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The present study examines the shrinkage behaviour of residually derived black cotton (BC) soil and red soil compacted specimens that were subjected to air-drying from the swollen state. The soil specimens were compacted at varying dry density and moisture contents to simulate varied field conditions. The void ratio and moisture content of the swollen specimens were monitored during the drying process and relationship between them is analyzed. Shrinkage is represented as reduction in void ratio with decrease in water content of soil specimens. It is found to occur in three distinct stages. Total shrinkage magnitude depends on the type of clay mineral present. Variation in compaction conditions effect marginally total shrinkage magnitudes of BC soil specimens but have relatively more effect on red soil specimens. A linear relation is obtained between total shrinkage magnitude and volumetric water content of soil specimens in swollen state and can be used to predict the shrinkage magnitude of soils. [ABSTRACT FROM AUTHOR]

The cohesive interactions between grains play a prevailing role in the mechanical behaviour of unsaturated granular materials such as fine sands. These interactions are generally bonds of various natures that evolve according to the surrounding hygrothermic conditions. We study the case where the liquid present in the material is a water solution saturated with sodium chloride. The bonds are then of capillary type and the cohesive interactions are mainly attractive. In this case, the mechanical strength in an unconfined compression test is relatively low. At low relative humidity, the phase change of water involves a crystallization of salt at the contact points between grains generating thus bonds of solid type. The mechanical strength of the material is thus enhanced. An experimental study of the variation of the mechanical strength during the crystallization of salt allowed us to show two distinct cohesive regimes: capillary and cemented. The transition between these two regimes does not seem to be correlated with the mass of the crystallized salt, but rather with the residual degree of saturation. An analysis of these results is proposed by comparison with numerical simulations based on the discrete element approach. [ABSTRACT FROM AUTHOR]

Suction is one important parameter affecting the shear behaviour of partially saturated soils. State variables such as void ratio and degree of saturation control the development of suction. A series of deviatoric triaxial tests on kaolinite clay with direct measurement of suction are reported. An appropriate elasto-plastic constitutive for this type of soil is presented and its parameters are determined from the test results. [ABSTRACT FROM AUTHOR]

In this paper a new experimental device for unsaturated soil testing is presented. The new Double Wall Biaxial Cell was designed to study the behavior of unsaturated granular material under plane strain conditions. The required calibration of the new device is presented in detail. Saturated soil samples were tested in the new device under isotropic consolidation conditions. The volume changes of the specimen were measured by two alternative methods to check the reliability of the new device. To verify the independent two stress state variables concept proposed by Fredlund and Morgenstern, Null-tests were performed on sand-kaolin mixture specimen. Axis translation technique was used for creating the desired matric suction. The details of the new device and the test procedures are described. The obtained result are presented and discussed in detail. [ABSTRACT FROM AUTHOR]

A series of high pressure oedometer compression tests were carried out on samples of Lixhe chalk (Belgium) containing various pore fluids: water, air (dry sample), oil (Soltrol) and oil/water under a controlled suction of 200 kPa. Strain curves with respect to time of tests carried out under a constant load were examined in a purpose of investigating the time dependent behaviour of chalk. A simple empirical exponential law able to account for the combined effects of stress and suction is proposed. Experiments show that it provides satisfactory results to predict a feature of multiphase chalk behaviour that is important in the study of the behaviour of oilfields. [ABSTRACT FROM AUTHOR]

A research project on the stability of temporary trenches in unsaturated soil is carried out in Belgium. The main objective of the project is to evaluate the seasonal variations of suction in the soil and to quantify the consequences of these suction variations on trench stability. Within the framework of the research, a full scale instrumented test trench with vertical sides has been excavated in June 2004 at the site of BBRI, characterized by quaternary loam (Limelette, Belgium), to compare calculations with full-scale observations. As expected first failures occurred during the winter, when suction in the soil was minimal. This paper presents the details of this experiment. [ABSTRACT FROM AUTHOR]

A simple technique is proposed to predict the variation of the bearing capacity of an unsaturated soil with respect to matric suction. This technique is based on extending conventional bearing capacity theory proposed by Terzaghi. The proposed equation in this paper is presented as a functional relationship such that the variation of the bearing capacity of an unsaturated soil with respect to matric suction can be predicted. This technique is developed extending the concepts for predicting the shear strength of unsaturated soils proposed by Vanapalli et al. (1996). Using the approach presented in this paper, the bearing capacity of an unsaturated soil can be predicted using the saturated shear strength parameters, c' and π' and the soil-water retention curve (SWRC). [ABSTRACT FROM AUTHOR]

The compaction of field soils due to repeated rolling of agricultural vehicles is one of the main reasons for the agricultural soil degradation. A good understanding of the compaction properties of these soils is essential for an optimum organisation of agricultural activities, and therefore for environmental protection in terms of nitrate migrations. In the present work, the compaction properties of agricultural soils from four sites in France are studied after experimental data from oedometer tests. In the oedometer tests, a quick loading procedure was applied to simulate the loading of tire rolling. The soils that were initially in unsaturated state were loaded under constant water content condition. The compaction properties of these soils (i.e. the precompression vertical stress, compression index and swelling index) were then determined. The effect of initial dry density and initial water content on these properties is discussed. A possible effect of loading velocity on the apparent compressibility was observed. The results are finally discussed in the context of unsaturated soil mechanics. [ABSTRACT FROM AUTHOR]

Preferential water movement is a frequently observed phenomenon in soil science. Especially on natural slopes hydraulic behaviour can sometimes be observed which arises from preferential water flow. If the soil consists of a more or less homogeneous material, the preferential water movement can be caused only by heterogeneously distributed water. A sprinkler irrigation test on a large scale homogeneous dyke model and corresponding measurement results using different techniques have shown on the one hand, that preferential water flow in the form of fingering possibly occurred during the experiment. On the other hand, lateral water movement due to heterogeneously distributed water content inside the dyke body could be observed. Both phenomena were also investigated in simple laboratory experiments. The contribution presents results from the above mentioned experiment which are analysed and discussed. [ABSTRACT FROM AUTHOR]

Copyright of Experimental Unsaturated Soil Mechanics is the property of Springer eBooks and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Plate-load tests are a common field method to estimate soil bearing pressure. Classic-result-test interpretations do not consider the matric suction effect. This paper analyzes the matric suction effect in bearing pressure from plate-load tests conducted in a lean clay soil. Seven plate-load tests were carried on in an unsaturated lean clay deposit; two of them were performed in saturated condition to verify the site homogeneity and test repeatability, five of them took into account different matric-suction values. Matric suction along the plate influence zone was monitored with four Jet Fill tensiometers, inserted at 0.1, 0.3, 0.6 and 0.9 m around every test pit. The results show bearing pressure values are highly influenced by matric suction changes. [ABSTRACT FROM AUTHOR]

This paper discusses the general liquefaction state of unsaturated soil related to the mudflow type slope failures observed during earthquakes in areas covered with volcanic ash sand deposits. It is found that the volume compressibility of soil structure, the degree of saturation and the confining pressure are key factors governing the liquefaction of unsaturated soils. [ABSTRACT FROM AUTHOR]

Because of the complexity of the metrological determination of the soil water retention curve (SWRC), so-called pedotransfer functions (PTF) have been developed for several years. Mostly these PTF are based on a more or less simple regression analysis using a limited set of data. In such methods the SWRC is predicted with data on the amount of soil components sometimes supplemented by values regarding the density or the amount of organic materials. Only few PTF deal directly with the particle size distribution. In many cases empirical factors are necessary to obtain a prediction for the water retention curve. A new method for determining the soil-hydraulic properties using the pore constriction distribution of a soil has been developed, whereby the pore constriction distribution is derived from the particle size distribution depending on the density of the soil. The contribution will present the new pedotransfer method and shows results in comparison to experimental investigations. [ABSTRACT FROM AUTHOR]

This paper aims at elucidating the influence of pore fluid properties on the shrinkage strains of deformable materials subjected to drying. Results of isothermal drying tests of two kinds of silts saturated with three different pore fluids are presented. Results show different strain amounts during drying and the final void ratios, depending on pore fluid. The rates of drying are consistent with saturated vapor pressures, while their amount with the surface tension. The shrinkage limit appears also to be controlled by a limitation in skeleton compressibility. [ABSTRACT FROM AUTHOR]

The soil water characteristic curve (SWCC) of a soil is often predicted from the pore size distribution (PSD) of the soil. Experiments show that the PSD may change in the drying or wetting process. It is necessary to consider the pore-size distribution changes in predicting SWCCs. In this research, different grain-size proportions of completely decomposed granite were separated and then mixed artificially to obtain five soil specimens of different grain-size distributions. These specimens vary from gravel to sand, and silty clay. The SWCCs of these specimens were measured using the axis-translation technique and a Dewpoint psychrometer; and the PSDs of these soil specimens were measured using a mercury intrusion porosimetry (MIP) method. The PSDs obtained from the MIP tests were used to predict the SWCCs, which were compared with the experimental results further. The PSDs of each soil sample at full saturation and at the end of the SWCC drying test were compared. The PSDs showed a considerable pore-size reduction after soil drying. This phenomenon is referred to as ‘pore shrinkage'. A model proposed by Simms and Yanful (2001) was adopted to consider the shrinkage influence in the prediction of the drying SWCC from the PSDs of saturated and dried soil samples. After applying this model, the predicted SWCCs were closer to the experimental SWCCs, especially for fine soils. For coarse soils, the pore volume with pore diameter larger than a specific value that cannot be measured by MIP tests is large. This volume was estimated and used to correct the predicted SWCC for each coarse soil. With this correction, the predicted SWCCs for coarse soils were also close to the experimental SWCCs. [ABSTRACT FROM AUTHOR]

A screening level model was developed for simulation of pollutant migration through the unsaturated-zone and subsequent mixing within the saturated-zone. This one-dimensional finite difference model simulates the transport processes of liquid-phase advection, liquid- and vapor-phase dispersion, sorption, and decay of the contaminant. The model estimates contaminant concentration in the saturated-zone by using a simple mass balance technique for mixing of the unsaturated-zone leachate with the groundwater. The model can be a useful tool in making preliminary assessments of the potential impacts of contaminants in the subsurface. The model can handle vertical heterogeneity of the soil columns and non-uniform initial contaminant concentration. It was verified by comparing its simulation results to an analytical solution and laboratory soil column experiments. In addition the model was validated against laboratory experiments with three different soil sample sizes of Ottawa quartz sand and 480 ppm saline water as a groundwater contamination source. [ABSTRACT FROM AUTHOR]

In order to obtain the retention curve of unsaturated soil which is defined as the relationship between water content and suction, numerous laboratory tests have been done for many soils with different clay contents. The laboratory tests concern different types of soils; the swelling and not swelling clays (natural clay with high silt content and the bentonite clay). Two complementary experimental ways are conducted. The first which leads to measure suction is based on the filter paper method. The second with the dessicator allows to impose a high suction values. The paper discusses the theoretical approaches for the grain-size distribution and water retention curve's relation. It discusses also their correlations according to each type of tested soil. The experimental data are used to validate the theoretical model selected in the study. The influence of the different parameters used by the model is also studied. All the parameters required to run the model can be obtained by performing independent, common laboratory tests and are related to the physical parameters like the initial dry density and the initial void ratio. After some numerical tests, the direct procedure to obtain the soil-water characteristic curve is improved. [ABSTRACT FROM AUTHOR]

Landfills are provided with cover systems in order to separate the waste from the environment and in order to prevent percolation of precipitation and recharge of leachate. The layers of a landfill cover system (restoration profile, drainage layer, compacted clay liner - CCL) have to be specifically designed for long-lasting effectiveness. Special care has to be taken to prevent the CCL from desiccation-cracking due to high matric suction. On a landfill in Northern Bavaria, test fields of some 260 m2 each were installed with different profiles: The test fields were built according to the recent German landfill ordinance, but with a thicker restoration profile (2.0 m and 1.5 m thick restoration layer, respectively). Water content and matric suction of the soil profiles was measured by FDR-probes and tensiometers. In test field 1 reduction of soil water content during summer was detected down to 1.8 m depth. In test field 2 (1.5 m thick restoration layer) decreasing water content was measured in the CCL, whereas in test field 1 (2.0 m thick restoration layer) the CCL was not affected by loss of water. In conclusion, at the given landfill site only the 2.0 m thick restoration profile is able to effectively shield the CCL from desiccation effects. [ABSTRACT FROM AUTHOR]

The measurement of soil parameters for the unsaturated soil constitutive models needs extensive laboratory tests. For most practical problems, it has been found that approximate soil properties are adequate for analysis. Thus, empirical procedures to evaluate unsaturated soil parameters would be valuable. The soil-water characteristic curve (SWCC) can be used to estimate various parameters used to describe unsaturated soil behavior. The SWCC is a relationship between soil suction and some measure of the water content. It can be measured or predicted based on soil index properties. Estimation based on index properties is highly desirable due to its simplicity and low cost. In this paper, a new model for predicting the SWCC based on soil index properties and Van Genuchten equation is presented. The comparisons show that the SWCC predicted by this model is in a good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Scaly clays are stiff and highly fissured soils due to their complex geological history. Owing to these characteristics, they may be placed and compacted as excavated, to obtain a material with adequate engineering properties, suitable as core material in earth dams and in waste isolation fills. With reference to these engineering applications, an exhaustive experimental programme is developed to characterise the hydro-mechanical behaviour of this compacted material under a variety of controlled-suction paths. This paper presents selected test results, focusing on the interpretation of specific behavioural features of the volume change of this complex material; namely, the strain accumulation and the volumetric irreversible features developed during suction cycling at different stress levels. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental study on variation of degree of saturation of a compacted unsaturated silty soil during isotropic loading and unloading. A series of laboratory experiments have been conducted in a double-walled triaxial cell (and a conventional triaxial cell for saturated samples) on samples of a compacted silty soil. In the experiments the soil samples were subjected to isotropic consolidation followed by unloading under constant suction. The results show that during consolidation a significant increase in degree of saturation was observed. In contrast, during subsequent isotropic unloading, where only a very small elastic component of swelling occurred, the changes of degree of saturation were very modest. Comparison has been made between the experimental and theoretical prediction using a relationship proposed in the literature. [ABSTRACT FROM AUTHOR]

Highly compacted bentonite has been proposed as buffer material in the Swedish concept for the disposal of nuclear waste. A laboratory program with focus on hydro-mechanical properties of unsaturated highly compacted bentonite has been running and one part included changes in volume. The results could be used to determine different moduli but are presented here as a verification of a model covering the impact of confinement on the retention properties. The tests were performed with suction control, which was achieved by the vapour equilibrium technique. The applied relative humidity was approximately 85% in the tests presented in this paper. The tests were done both as constant load tests with a change in relative humidity and as tests with constant relative humidity and a change in the applied load. The load was applied axially and the maximum constant load corresponded to an axial stress of 20 MPa. Also the radial stress was measured. All tests started from a compacted condition with a water content of 10% and a void ratio of approximately 0.6. The investigation showed that the model, which was mainly based on constant volume tests, also seems to be valid after volume change since good agreement was achieved between measured and calculated results in the presented examples. [ABSTRACT FROM AUTHOR]

Copyright of Experimental Unsaturated Soil Mechanics is the property of Springer eBooks and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Engineered barriers made up of compacted expansive clays are a basic component of the systems for the isolation of high-level radioactive waste (HLW). The barrier is initially unsaturated and during hydration the hydraulic gradient varies from high values (i.e. higher than 50000) at the beginning of the wetting to very low values (practically zero when reaching stationary conditions). The values of bentonite permeability are frequently obtained at the laboratory under high hydraulic gradients (i.e. higher than 15000), necessary to induce a measurable flow. A drawback of this practice is that the applied hydraulic gradients are very far from those (expected) in actual conditions. So, the experimental results obtained might not be realistic in many cases, affecting the reliability of the numerical analysis. To advance in the knowledge of expansive clays behaviour this work presents an experimental and numerical study. The hydraulic permeability of FEBEX clay samples has been measured under low injection pressures. This work presents the modelling of infiltration laboratory tests designed to reproduce the thermo-hydro-mechanical conditions of large-scale tests. The evolution of the tests is analysed and discussed in detail using non-standard flow models which consider the presence of a threshold gradient and thermo-osmotic effects. [ABSTRACT FROM AUTHOR]

In the following paper an influence of several state parameters on one dimensional time-dependent material behaviour of an unsaturated soil is presented. For identification of parameter values, laboratory experiments were performed. Standard oedometric compression tests were carried out to investigate stress-strain-time relationships. Apart from the degree of saturation the initial void ratio vary as parameters. For measuring the matrix suction a tensiometer is mounted inside the specimen. A detailed description of the equipment used and the test procedures are given in the paper. The tests reported here were carried out with a kaolinite to determine parameter values, depending on different state variables. The characteristic behaviour of unsaturated samples observed during consolidation and creeping is shown in a series of figures. Parameters like Cc, Cs and Cα are used in constitutive model that can simulate both consolidation processes as well as creep phenomenon for partially saturated clay in a single consistent analysis. [ABSTRACT FROM AUTHOR]

Large spoilheaps of overburden from open-cast coal mining in Northwestern Bohemia offer a space for development. However, they exhibit unfavourable features such as collapse potential caused by the lumpy structure with high overall void ratios. Suction oscillations contribute to the structure degradation by the intervoids closure. The paper presents in-situ suction monitoring and laboratory investigation of the collapse potential of spoilheaps. [ABSTRACT FROM AUTHOR]

The swelling behaviour of kaolinite clay is systematically investigated by means of two types of oedometer devices suitably modified to measure the variation of swelling pressure in dependence of the vertical and volumetric strain. A wide range of values for initial void ratio as well as initial and final degree of saturation has been covered. Based on the experimental results approximate equations for the swelling deformation are derived that are implemented in a FEM-Code. The application to a typical situation in practice is demonstrated by the numerical solution of the respective boundary value problem. [ABSTRACT FROM AUTHOR]

Two methods were developed to determine the retention curve for a fixed dry density and at high temperature. The materials used are the MX-80 and the FEBEX bentonites. The retention capacity of the FEBEX bentonite is higher than that of MX-80, i.e. for a given suction and dry density, the water content of the FEBEX bentonite is higher. However, the difference between both bentonites becomes smaller towards the lower suctions. In both bentonites the retention capacity has decreased as temperature increased, and the difference in the retention capacity of the two bentonites became less important at high temperature. [ABSTRACT FROM AUTHOR]

Like every human activity, the nuclear activities generate waste. Because of the particular characters of the nuclear waste, a special geological formation and also plug material for storage of the high level nuclear waste is necessary. The plug material plays an important role in confining the radioactivewaste. Therefore, one needs a material with the character of very low permeability and a good capacity of holding the radionuclides. The compacted bentonite will thus be employed as such plug material. So it is very important to evaluate the swelling characters of compacted bentonite. Here, it is presented an experimental study of thermo-hydro-mechanical behaviour of compacted bentonite of MX-80, based on tests carried out in an isotropic high-pressure cell (60 MPa) in the range 20 and 80˚ C (± 0.1˚ C). The results present the deformation of compacted bentonite as a function of temperature, suction and pressure. [ABSTRACT FROM AUTHOR]

The paper describes experimental results on triaxial paths at high temperature concerning an unsaturated clay (w_L = 38%, I_P = 19 and C_c = 0.23). Unsaturated drained triaxial compression tests on normally consolidated samples were carried out at constant temperatures varying from 22 to 80˚ C. Desaturation of samples were carried out by the imposition of suctions using the osmotic method. This required the development of a new triaxial cell equipped with a collar heating and an osmotic pedestal which allows the circulation of an osmotic solution of Poly Ethylen Glycol (PEG) 6000, in contact with the sample via a dialysis membrane. The principal phenomena simultaneously related on the temperature and saturation were highlighted, in particular the hardening of material on isotropic path, a secant modulus which decreases with temperature and increases with suction, a light reduction in the maximum stress on deviator path at high temperature and the increase in this maximum stress when suction increases. [ABSTRACT FROM AUTHOR]

We investigate the influence of temperature on the retention curve of soils. This curve represents the constitutive relation between water content w and suction s, for a given temperature T and a given void ratio e. We present a model based on the differential of suction as a function of T, w and e. When adjusted for a retention curve obtained at a given temperature, this model enables to predict this curve for any temperature. In parallel, we carried out experiments on a clayey silty sand by using a pressure cell immersed in a thermostatic bath. The model was validated by several tests on the clayey silty sand at 20 and 60˚ C. The application of the model to data found in the literature confirms its predictive power for a wide range of porous materials. These results allow us to plot the retention surface, from experimental tests obtained at a given temperature and from modelling. It can be considered as a generalization of the classical retention curve. Finally, we discuss the influence of the void ratio variation during experiments on the curve predicted by the model. [ABSTRACT FROM AUTHOR]

This paper focuses on the effect of moderately high temperature on the swelling pressure of compacted bentonite and bentonite-sand mixtures which are among the material used as buffer material in high level waste repository. Modified isochoric cell was used to measure the swelling pressure of the material at 80˚C. Two different methods were utilized in order to implement two transport mechanisms of water molecules in compacted mixtures. The equipment set-up, verification, and experimental programs adopted in this study are described. The results obtained are presented and discussed. [ABSTRACT FROM AUTHOR]

This paper presents results of an experimental study on shear strength behaviour of an unsaturated silty soil. A comprehensive set of laboratory experiments have been undertaken in a double-walled triaxial cell (and a conventional cell for saturated samples) on samples of a compacted silty soil. In the experiments the soil samples were subjected to isotropic consolidation followed by unloading and subsequent anisotropic reloading (shearing) under constant suctions. Volume change and shear strength data for the samples were monitored continuously during the experiments. In this paper, the results of the experimental study will be presented and the effects of suction on the shear strength and volume change of unsaturated soil will be discussed in detail. [ABSTRACT FROM AUTHOR]

This paper describes the influence of soil structure and soil suction on the tensile strength of a compacted clay. Laboratory tensile strength tests were carried out on a medium plastic clay. The soil samples were prepared by compacting a soil-water mixture of predetermined water content. The soil samples were either wetted or dried to different water contents corresponding to several suction levels. The test results showed an increase in the tensile strength with higher suction values and that samples compacted at different compaction states reach different magnitudes of tensile strength values. [ABSTRACT FROM AUTHOR]

In this paper tensile strength measuring apparatus developed by Tamrakar et al. (2005a,b) was used to measure the tensile strength of one dimensionally consolidated saturated NSF-clay and statically compacted unsaturated mixtures of NSF-clay, CFP-silt and Toyoura-sand. Tensile strength (qt) obtained from the tensile tests were compared with the unconfined compressive strength (qu). It was observed that the ratio qu/qt lied within the range of 2 to 3 for saturated NSF-clay and 4 to 16 for compacted mixtures. Effect of specimen thickness within the tensile mold, number of compaction layers and tensile pulling rates on the tensile strength were also examined. Comparing the specimen thickness within the tensile mold, it was found that the specimen having 5 cm thickness gave the minimum value. Also, tensile strength increased with the increase in the number of compaction layers. As in other shear strength, increment in the tensile strength was observed beyond tensile pulling rate of 0.34 mm/min. But below this pulling rate also, some increments were observed. [ABSTRACT FROM AUTHOR]

In order to determine shear strength of fine-grained unsaturated soils, a new design of a shear box for a modified direct shear device is described where a desired matric suctions is added easily with a hanging column. Simple principles were employed to develop the direct shear testing device so that it would be robust, easy to use, and readily assembled and disassembled for testing and maintenance. Tests were conducted with sandy silts under several net normal stresses (σn ua) for different desired matric suction (ua-uw). The results show that unsaturated shear strength and friction angle (πb) is consistent with results from prediction procedure (Fredlund and Barbour 1996) and estimated friction angle (πb) based on a soil-water characteristic curve (SWCC) of the sandy silt, respectively. [ABSTRACT FROM AUTHOR]

Suction tension acts within the gas and liquid filled grain-pore-system in unsaturated fine grained soils and should partly control the shear strength. The development of pore pressure in a completely water saturated grain structure will reduce the shear resistance, whereas the suction tension within an unsaturated soil will cause additional grain-to-grain forces. These are changing with varying degree of water saturation and thus may influence the shear strength probably by favouring the formation of coarse grained aggregates. An experimental approach was started to investigate this expected relation in overconsolidated Tertiary clay and in Quaternary loess (silt) using triaxial and direct shear test results and comparing them with the results of suction tension measurements obtained by using pressure membrane apparatus. Based on the common classifications, one should argue that shear velocity will control the shear strength due to pore pressure effects in the shear zone. However, the antagonistic effects of overpressure of the pore fluid and compression of grains due to suction tension act on a micro-scale in unsaturated fine grained soils and influence the shear behaviour differently. Effects of suction tension are noticeable in triaxial and direct shear tests in unsaturated fine grained soils. Quantification is difficult because other stress influences like load level act more effectively. [ABSTRACT FROM AUTHOR]

The dew point method, which determines suction by measuring sample temperature and dew point temperature of air equilibrated with the sample, provides a quick and accurate method for measuring suction in the range 1 to 400 MPa (pF 4 to pF 6.6). We present a procedure, using the dew point method, to prepare samples in the relevant suction range, measure suction and water content, and obtain an equation describing the soil water characteristic (SWC). Characteristics for four soil samples ranging in texture from sand to bentonite are presented. All show a linear relationship when water content is plotted vs. logarithm of suction. The slope of the characteristic is easily obtained for use in expansive soil identification. [ABSTRACT FROM AUTHOR]

Suction as one of the stress state variables of unsaturated soils is usually either imposed to the soil or measured. Measurements of suction therefore become commonly practiced when dealing with unsaturated soil problems. Unlike the measurement of matric suction, whereby one can arrive at a sufficient accuracy, the accuracy in total suction measurements is questionable. Total suction measurements involve equilibration of sensors used with the relative humidity of the vapour space in or above the soils. Many factors have been cited to cause inaccuracy in the total suction measurements such as temperature gradient and the inaccuracy of the sensors used to measure total suction. In this paper, the total suction measurement inaccuracy of several sensors commonly used is discussed. It is found that the total suction measurements can only be performed to lowest suction of 1000 kPa when sufficient accuracy is to be obtained. [ABSTRACT FROM AUTHOR]

Copyright of Experimental Unsaturated Soil Mechanics is the property of Springer eBooks and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An extensive experimental study was performed to compare the measurement capabilities within different ranges of two total suction measurement equipment: SMI transistor psychrometers and a chilled-mirror dew-point psychrometer (WP4 Dewpoint PotentiaMeter). The equipment were used in a systematic way to determine the relative humidity of the environment surrounding different compacted clayey soils along drying paths and covering a wide total suction range (0.1 to 70 MPa). The equipment description and the calibration protocols followed are presented, as well as suggestions regarding the improvement of their performance. The water retention curves of two different compacted clayey soils are presented and commented by taking into account the corrections proposed for the readings. A possible explanation for differences in the measurements observed between both instruments in the high suction range is presented in terms of the hydraulic paths undergone by the soils during the measurement period. [ABSTRACT FROM AUTHOR]

Coarse granular materials such as rockfill have been described in recent years by means of strain and work hardening plasticity models Oldecop and Alonso (2001), Chàvez and Alonso (2003), Alonso et al. (2005) which require a proper definition of the flow rule. The paper presents experimental information on dilatancy rates obtained in suction controlled triaxial tests performed on large diameter (25 cm) specimens of compacted coarse gravels of hard limestone. Tests involved confining stresses in the range 0.3-1 MPa and Relative Humidity in the range 10-100%. Unloading-reloading during the tests provided information on the elastic response. Volumetric and deviatoric plastic strains rates were determined from records of total vertical and volumetric deformations. In general, a steady (critical) state was not found. Plots have been prepared showing the variation of the plastic flow direction, d, with a number of variables: vertical deformation, stress ratio, η, confining stress, p, plastic work, Wp, suction, s, and some derived normalized variables. It was found that the common framework of dilatancy being a function of the current stress ratio and the limiting stress ratio is far from being appropriate to describe the behaviour of the tested aggregates. It was found that relationships d=f

This paper presents results when using a tensiometer designed in the Soil Mechanics Laboratory at COPPE/UFRJ, and several other instruments. This new instrument measures suction values up to 1500 kPa. In more typical tensiometers, the cavitation of the system hinders the measurement of suction with values over 100 kPa. Ridley and Burland (1993) designed a new model of tensiometer to measure suction of more than 100 kPa. Mahler et al. (2002) presented a new tensiometer with which suction values up to 350 kPa were measured. This paper introduces an updated model of a tensiometer, using a variation of the equipment proposed by Mahler et al. (2002). The updated model worked extremely well and cost little to build. The equipment used allows suction to be measured relatively quickly and, as previously stated, is economical to produce (about US$300). To date, the range of suction levels that can be measured reaches 1500 kPa with no difficulty. The tests were carried out in two boxes of 160× 50× 60 cm under laboratory conditions. The equipment used included a 15 m.c.a. ceramic block pressure sensor, de-aerated water and a special acrylic tube specifically designed for this instrument. The results were compared to two simple automated tensiometers and equivalent tensiometers. In general very good results were obtained. The main final remarks so far are as follows: • the high bubble air entry of the ceramic block inhibits the presence of air bubbles, but the response time is slower for suction values of more than 200 kPa; • the saturation process used for the ceramic stone worked very well; • as expected, the position of the equivalence tensiometer influences the value measured; • the mini-lysimeter system proved to be a very good alternative for laboratory tests and for the development of instruments that measure suction; • the new instrument presented herein proved to be a good and an economical alternative for measuring matrix suction in the soil. [ABSTRACT FROM AUTHOR]

An alternative technique for the determination of the soil water retention curve has recently been proposed whereby a tensiometer is used to measure soil suction and a balance to record the water content variations. The soil water retention curve is obtained by drying the soil either continuously or by stages (i.e. each drying stage is followed by an equalization period). Initial results from tests on compacted soil suggest that the relatively fast evaporation rate during continuous drying affects the water retention curve whereas the stage drying procedure provides more accurate results. Factors such as sample geometry and tensiometer position (relative to the sample) are also likely to affect the response obtained during continuous drying. These are the object of future investigation. [ABSTRACT FROM AUTHOR]