Expansive characteristics of gypsiferous/anhydritic soil formations

Engineering Geology 51 (1998) 89–107

Expansive characteristics of gypsiferous/anhydritic soil formations

Shahid Azam a, Sahel N. Abduljauwad b,*, Naser A. Al-Shayea b,Omar S.B. Al-Amoudi b

a Department of Projects and Maintenance, KFUPM, Dhahran, Saudi Arabiab Department of Civil Engineering, KFUPM, Dhahran, Saudi Arabia

Received 14 January 1998; accepted 5 August 1998

Abstract

Geology and climatic and environmental conditions have led to the formation of expansive soils in the EasternProvince of Saudi Arabia. Calcium sulphate, which commonly occurs in such soils, is well known for phasetransformation and dissolution. Phase changes from gypsum to anhydrite and vice versa, and dissolution of thesephases, add to the potential hazards of local expansive soils. This paper discusses the behaviour of the expansive soilformations of eastern Saudi Arabia containing gypsum and anhydrite. © 1998 Elsevier Science B.V. All rights reserved.

Keywords: Calcium sulphate; Dissolution; Expansive soil; Phase transformation

1. Introduction Al-Amoudi, 1995) and may dissolve in flow-ing fluids. Both these phenomena are influencedby the ambient temperature, pressure, relativeGeology, parent material and climatic condi-humidity and water activity (which is the effectivetions are the most important factors which haveconcentration required to retain the generalgoverned the formation of expansive soils in thethermodynamic treatment of solutions andKingdom of Saudi Arabia (Erol and Dhowian,decreases with temperature). The Arabian Gulf1990). Gypsum and anhydrite (hydrated and anhy-coastal region, which is characterized by hostiledrous phases of calcium sulphate) as well as bas-climatic and environmental conditions (Fookes,sanite (partially hydrated calcium sulphate) are1978), is naturally suitable for phase transforma-commonly encountered in the expansive soil for-tion and dissolution of calcium sulphate.mations of semi-arid and arid regions (Mitchell,

Argillaceous sediments can cause heave when1993). Abu Hujair (1994) has recently reportedtheir moisture content is increased, mainly due tothe presence of various calcium sulphate phases inwater adsorption. Sometimes, heave may be duemany expansive clays in eastern Saudi Arabia.to the hydration of anhydrite to gypsumCalcium sulphate is known to undergo alternate(Abduljauwad, 1994) as gypsification of anhydritedehydration and hydration (Abduljauwad andresults in a volume increase of up to 62% (Blattet al., 1980). Hydrating anhydrite of these sedi-ments creates swell pressure and floor heave in* Corresponding author. Fax: +966 3 860 2879;

e-mail: [email protected] tunnels and massive rock uplift in dams (Brune,

0013-7952/98/$ – see front matter © 1998 Elsevier Science B.V. All rights reserved.PII: S0013-7952 ( 98 ) 00044-1

90 S. Azam et al. / Engineering Geology 51 (1998) 89–107

1965). Serious structural damage can be attributed 2. Geologyto heaving and settlement of soils containing anhy-

The surface rocks of eastern Saudi Arabiadrous calcium sulphate, which is worsened wheninclude formations of consolidated sediments rang-these types of soil are periodically and/oring from the Palaeocene to the middle Eocenedifferentially exposed to wetting. Conversely, evenage and the Miocene to the Pliocene agewithout a rise in the level of the ground water(Abduljauwad, 1993). Poorly consolidated materi-table, expansive clay minerals in the vicinity ofals such as beach sand, sabkha, claystone anddehydrating gypsum can imbibe the liberated watershale belong to the Quaternary age (Abduljauwad,of crystallization, and can lift existing structures1994). Furthermore, argillaceous rocks exist in(Azam, 1997). Dehydration of gypsum is associ-several formations of the Phanerozoic successionated with a volume decrease of up to 38% (Zanbakin the Arabian peninsula (Saint-Marc, 1978).and Arthur, 1986), which may lead to excessiveExpansive soils are derived from these argillaceoussettlement of the overlaying structures. Further-rocks of the Permian, Cretaceous and Tertiarymore, shrinkage in the gypsum layer and the poreages (Okasha and Abduljauwad, 1992). Clayeypressure effects of released water from the crys-strata are present in the Eocene Rus and Dammamtal structure of gypsum, change the state of stressformations, and in the Miocene Hadrukh, Damwithin the sediment, which causes significantand Hofuf formations (Al-Sayyari and Zotl, 1978).deformation and fracturing ( Ko et al., 1995).

Geological materials generally associated withLeaching of chemicals and colloids from clayeyexpansive soil formations include highly overcon-soils by flowing water can decrease the soilsolidated clays (Dhowian et al., 1985), alluvialstrength, thereby increasing its sensitivity to theand colluvial deposits of the Tertiary andextent that quick clays may form which becomeQuaternary ages (Donaldson, 1969), and weath-fluid on remoulding (Mitchell, 1993). Dissolutionered shales and basalts ( Krumbein and Sloss,of gypsum and/or anhydrite in earth dams often1963). Parent materials associated with expansive

leads to an increase in the permeability of the claysoils in eastern Saudi Arabia are sedimentary rocks

core leading to uncontrollable seepage forces and which consist of calcareous limestone, marl andwater leakage (Calcano and Alzura, 1967). chert (Abduljauwad et al., 1992). By the processesGypsum can cause serious hazards when it acts as of chemical and physical weathering, these rocksa cementing agent because its dissolution results were converted to clay (Abduljauwad, 1994).in washing away of the soil itself and an increasing According to Potter et al. (1980), the claytendency for channel formation (Abduljauwad and mineral content of an argillaceous rock is a func-Al-Amoudi, 1995). Anhydrite dissolves even more tion of climate, lithology and topography. Thecatastrophically; even small fissures are enlarged effect of climate on clay mineralogy is well docu-swiftly to produce uncontrollable "runaway" situa- mented in the literature ( Keller, 1970). Extremetions (James and Lupton, 1978). The formation disintegration, strong hydration and restrainedof cavities due to leaching of gypsum and anhydrite leaching are necessary for the formation of expan-in the subsoil may trigger the collapse of light sive clay minerals such as smectite (Tourtelot,structures without adequate warning. 1973). This can be brought about by an alkaline

This paper presents the interaction of calcium environment, the presence of sulphate, magnesium,sulphate phases (especially gypsum and anhydrite) calcium, sodium and iron ions, and minimal leach-with naturally occurring indigenous calcareous ing (McMahone, 1989; Mitchell, 1993). Suchexpansive clays. Based on laboratory investigation, favourable conditions exist in eastern Saudithe paper discusses geotechnical properties, miner- Arabia, where rainfall is scanty and sporadicalogical composition, volume change and leaching (Abduljauwad and Al-Amoudi, 1995). A compari-characteristics of a selected expansive clay and its son of the geological age of known expansive soilsinteraction with calcium sulphate phases, as well in the arid and semi-arid regions of the USA with

the geological age of the Eastern Province of Saudias their mixtures.

91S. Azam et al. / Engineering Geology 51 (1998) 89–107

Arabia indicates that the Tertiary and Quaternary Clay–calcium sulphate mixtures were preparedsediments have moderate to high swell potential according to the dry weight of the constituents.(Slater, 1983). Similarly, natural field samples were collected from

Youthful soils of semi-arid and arid regions, Al-Qatif area which contained variable amountswhich are in their early weathering stages contain of calcium sulphate. A laboratory test programvarious physical forms and chemical phases of was designed to investigate the swelling behaviourcalcium sulphate (Deer et al., 1972; Jackson and of these synthetic mixtures. Selected material prop-Sherman, 1953; Mitchell, 1993). Gypsum and erties were studied, in conjunction with the resultsanhydrite are very common in sedimentary depos- of thermal and X-ray diffraction analyses andits throughout the geological column, especially in scanning electron microscopy, for a qualitativethe Paleozoic and younger deposits (Bain, 1984). evaluation of results. Furthermore, direct deter-In sedimentary deposits, gypsum and anhydrite minations of volume change and leaching charac-occur in association with limestone, shale, marl teristics were made using both conventional andand clay (Dunham, 1948). The uplift during the modified odometer tests, respectively.Middle to Upper Miocene age brought the calcare-ous soil formations to a shallower environment,ideal for basin evaporation, resulting in the forma- 4. Geotechnical propertiestion of gypsum (Papadopoulos et al., 1994).Similarly, during the late Miocene–Pliocene ages, Water content was determined according tothese gypsum deposits were locally exposed to ASTM D 2216. Specific gravity and unit weightmeteoric waters, and were intensively eroded at were determined according to ASTM 854 andthe low sea level strand leading to the formation ASTM 2937, respectively. Similarly, the liquidof anhydrite ( Kasprzyk, 1995). The possible mech- limit (LL), plastic limit (PL) and shrinkage limitanism by which gypsum and anhydrite may have (SL) were found according to ASTM 423, ASTMevolved is by extensive dolomitization of recently

D 424 and ASTM D 427, respectively. Table 1 anddeposited calcareous mudstone which usuallyFig. 1 summarizes the geotechnical properties ofoccurs in shallow waters (Blyth and de Frietas,various clay–gypsum and clay–anhydrite mixtures.1984). The mudstone contains aragonite andThe variation in all properties is observed tohigh-Mg calcite as predominant componentscorrelate with the weighted average of both the(Cook et al., 1985), but neither of these mineralsclay and the respective calcium sulphate phase.is diagenetically stable outside the marine environ-Fig. 1(a) indicates that the water content of fieldment (Longman, 1980). Mg2+ replaces some ofsamples of clay–calcium sulphate mixtures reducesthe Ca2+ in the crystal lattice of aragonite. Theas the amount of calcium sulphate in the claydisplaced Ca2+ combines with SO2−

4present in the

increases. Furthermore, the water content of thesea water to precipitate as individual crystals ofclay–anhydrite samples is observed to be loweranhydrite and/or gypsum (Blyth and de Frietas,than that of the clay–gypsum samples. Fig. 1(b)1984).shows that the dry unit weight of field samples ofexpansive clay with variable quantities of calciumsulphate increases as the amount of calcium sul-3. Experimentalphate in the clay increases. Moreover, the clay–anhydrite samples, exhibited higher values of dryA highly expansive clay from the Al-Qatif areaunit weight compared to the clay–gypsum samples.of the Eastern Province of Saudi Arabia wasThis should be attributed to the difference in waterselected. Gypsum was retrieved from a calcareouscontent of the two types of mixtures. The variationdeposit around Dhahran vicinity. Anhydrite wasin specific gravity of the synthetic clay–gypsumobtained by heating this gypsum to 300°C for 48 hmixtures, as shown in Fig. 1(c), is opposite to thatand thereafter keeping it at a relative humidity ofof the dry unit weight due to the high void ratio<70%. All of these materials were pulverized,

to pass ASTM Sieve No. 40 (0.425 mm). of clay compared to that of gypsum. Conversely,


Table 1Geotechnical properties of various clay–gypsum and clay–anhydrite mixtures

% ofGypsum % ofAnhydrite Propertyin mixture in mixture

va (%) cad (g cm−3) Gs LL (%) PL (%) SL (%) PI (%)

0 42.3 1.10 2.78 175 64.4 15.9 110.60 42.3 1.10 2.78 175 64.4 15.9 110.6

5 1.11 2.75 164 62.2 16.0 101.85 1.12 2.80 170 62.2 16.0 107.8

10 40.0 1.12 2.71 156 60.5 16.8 95.510 38.0 1.15 2.82 165 60.5 16.0 104.5

20 37.0 1.15 2.66 145 56.9 18.0 88.120 33.5 1.20 2.83 150 56.9 16.5 93.1

35 2.60 123 55.0 19.5 68.035 2.84 129 55.0 17.5 74.0

50 1.20 2.55 103 54.7 21.0 48.350 1.37 2.85 114 54.7 18.3 59.3

65 2.50 85 50.0 24.0 35.065 2.86 99 52.0 19.0 47.0

80 1.40 2.43 62 45.0 26.0 17.080 1.66 2.89 80 51.4 21.0 28.6

90 1.46 2.38 53 41.0 28.0 12.090 1.75 2.90 67 47.7 23.0 19.3

95 1.50 2.34 46 38.5 30.0 7.595 1.80 2.91 64 45.8 24.0 18.2

100 21.0 1.50 2.31 43 36.0 32.0 7.0100 0.0 1.81 2.92 61 44.3 25.0 16.7

aNatural field samples.

for clay–anhydrite mixtures, the variation in 5. Thermal analysisspecific gravity is similar to that of the dry unitweight as the specific gravity is governed by the Thermal analysis was conducted using a

Simultaneous Thermal Analyser (Netzcsh Modelhigh dry unit weight of anhydrite.Fig. 1(d) shows that the LL and the PL decrease, STA 429). A 100 mg sample was placed in an

alumna crucible, with the same weight of pre-whereas the SL increases with an increase in theamount of both gypsum and anhydrite in clay. calcined alumna oxide (Al2O3) placed in an iden-

tical alumna crucible as a reference sample. TheThe high LL and PL and the low SL for theexpansive clay are due to the high smectite content reference sample is not susceptible to any thermal

change, as the temperature was raised from 20 towhich increases the intake of water molecules bythe clay, facilitated by the negatively charged clay 1000°C at a uniform rate of 10°C min−1. Fig. 2

depicts the results of the thermal analysis of asurfaces and the large specific surface area of theclay minerals. When gypsum is added to the clay, natural field sample of gypsum. The weight loss

with an increase in temperature, as given by theits inert particles only act as a filler and do notattract water molecules owing to the fact that it is TG curve, indicates that there is a slight reduction

in weight due to small amount of loss in water atfully saturated with water and its crystal bound-aries are devoid of unsatisfied charges. This is low temperatures. However, major reduction has

taken place at a temperature of 130°C, setting theopposite to the addition of anhydrite to claywhereby anhydrite attracts water due to which the upper bound of gypsum stability. This temperature

is associated with phase transformation of gypsum–consistency limits of the clay–anhydrite mixturesare higher than those of clay–gypsum mixtures. bassanite–anhydrite. Complete dehydration of


Fig. 1. Geotechnical properties of clay–calcium sulphate mixtures (a) water content, (b) dry unit weight, (c) specific gravity and (d)Atterberg limits.

gypsum, which terminates at 220°C, is accompa- dration reaction is described by the singleendothermic peak between 130 and 220°C (DTAnied by a total reduction in mass of 21%. Beyond

220°C, the curve is asymptotic to the abscissa up curve). At a temperature of 200°C, the DTA curvealso shows another smaller endothermic peak per-to a temperature of 1000°C, suggesting that anhy-

drite is the stable phase beyond 220°C. This dehy- taining to the transformation of gypsum to bassin-


between 800 and 1000°C is due to the decomposi-tion of carbonate ions present in the expansiveclay, which is calcareous in nature (Abduljauwadand Al-Sulaimani, 1993).

6. X-ray diffraction analysis

X-ray diffraction analysis ( XRD) analysis wascarried out on a Philips diffractometer, Model Pw173/10, using a Cu broad focus tube at 40 kV and40 mA, alongside a monochromatic incident ray.The scanning speed and interval of data collectionFig. 2. Thermal analysis of gypsum.was 0.01° 2h s−1, and the angle scanned was 4–80°.Randomly oriented samples were prepared by

ite. Further, the small hump in the DTA curve atmanual grinding in a porcelain mortar pestle to

a temperature of 350°C indicates the conversionpowder form. After conducting the tests, the

of soluble anhydrite to insoluble anhydritediffraction pattern for each sample was matched

(MacKenzie, 1992).with the standard patterns prepared by the Joint

The results of the thermal analysis of expansiveCommittee of Powder Diffraction Data Service

clay, shown in Fig. 3, indicate that the removal of(JCPDS). Both qualitative and quantitative eval-

water occurs in more than one stage, in contrastuations were conducted to determine the type and

to calcium sulphate, which is characterized by theamount of the various minerals present in the

single dehydration reaction. The DTA curve showssamples. Three sets of gypsum samples were heated

a large low temperature endothermic peak betweenfor 48 h to temperatures of 130, 200 and 300°C,

20°C and 400°C as adsorbed or interlayer water isrespectively. They were then cooled under various

removed. This is accompanied by a reduction inconditions of temperature and relative humidity.

mass of ca 11% (TG curve) which is a goodTwo cooling temperatures of −10 and 23°C and

indicator of the presence of clay in the samplethree relative humidity conditions of zero (desicca-

(MacKenzie, 1992). The second endothermic peaktor), ca 70% (as measured in open air) and 100%

and the corresponding reduction in mass (3%)(water tub) were employed. Fig. 4 shows typical

between 400 and 800°C is associated withX-ray diffractograms for the various phases of

de-hydroxylation (removal of OH-ions). The thirdcalcium sulphate and clay.

endothermic peak and the reduction in mass (1%)A summary of the results of XRD analysis for

the calcium sulphate phases is given in Table 2.The results indicate that samples cured in waterwere completely converted back to gypsum irre-spective of the heating and cooling temperatures.This is because of the high water affinity of anhy-drite (completely devoid of water) and bassanite(partially hydrated), both of which readily takeup any available water. Furthermore, the samplesheated to higher temperatures show a larger anhy-drite phase, the quantity of which depends on thecooling temperature and relative humidity.Likewise, the samples heated to 300°C did notre-hydrate irrespective of the cooling temperature,

Fig. 3. Thermal analysis of expansive clay. provided that the relative humidity did not exceed


Fig. 4. XRD results for calcium sulphate (a) gypsum, (b) anhydrite, (c) bassanite and (d) expansive clay (S, smectite; I, illite; P,palygorskite; Q, quartz).

70%. This permanent change may be attributed to of 300°C, so that re-conversion is possible onlywhen complete access to water is given. Thechanges in the crystal structure of calcium sulphate

on heating the mineral to or above a temperature samples heated to 130 and 200°C and subsequently

Table 2Mineralogical composition of calcium sulphate phases

Heating temperature (°C) 130 200 300

Cooling temperature (°C) −10 23 −10 23 −10 23

Humidity condition D W D O W D W D O W D W D O W

Gypsum (%) — 100 — — 100 — 100 — — 100 — 100 — — 100Bassanite (%) 85 — 56 59 — 75 — 55 59 — — — — — —Anhydrite (%) 13 — 41 38 — 25 — 45 41 — 100 — 100 100 —

D, Desiccator; O, open air; W, Water tub.


cooled in a desiccator displayed more anhydrite( less bassanite) than those cooled in the open air(relative humidity 70%). Furthermore, the varia-tion in the amounts of anhydrite and bassanite atthe two temperatures is only marginal, whichconfirms the observation of thermal analysis: thatcalcium sulphate is in the semi-hydrous state withinthis range of temperatures.

Quantitative analysis of XRD results for theexpansive clay revealed that the main constituentsof the clay are smectite (52%), illite (23%), palygor-skite (5%), dolomite (9%), quartz (5%) andgypsum (6%) (Abduljauwad, 1994).

7. Swell tests

Swell tests were performed in a fixed-ringodometer under a seating pressure of 7 kPa Fig. 5. Percent swell of expansive clay and calcium sulphate

phases.(Abduljauwad and Al-Sulaimani, 1993). To corre-late the morphology with volume change, a fabricstudy was made on thin sections cut from the shows poorly developed rosettes of lath-like

gypsum crystals. Both long and short laths aresamples before and after the inundation with waterin the swell tests. The scanning electron microscopy visibly aggregated in separate colonies. The EDX

spectrum [Fig. 7(b)] reveals the major elements of(SEM) analysis was carried out using GEOL(JSM-840), which performs morphological and gypsum (nearly equal amounts of Ca and S). The

spectrum also indicates the possible presence ofmicro-structural assessment and gives a full ele-mental description using the energy dispersive underlying clay minerals as it shows Si, Al and

Mg peaks. The presence of clay will contributeX-ray analyser (EDX ). Each sample was held inan aluminum sample holder and sputter coated partially to swell potential of the gypsum sample.

Contrary to gypsum, anhydrous calcium sul-with a fine film of gold. The micrographs weretaken on a split screen mode with enlargements of phate exhibits a higher swell of 8.0%, which is due

to the fact that it imbibes water, thereby increasing1000 and 6000 times.The results of the swell tests are presented in in volume. This hydration of anhydrite is con-

firmed by comparing the morphology of theFig. 5 for the clay and calcium sulphate phases inthe form of percent swell (Dh/h) versus time. The samples before and after the addition of water in

the swelling tests. Fig. 8(a) shows thin, prismatic,high percent swell of the expansive clay (34.6%)can be largely attributed to its high smectite pore-filling, lath-like anhydrite cement before the

inundation of water. Furthermore, the micrographcontent, which is confirmed by SEM analysis.Fig. 6(a) shows the SEM micrograph for the highlights the sparry, pore-filling nature of anhy-

drite as its elongated laths fill pores and cementexpansive clay and depicts thin sheets of smectitestacked on one another which is supported by the two detrital quartz grains ( left). Fig. 8(b) shows

gypsified calcium sulphate crystals when the samecrenulated morphology of the specimen. The wholestructure of the clay appears as a thin webby crust. sample is flooded with water.

Fig. 9 shows the results of swell tests for clayThe EDX spectrum, as shown in Fig. 6(b), pres-ents typical relative peak heights of the major and calcium sulphate phases in the form of percent

swell versus swell pressure curves. The swell pres-elements of smectite like Si, Mg, Ca, Al and K.The SEM micrograph of gypsum [Fig. 7(a)], sure for the expansive clay measured 3200 kPa,


Fig. 6. Micro-structural assessment of expansive clay: (a) SEM micrograph, split mode with magnification ×1000 ( left), ×6000(right) and (b) EDX spectrum.

while that of pure gypsum was 330 kPa, which is This has taken place due to the smaller initial voidratio of calcium sulphate phases compared to thatonly ca 10% of that of the clay. Such a large

difference is ascribable to the negligible swell of the clay (Azam, 1997). The initial void ratiosfor gypsum, bassanite and anhydrite were 0.28,potential of gypsum. The swell pressure for anhy-

drite measured 1660 kPa, which is almost 50% of 0.50 and 0.61, respectively, compared to 0.79 forthe expansive clay.the expansive clay, despite the fact that the percent

swell was found to be only ca 25% of the pure Fig. 10 compares the percent swell for the vari-ous synthetic clay–calcium sulphate mixtures. Theclay. The same was observed when bassanite was

inundated with water and loaded thereafter. The figure depicts a decrease in the percent swell of theclay, with an increase in the amount of calciumswell pressure for bassanite was found to be

1400 kPa, corresponding to a percent swell of 6.4. sulphate owing to the lower expansion capabilities


Fig. 7. Micro-structural assessment of gypsum: (a) SEM micrograph, split mode with magnification ×1000 ( left), ×6000 (right) and(b) EDX spectrum.


Fig. 8. SEM micrograph of anhydrite, split mode with magnification ×1000 ( left), ×6000 (right): (a) before and (b) after theinundation with water in the swell test.

and the cementation properties of calcium sul- gypsum following hydration is also accompaniedby a volume increase.phate. Moreover, the curve for the clay–anhydrite

mixtures plots above that of the clay–gypsum The percent swell curve for clay–gypsum mix-tures (Fig. 10) can be split into three distinct zones.mixtures, because the conversion of anhydrite to


20–80% gypsum content, cementation is the gov-erning factor, causing clods to form, which in turnact like coarse sand particles. These clods, coupledby the pore-filling nature of gypsum, tend to reducethe permeability of the whole sample, therebyrestricting the tendency of the clay to increase involume. This is confirmed by studying the SEMmicrograph shown in Fig. 11(a), taken after wateraddition in a swelling test of a clay–gypsum mix-ture containing 20% gypsum. The figure clearlyindicates the formation of clay–gypsum granulesor clods (top right). The micrograph also showsgypsum laths partly coating and filling the porespace adjacent to a large detrital quartz grain( left). As the amount of gypsum is increased inthe clay, these clods grow in size and becomeprogressively bigger. However, once a particularsize is achieved, further enlargement in the size ofthese clods is no longer effective in reducing theFig. 9. Swell pressure of expansive clay and calcium sulphatepercent swell of the mixtures. The SEM micro-phases.graph shown in Fig. 11(b), taken after water addi-tion in a swell test of a clay–gypsum mixturecontaining 80% gypsum, confirms the enlargementof the clods. The micrograph also shows pore-filling, authigenic and filamentous illite (right).

Finally, the curve (Fig. 10) drops sharply atgypsum contents >80%. This may be attributedto the low void ratio of gypsum, the flaky clayparticles being squeezed in small crevices andpores. These soft clay particles are therefore givenlittle freedom, if any, by the inert gypsum particlesto expand.

The percent swell curve for the clay–anhydritemixtures (Fig. 10) also follows the same patternas that of the clay–gypsum mixtures but cannotbe distinctly divided into smaller segments. This isbecause of the negligible enlargement in size of theclods in the range of 20–80% anhydrite, coupledby the change in volume of the anhydrite. Bothgypsification of anhydrite and the insignificant

Fig. 10. Percent swell of various synthetic clay–calcium sul- increase in the clod size, despite an increase in thephate mixtures. amount of anhydrite, are confirmed by SEM analy-

sis. Figs. 12 and 13 give the morphology of theIn samples containing up to ca 20% gypsum, there clay–anhydrite mixtures containing 20 and 80%is a drastic decrease in the percent swell due to the anhydrite, respectively; both before and after thereduction in clay content. In this zone, gypsum flooding with water in the swell tests. Figs. 12(a)acts mainly as an inert filler and tends to reduce and 13(a), both taken before the inundation withthe percent swell of the mixture in a proportion water in the swell test, indicate the presence of

prismatic and elongated anhydrite laths along withhigher than its weight percentage. In the range of


Fig. 11. SEM micrograph, split mode with magnification ×1000 ( left), ×6000 (right), of clay–gypsum mixtures containing (a) 20%and (b) 80% gypsum.

smectite flakes and occasional illite filaments. during the swelling test. Furthermore, these figuresreveal the bridging and cementing action ofFigs. 12(b) and 13(b), illustrating the same

samples after water was added, show gypsum gypsum which reduce the volume change charac-teristics of the whole mixture.crystals, indicating the hydration of anhydrite


Fig. 12. SEM micrograph, split mode with magnification ×1000 ( left), ×6000 (right), of clay–anhydrite mixtures containing 20%anhydrite (a) before and (b) after inundation with water in the swell test.

8. Leaching tests that allow the percolating fluid to flow throughthe consolidating specimen. Distilled water andbrine were used as percolating fluids. Table 3 sum-Leaching tests were conducted using the odome-

ter modified by Al-Amoudi and Abduljauwad marizes the average concentration of the majorions of the brine used. During the various stages(1995), in which the bottom plate has two holes


Fig. 13. SEM micrograph, split mode with magnification ×1000 ( left), ×6000 (right), of clay–anhydrite mixtures containing 80%anhydrite (a) before and (b) after inundation with water in the swell test.

of the test, samples of circulating fluid were col- ions. The sulphate ion concentration was deter-mined by the calorimetric method while thelected on which chemical analysis was conducted

to identify the various leached and/or dissolved calcium ion concentration was determined using


Table 3Chemical analysis of brine [ from Abduljauwad and Al-Amoudi (1995)]

Ion type Na+ Mg2+ K+ Ca2+ Cl− SO2−4

HCO−3

Ion concentration (g l−1 or parts per thousand) 78.8 10.32 3.06 1.45 157.2 5.48 0.09

an atomic absorption spectrophotometer (AAS),Perkin–Elmer 4000. An SEM analysis of thesamples was carried out before and after theleaching tests. Micrographs were taken with anenlargement of 500×.

Fig. 14 shows the relationship between the pres-sure and void ratio for both the modified ( leached)and the conventional odometer (unleached) testson a clay–anhydrite mixture containing 50% clay.The void ratio of the mixture decreased by 0.081and 0.167 for distilled water and brine, respec-tively. The change in values of the void ratiocorresponds to ca 26% and 55%, respectively, fordistilled water and brine, compared to the totalchange in the void ratio of the conventional odom-eter. This can be attributed to the profound effectof pore fluid, characterized by high Na+ andCl− ion concentrations in the brine, on the dissolu-tion of calcium sulphate. The results of the meas-

Fig. 15. Flow-time data for clay–anhydrite mixture containingurement of water and brine percolation through 50% anhydrite.the samples, shown in Fig. 15, support an increase

Fig. 16. Chemical analysis of percolating water through a clay–Fig. 14. Void ratio–pressure test results for clay–anhydrite mix-ture containing 50% anhydrite. anhydrite mixture containing 50% anhydrite.


Fig. 17. SEM micrograph, magnification ×500, of clay–anhydrite mixtures containing 50% anhydrite leached with (a) water and(b) brine.

in both the amount and rate of dissolution of decreases with time for both fluids due to loading,which reduces the void ratio and hence the perme-calcium sulphate with an increase in concentration

of the Na+ and Cl− ions in the pore fluid. In ability of the samples.Fig. 16 presents the results of the chemical analy-addition, the discharge through the samples


sis of the permeated fluids. The figure indicates only when the relative humidity does not exceed70%. Complete gypsification of anhydrite and bas-that significant leaching of Ca2+ and SO2−

4ions

took place in the initial stages of the test, depriving sanite takes place irrespective of the heating andcooling temperature when they are giventhe anhydrite of fully exhibiting its volume change

capacity. Percolation of fluids and the associated unrestricted access to water. Partial re-hydrationoccurs when the heating temperature is in theleaching of Ca2+ and SO2−

4ions causes the break-

down of the crystalline bonds of anhydrite. Also, range of 130–220°C, at all cooling temperatures.The engineering geological properties of calciumthe concentration of Ca2+ ions is always higher

than that of and SO2−4

, for both the fluids, resulting sulphate-bearing expansive clays vary according tothe weighted average of the constituents. Amongin large and numerous interfacial vacancies being

left in the samples. These vacancies are compressed the various calcium sulphate phases, anhydritehas the highest swell capabilities, whereas gypsumby the subsequent addition of loads, leading to

soil grain adjustment and hence to denser struc- swells only marginally. The swell potential of claydecreases as the amount of calcium sulphate istures. This is manifested by the reduction in the

void ratio of the various samples. The data in increased and the effect is more pronounced ingypsiferous soils. Depending on the concentrationFig. 16 supports the fact that leaching by brine

percolation was more than that by water because of Na+ and Cl− ions, percolating fluids reducethe void ratio of calcium sulphate bearing soils.the dissolution of calcium sulphate is enhanced by

chloride-bearing solutions as compared with water.This is further confirmed by SEM analysis.Fig. 17(a), which shows a clay–anhydrite mixture Acknowledgmentwith 50% anhydrite leached with water, indicatesthat most of the cementation of the calcium sul- The authors are grateful to King Fahdphate has been washed away by the seeping water, University of Petroleum and Minerals for provid-leaving behind channels and empty spaces. ing laboratory space and computer facilities.Fig. 17(b), which shows a sample of the same Thanks are due to Mr Hasan Zakaria Saleh of thecomposition leached with brine, indicates enlarged soil laboratory for providing valuable help.pore sizes as a result of increased leaching.

References9. Conclusions

Abduljauwad, S.N., 1993. Study on the performance of calcare-ous expansive clays. Bulletin of the Association of Engineer-The geology, climate and alkaline environmenting Geologists 30 (4), 481–498.of the area have a great influence on the formation

Abduljauwad, S.N., 1994. Swelling behaviour of calcareousand behaviour of expansive soils containingclays from the Eastern Province of Saudi Arabia. Quarterly

gypsum and/or anhydrite. The formation of such Journal of Engineering Geology 27, 333–351.expansive soils is the result of the weathering of Abduljauwad, S.N., Al-Sulaimani, G.J., 1993. Determination

of swell potential of Al-Qatif clay. ASTM Geotechnical Test-dolomitic limestone and marls in which gypsuming Journal 16 (4), 469–484.and anhydrite have been produced due to extensive

Abduljauwad, S.N., Al-Amoudi, O.S.B., 1995. Geotechnicaldolomitization of mudstone. The behaviour ofbehaviour of saline sabkha soils. Geotechnique 45 (3),

these deposits is characterized by the unique fea- 425–445.tures of calcium sulphate which are described by Abduljauwad, S.N., Hameed, R.A., Al-Sulaimani, G.J., Basun-

bal, I.A., Safar, M.M., 1992. Expansive soils in Eastern Prov-phase transformation and dissolution. The phaseince of Saudi Arabia. In: Proceedings, 7th Internationaltransformation of calcium sulphate dependsConference on Expansive Soils, Dallas, TX, vol. 1,mainly on temperature, relative humidity and brinepp. 426–431.

concentration. Gypsum is the stable phase of Abu Hujair, O.M., 1994. Swelling potential and treatment ofcalcium sulphate up to 130°C at all relative humidi- expansive clays. MS Thesis, King Fahd University of Petro-

leum and Minerals, Dhahran, Saudi Arabia.ties, whereas anhydrite is stable beyond 220°C


Al-Amoudi, O.S.B., Abduljauwad, S.N., 1995. Compressibility James, A.N., Lupton, A.R.R., 1978. Gypsum and anhydrite infoundations of hydraulic structures. Geotechnique 28 (3),and collapse potential of an arid, saline sabkha soil. Engi-

neering Geology 39 (3), 185–202. 249–272.Kasprzyk, A., 1995. Gypsum to anhydrite transition in the Mio-Al-Sayyari, S.J., Zotl, J.G., 1978. Quaternary Period in Saudi

Arabia. Springer Verlag, Wien, Austria. cene of southern Poland. Journal of Sedimentary ResearchA65 (2), 348–357.Azam S., 1997. Effect of gypsum–anhydrite on the behaviour

of expansive clays. MS Thesis, King Fahd University of Keller, W.D., 1970. Environmental aspects of clay minerals.Journal of Sedimentary Petrology 40, 788Petroleum and Minerals, Dhahran, Saudi Arabia.

Bain, R.J., 1984. Diagenetic, nonevaporative origin for gypsum. Ko, S., Olgaard, D.L., Briegel, U., 1995. The transition fromweakening to strengthening in dehaydrating gypsum: evolu-Geology 18, 447–450.

Blatt, H., Middleton, G., Murray, R., 1980. Origin of Sedi- tion of excess pore pressure. Geophysical Research Letters22 (9), 1009–1012.mentary Rocks, 2nd edn. Prentice–Hall, New York,

pp. 538–567. Krumbein, W.C., Sloss, L.L., 1963. Stratigraphy and Sedi-mentation, 2nd edn. Department of Geology, Evanston, IL.Blyth, F.G.H., de Frietas, M.H., 1984. A Geology for Engi-

neers, 7th edn. Butler and Tanner Limited, Frome, UK. Longman, M.W., 1980. Carbonate diagenetic textures fromnear-surface diagenetic environments. American AssociationBrune, G., 1965. Anhydrite and gypsum problems in engineer-

ing geology. Engineering Geology 2 (1), 26–38. of Petroleum Geologists Bulletin 64, 461–487.MacKenzie, R.C., 1992. The Differential Thermal InvestigationCalcano, C.E., Alzura, P.R., 1967. Problems of dissolution of

gypsum in some dam sites. Bulletin of the Venezuelan Society of Clays. Mineralogical Society, Clay Minerals Group,London.on Soil Mechanics, Foundation Engineering July–Sep-

tember, 75–80. McMahone, D., 1989. Properties of sodium sulphate attack,salt heave, lime sulphate heave on earthening. Master Inde-Cook, D.J., Randazzo, A.F., Sprinkle, C.L., 1985. Authigenic

fluorite in dolomitic rocks of the Floridan aquifer. Geology pendent Study Project, University of California at Berkeley.Mitchell, J.K., 1993. Fundamentals of Soil Behaviour, 2nd edn.13, 390–391.

Deer, W.A., Howie, R.A., Zussman, J., 1972. Rock Forming Wiley, New York.Okasha, T.M., Abduljauwad, S.N., 1992. Expansive soil inMinerals. Lowe and Brydon, London.

Dhowian, A., Ruwiah, I., Erol, A., 1985. The distribution and Al-Madinah, Saudi Arabia. Journal of Applied Clay Science7, 271–289.evaluation of the expansive soils in Saudi Arabia. In: Pro-

ceedings, 2nd Saudi Engineering Conference, King Fahd Papadopoulos, Z., Kolaiti, E., Mourtzas, N., 1994. The effectof crystal size on geotechnical properties of Neogene gypsumUniversity of Petroleum and Minerals, Dhahran, vol. 4,

pp. 1969–1990. in Crete. Quarterly Journal of Engineering Geology 27,267–273.Donaldson, G.W., 1969. The occurrence of problems of heave

and the factors affecting its nature. In Proceedings, 2nd Potter, P.E., Maynard, J.B., Pryor, W.A., 1980. Sedimentologyof Shale. Springer, New York.International Research and Engineering Conference on

Expansive Clay Soils. Texas A&M Press, College Station, Saint-Marc, P., 1978. Arabian Peninsula: in the PhanerozoicGeology of the World II, the Mesozoic. A. Elsevier,TX.

Dunham, K.C., 1948. A contribution to petrology of the Per- Amsterdam.Slater, D.E., 1983. Potential expansive soils in Arabian Penin-mian evaporite deposits of north-eastern England. Proceed-

ings, Yorks Geological Society 27, 217 sula. ASCE Journal of Geotechnical Engineering 109 (5),744–746.Erol, A.O., Dhowian, A., 1990. Swell behaviour of arid climate

shales from Saudi Arabia. Quarterly Journal of Engineering Tourtelot, H.A., 1973. Geologic origin and distribution of swell-ing clays. In: Proceedings, Workshop on Expansive Clay andGeology 23, 243–254.

Fookes, P.G., 1978. Middle East — inherent problems. Quar- Shale in Highway Design and Construction, vol. 1.Zanbak, C., Arthur, R.C., 1986. Geochemical and engineeringterly Journal of Engineering Geology 11, 33–39.

Jackson, M.L., Sherman, G.D., 1953. Chemical weathering of aspects of anhydrite/gypsum phase transitions. Bulletin ofthe Association of Engineering Geologists 23 (4), 419–433.minerals in soils. Advances in Agronomy 5, 219

Documents

Expansive characteristics of gypsiferous/anhydritic soil formations