Showing papers on "Expansive clay published in 2009"

Cyclic swell-shrink behaviour of a compacted expansive soil

Abstract: Laboratory cyclic swell–shrink tests were carried out on compacted expansive soil specimens to study in detail the effect of changes in shrinkage pattern on the swell–shrink behaviour of compacted expansive soils. Compacted soil specimens were allowed to swell and either shrank fully or partially shrank to several predetermined heights in each cycle. The tests were carried out at a surcharge pressure of 50 kPa. The test results revealed that shrinkage of compacted saturated soil specimens to predetermined height in each shrinkage cycle provides similar conditions as that of the controlled suction tests with an increasing number of swell–shrink cycles. The water content of soil specimens and hence soil suction was found to remain nearly constant for each pattern of shrinkage. For soil specimens equilibrated to a given swell–shrink pattern, suction at the end of shrinkage cycles was changed from a higher suction to a lower suction, and also from a lower to a higher suction. The experimental results showed that there may be an immediate equilibrium state attained by the soil in terms of swell–shrink potential if suction at the shrinkage cycles was less than the past suction; otherwise, the equilibrium state was accompanied by fatigue of swelling. The volumetric deformation of the soil specimen subjected greater shrinkage was found to be much larger than the corresponding vertical deformation. The compressibility index of microstructure, κm, was determined for several shrinkage patterns. It is shown that κm is heavily influenced by suction at the end of shrinkage cycles.

Soil stabilization with flyash and rice husk ash.

Abstract: The objective of this paper is to upgrade expansive soil as a construction material using rice husk ash (RHA) and flyash, which are waste materials. Remolded expansive clay was blended with RHA and flyash and strength tests were conducted. The potential of RHA-flyash blend as a swell reduction layer between the footing of a foundation and subgrade was studied. In order to examine the importance of the study, a cost comparison was made for the preparation of the sub-base of a highway project with and without the admixture stabilizations. Stress strain behavior of unconfined compressive strength showed that failure stress and strains increased by 106% and 50% respectively when the flyash content was increased from 0 to 25%. When the RHA content was increased from 0 to 12%, Unconfined Compressive Stress increased by 97% while CBR improved by 47%. Therefore, an RHA content of 12% and a flyash content of 25% are recommended for strengthening the expansive subgrade soil. A flyash content of 15% is recommended for blending into RHA for forming a swell reduction layer because of its satisfactory performance in the laboratory tests.

Stabilization of Expansive Clays Using Granulated Blast Furnace Slag (GBFS) and GBFS-Cement

Abstract: Expansive clays undergo swelling when subjected to water. This can cause damage, especially to light weight structures, water conveyance canals, lined reservoirs, highways, and airport runways unless appropriate measures are taken. In this study, granulated blast furnace slag (GBFS) and GBFS-cement (GBFSC) were utilized to overcome or to limit the expansion of an artificially prepared expansive soil sample (sample A). GBFS and GBFSC were added to sample A in proportions of 5–25% by weight. The effects of these stabilizers on grain size distribution, Atterberg limits, swelling percentage and rate of swell of soil samples were determined. GBFS and GBFSC were shown to successfully decreasing the total amount of swell while increasing the rate of swell.

Effect of lime and fly ash on swell, consolidation and shear strength characteristics of expansive clays: a comparative study

Abstract: Expansive soils swell on absorbing water and shrink on evaporation thereof. Because of this alternate swelling and shrinkage, civil engineering structures founded in them are severely damaged. For counteracting the problems of expansive soils, different innovative techniques were suggested. Stabilization of expansive clays with various additives has also met with considerable success. This paper presents, by comparison, the effect of lime and fly ash on free swell index (FSI), swell potential, swelling pressure, coefficient of consolidation, compression index, secondary consolidation characteristics and shear strength. Lime content (weight of lime/weight of dry soil) was varied as 0%, 2%, 4% and 6% and fly ash content (weight of fly ash/weight of dry soil) as 0%, 10% and 20%. A fly ash content of 20% showed significant reduction in swell potential, swelling pressure, compression index and secondary consolidation characteristics and resulted in increase in maximum dry density and shear strength. Swell pote...

Modelling the thermomechanical volume change behaviour of compacted expansive clays

Abstract: Compacted expansive clays are often considered as a possible buffer material in high-level deep radioactive waste disposals. After the installation of waste canisters, the engineered clay barriers are subjected to thermohydromechanical action in the form of water infiltration from the geological barrier, heat dissipation from the radioactive waste canisters, and stresses generated by clay swelling under almost confined conditions. The aim of the present work is to develop a constitutive model that is able to describe the behaviour of compacted expansive clays under these coupled thermo-hydromechanical actions. The proposed model is based on two existing models: one for the hydromechanical behaviour of compacted expansive clays and another for the thermomechanical behaviour of saturated clays. The elaborated model has been validated using thermo-hydromechanical test results on compacted MX80 bentonite. Comparison between the model prediction and the experimental data shows that this model is able to reprod...

Highway Subgrade Construction in Expansive Soil Areas

Abstract: Engineering problems with expansive soils in subgrades complicate highway construction in expansive soil areas of China. To research and solve the engineering problems, a Chinese research group carried out extensive research as part of the construction of a highway in Ningming Basin, a typical expansive soil area in China. The research on Ningming expansive soils is presented, including laboratory studies of soil properties, modified California bearing ratio tests for evaluating the bearing capacity, and wet compaction tests for obtaining the parameters to control field compaction when using expansive soils as embankment fill. The field investigations of slope failures also are introduced, including analysis of the investigations. New techniques for using expansive soils in embankments, and stabilizing cut slopes consisting of expansive soils, were developed and applied into the trial sections of the highway by the research group, based on their research and investigations. The measures proved successful and were used to solve the technical problems related to the NanYou Highway subgrade construction. The outcomes of the research also may prove useful in the construction of such projects as railway and hydraulic works.

Analyse du comportement d'un sol argileux sous sollicitations hydriques cycliques Analysis of the behaviour of a natural expansive soil under cyclic drying and wetting

Abstract: Expansive soils swell and shrink regularly when subjected to moisture changes. Clayey soils are available worldwide and are a continual source of concern causing substantial damage to civil engineering structures. Cyclic expansion and shrinkage of clays and associated movements of foundations may result in cracking and fatigue to structures. In France, the damage caused by this phenomenon was estimated to be more than 3.3 billion euros in 2002 (Vincent in 3 eme conference SIRNAT-Forum

Effect of polymers on swelling potential of expansive soils

Abstract: This paper introduces new soil stabilisers for reducing the swelling potential of expansive soils. In this study three different polymers (furan, poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVA)) were utilised as soil stabilisers. For evaluating the effect of these polymers on swelling potential and microfabric of expansive soils, three soil samples of high plasticity index were selected. First the engineering, chemical and mineralogical characteristics of the untreated soils were determined, and three different pairs of dry density and water content (dry of optimum, optimum and wet of optimum) were chosen, from standard Proctor compaction curve. Treated soil specimens were prepared at 3%, 5% and 10% of furan content and 1%, 3% and 5% of polymethyl methacrylate and polyvinyl acetate content. The addition of polymethyl methacrylate and polyvinyl acetate can also diminish the swelling potential of soil specimens, but to a lesser degree. The addition of additives produced aggregations and clay-...

Analysis of the behaviour of a natural expansive soil under cyclic drying and wetting

Abstract: Expansive soils swell and shrink regularly when subjected to moisture changes. Clayey soils are available worldwide and are a continual source of concern causing substantial damage to civil engineering structures. Cyclic expansion and shrinkage of clays and associated movements of foundations may result in cracking and fatigue to structures. In France, the damage caused by this phenomenon was estimated to be more than 3.3 billion euros in 2002 (Vincent in 3eme conference SIRNAT-Forum des journees pour la Prevention des Risques Naturels, Orleans, janv. 2003) and the Paris region is one of the most affected. The objective of this study is to investigate the swell–shrink behaviour of a natural clayey soil considered to be responsible for a lot of damage observed on buildings in the Paris region, and thus contributing to the characterisation and understanding of expansive clayey soils. The studied soil, Argile verte de Romainville, is a lagoonal-marine deposit and is part of the Paris Basin Tertiary (Oligocene) formations (Fig. 1). It is a clayey soil sampled in the eastern region of Paris. The mineralogical and geotechnical properties of the soil are presented in Table 1. The soil contains quartz (15–20%), carbonates (12–20%) and traces of mica and feldspars. X-ray diffraction showed that carbonates are essentially dolomite and the clay minerals are dominantly illite, kaolinite and a small amount of smectite (Fig. 2). A grain size analysis shows that the clay content (<2 μm) varies between 78 and 80%. The study of its microstructure by means of the scanning electron microscope indicates that the clayey soil has structural elements oriented in the direction of bedding. The structure of the sample generally consisted of dense and continuous clay matrices with very limited visible pore spaces (Fig. 3). At its natural water content (w = 25%), the soil shows mainly a unimodal pore size distribution with an average pore radius of 0.07 μm and a very limited porosity with radii larger than 10 μm (Fig. 4). To assess the effect of suction on the simultaneous changes in void ratio and degree of saturation under zero external stresses, drying–wetting tests are performed on the natural samples. The osmotic technique (Polyethylene glycol solutions) and various salt solutions are used to control the suction values ranging from 1 to 300 MPa. Once equilibrium is reached at the given suction, the samples are weighed and their volume is measured. A synthesis of the drying–wetting paths is given on Fig. 5. The swelling potential of the soil is evaluated using both indirect (or empirical methods Tables 2 and 3) and direct methods. Swell percentage and swell pressure of the soil are measured in a conventional oedometer apparatus according to ASTM (D 4546-85). The test specimens are 70 mm in diameter and the height varies between 12 and 24 mm. The swell percentage is measured under a nominal pressure of 0.7, 2.0 and 6.3 kPa. Swelling pressure of the soil is measured by the conventional consolidation test method (free swell and load, ASTM D 4546-85 method A) and by a constant volume method (ASTM D 4546-85 method C). The test parameters and results for each specimen are given in Tables 4 and 5, and on Fig. 7. Cyclic swell–shrink tests are carried out on similar samples taken from the same monolith. A scheme that permits the study of the clayey soil behaviour at the extreme states of wetting and drying is chosen. The test begins by wetting the samples at their natural moisture content and density. When swelling is stabilized, the water is removed from around the samples and they are dried in an oven maintained at 45°C until the vertical deformation (shrinkage) is stabilised and are then rewetted and so on. Some experiments are stopped at different swelling phases for microstructural study of the soil. The test parameters of the specimens are given in Table 9 and the results are shown in Figs. 9 and 10. The evolution of the microstructure during wetting and drying cycles is investigated using scanning electron microscope and mercury intrusion porosimetry. Observations are made only on soil specimens taken at the end of the swelling phase of the selected cycles. In order to preserve the microstructure, the specimens are cut in small pieces, frozen by liquid nitrogen and finally sublimated. The results of the drying–wetting path including the water retention curve are shown on Fig. 5. The results show that on the drying path (in the void ratio versus water content plane) the soil first follows nearly the saturation line and then, as the water content decreases, the void ratio tends towards a constant value. A shrinkage limit of w = 14.5 % and a corresponding suction value of 15 MPa is deduced from this path. An air entry value of 10 MPa is obtained from degree of saturation versus suction curve. The wetting path shows that the wetting–drying path is reversible for suction values higher than 60 MPa. The different indirect methods used to assess the swelling potential of the Argile verte de Romainville show a general agreement with respect to its swelling potential ranging from high to very high (Table 3). Examination of the free swell test results shows that the Argile verte de Romainville exhibits swell percentage in the range of 15–26% and that its degree of swelling depends on the initial conditions (water content, dry density) and the applied load (Table 4). The higher the water content and the applied load, the lower the swell percentage. A specimen taken parallel to the bedding plane shows similar values of swell percentage with a steep volume change versus time curve indicating an anisotropy of permeability. The two direct methods used to assess the swelling pressure of the Argile verte de Romainville give different values (Table 5). The values obtained by the constant volume method are relatively close and are about 700 kPa. Lower values varying between 360 and 540 kPa are obtained by the conventional consolidation test (free swell-consolidation). This indicates that besides the initial conditions, the swelling pressure is strongly dependent on the stress path followed. The results obtained from the wetting–drying cycle tests show that the magnitude of the first swell cycle is controlled by the initial water content, the maximum deformation occurring on the second cycle and the stabilization of swelling deformation from the third cycle (Figs. 9, 10). Furthermore, the experimental data indicate that upon repeated wetting and drying, the swelling rate of the soil becomes faster, which is explained by an increase in permeability of the soil due to the development of preferential flow paths (micro cracks) on drying. With an increasing number of cycles, a permanent increase in the volume of the samples is observed. This suggests that the swelling–shrinkage behaviour of expansive soils is not completely reversible. Mercury intrusion porosimetry analysis and SEM observations before and after different numbers of cyclic swelling indicate that the swelling–shrinkage cycles are accompanied by a continual reconstruction of the soil structure (Figs. 11, 12). The mercury intrusion porosimetry results show that with an increasing number of wetting–drying cycles the pore volume and the average diameter of the pores increase progressively (Fig. 11). Larger modifications are observed in the pores with radius in the range of 0.1–5 μm. SEM observations also show further destruction of large aggregates and disorientation of structural elements as the number of cycles increases (Fig. 12). After the fifth cycle, the soil original structure is totally lost and a disoriented homogeneous and loose structure with more homogeneous pore spaces is observed (Fig. 12d).

Bentonite THM behaviour at high temperatures: experimental and numerical analysis

Abstract: The Temperature Buffer Test is a heated full-scale field experiment carried out at the Aspo Hard Rock Laboratory in Sweden, simulating repository conditions for radioactive waste. The initial thermo-hydro-mechanical (THM) evolution in the clay barrier was investigated in a separate mock-up test. The paper describes this laboratory experiment and the corresponding numerical simulations. Most of the related work refers to THM analyses of bentonite barriers well below 100°C, but here higher temperatures are considered. A 20 cm closed specimen of compacted MX-80 bentonite was subjected to a temperature gradient (84°C and 120°C at the end points). The evolution of temperature, relative humidity, pore pressure and stresses was monitored at several points. The test was allowed to reach steady-state conditions. The specimen was then sampled and analysed in terms of water content and bulk density. Several finite element analyses considering different coupled THM interactions were performed, and compared with measurements. Bentonite properties were obtained from independent tests. Additionally, retention properties were also obtained from measured saturation ratios and steady-state suction values. For the mechanical problem the Barcelona Expansive Model was used, which includes explicitly the two structural levels that actually exist in expansive clays (macro- and microstructure). This model made it possible to simulate the evolution of stresses as well as the expansion of bentonite at the 'cold' side and the compression at the 'hot' side, using a single set of parameters.

Critical Evaluation of Determining Swelling Pressure by Swell-Load Method and Constant Volume Method

Abstract: For any construction activity in expansive soils, determination of swelling pressure/heave is an essential step. Though many attempts have been made to develop laboratory procedures by using the laboratory one-dimensional oedometer to determine swelling pressure of expansive soils, they are reported to yield varying results. The main reason for these variations could be heterogeneous moisture distribution of the sample over its thickness. To overcome this variation the experimental procedure should be such that the soil gets fully saturated. Attempts were made to introduce vertical sand drains in addition to the top and bottom drains. In this study five and nine vertical sand drains were introduced to experimentally find out the variations in the swell and swelling pressure. The variations in the moisture content at middle, top, and bottom of the sample in the oedometer test are also reported. It is found that swell-load method is better as compared to zero-swell method. Further, five number of vertical sand drains are found to be sufficient to obtain uniform moisture content distribution.

Reinforcement of pavements over expansive clay subgrades

Abstract: Basal reinforcement of pavement systems has been used for the purposes of: (i) increasing the lifespan of a pavement while maintaining the thickness of the base course, and (ii) decreasing the thickness of the base course while maintaining the lifespan of the pavement. This paper describes a third application of basal reinforcement of pavements, namely, the mitigation of longitudinal cracks induced in pavements constructed over highly plastic, expansive clay subgrades. This includes information showing that: (i) geogrid reinforcement has precluded the development of longitudinal cracks in pavement sections located in projects where unreinforced sections have shown significant cracking, (ii) longitudinal cracks are ‘shifted’ beyond the reinforced pavement zone, avoiding their development within the pavement itself, and (iii) that current specifications, which often rely on geogrid properties defined in isolation, are insufficient to fully characterize the reinforcement requirements for reinforced pavement project. Overall, the field observations highlight the significant benefits associated with the use of geogrids in pavements over expansive clay subgrades, although there is still the need for more rationale design methodologies. RÉSUMÉ Le renfort basique des systèmes de trottoir a été employé aux fins de : (i) augmentater de la durée de vie du trottoir tout en maintenant l'épaisseur de la couche de base, et (ii) diminuner l'épaisseur de la couche de base tout en maintenant la durée de vie du trottoir. Cet article décrit une troisième application du renfort basique des trottoirs, à savoir, la réduction des fissures longitudinales induites en trottoirs construits au-dessus plastique dur, sous-grades expansibles d'argile. Ceci inclut des informations démontrant que : (i) le renfort de geogrid a exclu le développement des fissures longitudinales dans des sections de trottoir situées dans les projets où les sections non renforcées ont montré la fissuration significative, (ii) les fissures longitudinales glissé au dessus, continué au delà `au delà de la zone renforcée de trottoir, évitant leur développement dans le trottoir lui-même, et (iii) que les caractéristiques courantes, qui se fondent souvent sur des propriétés de geogrid définies en isolation, sont insuffisantes pour caractériser entièrement les conditions de renfort de renforcement du. De façon générale, les observations sur le terrain ont souligné les avantages significatifs liés à l'utilisation des geogrids sur les au dessus des sous grades expansibles d'argiles dans les trottoirs, bien qu'il reste le besoin de plus de méthodologies de conception de raisonnement.

Evaluation of the influence of boundary confinement on the behaviour of unsaturated swelling clay soils

Abstract: Swelling soils are found in many regions throughout the world. Damage caused to infrastructure by these types of soils is measured annually in billions of dollars. These excessive damages are, in p...

Engineering characteristics of a glacio-lacustrine clay deposit in a semi-arid climate

Abstract: Parent material composition, particle disintegration by glaciers and lacustrine environment govern the geological development and engineering characteristics of clay deposits in southern Saskatchewan. The pre-existing expansive clay minerals were preserved due to the restrained leaching in the Regina Lake and the prevalent aridity in the area. The main objective of this paper was to develop a fundamental understanding of the clay deposit for the use in the design and construction of civil infrastructure. The results indicated the presence of expansive clay minerals in the deposit, with smectite accounting for 35% of the material. The major exchangeable cation was found to be Ca2+ which accounted for more than half of the total measured cation exchange capacity of 40 (cmol(+)/kg). The most likely exchange complex governing water adsorption of the clay was determined to be Ca2+-smectite. Alongside a high initial saturation (86%), this complex resulted in moderate volume changes in the clay. The swelling pressure was fully developed within the first hour of the constant volume test. The corrected swelling pressure was determined to be 120 kPa leading to an estimated heave of 36 mm in the surface layer of the deposit. The compression index and the swelling index were found to be 0.25 and 0.08, respectively.

Effect of polypropylene tape fibre reinforcement on swelling behaviour of an expansive soil

Abstract: The objective of this study was to examine the influence of discrete and randomly distributed fibres on heave of an expansive soil. One-dimensional swell tests were conducted on a remoulded expansive soil with and without fibres. In this study, fibre content was varied as 0.25 and 0.5% and fibre length as 30, 60 and 90 mm. A twin semi-circular-shaped fabricated mould with a front Perspex sheet was developed for testing. Digital imaging technique was used to observe heave of the soil in both unreinforced and fibre-reinforced conditions. Displacement profiles obtained from image analysis were used for interpreting swell or upward movement profiles of the specimens. Heave observed in the digital image analysis was compared with that obtained from dial gauge readings. Reduction in heave was directly proportional to fibre content and fibre length. Reduction in heave was the maximum at low aspect ratios at both fibre contents of 0.25 and 0.5%. Test results revealed that fibre length is a key factor th...

Effect of Sulfuric Acid on Swelling Behavior of an Expansive Soil

Abstract: Soil often becomes contaminated with a variety of chemicals due to leakage of under/aboveground chemical storage tanks, improper discharge of waste, or improper design of waste containment facilities. Contaminated soil water can influence the soil's behavior seriously. Mineralogical alterations play a vital role in such circumstances. This paper describes the impact of varying concentrations of sulfuric acid solutions on the swell behavior of expansive soil containing predominantly montmorillonite. Using the conventional oedometer tests, the swell behavior of soil compacted with water inundated with acid solutions was studied. The soil swell, which is about 2% in water, increases to about 9% with 1N and to 50% with 4N acid solutions. The induced swell in acid solutions is attributable to mineralogical changes. The formation of new minerals and their associated fabric changes are investigated by scanning electron microscopy, X-ray diffraction, and energy dispersive analysis of X-ray on soil samples treated...

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

Abstract: 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.

Integrated porous rigid wall and flexible wall permeability test device for soils

Abstract: An apparatus for measuring permeability accurately in expansive clay and non-expansive soils is provided. The apparatus includes hollow porous stone cylinders which prevent the sample from bulging and at the same time allow application of confining pressure on the soil sample enclosed in a flexible membrane, which simulates the field condition and allows for application of back pressure to aid in saturation. The apparatus also allows for accurate comparison of hydraulic characteristics of swelling clays with fluids of various dielectric and other properties. The apparatus can also be used to consolidate the sample either three dimensionally or in one direction and perform permeability tests as well as find out the consolidation characteristics of the sample.

Research on meso-structures and their evolution laws of expansive soil and loess

Abstract: The characteristics of meso-structure evolution of expansive soil and loess were studied systematically with a CT-triaxial apparatus in various stress paths,wet-dry circle,soaking swelling and inundation-collapse. The expansive soil samples were taken from two sites located in the canal slope of the Middle Route Engineering of South-to-North Water Transfer Project in China. The loess simples include Q3 loess and Q2 loess,and the former was taken from the site of Pumping Station 11 in Ningxia Province,and the later was taken from the site of Pucheng Power Plant in Shaanxi Province. A number of CT images and CT data of meso-structure evolution of the samples were obtained. The research results show that the macro-behaviors of samples are closely related with their meso-structure changes and CT data. The fissures sprout and develop during loading and lateral unloading on undisturbed expansive soil and during wet-dry circles on remolded expansive soil in free state;and their meso-structure are damaged. However,the original fissure in remolded expansive soil is toward close under loading and immersion;and the meso-structure of the soil is repaired. The tendency of meso-structure change of intact loess in loading process is dependent on the stress and suction level. The holes and fissures of intact loess become gradually small even disappear during inundation;and the original structure of intact loess failure and a new homogenous structure would be formed. The macro-void of intact loess cannot be destroyed ether by high stress or by the combination action of low stress and immersion. On the basis of CT test data,the quantitative indexes describing the meso-structure of expansive soil and loess were defined;and the structure evolution equations for the soils under various test conditions were proposed;as well as a method to determine the yield stress in triaxial test was suggested. Thus,CT technology makes the research of meso-structure of soils to reach the quantitative stage;and the technique also provides a practice test foundation to establish the evolution equations of meso-structure of soils and corresponding structural constitutive model.