Expansive Clay Beds Research Articles

Heave and pullout studies of geogrid-encased granular pile-anchors in expansive clay beds

This paper presents heave and pullout studies of plain granular pile-anchors (GPAs) and geogrid-encased GPAs. Experiments were conducted in California bearing ratio (CBR) moulds and fabricated moulds of size 381 × 381 × 457 mm in expansive clays. The GPA method is an innovative technique developed for reducing heave and improving bearing capacity and pullout capacity. In this study, GPAs were encased in geogrids to augment the engineering performance of the system. Tests were conducted in CBR moulds and fabricated larger moulds to study and compare the heave and pullout behaviour of plain GPAs and geogrid-encased GPAs. The results indicated that the clay beds reinforced with geogrid-encased GPAs showed better heave and pullout behaviour. Heave decreased by 90.8% and 92.5%, respectively, in the case of plain and geogrid-encased GPAs installed in the CBR moulds and by 95.12% and 98.3% in the case of plain and geogrid-encased GPAs installed in fabricated large moulds. Pullout load on geogrid-encased GPAs in CBR moulds improved by 42.17% over that on plain GPAs and pullout load on geogrid-encased GPAs in the fabricated large moulds improved by 52.25% over that on plain GPAs.

Heave and load-settlement behaviour of a chemically stabilised expansive clay bed

ABSTRACT Structures found in expansive soils are subjected to heave and downward movement when they absorb water and lose water to the atmosphere, respectively. The upward and downward movements of structures built on the expansive clay strata are controlled through various treatment methods such as chemical stabilisation. As these clay strata are subjected to stresses due to superstructures, an understanding of their load-carrying capacity in the light of changing moisture content is required to assess this behaviour. This paper presents the heave and load-settlement behaviour of a remoulded expansive clay bed stabilised with varied amounts of lime, cement, fly ash and ground granulated blast furnace slag (GGBS). A series of laboratory-scale plate load tests were conducted on the beds of chemically stabilised clay compacted at the respective OMC and MDD. The plate load tests were conducted in two series: one on the as-compacted beds of the blends, and the other on the saturated beds of the blends to compare their stress-settlement behaviour. The amount of heave and the rate of heave were also monitored during the process of saturation. Chemically stabilised expansive clay beds reflected improved load-settlement behaviour in both the as-compacted and the saturated states.

Long-term Field Heave Studies on Various Foundation Techniques in Expansive Soils

Expansive soils being susceptible for moisture variations undergo cyclic seasonal movements that pose serious stability concerns for structures resting on them, especially when they are lightly loaded ones. The concerted efforts made by various researchers across the world enabled them to develop remedial solutions to mitigate these problems with varied degree of success. The present work is an effort to study the relative performance of the different remedial techniques in vogue and those proposed in the recent years. These techniques were adopted below the shallow footings at a site on NIT Warangal campus where natural expansive clay bed is present. This study revealed that the sand cushion and CNS cushion could reduce the heave by 56 to 64%; but in case of sand cushion, an increasing trend of heave with number of cycles of wetting and drying was observed. The chemical alteration by lime could reduce the heave by 59% and by CaCl2 and CaCl2–Na2SiO3 the heave could be reduced by 70 and 73%, respectively. The recently promulgated concrete and granular anchor piled footings have shown the heave reduction up to 63 and 78%, respectively. Further, it is found that the combined effect of CNS cushion along with chemical modification and/or tension/anchor piled footing systems were found to be synergistically more effective than individual techniques in controlling the seasonal movements of footings and flooring/lining panels. Interestingly, none of these remedial techniques could overcome the shrinkage movements though these movements are observed to be insignificant in case of piled footings.

Improving expansive clay beds with granular pile anchors (GPAs) and geogrid-encased GPAs

Granular pile anchors (GPAs) are an innovative foundation technique developed for reducing the heave of expansive clay beds. Other engineering characteristics of expansive clay beds have also been found to improve through GPA reinforcement. This paper presents experimental data on heave, compressive load response and pullout response of expansive clay beds reinforced with plain GPAs and geogrid-encased GPAs. The heave of the expansive clay beds decreased by 95·12% on the installation of plain GPAs and it further decreased (by 98·3%) in the case of geogrid-encased GPAs. Plate load tests were conducted on unreinforced expansive clay beds and clay beds reinforced with plain GPAs and geogrid-encased GPAs for a comparative study. Similarly, pullout tests were conducted on clay beds reinforced with plain GPAs and geogrid-encased GPAs. The clay beds reinforced with geogrid-encased GPAs resulted in a higher load capacity in compressive as well as pullout tests than the beds reinforced with plain GPAs.

Efficacy of Geopile–Anchors in Controlling Heave of Expansive Clay Beds

This paper presents the efficacy of a new technique in the form of geopile–anchors in arresting heave of expansive soils. Heave behaviour of a remoulded expansive clay reinforced with vertical cylindrical cells made of geogrid and filled with geomaterials (geopiles) with a central anchor inside is presented. A geogrid cylinder installed vertically in an expansive soil (forming a geopile), with an anchor inside is a geopile–anchor. In a geopile–anchor, foundation is anchored to an anchor plate at the bottom of the geopile with the help of an anchor rod. The upward movement of foundation due to swelling of clay is resisted by anchorage and by friction mobilized at the interface formed by the fill material (expansive soil)–geogrid–expansive soil. Filling the geopile with granular material can augment uplift resistance. Tests were conducted on expansive clay beds reinforced with geopile–anchors varying geopile diameter and type of geopile-fill material. In the case of group of geopile–anchors, spacing was varied and its effect on heave studied. The experimental results indicated that geopile–anchors reduced heave of expansive clay beds. With expansive clay fill, a maximum reduction in heave of 78.50% was obtained. When gravel fill was used, a percentage reduction of 92.50% was obtained. At a radial distance of 60-mm the reduction in heave obtained was 50%, 58%, 67% and 73% for single geopile–anchor, and 69%, 73%, 81% and 88% for two group geopile–anchors installed at a spacing of 2d when the fill materials were clay, fine sand, coarse sand and gravel respectively.

Behaviour of expansive clay beds with fly-ash-stabilised clay cushion

Stabilisation of expansive soils with various additives such as lime and fly ash has been shown to be a viable technique to counteract heave and shrinkage. This paper presents experimental results obtained from tests performed on expansive clay beds with fly-ash-stabilised clay cushions of varying thicknesses and fly-ash content. The amount and rate of heave, swelling pressure and stress–settlement characteristics of the expansive clay beds were studied. The results indicated that when fly-ash-stabilised clay cushions were provided over expansive clay beds, heave and swelling pressure decreased in comparison with the heave and swelling pressure of untreated expansive clay beds but, heave and swelling pressure increased with increasing fly-ash content for a given thickness of the cushion. For a given fly-ash content, however, heave and swelling pressure decreased with increasing thickness. Heave reduced by 70% when a 75 mm thick clay cushion stabilised with 10% fly-ash content was used. The stress–settlement characteristics of the expansive clay beds with a fly-ash-stabilised clay cushion improved. The settlement of the footing on a 50 mm thick clay cushion decreased by about 43% when the fly-ash content was increased from 0 to 10%.

Influence of wetting–drying cycles on swell–shrink behaviour of GPA-reinforced expansive clay beds

ABSTRACT Granular pile-anchor (GPA) technique is an innovative tension-resistant foundation technique which can effectively ward off the dual swell–shrink problem posed by expansive clays. The other tension-resistant foundation techniques are drilled piers, belled piers and under-reamed piles. Laboratory scale model studies and field scale experiments on GPAs revealed that swelling of expansive clay beds could be effectively controlled by GPA technique. This paper presents results obtained from laboratory scale model studies on GPA-reinforced expansive clay beds subjected to alternate cycles of wetting and drying. Swelling and shrinkage of the clay beds were monitored for three wetting–drying cycles (N) spanning a time period of 300 days. The clay beds were reinforced with varying number of GPAs (n = 0, 1, 2 and 3). Swelling (mm) and shrinkage (mm) of the clay beds in a given wetting–drying cycle decreased with increasing number of GPAs. Further, swelling (mm) and shrinkage (mm) significantly decreased with increasing number of wetting–drying cycles (N) also. For a given number of GPAs (n), swelling and shrinkage decreased with increase in depth from the top of the clay bed too.

Comparative study on the behaviour of granular pile anchors and helical pile anchors in expansive soils subjected to swelling

Several foundation techniques, such as belled piers, under-reamed piles, helical piles are adopted in expansive soils to avoid the problem posed by its swelling nature. In recent years, the granular pile anchor (GPA) technique has been in practice for resisting the uplift of foundation caused by expansive clay beds. Model and prototype studies on GPA revealed that swelling of expansive clay beds can be effectively controlled by the GPA technique. This paper presents a comparative study on the behaviour of GPA and helical pile anchors (HPAs) in expansive soil subjected to swelling. The data presented in this paper pertain to model tests of clay beds reinforced with varying number of GPAs (N = 0, 1, 2 and 3). Similarly, the model tests were conducted on clay bed reinforced with varying number of HPAs (N = 0, 1, 2 and 3). Tests were also conducted by varying the number of helix. Test results shows that the heave (mm) decreases with an increase in the number of GPAs. Similarly, the heave decreases with an increase in the number of HPA. Further, heave (mm) also decreased with increase in the number of helix. The resultant heave reduction is found to be more in case of expansive soil reinforced with GPA when compared to expansive soil reinforced with helical pile.

Study of Swelling Potential of Copper Slag Cushion Laid Over Expansive Soil Bed

Expansive soils are subjected to changes in volume with seasonal water content variations. Techniques like sand cushion and cohesive non-swelling cushion have been tried to minimize the heave of expansive soils. But, they have inherent limitations. Utilization of waste materials in civil engineering has been in vogue all over the world in recent times and is primarily needed because of the problems associated with their disposal. Copper slag is one such waste material. Research carried out by the authors using lime-stabilized and cement-stabilized copper slag as cushioning material over expansive soil beds was found effective in minimizing heave of expansive clay beds. Heave studies were conducted using the stabilized cushions over expansive clay beds with thickness ratios of the cushion to the soil bed varying as 0.25, 0.50, 0.75 and 1.00. Percentage of lime and cement was also varied from 2 to 10%. The present paper discusses the experimental results of the swelling studies conducted on the cushion-soil system. It was noticed that, with an increase in the percentage of lime or cement, there is an increased reduction in heave.

Swelling behaviour of expansive clay beds reinforced with encased granular pile anchors

Granular pile anchor (GPA) system is a simple and cost-effective foundation technique for resisting the uplift of foundation caused by swelling of expansive clay. This paper presents the heave results obtained from the laboratory-scale studies of the clay beds reinforced with varying number of GPAs (n = 0, 1, 2 and 3) with and without encasement. Tests were also performed by varying the stiffness of the geosynthetic encasement as (15kN/m, 22kN/m and 38kN/m). Heave of expansive clay bed decreased with increase in number of GPAs. Further, for a given number of GPAs (n), heave decreased significantly when encased with geosynthetics and also heave decreased with an increase in the stiffness of the encasement. The results indicate that stiffness of the encasement plays a significant role in the uplift resistance of the granular pile anchors introduced in expansive soils.

Influence of Geogrid Reinforcement on Pullout Response of Granular Pile-Anchors (GPAs) in Expansive Soils

This paper presents the influence of geogrid reinforcement on uplift capacity of granular pile-anchor (GPA) in expansive clay beds. In granular pile-anchor foundation system, footing is connected to the anchor plate provided at the bottom of granular pile through an anchor rod so that the uplift force on the footing due to swelling of expansive clay is reduced. Prediction of uplift capacity is necessary in the design of granular pile-anchors. Uplift capacity of GPAs can be increased by reinforcing it with geogrid layers placed at different depths from the base. Geogrid reinforcement prevents granular material reorientation due to uplift stress concentration on the anchor plate, leading to failure. The pullout capacity increased with increasing number of geogrid layers, decreasing spacing between them, and with decreasing distance between anchor plate and bottom geogrid. Uplift capacity increased by 65.61 % when 4 geogrid layers were used at a spacing of 20 mm. Pullout resistance was maximum when the bottom geogrid was placed at 20 mm above the anchor plate.

Swelling behaviour of GPA-reinforced expansive clay beds subjected to swell-shrink cycles

Granular pile-anchor (GPA) technique has been found to be an innovative foundation technique for expansive clays posing the dual problem of swelling and shrinkage. Swelling occurs during absorption of water and shrinkage during evaporation of water. Generally, in field expansive clay beds, swelling takes place during rainy seasons and shrinkage during summers. GPA is a recent innovative foundation technique devised to ameliorate the dual swell-shrink problem of structures founded on expansive clay beds. The other innovative techniques are drilled piers, belled piers and under-reamed piles. Laboratory scale model studies and field scale experiments on GPAs yielded useful results and revealed that swelling of expansive clay beds was effectively controlled by GPA technique. Studies on swell-shrink behaviour of GPA-reinforced clay beds have not been performed so far. This paper presents results obtained from laboratory scale model studies on GPA-reinforced expansive clay beds subjected to alternate cycles of swelling and shrinkage. The data presented in this paper pertain to the swelling of test clay beds under the influence of three swell-shrink cycles (N) spanning a time period of 300 days. The test clay beds were reinforced with varying number of GPAs (n = 0, 1, 2 and 3). Heave (mm) in a given swell-shrink cycle decreased with increasing number of GPAs. Further, for a given number of GPAs (n), heave (mm) also decreased with increase in depth from the top of the clay bed. It was found that the resultant thickness of the clay bed (Hr) for swelling increased with increasing number of cycles. However, the percentage heave (ΔH/Hr) decreased as the number of swell-shrink cycles (N) increased.

Shrinkage Behaviour of GPA-Reinforced Expansive Clay Beds Subjected to Swell–Shrink Cycles

Expansive soils undergo alternate swelling and shrinkage respectively in rainy seasons when they absorb water and in summers when water evaporates from them. Hence, all types of foundations constructed in expansive soils are also subjected to alternate swelling and shrinkage in rainy and summer seasons. As a result, super-structure members are also affected, undergoing severe distress. Various tension-resistant and innovative foundation techniques such as belled piers and under-reamed piles have been devised for arresting the problems posed by expansive soils. Granular pile-anchor (GPA) is a recent innovative technique suggested for expansive clay beds. GPA is quite effective in controlling heave or swelling. Useful experimental heave data were obtained on laboratory scale and field scale GPAs. However, it is also necessary to study the behaviour of GPA-reinforced expansive clay beds subjected to swelling and shrinkage. This paper presents experimental data on shrinkage of GPA-reinforced expansive clay beds. Laboratory scale GPA-reinforced expansive clay beds were subjected to alternate swell–shrink cycles, each cycle for a duration of 300 days. Each clay bed was subjected to three swell–shrink cycles (N = 1, 2 and 3), each cycle monitoring swelling for 10 days and shrinkage for 90 days. The number of GPAs (n) reinforcing the clay beds was varied as 0, 1, 2 and 3. Shrinkage (mm) of a clay bed, recorded in a given swell–shrink cycle, decreased with increasing number of GPAs (n). Further, shrinkage of a given clay bed decreased significantly with increasing number of swell–shrink cycles (N) also. It was also found that shrinkage (mm) of a particular layer in the clay bed decreased with increasing depth (z) of the layer from the top of the clay bed.

Reducing heave of expansive clay beds through granular pile–anchor groups

The granular pile-anchor (GPA) foundation system, a more recent technique, has also been found to be quite successful in controlling heave of expansive clay beds. This paper presents experimental data obtained from laboratory-scale heave tests conducted on an unreinforced expansive clay bed (n = 0) and expansive clay beds reinforced by a single GPA (n = 1), twin GPAs (n = 2) and a group of GPAs laid in equilateral triangular pattern (n = 3). The thickness of all the test clay beds was 200 mm. Heave was monitored at different depths of clay beds as they were inundated. Ground heave (or surface heave) was also monitored at different radial distances (r) from the centre of the test tank. The unreinforced clay bed and the GPA-reinforced clay beds were identical with regard to thickness (H), placement water content (w%) and dry density (γd). Heave decreased at all depths of the clay beds as the number of the GPAs (n) increased. Furthermore, heave decreased with increasing depth (z) from the top of the clay beds. Heave was measured to be 56·5, 48, 28·5 and 24 mm at the top of the clay bed, respectively, for n = 0 (unreinforced expansive clay bed), n = 1, 2 and 3, indicating increased resistance to heave with increasing number of GPAs. The factor of safety of the GPA foundation system against uplift also increased with increasing number of GPAs.

Fly ash columns (FAC) as an innovative foundation technique for expansive clay beds

Various innovative foundation techniques have been in practice to counteract the swell–shrink problems posed by expansive soils. Apart from techniques such as belled piers and under-reamed piles, chemical stabilisation of expansive soils has also met with considerable success. Lime, cement and fly ash are the various additives used in chemical stabilisation. This paper presents an innovative foundation technique in the form of fly ash columns (FAC) for expansive clay beds. Results from a laboratory experimental study on expansive clay beds reinforced with fly ash columns (FAC) are presented. Heave tests and compressive load tests were performed on expansive clay beds into which fly ash was introduced as compacted columns. Heave decreased significantly on reinforcing the clay beds with FACs. Stress-settlement characteristics of expansive clay beds also improved when reinforced by FACs. Curing of FAC-reinforced expansive clay beds improved stress-settlement characteristics.

Field behaviour of granular pile-anchors in expansive soils

Different innovative foundation techniques have been suggested for controlling the detrimental volume change behaviour of expansive soils. The efficacy of a recent innovation in the form of granular pile-anchors in controlling heave of expansive clay beds and improving the engineering behaviour of the ambient soil has also been reported, based on results obtained from laboratory model tests. Before suggesting granular pileanchor foundations for installation in field practices, however, an in situ study of the behaviour of granular pile-anchors is also required as a support to the laboratory study. This paper describes an extensive field study of the behaviour of granular pile-anchor foundations of expansive clay beds. The field study was performed to study the rate of heave, reduction of heave and variation of heave with radial distance and with depth. Heave was found to be reduced by about 90% upon installation of granular pile-anchors. Final heave was reached in just about half the time required for final heave in the case of an unreinforced expansive clay bed. Improvement in the engineering behaviour of the ambient clay was studied through Proctor needle penetration tests and unconfined compression tests. It was found that a maximum increase of about 120% was observed in penetration resistance in the case of expansive clay beds reinforced with granular pileanchors.

Response of granular pile-anchors under compression

The granular pile anchor (GPA) is an innovative foundation technique, devised for mitigating heave of expansive clay beds and improving their engineering behaviour. It is a modification of the conventional granular pile wherein an anchor is provided in the pile to render it tension-resistant. This paper presents the results of a field-scale test programme conducted to study the response of anchors embedded in expansive clay beds. Plate load tests were conducted on unreinforced expansive clay beds and clay beds reinforced with GPAs to compare the compressive load response. The bulging pattern of the anchors was also studied. It was found from the field load tests that expansive clay beds reinforced with GPAs showed higher load-carrying capacity and improved compressive load response than unreinforced clay beds. Whereas the stress required to cause a settlement of 25 mm in the unreinforced expansive clay bed was 200 kN/m2, the clay bed reinforced with a GPA 1000 mm long and 150 mm in diameter (lgp/dgp=6·67) required 500 kN/m2to cause the same settlement, showing an improvement of 150%. Of the various single anchors with lgp/dgp values between 2.5 and 10, that of length 1000 mm and diameter 100 mm (lgp/dgp=10) showed the best load response when tested alone, resulting in an improvement of 440%. The maximum bulge diameter increased with increasing diameter and length of the GPA. The effect of GPA length is more pronounced in the increase in maximum bulge length than that of diameter.

Pullout Behavior of Granular Pile-Anchors in Expansive Clay Beds In Situ

Granular pile anchors (GPA) are one of the recent innovative foundation techniques devised for mitigating the problems posed by swelling clay beds. In a granular pile anchor, the footing is anchored to an anchor plate at the bottom of the granular pile. This makes the granular pile tension resistant and enables it to absorb the tensile force caused on the foundation by the swelling clay. An understanding of the amount of uplift resistance offered by the GPA is important in the design of granular pile-anchor foundations in field situations causing tensile forces on foundations, such as in expansive clay beds. This paper presents the results of a field-scale test program conducted to study the pullout response of GPAs embedded in expansive clay beds. Pullout load tests were conducted on GPAs of varying lengths and diameters. It was found from the field pullout load tests that granular pile anchors of larger surface area resulted in higher pullout capacity. Of the various single granular pile anchors with l∕...

Amelioration of Expansive Clay Slopes Using Calcium Chloride

Lime continues to be one of the most popular chemical admixtures used to modify expansive clays despite the associated mixing and pulverization problems. In the present investigation, the efficacy of CaCl2 in place of conventionally used lime is studied by conducting laboratory and field tests. These investigations were carried out on the slopes of a trapezoidal trench made in expansive clay bed. Heave measurements were taken on the lime and CaCl2 treated slopes and also on untreated slopes for four consecutive cycles of wetting and drying. The field cyclic seasonal movements and the subsequent laboratory tests on undisturbed and disturbed soil samples revealed that the CaCl2 could be a promising chemical modifier instead of conventionally used lime, not only due to its multifold influence on heave control, plasticity reduction, and swell properties but also its easy application in the form of solution without any need for pulverization and mixing. Though an apparent reduction in unconfined compressive strength of treated samples is observed, the drained triaxial tests on treated and untreated samples revealed that there is an increase in the angle of internal friction of treated samples.

Stabilisation of expansive clay bed using calcium chloride solution

Expansive clays experience cyclic volumetric changes upon moisture fluctuation because of their intrinsic mineralogical behaviour. As these volumetric changes threaten the stability of almost all lightly loaded structures, various remedial techniques have been developed to reduce the damage they cause. Among these measures, chemical stabilisation using multivalent cations is aimed at altering the chemical environment around the clay particles upon which the behaviour of clay depends to a great extent. In the present work, an attempt is made to study the efficacy of calcium chloride (CaCl2), a strong electrolyte, on the plasticity and swell characteristics of an expansive clay bed. One per cent CaCl2 solution was applied to the expansive clay bed by ponding and also through bore-holes. The relative influences of lime and calcium chloride on the properties of the clay bed are brought out by using data from a previous study of lime piles on an adjacent site. The plasticity index of the clay bed is decreased by 7–15% and 40–60% with lime and calcium chloride treatments respectively. Similarly, the swell pressure of the clay is decreased by 20–25% and 50–65% respectively. From this study, it is revealed that the modification of clay properties with calcium chloride is several times greater than that for the conventionally used lime. Les argiles expansives connaissent des changements volumétriques cycliques lors des fluctuations d'humidité en raison de leur comportement minéralogique intrinsèque. Comme ces changements volumétriques menacent la stabilité de presque toutes les structures légèrement chargées, on a développé diverses techniques visant à réduire les dégâts ainsi causés. Parmi ces mesures il faut citer la stabilisation chimique qui utilise des cations multivalents pour changer l'environnement chimique autour des particules d'argile dont dépend, dans une grande mesure, le comportement de l'argile. Dans ce travail, nous essayons d'étudier l'efficacitédu chlorure de calcium (CaCl2), électrolyte puissant, sur la plasticité et les caractéristiques de gonflement d'un lit d'argile expansive. Nous avons appliqué une solution à un pour cent de CaCl2 au lit d'argile en accumulant l'eau audessus et aussi en l'injectant par des forages. Nous montrons les influences relatives de la chaux et du chlorure de calcium sur les propriétés du lit d'argile en utilisant les données provenant d'une étude précédente sur des piles de chaux dans un site adjacent. L'indice de plasticité du lit d'argile diminue respectivement de 7 à 15% et de 40 à 60% après les traitements à la chaux et au chlorure de calcium. De même, la pression de gonflement de l'argile diminue de 20 à 25% et de 50 à 65% respectivement. Cette étude montre que la mod-ification des propriétés de l'argile provoquée par le chlorure de calcium est de plusieurs fois supérieure à celle provoquée par la chaux utilisée de manière conventionnelle.