed, M.I., Youash, Y, Matt1, M., Akber, A., Mollah, M.A., Salman, A.S and Mukhopadhyay, A., 1984 Study of the Gatch Deposits m Kuwait City and Suburbs KISR 1399, Kuwait Institute for Scientffic Research, Kuwait (Unpublished) Blssada, A.F. and Qabazard, J , 1974. Low cost road pavement situation in Kuwait. Arab Engineers Federation Conference, Kuwait. Fuchs, F., Gattmger, T.E. and Holzer, H.F., 1968. Exploratory Text to the Synoptic Geologic Map of Kuwmt Geol. Surv. Austria, Vmnna Ismael, N.F., A1-Khalidl, O. and Abdul-Hadl, S., 1984. Sub-soils Condition m A1-Andalus Area Research Report, Government Laboratories and Testing Station, MPW, Kuwait (Unpubhshed). Poers, R.W., Ramlres, L.F, Redmond, C.D. and Elberg, E.L., 1963. Geology of the Arabian Peninsula; sedimentary geology of Saudl Arabia. Geol Surv Prof. Pap. 560-D Rmdel, G. and Simon, A.B., 1973. Geotechmcal properties of Kuwait "gatch" and their improvement. Eng. Geol, 7. 155-165 Umted States Bureau of Reclamation, 1977. Design of Small Dams. Washington, D.C, rev 2nd ed.