scholarly journals Unification of plastic compression in a coupled mechanical and water retention model for unsaturated soils

2014 ◽  
Vol 51 (12) ◽  
pp. 1488-1493 ◽  
Author(s):  
Martí Lloret-Cabot ◽  
Simon J. Wheeler ◽  
Marcelo Sánchez
Keyword(s):  
Unsaturated Soils ◽  
Water Retention ◽  
Yield Curve ◽  
Stress Path ◽  
Degree Of Saturation ◽  
Retention Model ◽  
Plastic Compression ◽  
Single Process ◽  
Elastoplastic Constitutive Model ◽  
Water Retention Behaviour

In 2003, Wheeler, Sharma, and Buisson presented an elastoplastic constitutive model for unsaturated soils that represents both the mechanical behaviour and water retention behaviour, including the coupling between them. A crucial feature of the model is that the occurrence of plastic compression during all types of stress path is unified as a single process, with plastic compression during loading, plastic compression during wetting (collapse compression), and plastic compression during drying (irreversible shrinkage) all represented by yielding on a single loading–collapse yield curve. This paper explains how the model is able to predict the possible occurrence of plastic compression during each type of stress path and, in each case, links this to a physical explanation of the process involved. A simulation of an experimental test demonstrates the capability of the model to accurately predict the variation of both the void ratio and degree of saturation during successive stages of drying, loading, and wetting, where large magnitudes of compression occurred in all three test stages.

scholarly journals Relative performance of two unsaturated soil models using different constitutive variables

2014 ◽  
Vol 51 (12) ◽  
pp. 1423-1437 ◽  
Author(s):  
Martí Lloret-Cabot ◽  
Simon J. Wheeler ◽  
Jubert A. Pineda ◽  
Daichao Sheng ◽  
Antonio Gens
Keyword(s):  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Water Retention ◽  
Experimental Tests ◽  
Experimental Results ◽  
Degree Of Saturation ◽  
State Variables ◽  
Retention Behaviour ◽  
Model Predictions ◽  
Water Retention Behaviour

Mechanical and water retention behaviour of unsaturated soils is investigated in the context of two well established coupled constitutive models, each of which is formulated in terms of a different set of stress state variables or constitutive variables. Incremental relationships describing the volume change and variation of the degree of saturation are derived for each model. These incremental relationships are used to simulate a set of experimental tests on compacted Speswhite kaolin previously reported in the literature. Six individual tests, involving isotropic compression and various forms of shearing, are analyzed in the context of the incremental forms developed, and the model predictions are then compared against experimental results. The results show that, although each constitutive model uses a different set of constitutive variables and a different scheme for coupling mechanical and water retention behaviour, the two sets of model predictions are similar and both sets provide a reasonable match to the experimental results, suggesting that both models are able to capture the relevant features of unsaturated soil behaviour, despite expressing the constitutive laws in different ways.

Coupling cyclic and water retention response of a clayey sand subjected to traffic and environmental cycles

Géotechnique ◽  
2021 ◽  
pp. 1-45
Author(s):  
Arash Azizi ◽  
Ashutosh Kumar ◽  
David G. Toll
Keyword(s):  
Unsaturated Soils ◽  
Water Retention ◽  
Resilient Modulus ◽  
Degree Of Saturation ◽  
Triaxial Tests ◽  
Soil Water Retention ◽  
Clayey Sand ◽  
Retention Model ◽  
Cyclic Response ◽  
The Impact

Compacted soils used as formation layers of railways and roads continuously undergo water content and suction changes due to seasonal variations. Such variations together with the impact of cyclic traffic-induced loads can alter the hydro-mechanical behaviour of the soil, which in turn affects the performance of the superstructure. This study investigates the impact of hydraulic cycles on the coupled water retention and cyclic response of a compacted soil. Suction-monitored cyclic triaxial tests were performed on a compacted clayey sand. The cyclic response of the soil obtained after applying drying and wetting paths was different to that obtained immediately after compaction. The results showed that both suction and degree of saturation are required to interpret the cyclic behaviour. A new approach was developed using (i) a hysteretic water retention model to predict suction variations during cyclic loading and (ii) Bishop's stress together with a bonding parameter to predict accumulated permanent strain and resilient modulus. The proposed formulations were able to predict the water retention behaviour, accumulated permanent strains and resilient modulus well, indicating the potential capability of using the fundamentals of unsaturated soils for predicting the effects of drying and wetting cycles on the coupled soil water retention and cyclic response.

Evaluation of capillary water retention effects on the development of the suction stress characteristic curve

2020 ◽  
Vol 57 (10) ◽  
pp. 1439-1452 ◽  
Author(s):  
Emad Maleksaeedi ◽  
Mathieu Nuth
Keyword(s):  
Shear Strength ◽  
Soil Water ◽  
Unsaturated Soils ◽  
Water Retention ◽  
Characteristic Curve ◽  
Degree Of Saturation ◽  
Soil Water Retention ◽  
Retention Model ◽  
Suction Stress ◽  
Effective Degree

The suction stress characteristic framework is a practical approach for relating the suction and the water-filled pore volume to the stress state of unsaturated soils. It predicts the effective stress by developing the suction stress characteristic curve from the soil-water retention curve. In this framework, the effective degree of saturation is usually calculated by the empirical water retention model of van Genuchten (published in 1980). In this paper, the use of a generalized soil-water retention model proposed by Lu in 2016, which differentiates the role of capillary and adsorption mechanisms, in the suction stress characteristic framework is studied. A redefinition of the effective degree of saturation is suggested, by choosing the retention state where capillarity approaches zero instead of the residual retention state. The validity of this assumption is examined using experimental data obtained by unsaturated shear strength and retention tests and datasets collected from the literature. The proposed definition is applicable for a variety of soils where capillarity is the dominant mechanism in producing suction stress within the range of suction 0–1500 kPa. In addition, it is observed that the generalized soil-water retention model presents a more realistic prediction of unsaturated shear strength compared with empirical water retention models.

scholarly journals A coupled hydro – mechanical approach for modelling the volume change behaviour of compacted bentonite

2020 ◽  
Vol 195 ◽  
pp. 04006
Author(s):  
Jose A. Bosch ◽  
Alessio Ferrari ◽  
Lyesse Laloui
Keyword(s):  
Effective Stress ◽  
Volume Change ◽  
Water Retention ◽  
Expansive Soils ◽  
Numerical Models ◽  
Degree Of Saturation ◽  
Retention Model ◽  
Retention Behaviour ◽  
Mechanical Approach ◽  
Water Retention Behaviour

The volumetric response of compacted bentonites against environmental actions is a key aspect in most designs of nuclear waste repositories. The safety assessment of such repositories must account for robust and reliable models of stress–strain for bentonites. While many models for unsaturated low activity clays take advantage from the use of a generalized effective stress, its application to expansive soils has not found the same degree of success. One of the possible reasons is the complex water retention behaviour of these materials, which only recently has been successfully reproduced by numerical models. Here, by adopting an appropriate water retention model, a coupled hydro-mechanical approach to simulate the volume change behaviour of compacted bentonites is suggested. An explicit distinction between interlayer adsorbed water and capillary water is used to simulate the water retention behaviour. It is then shown that by using a precise water retention formulation, the volumetric behaviour can be interpreted within an effective stress–degree of saturation based framework. Some interesting results derived from the use of the effective stress include the shrinkage limit, the increase in stiffness of the elastic regime and the use of a single elastic coefficient for both wetting–swelling and reloading stress paths.

scholarly journals A general mathematical framework for modelling soil-water retention behaviour

2021 ◽  
Vol 337 ◽  
pp. 02006
Author(s):  
Carlos Pereira ◽  
João Ribas Maranha ◽  
Rafaela Cardoso
Keyword(s):  
Soil Water ◽  
Specific Volume ◽  
Unsaturated Soils ◽  
Water Retention ◽  
Degree Of Saturation ◽  
Mathematical Framework ◽  
Soil Water Retention ◽  
Retention Behaviour ◽  
Entrapped Air ◽  
Water Retention Behaviour

A new constitutive model for the soil-water retention behaviour of unsaturated soils is proposed, able to reproduce the main drying and wetting paths, the cyclic retention behaviour and its dependence on the specific volume. The most significant aspect is the inclusion of the evolution, with the specific volume, of the degree of saturation when suction tends to zero in wetting paths considering the presence of entrapped air bubbles. The model is used to reproduce with success the drying/wetting cycles of two Pearl clay samples.

Capillary-based effective stress formulation for predicting shear strength of unsaturated soils

2015 ◽  
Vol 52 (12) ◽  
pp. 2067-2076 ◽  
Author(s):  
Jean-Marie Konrad ◽  
Marc Lebeau
Keyword(s):  
Shear Strength ◽  
Effective Stress ◽  
Unsaturated Soils ◽  
Water Retention ◽  
Adsorbed Water ◽  
Soil Strength ◽  
Liquid Films ◽  
Degree Of Saturation ◽  
Stress Parameter ◽  
Effective Stress Parameter

A number of investigations have shown that the shear strength of unsaturated soils can be defined in terms of effective stress. The difficulty in this approach lies in quantifying the effective stress parameter, or Bishop’s parameter. Although often set equal to the degree of saturation, it has recently been suggested that the effective stress parameter should be related to an effective degree of saturation, which defines the fraction of water that contributes to soil strength. A problematic element in this approach resides in differentiating the water that contributes to soil strength from that which does not contribute to soil strength. To address this difficulty, the paper uses theoretical considerations and experimental observations to partition the water retention function into capillary and adsorptive components. Given that the thin liquid films of adsorbed water should not contribute to effective stress, the effective stress parameter is solely related to the capillary component of water retention. In sample calculations, this alternative effective stress parameter provided very good agreement with experimental data of shear strength for a variety of soil types.

Oedometric and water-retention behaviour of highly compacted unsaturated smectites

1999 ◽  
Vol 36 (4) ◽  
pp. 675-684 ◽  
Author(s):  
M Al-Mukhtar ◽  
Y Qi ◽  
J -F Alcover ◽  
F Bergaya
Keyword(s):  
Relative Humidity ◽  
Water Retention ◽  
Axial Stress ◽  
Degree Of Saturation ◽  
Experimental Program ◽  
Initial Void Ratio ◽  
Smectite Clays ◽  
Hydromechanical Behavior ◽  
Constant Axial Load ◽  
Water Retention Behaviour

This paper summarizes the findings from an experimental program concerning the hydromechanical behavior of two smectite clays tested under high stresses. Increasing axial stress on the smectite samples under controlled relative humidity (suction) leads to collapse in the soil structure and increases the degree of saturation. Irreversible volume change is observed in samples tested under cyclic suction with constant axial load. Water-retention (adsorption and desorption) behavior of the smectite clays tested in this study is affected by particle size, initial void ratio, and confinement conditions during the tests. Laponite, which has a large specific surface area, tends to hold more water than hectorite at a given relative humidity. More water is adsorbed by samples compacted at lower axial stress.Key words: smectite clays, hydromechanical stresses, behavior, relative humidity and suction, water retention, degree of saturation.

scholarly journals Investigation into water retention behaviour of deformable soils

2013 ◽  
Vol 50 (2) ◽  
pp. 200-208 ◽  
Author(s):  
Simon Salager ◽  
Mathieu Nuth ◽  
Alessio Ferrari ◽  
Lyesse Laloui
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Water Retention ◽  
Void Ratio ◽  
Degree Of Saturation ◽  
Retention Data ◽  
Soil Water Retention ◽  
Retention Behaviour ◽  
Wide Range ◽  
Water Retention Behaviour

The paper presents an experimental and modelling approach for the soil-water retention behaviour of two deformable soils. The objective is to investigate the physical mechanisms that govern the soil-water retention properties and to propose a constitutive framework for the soil-water retention curve accounting for the initial state of compaction and deformability of soils. A granular soil and a clayey soil were subjected to drying over a wide range of suctions so that the residual state of saturation could be attained. Different initial densities were tested for each material. The soil-water retention curves (SWRCs) obtained are synthesized and compared in terms of water content, void ratio, and degree of saturation, and are expressed as a function of the total suction. The studies enable assessment of the effect of the past and present soil deformation on the shape of the curves. The void ratio exerts a clear influence on the air-entry value, revealing that the breakthrough of air into the pores of the soil is more arduous in denser states. In the plane of water content versus suction, the experimental results highlight the fact that from a certain value of suction, the retention curves corresponding to different densities of the same soil are convergent. The observed features of behaviour are conceptualized into a modelling framework expressing the evolution of the degree of saturation as a function of suction. The proposed retention model makes use of the theory of elastoplasticity and can thus be generalized into a hysteretic model applicable to drying–wetting cycles. The calibration of the model requires the experimental retention data for two initial void ratios. The prediction of tests for further ranges of void ratios proves to be accurate, which supports the adequacy of formulated concepts.

scholarly journals Recent Developments and Limitations of the SFG Model

2016 ◽  
pp. 41-49
Author(s):  
Daichao Sheng
Keyword(s):  
Shear Strength ◽  
Unsaturated Soils ◽  
Water Retention ◽  
Compacted Soils ◽  
Consistent Description ◽  
Strain Behaviour ◽  
Recent Developments ◽  
Density Dependency ◽  
Significant Attention ◽  
Water Retention Behaviour

The SFG model was proposed in attempt to provide a consistent description of the stress-strain behaviour of unsaturated soils, including compacted soils and soils dried from slurry. It differs from existing models mainly through two aspects: a consistent description of volume change, yield stress and shear strength behaviour of unsaturated soils and a smooth and natural transition between saturated and unsaturated states. The model has attracted significant attention since it was first proposed and has been extended to cover coupled hydro-mechanical behaviour, hysteretic water retention behaviour and density-dependency. This paper presents a summary of the latest developments of the model, as well as the aspects that require further refinements.

scholarly journals Implementation of biocementation for a partially saturated problematic soil of the UK railway network

2020 ◽  
Vol 195 ◽  
pp. 05006
Author(s):  
Muhammad Umair Safdar ◽  
Maria Mavroulidou ◽  
Michael J. Gunn ◽  
Christopher Gray ◽  
Diane Purchase ◽  
...  
Keyword(s):  
Unsaturated Soils ◽  
Water Retention ◽  
Degree Of Saturation ◽  
Water Retention Curve ◽  
Soil Water Retention Curve ◽  
Soil Water Retention ◽  
Railway Network ◽  
Foundation Soil ◽  
The Uk ◽  
Problematic Soil

This paper refers to biocementation of a problematic soil of the UK railway network as a potential stabilisation technique of this soil using indigenous ureolytic bacteria. The soil is peat, a soft foundation soil also subject to oxidation wastage. As the peat is under existing embankments, electrokinetics (EK) is proposed as a promising technique to implement treatments. In the context of unsaturated soils the paper thus focuses on two particular aspects relevant for the implementation of treatments and the stability of this soil, namely: a) the effect of degree of saturation of the peat on the bio-electrokinetic treatment ; b) the soil water retention curve of the soil affecting flow and transport; these are relevant as we focus on understanding and modelling the implementation of treatments through electrokinetics; moreover for the peat it is of importance to understand moisture exchange in the vadose zone and control groundwater table levels (e.g. during electrokinetics) in order to prevent further oxidation. After isolation and screening of indigenous microorgansisms Bacillus licheniformis was selected for further testing. The results in terms of unconfined compressive strength, CaCO3 content, swelling and compression behaviour and water retention proved the feasibility of biocementation using this indigenous microorganism. Ongoing work is assessing the required treated soil characteristics and related required biocementation degree to solve UK rail's peat foundation problems. Upscaling of the techniques towards in situ implementation is also planned in the next stage of the research.

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