Change In Void Ratio Research Articles

Alternative Method for Analysing Hydromechanical Behaviour of Unsaturated Soils

The suction-control techniques commonly used for laboratory studies of mechanical behaviour of unsaturated soils are much more time consuming than standard soil mechanics tests. In addition, few laboratories have the required apparatus for testing unsaturated soils. This paper proposes an alternative method of analysing hydromechanical behaviour of unsaturated soils with high-porosity. The method is divided in three tasks: 1) verification of the effect of void ratio changes on the water retention curve using filter paper; 2) determining water content changes by evaporation under the same test conditions; and 3) performing saturated and unsaturated consolidation tests. Unsaturated tests make use of samples that are less than 100% saturated and there is no suction control during the test. Therefore, only initial water content is known. Significant suction changes take place due to void closure and evaporation while testing. The results obtained using the proposed methodology showed the stress and suction path and enhance the understanding of the hydromechanical behaviour of unsaturated soils. The results also showed that analyses of water content alone cannot explain some unexpected results, such as: 20% initial water content samples present less deformation than 16% samples.

Water Permeability Function for Soils that Undergo Volume Change as Suction Changes

The saturated/unsaturated coefficient of permeability is required when modeling engineering problems involving transient seepage and contaminant transport. Inaccuracies in the estimation of the coefficient of permeability function can cause errors in numerical modeling results and as a result, affect subsequent engineering decisions. Void ratio changes and degree of saturation changes influence the coefficient of permeability function of a soil. Existing methodologies for estimating the unsaturated permeability function give consideration to degree of saturation changes and may produce reasonable results for soils such as sands and silts which exhibit little volume change with suction change. However, inaccurate results are generated when the soils involved change volume as soil suction changes (e.g., initially slurry Regina clay). Revisions to previously proposed methodologies are needed for the estimation of a saturated/unsaturated coefficient of permeability function that accommodates both void ratio change and degree of saturation change when simulating the drying process. A modification of the Fredlund–Xing–Huang (Can Geotech J 31(4):533–546, 1994) estimation procedure for the permeability function is presented in this paper. Consideration is given to both volume change and desaturation of the soil as soil suction is increased. A laboratory data set for Regina clay is presented and interpreted using the revised methodology. The results illustrate a procedure that can be used to estimate the saturated/unsaturated coefficient of permeability function for a soil that undergoes volume change and desaturation as soil suction increases.

A new and simple water retention model for root-permeated soils

Vegetation can affect soil hydrology not only through evapotranspiration but also through changes in soil water retention curve (SWRC). Models that are able to predict root-induced change in SWRC are limited. Such models often contain many empirical parameters that are not easy to be obtained and calibrated. This letter proposes a new and simple model with only one root parameter, namely root volume ratio Rv, needed for predicting the SWRC of a root-permeated soil. The new model considers void ratio change through volume reduction of air void of soil due to the presence of roots. The modified void ratio of a root-permeated soil is then fed into a void-ratio-dependent SWRC model to predict any resultant change in SWRC. The performance of this new model is validated against three case studies. Good agreement between measurements and predictions is obtained, with discrepancies of degree of saturation <13% for a given suction.

Hydromechanical behaviour of an unsaturated Algiers clay

This article presents the results of the volumetric behaviour of an Algiers clayey soil. An experimental work was carried out both in situ (core drilling; pressuremeter testing) and in the laboratory (drying–wetting and oedometric tests). Drying–wetting paths of soil samples were obtained using vapour equilibrium method and osmotic technique. These suction-controlled methods have gained widespread acceptance as reliable methods for imposing suction on soil specimens. They allowed for tests to be performed in the range of suction comprised between 0 and 300 MPa. The ability to impose suction on soil specimens allows for drying and wetting stress paths to be imposed to evaluate resulting changes in void ratio, degree of saturation and water content. These paths were explored at different initial states of clay. Slurries of soil were used to characterise the reference behaviour, whereas undisturbed soil samples allow characterising the material under in situ conditions.

Consolidation settlement properties of seashore landfills for municipal solid wastes in Korea

ABSTRACTThe large amount of wastes is generated in metropolitan area where population is heavily concentrated. As a result, treatment of wastes became a social problem and geotechnical problems related to landfill have emerged in Korea. Settlement behavior of waste landfill is similar to behavior of peat that possesses relatively small time-dependent secondary compression alongside large initial compression. A number of researchers published their own settlement computations. However, accurate computation method for waste-reclaimed landfill has yet to be determined as the settlement mechanism is very complicated. Hence, it is important to examine the accurate settlement behavior of reclaimed ground by comparing the material properties from laboratory test and field monitoring and comparing the results with the theoretical equation. This study determines the consolidation coefficients according to the change of organic contents through the total volume reduction in fresh waste layer and initial void ratio change and examines the feature of settlement in each load stage. Moreover, the article attempts to investigate the characteristics of consolidation of the relevant reclaimed landfill and to determine the suitability of the equation by comparing the variables in theoretical equations obtained from the laboratory test and field monitoring. Moreover, to verify the compression characteristics of the waste-reclaimed landfill upon loading, consolidation test results were analyzed to conduct index study on the consolidation characteristics of the waste-reclaimed landfill.

Shear strength and compressibility behaviour of lime-treated organic clay

Apart from strength characteristics, a review of studies on the compressibility of lime-treated soils is equally important that influenced the stability of soil structures. Due to the fact that no study has been carried out, an investigation on the effects of humic acid on strength and compressibility behaviour of lime-stabilised organic clay is presented in this paper. Unconfined Compressive Strength (UCS) and oedometer tests were carried out at different curing periods of 7, 28 and 90 days. Consolidation data was analysed in terms of changes in void ratio (e), volumetric strain (ε1), compression index (Cc), and coefficient of consolidation (cv) which defines a soil's compressibility. The results showed a similar behaviour when compared to both tests. It can be conclude that the cementation bonding was associated with the fabric arrangement of soil structures.

Investigation on relations between grain crushing amount and void ratio change of granular materials in one-dimensional compression and creep tests

Grain crushing plays an important role in one-dimensional (1D) compression and creep behaviors of granular materials under high stress. It is clear that the macro-properties of granular materials are closely related to the micro-fracture properties of grains in 1D compression and creep tests. In this paper, a series of 1D compression and creep tests were performed on Ottawa sand to investigate the deformation and grain crushing properties of granular materials, and it shows that the void ratio is correlated to the grain crushing amount (the quantity of crushed grains) for granular materials subjected to grain crushing. The test results, combining with the existing test data related to grain crushing of granular materials, were used to verify the relation. Moreover, the implications of these relations on the yield of granular material, and the equivalent effect of stress and time in changing soil fabric are presented.

Dynamics of potential fill–backfill material at very small strains

The paper presents a synthesis of past and recently acquired laboratory test results on granular soils using wave propagation techniques at very small strain amplitudes. Resonant column tests on uniform to well-graded coarse sands and gravels of angular and low sphericity grains were analyzed. Empirical-type equations were developed for the prediction of the elastic modulus and material damping at small strains considering the effects of the grading characteristics, the isotropic effective stress and the void ratio. The G0–p' relationship, expressed through exponent nG, was affected by the sample preparation method. For the narrow range in relatively low pressures adopted in the study, it was observed that nG decreased slightly with an increase in relative density. Due to the limited initial void ratios of those tests, the effect of the preparation method was not incorporated into the proposed formulae for the nG prediction. In this direction, additional experiments from the literature, which adopted the resonant column and bender element methods, were further analyzed, including soils of variable types tested with a wider range in relative densities. By employing typical formulae from the theory of elasticity, the bulk modulus and the changes in void ratio were estimated based on the change in isotropic effective stress in the literature data. Considering the recent micromechanical experimental findings associated with the nature of the contact response of soil particles, the importance of soil type and particle-contact behavior in the constant-state response of soils was demonstrated and quantified. Material damping values ranged from about 1.10% to about 0.45% for p' from 25 to 200kPa with a slight decrease in Ds0 with an increase in pressure.

Mechanism of improvement in the strength and volume change behavior of lime stabilized soil

An attempt has been made to bring out the influence on strength and volume change behavior of fabric changes and new cementitious compound formation in a soil upon addition of various lime contents and with curing periods. The effects of changes in fabric of treatment with various lime contents (0, 2, 4 and 6%) and with curing periods (0, 7, 14 and 28days) have been evaluated by one-dimensional consolidation tests, in terms of void ratio changes and compressibility. The strength of soil treated with different lime contents with curing periods up to 28days, and with the optimum lime content of 6% up to one year has been determined by unconfined compression tests. Comparison of effects of lime on the strength and volume change behavior of the soil brings out that the formation of flocculated fabric and cation exchange significantly reduces the compressibility of soil but marginally increases the strength. Cementation of soil particles and filling with cementitious compounds of the voids of flocculated fabric in the soil marginally reduces the compressibility but significantly increases the strength. Thus, the mechanism of volume change behavior of soil treated with lower lime content at short curing periods is distinctly different from that of the soil treated with optimum lime content at longer curing periods. This is consistent with the increase in the permeability caused by the addition from 2 to 4% lime and the decrease following the addition of 6% lime. Changes consistent with mechanical behavior have been determined by scanning electron microscope, X-ray diffraction and thermal analyses, energy dispersive X-ray spectrometer and pH value in microstructure, mineralogy, chemical composition and alkalinity, respectively.

Investigation of Geotextile Yarn Effects on Improvement of Long-Term Deformation of Sandy Soil

Accurate predictions of the amount and the rate of long- term deformation of reinforced soils under an applied load are important key issue in geotechnical engineering, in which the deformation of soil develops with time at a state of constant effective stress. Since geosynthetic is generally considered creep sensitive therefore, evaluation of creep behavior of geosynthetic reinforced soil (GRS) is necessary. In this study, to investigate the effect of reinforcing on the creep behavior of sandy clay soil, experimental tests on soil creep of reinforced sandy clay soil with geotextile yarn in one dimensional consolidation test are conducted anddata analysis is explained based on relationship of the change in void ratio (∆e) and coefficient of secondary compression (Cα). Test results indicate that in reinforced water saturated samples with geotextile yarn, with increasing the percent of geotextile yarn creep, deformation decreases and time required for beginning the creep deformation increases.

Benchmark Problems for Large Strain Consolidation

AbstractModeling of the one-dimensional consolidation process for soil and other compressible porous media is important for a variety of engineering applications. This paper presents solutions for two benchmark problems for large strain consolidation of a saturated soil layer that can be used to check other analytical and numerical analysis methods. The solutions include effects of vertical strain, soil self-weight, nonlinear constitutive relationships, and changing material properties during the consolidation process. High-accuracy data are presented for each problem and include changes of settlement, void ratio, and excess pore pressure with time.

Spatial variability of some soil shrinkage indices in hilly calcareous region of western Iran

This study was conducted as a first one to explore the spatial variability of some soil shrinkage indices and their spatial correlations with soil chemical and physical properties in calcareous soils in western Iran. Ninety nine undisturbed clods were collected from 0 to 10cm soil depth in hilly calcareous regions of Cherlgerd watershed in western Iran. Soil shrinkage curve was measured, according to Archimedes’ principle, by covering the undisturbed clods with an acrylic resin which was slowly permeable to water vapor and impermeable to liquid water. Then, void ratio (e) vs. moisture ratio (ϑ) pairs were plotted and the shrinkage curve data were modeled using sigmoidal Peng and Horn (2005) model. Derivatives of Peng and Horn (2005) model were solved to discriminate different shrinkage zones and to derive shrinkage indices related to the different zones. Geostatistical technique was employed to evaluate spatial variability of soil shrinkage indices including relative void ratio changes, mean slopes at various shrinkage zones, COLE index, and total and relative shrinkage capacities. Spherical and exponential models were successfully fitted to experimental semi-variograms. The studied shrinkage indices showed moderate to strong spatial dependency in the studied area. Results of co-regionalization analysis showed that relative void ratio change in the proportional zone had inverse spatial pattern with relative void ratio change in the residual and zero shrinkage zones. Also, spatial pattern of shrinkage indices had superior agreement with spatial variability of some soil properties (i.e., particle size distribution and calcium carbonate equivalent) which predominantly affected soil shrinkage behavior in the study area. Comparing regression kriging (RK) using environmental variables with ordinary kriging (OK) showed that RK could improve the spatial prediction of relative shrinkages in the structural, proportional and zero shrinkage zones, and total and relative shrinkage capacities.

Discussion of “Viscous behaviour of clays in one-dimensional compression”

Wong and Varatharajan hypothesize that the time-dependent or creep deformation under one-dimensional constant effective stress involves creep deformations of individual particles and creep shear deformation at interaggregate contacts. They have conducted different experiments on reconstituted kaolinite clay samples to investigate certain creep mechanisms. In the rheological model they tend to advocate, an implicit assumption made is that the creep strain starts at end of primary (EOP) consolidation and the void ratio at EOP, eEOP, is unique. Consequently, the authors interpreted their test data with this assumption and ended up asserting that “... the creep compression behaviour of claymay be uniquely related to its eEOP ...”. This is in contradiction to the opening statement of their Introduction where they state that creep deformation occurs in the entire compression process involving primary consolidation and secondary compression. The authors’ attempt to investigate the effect of drainage path on resulting void ratio, by conducting tests with top and radial drainages, is too limited to appreciate and be conclusive about this important effect. However, Degago et al. (2009) interpreted experimental data by Feng (1991) and showed that EOP tests on 127 and 508 mm thick samples, under similar loading and drainage boundary conditions, yielded a nonunique eEOP. Differences in eEOP can further be demonstrated by differences in vertical deformation of a soil element located closest to and farthest from a drainage boundary. Tests by Feng (1991) configured in such a way revealed that soil elements closer to the drainage boundary have lower eEOP values when compared with elements farthest from the drainage boundary (Degago et al. 2011) The authors tried to demonstrate unique EOP values by comparing multiand singlestage tests. The discussers do not see how the authors “proof” for unique eEOP values holds true. In Figs. 4 and 7, the authors plot log (that can be reformulated into inverse of strain rate over stress) versus strain after EOP. The inclination of this line is the reciprocal value of C (for a remolded sample in practice a constant value is expected) and the shift in vertical direction as plotted by the authors is close to log( ), which comes from multiplying the inverse of strain rate with stress. If the authors had instead presented a plot of the inverse of the rate of void ratio change versus void ratio for the different stress levels, the plot would have shown a unique relation between void ratio, rate of change in void ratio, and effective stress level as stated in the isotache concept (Suklje 1957). This demonstrates that the isotache concept also holds for the tests conducted and presented by the authors. This, thus, implies that that eEOP cannot be unique, but depends on the experienced strain rate, i.e., time it takes to reach “EOP”, and the position of the material with respect to the drainage boundary. In conclusion, the discussers believe the primary aim of such laboratory tests is to enable proper characterization of the field behavior of soils and in this aspect the extension from laboratory to field condition is observed to follow isotache formulation (Leroueil 2006) — this implies that creep occurs during the entire soil compression process and eEOP cannot be unique and therefore cannot be considered as a soil parameter.

준설토의 간극비 변화 관찰을 위한 물리탐사기법의 적용

해성점토를 활용한 준설매립공사에서는 준설토의 거동분석이 선행되어야 한다. 본 연구에서는 침강압밀하는 준설토의 밀도와 간극비 변화를 관찰하기 위해 물리탐사기법을 적용하였다. 서해안에서 채취한 흙에 대한 기본물성시험을 실시하였고, 침강압밀시험기에 시료를 단계적으로 투기하여 시간에 따른 계면고와 탄성파의 변화를 관찰하였다. 흙의 침강압밀이 완료된 후 하방향의 투수시험을 실시하여 조간대의 영향이 준설토의 물리적 특성에 미치는 영향을 관찰하였다. 또한 초소형 전기저항탐침을 관입하여 깊이에 따른 시료의 전기비저항을 측정하였다. 모든 실험이 완료된 후, 시료를 채취하여 간극비를 계산하였다. 실험결과, ML 시료의 특성상 급격한 침강을 보여 침강압밀특성을 육안으로 관찰하기 어려웠으나, 단계투기가 계속될수록 탄성파의 속도는 증가하는 경향을 보였다. 하방향 투수에 따른 조간대 영향은 매우 적어 관찰할 수 없었다. 한편 탄성파 속도로 추정한 시료의 간극비는 단계투기에 따라 선형적으로 증가하는 경향을 나타내었다. 전기비저항으로부터 계산된 간극비는 깊이에 따라 반복적으로 증가, 감소하는 형태를 나타내었으며 이는 단계투기에 따라 층을 이루고 있는 시료의 영향으로 파악된다. 시료채취, 탄성파 속도, 그리고 전기비저항으로부터 구한 간극비를 비교한 결과, 서로 유사한 관계를 나타내었다. 본 연구는 물리탐사기법이 준설토의 간극비 관찰에 효과적으로 활용될 수 있음을 보여준다. It is necessary to understand the behavior of the soils for the dredging constructions. The objective of this study is to estimate void ratio and density changes of the dredged soils by using the geophysical testing methods. A series of laboratory tests is performed to obtain geotechnical index properties of the specimen, retrieved from the west coastal of Korea. The sedimentation and self-weight consolidation tests are carried out with observing changes of the interfacial height and the elastic wave velocities. The same amounts of the soils are poured into the testing column at intervals of 12 hours until the interheight reaches to a certain level. After the completion of the sedimentatation and self-weight consolidation tests, downward permeability test is performed to assess a tidal influence in the nearshore. The mini resistance cone is penetrated into the specimen to measure the electrical resistivity with depth. All tests are completely finished, the weight of specimens are measured to calculate the void ratio with the depth. Experimental results show that the aspects of the self-weight consolidation are invisible during dredging process because of rapid sedimentation characteristics of ML. However, the elastic wave velocities increase with increasing in the effective stresses. During permeability test, measured permeability and the elastic wave velocities maintain almost identical values. Void ratio based on the elastic wave velocities changes linearly with time during the step dumpings. Void ratio estimated by the electrical resistivity represents the repeatedly layered depositions according to the step-by-step dumpings. Void ratio determined by soil sampling is similar to those of elastic waves and electrical resistivity profiles. This experimental study demonstrates that the geophysical testing methods may be an effective method for evaluating the behavior of dredged soils.

Modeling the dependency of Suction Stress Characteristic Curve on void ratio in unsaturated soils

Geotechnical problems associated with unsaturated soils are common in semi-arid climates, where the upper soil layers are naturally unsaturated. Once a soil becomes unsaturated, its mechanical properties become different from its saturated counterpart. The main part of effective stress in unsaturated soils resulting from the soil moisture can be defined by the Suction Stress Characteristic Curve (SSCC). Although, the suction stress characteristic curve is determined from shear strength tests, but recent works show that the SSCC can be connected to the Soil Water Characteristic Curve (SWCC). This paper presents a simple and novel approach to model the effect of void ratio changes on SSCC in unsaturated soils. The proposed approach can be easily utilized with existing Soil Water Characteristic Curve (SWCC) equations to model any changes in suction stress for unsaturated soils. The main advantage of the suggested method is in fact its dependency to just one parameter, simply calibrated by the conventional water retention tests. This characteristic is so applicable in hydro mechanical constitutive models of unsaturated soils. Finally, the efficiently predicting of the experimental results implicitly demonstrates the applicability of effective stress principle using the concept of Suction Stress Characteristic Curve (SSCC) for unsaturated soils.

Characterization of gas flow through low-permeability claystone: laboratory experiments and two-phase flow analyses

Abstract For the characterization of gas migration through a low-permeability clay host rock for deep underground repositories, a comprehensive understanding of the relevant phenomena of gas and fluid flow through low-permeability clay is required. The National Cooperative for the Disposal of Radioactive Waste (Nagra) in Switzerland has developed a comprehensive programme to characterize gas flow in low-permeability Opalinus Clay through laboratory tests and detailed numerical analyses for developing appropriate constitutive models. Laboratory tests were performed on cores by two different laboratories, the Laboratory for Soil Mechanics at EPFL and the Department of Geotechnical Engineering and Geosciences at UPC. Loading tests were performed by both laboratories to study rock compressibility at different stress levels and water permeability dependence on void ratio. The water retention behaviour demonstrated by EPFL and UPC produced comparable results. Water permeability tests and fast controlled-volume air injection experiments were performed in a triaxial cell under isotropic stress conditions on two samples with flow parallel and normal to the bedding planes. A confining stress of 15 MPa was applied during gas testing, corresponding to a lithostatic pressure at a depth of c. 600 m below ground. For detailed analyses, the two-phase flow code TOUGH2 ( Pruess et al. 1999 ) was used. This considers fluid flow in both liquid and gas phases under the influence of pressure, viscous and gravity forces, according to Darcy's law. The standard analyses could not reproduce the measured pressure responses well, and the calibrated hydraulic and two-phase parameters were not consistent with the preceding water test and laboratory analyses. Implementing the non-linear behaviour in terms of the observed relationship between changes in void ratio and associated changes in permeability under different stress conditions significantly improved the simulated results, resulting in a conceptual model that well reproduced the observed injection pressure and outflow responses for both tests, parallel and normal to bedding, using a consistent parameter set.

Research of Consolidation Experiment of Bentonite in GMZ

Bentonite is usually used as the material to buffer and backfill in the deep geological disposal of radioactive waste area.Compression properties of bentonite are important parameters in the evaluation of bentonite.Through the consolidation experiment indoor, the change of void ratio in different pressure and the compression of bentonite of GMZ are concluded. The gotten compression feature have a great significance to the judgment of compression index of the bentonite in GMZ.

Soil-water characteristics of Gaomiaozi bentonite by vapour equilibrium technique

Soil-water characteristics of Gaomiaozi (GMZ) Ca-bentonite at high suctions (3–287MPa) are measured by vapour equilibrium technique. The soil-water retention curve (SWRC) of samples with the same initial compaction states is obtained in drying and wetting process. At high suctions, the hysteresis behaviour is not obvious in relationship between water content and suction, while the opposite holds between degree of saturation and suction. The suction variation can change its water retention behaviour and void ratio. Moreover, changes of void ratio can bring about changes in degree of saturation. Therefore, the total change in degree of saturation includes changes caused by suction and that by void ratio. In the space of degree of saturation and suction, the SWRC at constant void ratio shifts to the direction of higher suctions with decreasing void ratio. However, the relationship between water content and suction is less affected by changes of void ratio. The degree of saturation decreases approximately linearly with increasing void ratio at a constant suction. Moreover, the slope of the line decreases with increasing suction and they show an approximately linear relationship in semi-logarithmical scale. From this linear relationship, the variation of degree of saturation caused by the change in void ratio can be obtained. Correspondingly, SWRC at a constant void ratio can be determined from SWRC at different void ratios.

Predissolution and Postdissolution Penetration Resistance

AbstractMineral dissolution is a common chemomechanical digenetic process in geological systems. The penetration resistance in sediments that have experienced dissolution is studied using a laboratory-scale cone penetration test device and a calibration chamber. Variables include the initial sediment density and mass fraction of soluble grains. Results show that the void ratio increases with the extent of mineral dissolution; the magnitude of the void ratio change is higher in initially dense sediments. A terminal void ratio is found for dissolution; the void ratio after dissolution will not exceed this terminal void ratio regardless of the extent of dissolution. For boundary conditions applied in this study, the terminal void ratio for dissolution corresponds to a relative density of Dr≈15% , which is attained when dissolution exceeds a mass fraction loss of 10%. While the tip resistance decreases after dissolution, the drop in tip resistance is most pronounced in initially dense sands. A single penetrat...

Investigation of the hydro-mechanical behaviour of compacted bentonite/sand mixture based on the BExM model

This study focuses on the hydro-mechanical behaviour of a MX80 bentonite/sand mixture. Barcelona Expansive Model (BExM) was used to describe this behaviour. For this purpose, experimental data obtained in the laboratory were analysed, allowing determination of the parameters used in the model. These parameters were then used to simulate the hydro-mechanical (H-M) responses of the material from other tests with different stress paths. It was observed that the model reproduced well the main feature of swelling pressure development and micro-structural volume change during suction decrease. On the other hand, the simulations also showed some limitations of the model which is based on the consideration of two levels of soil structure or double structure: the pore size distribution curve determined by the technique of mercury intrusion porosimetry (MIP) in the range of low suctions (4.2 and 1MPa) being revealed to be tri-modal, the BExM model cannot capture this aspect to correctly describe the macro-structural and micro-structural void ratio changes. Moreover, because the BExM model lumps clay intra-particle spaces and inter-particles voids together as micro-pores, it leads to overestimation of the micro-structural water content compared to the experimental value.