Behaviour Of Expansive Clays Research Articles

Infiltration Column for Studying the Lateral Swell Behavior of Expansive Clay

Abstract Infiltration column is usually used to investigate the hydro-mechanical processes in unsaturated expansive clay. In this test, the moisture transfer is often monitored along the column during water infiltration using suction or water content probes. Nevertheless, the lateral swelling pressure developed is rarely considered. This paper describes an infiltration column for studying the lateral swell behavior of expansive clay. The column consists of a rigid cell ensuring the constant-volume condition and a hydraulic system enabling the water intake of the hosted sample. It is equipped with three types of sensors: pressure sensors, force transducers, and displacement transducers to, respectively, monitor the radial and axial swelling pressure of the sample at different positions and to check whether any axial displacement is taking place. A detailed description of the different parts of the cell is first presented. Second, analysis on the results of a test on a compacted bentonite/sand mixture allows the pertinence of such a device to be evaluated.

Evaluation of Isotherm Models for Water Vapor Sorption Behavior of Expansive Clays

AbstractMeasuring water vapor sorption behavior has emerged as a potentially important alternative for characterizing expansive soil behavior. Mathematical models for representing measured water vapor sorption isotherms and for calculating properties such as heat of adsorption, monolayer coverage, and specific surface area (SSA), however, have not been evaluated in detail for clay-water systems. This paper evaluates fitting performance and correlations among four theoretical models previously developed for general sorbent-sorbate interactions (e.g., colloid science) for specific application to water vapor sorption on expansive clays. Models evaluated include those by Freundlich, Brunauer-Emmet-Teller, Frenkel-Halsey-Hill, and Guggenheim-Anderson-de Boer. Model performance is evaluated for a suite of bentonite-kaolinite mixtures representing a wide range of swelling potential and along adsorption and desorption paths. Trends in model parameters are evaluated as functions of bentonite content, correlated am...

Evaluation of swell behaviour of expansive clays from specific moisture capacity

Current swell characterization techniques used to interpret the mechanical volume change occurring during the swelling process are not successful due to lack of inclusion of influential properties. Accurate prediction of swelling behaviour allows us to design more efficiently and with better reliability. This research aims at developing a more comprehensive framework to predict swell potential. Laboratory studies are conducted on five natural expansive soils with different degree of expansiveness. Initial studies include determination of basic soil characterization, swell strains and swell pressures at their compacted state along with their inherent mineralogy. Later, replicate samples were studied for soil water characteristic curves using standard pressure cell apparatus and filter paper techniques. The path traversed by the specimen during swelling process is representative of the soil water characteristic curve of the same specimen. Hence, studies are pursued to understand the relationship between degree of expansiveness and the specific moisture capacity relative to that particular range of suction head. Test results showed that the degree of expansion represented by swelling strain or swelling pressure is proportional to the specific moisture capacity determined during the swelling process.

A semi-empirical swell prediction model formulated from ‘clay mineralogy and unsaturated soil’ properties

Swell behavior of expansive clays is an inherent property that can be better explained through its hydro mechanical volume change behavior arising from soil attributes like matric suction and clay mineralogy information. Previous swell related modeling studies have not incorporated these attributes for swell behavior, thereby leading to poor to erroneous characterization practices. Both chemical and hydrological attributes of the soils are targeted in this expansive soil modeling. Eight natural expansive soils were collected and their swell strains were measured under different confining pressure conditions. Soil suction properties of expansive soils as well as soil water characteristic curves (SWCC's) were determined using standard measurement procedures including pressure plate and filter paper techniques. Slope of the paths traversed by the soil specimens in a void ratio — soil matric suction framework are determined and used as mechanical input parameters for the heave modeling. A new parameter, Mechanical Hydro Chemical Parameter (MHCP) is used that accounts for both matric suction and clay mineralogy information. This parameter is correlated with swell property measurements and the correlations developed provided reliable and reasonable swell property predictions. Independent validations with other soils are still needed for further enhancement of the MHCP framework for more reliable predictions.

Evaluation of Swell Behavior of Expansive Clays from Internal Specific Surface and Pore Size Distribution

AbstractThe interdependency of microsoil fabric-related properties and swell/shrink behavior of expansive soils needs to be identified to achieve a more thorough and accurate prediction of heave of expansive soils. In a recent research study, two microsize-related properties of a soil—pore size distribution and specific surface area—were identified and examined in an effort to address their synergistic effects on swelling behavior of soils. To study this aspect in detail, eight natural expansive clayey soils from known expansive soil regions were sampled and studied by using two test methods: conventional one-dimensional vertical swell tests and novel three-dimensional volumetric swell strain tests. Microinternal structural details, including pore void distribution, were obtained from mercury intrusion porosimetry (MIP) studies on compacted soil specimens. Specific surface area (SSA) details of the same soils were determined using the chemical ethylene glycol monoethyl ether (EGME) method. Attempts were m...

The effect of different types of water on the swelling behaviour of expansive clays

In the design of foundations of structures, especially light buildings, on clayey soils, the main soil behaviours to be considered are swelling properties and surface heave. Therefore, determination of swelling properties by means of swell percent and maximum swell pressure as well as estimation of the surface is very important in the investigation of such soils and light structures on them. In order to obtain the swelling parameters of clayey soils, experimental laboratory tests were carried out and standardised. Distilled water is generally used during these experimental tests; however, the soil in situ interacts with different types of water having different water chemistries. Therefore, the swelling behaviour of expansive soils tested with distilled water would naturally be different from the behaviour of expansive soils tested with different water types and chemistries. For this reason, it was anticipated that determination of the realistic swell behaviour in laboratory experiments requires the use of the same water as in the in situ condition. In this article, the effect of the water type and chemistry on the swelling behaviour of the clays was investigated by testing the clay samples with eight different types of water collected from the sea, river, lake and different rock formations. The main result of this research was that the anticipated clay swell percentages and pressures for different types of water were lower than for the distilled water routinely used in testing.

The role of suction and degree of saturation on the hydro-mechanical response of a dual porosity silt–bentonite mixture

To better understand the hydro-mechanical behavior of dual porosity expansive clays, three groups of tests were carried out. First, isotropic free drying and free wetting tests were performed to determine both branches of the soil water retention curve of a silt–bentonite mixture and its parameters. Next, constant suction oedometer tests at different matric suctions were employed using osmotic method. Finally, wetting–drying cycles were imposed on the samples in oedometric condition. At the end of wetting–drying tests, different suction values were enforced on the specimens and consolidation tests were performed, while the suction values were regulated through the samples using the osmotic method.Cross-examination of results indicates good consistency between the observed behaviors from different tests: Results of constant suction oedometer tests confirm the hardening phenomenon at low suctions indicated by the free drying test. Besides, all tests show that the amount of the suction hardening is negligible at suctions between the air entry of macropores and that of the micropores.However, the results contradict the physical models of hydro-mechanical behavior of expansive clays which do not take into account the suction induced hardening in the range of suctions less than the air entry value. Moreover, while most of the models assume that the shrinkage limit and air entry suction are coincident; results of the free drying test show the coincidence of the shrinkage limit and the air entry value of micropores.

THM analysis of a large‐scale heating test incorporating material fabric changes

SUMMARYEngineered barriers are basic elements in the design of repositories for the isolation of high‐level radioactive waste. This paper presents the thermo‐hydro‐mechanical (THM) analysis of a clay barrier subjected to heating and hydration. The study focuses on an ongoing large‐scale heating test, at almost full scale, which is being carried out at the CIEMAT laboratory under well‐controlled boundary conditions. The test is intensely instrumented and it has provided the opportunity to study in detail the evolution of the main THM variables over a long period of time. Comprehensive laboratory tests carried out in the context of the FEBEX and NF‐PRO projects have allowed the identification of the model parameters to describe the THM behaviour of the compacted expansive clay. A conventional THM approach that assumes the swelling clay as a single porosity medium has been initially adopted to analyse the evolution of the test. The model was able to predict correctly the global THM behaviour of the clay barrier in the short term (i.e. for times shorter than three years), but some model limitations were detected concerning the prediction of the long‐term hydration rate. An additional analysis of the test has been carried out using a double structure model to describe the actual behaviour of expansive clays. The double structure model explicitly considers the two dominant pore levels that actually exist in the FEBEX bentonite and it is able to account for the evolution of the material fabric. The simulation of the experiment using this enhanced model provides a more satisfactory reproduction of the long‐term experimental results. It also contributes to a better understanding of the observed test behaviour and it provides a physically based explanation for the very slow hydration of the barrier. Copyright © 2011 John Wiley & Sons, Ltd.

Porosity Evolution of Free and Confined Bentonites during Interlayer Hydration

AbstractMethods for predicting the volume change and swelling-pressure behavior of expansive clays require detailed understanding of coupled interactions between clay microstructure and macrostructure under hydraulic, thermal, and mechanical loads. In this study a suite of water-vapor sorption experiments was conducted using compacted bentonites hydrated in controlled relative humidity (RH) environments maintained under free and constrained volume-change boundary conditions. Emphasis was placed on examining the influences of compaction and predominant exchange cation on the water uptake, volume change, and swelling pressure response. Densely compacted specimens exhibited greater volume changes under free swelling conditions and greater swelling pressures under fully confined conditions. Water uptake, volume change, and swelling pressure were all more significant for Colorado (Ca2+/Mg2+) bentonite than forWyoming (Na+) bentonite. Plastic yielding, evident as a peak in the relationship between swelling pressure and RH, was more evident and occurred at lower RH for the Colorado bentonite. This observation was interpreted to reflect the limited capacity for interlayer swelling in Ca2+/Mg2+ bentonites and corresponding structural collapse induced by the onset of water uptake in larger intra-aggregate and inter-aggregate pores. A semi-quantitative model for the evolution of clay microstructure resulting from interlayer hydration was considered to attribute the experimental observations to differences in the efficiency with which transitions in basal spacing translate to bulk volume changes and swelling pressure. Results provide additional insight and experimental evidence to more effectively model the mechanical behavior of compacted bentonites used as buffer or barrier materials in waste repository applications.

Effect of potassium chloride on cyclic behavior of expansive clays

Some clay minerals suffer significant swell and shrink when exposed to wetting and drying respectively. The different electrical forces acting within the particle-pore fluid system is one of the reasons behind this behavior. These forces are influenced by the type and concentration of ions present in the pore fluid. To study the effect of KCl on swelling characteristics of soil, three types of expansive soils were used having different initial plasticity indices. The soils were mixed with various proportions of KCl; these are: 0.0, 2.5, 5.0 and 7.5% by weight of dry soil. The purity of the used KCl was more than 99%. The investigation showed that the addition of 5.0% KCl was the most beneficial in reducing the optimum moisture content, increasing the maximum dry density, reducing the free swell and the swelling pressure. The main findings of this study were indicated by the cyclic tests of wetting and drying. Even for the extreme conditions where the soils were subjected to many cycles of wetting and drying the potassium ions (K⁺) seem not to be removed from the soil. Potassium ions are strongly bonded to the surface of the particles resulting in lowering the swelling and shrinkage magnitudes as well as the swell-shrink band. Again, the addition of 5.0% KCl gives the best enhancement. For the 5.0% proportion of KCl the improvement factors for swell and shrink are always greater than 40%.

Behavior of Expansive Clay of Ngawi Region (East Java) Under Water Content Variation

Behavior of Expansive Clay of Ngawi Region (East Java) Under Water Content Variation

Behavior of expansive soils under stabilized fly ash cushions during cyclic wetting and drying

Structures built in expansive clays are likely to be damaged due to the strains caused in them by alternate swelling and shrinkage. Variations in the moisture regime during monsoon and summer are the cause of this alternate swelling and shrinkage. Several innovative foundation techniques have been suggested to overcome the problems associated with expansive soils. Belled pier and under-reamed pile are some of the foundation practices adopted in these soils. Besides, overburden in the form of a sand cushion or a cohesive non-swelling soil (CNS) cushion has also been tried for arresting heave. But, most of them suffer from one shortcoming or the other. In order to overcome the drawbacks of the existing foundation practices, fly ash cushion, stabilized with lime or cement, has been tried by the authors. The principle of this technique is the same as that of a CNS cushion. This proved to be very effective in arresting heave. However, its efficacy over a few cycles of wetting and drying needs to be established since CNS cushion, which was found to be effective in arresting heave during the first cycle of wetting and drying was ineffective during the subsequent cycles. The present study relates to the behavior of expansive clays under lime- or cement-stabilized fly ash cushion subjected to several wetting and drying cycles.

Engineering Behavior of a Remolded Expansive Clay Blended with Lime, Calcium Chloride, and Rice-Husk Ash

This paper presents experimental results obtained from tests conducted on remolded expansive soil specimens blended with rice-husk ash (RHA) and stabilized with lime and calcium chloride. The amounts of RHA, lime, and calcium chloride were varied from 0 to 16%, 0 to 5%, and 0 to 2%, respectively, by dry weight of the soil. The effect of additives on unconfined compressive strength (UCS) and California bearing ratio (CBR) is reported. It was found that the stress-strain behavior of expansive clay improved upon the addition of up to 5% lime or up to 1% calcium chloride. A maximum improvement in failure stress of 225 and 328% was observed at 4% lime and 1% calcium chloride, respectively. A RHA content of 12% was found to be the optimum with regard to both UCS and CBR in the presence of either lime or calcium chloride. An optimum content of 4% in the case of lime and 1% in the case of calcium chloride was observed even in clay-RHA mixes.

Effect of Chemical Solute Concentration Changes on Deformation Behavior of Expansive Clays

Effect of Chemical Solute Concentration Changes on Deformation Behavior of Expansive Clays

Expansive bentonite–sand mixtures in cyclic controlled-suction drying and wetting

Expansive clay buffers in radioactive waste disposal designs experience cyclic drying and wetting paths during different stages of their design life. Clayey soils subjected to these processes develop swelling and shrinkage deformations, which give rise to the accumulation of compression or expansion strains during suction cycles. Experimental studies were undertaken using oedometer tests on an artificially prepared bentonite–sand mixture (80% bentonite by dry mass). In order to study these processes and to identify the most important features controlling soil behaviour, several wetting–drying cycles with suctions ranging between 130 and 4 MPa were applied using vapour equilibrium technique and covering a wide range of overconsolidation ratios (OCR). The tested samples showed cumulative shrinkage strains along the successive cycles, which became more significant at increasing vertical net stresses (low OCR values). However, no accumulation of expansion strains was detected at elevated OCR values. Test results were interpreted and predicted within the context of an elastoplastic model proposed by Alonso et al., 1999, [Alonso, E.E., Vaunat, J., Gens, A., (1999). Modelling the mechanical behaviour of expansive clays. Engineering Geology, 54, 173–183.] which takes into account the accumulation of strains. A good correspondence between measured soil response and model predictions was observed. The paper also presents the methodology to derive the constitutive parameters.

Laboratory Study of Heave Behavior of Expansive Clay Reinforced with Geopiles

This paper presents heave behavior of an expansive clay reinforced with geopiles, which are vertical cylindrical cells made of geogrid and filled with geomaterials. When a geopile is installed vertically in an expansive soil, heave is controlled because of the friction mobilized at the interface formed by the fill material, geogrid-expansive soil. The effects of diameter of the geopile and the type of the fill material on heave response have been investigated in this study. The results indicated that heave decreased with increasing diameter of the geopile and increase in the particle size of the fill material. Results are also presented from tests conducted on groups of geopiles using two and four geopiles together to investigate the influence of spacing on heave between the geopiles. In the case of a group of geopiles, spacing between the geopiles was varied and its effect on heave studied. Heave decreased with closer spacing between the geopiles. No group effect of geopiles was observed when the spacing...

Influence of Gypsification on Engineering Behavior of Expansive Clay

Influence of Gypsification on Engineering Behavior of Expansive Clay

Influence of Gypsification on Engineering Behavior of Expansive Clay

Volume change in argillaceous sediments can take place due to either swelling of expansive clay or gypsification of anhydrous calcium sulfate. Gypsification offers a variety of serious geotechnical hazards such as high swell pressure, floor heave in tunnels, massive rock uplift in dams, and damages to light structures and pavements. Some of these phenomena have been observed in the Arabian Gulf coastal region, where the behavior of local argillaceous sediments is controlled by severe climatic and environmental conditions. Based on laboratory investigation of natural and synthetic samples, this paper studies the influence of gypsification of anhydrite on the engineering behavior of calcareous expansive clay.

Modelling the mechanical behaviour of expansive clays

A simple formalism is presented to model the behaviour of expansive clays. Two levels of structure are considered. The behaviour of the macrostructure follows the model developed for unsaturated materials by Alonso et al. [Géotechnique 40 (3) (1990) 405–430]. The behaviour of the microstructure is adapted from the work of Gens and Alonso [Can. Geotech. J. 29 (1992) 1013–1032] in order to include the possibility of the micropores being partially saturated. Mechanical coupling between both levels of structure are defined through two functions, one for wetting and the other for drying. They express the change in macrostructural void ratio due to a change in microstructural void ratio, and their value depends on the state of compaction of the macrostructure. The general shape of these curves is discussed on the basis of experimental evidence. Phenomena such as the dependency of strain on stress–suction path, accumulation of expansion strain during suction cycles at low confining stress, accumulation of compression strain during suction cycles at high confining stress, strain fatigue during drying–wetting cycles, macropore invasion by expanded microstructure and development of macroporosity during strong drying can be represented. A mathematical formulation of the model is described and its performance finally assessed by comparison with laboratory tests.

Swelling-shrinkage behavior of natural expansive clays

The swell-shrinkage behavior of expansive clays was investigated in four soils of different plasticity cyclic swelling. To simulate drying temperatures typical of site conditions, two shrinkage schemes were adopted, partial and full shrinkage. After each cycle, the expansive characteristics of the soils were assessed. Furthermore, the physical and microstructural changes due to cyclic swelling were also studied, respectively, through an ultra-sonic investigation and scanning electron microscope observations. The results showed that cyclic swelling and shrinkage has a marked influence on the expansive behavior of clays. Generally speaking, a decrease in the swelling ability of the clays, corresponding to a reduced water absorption capability, was observed when the soils were alternately wetted and partially shrunk. On the other hand, an increase in the swelling potential was noted when the soils were fully shrunk. In either case, equilibrium can be attained after several cycles. As the number of cycles increase, further destruction of large aggregates and disorientation of structural elements takes place. Approximately after the fifth cycle, the fabric becomes almost disoriented, consequently further changes in expansibility disappear. The scanning electron microscope analysis showed that for partial shrinkage the structural elements exist mainly as edge to face contacts with a tendency to form a turbulent flocculated system while a horizontal clay particle orientation was observed when the specimens were cyclicly wetted the fully shrunk. In parallel, the ultrasonic wave transmission velocity increased with the number of cycles in the first case, and decreased when transmitted through a fully shrunk soil sample.