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

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.

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Relative performance of two unsaturated soil models using different constitutive variables

Canadian Geotechnical Journal ◽

10.1139/cgj-2013-0462 ◽

2014 ◽

Vol 51 (12) ◽

pp. 1423-1437 ◽

Cited By ~ 7

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.

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Investigation into water retention behaviour of deformable soils

Canadian Geotechnical Journal ◽

10.1139/cgj-2011-0409 ◽

2013 ◽

Vol 50 (2) ◽

pp. 200-208 ◽

Cited By ~ 65

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.

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

Canadian Geotechnical Journal ◽

10.1139/cgj-2013-0360 ◽

2014 ◽

Vol 51 (12) ◽

pp. 1488-1493 ◽

Cited By ~ 5

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.

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A water retention model accounting for void ratio changes in double porosity clays

Acta Geotechnica ◽

10.1007/s11440-020-01126-0 ◽

2021 ◽

Author(s):

Gema De la Morena ◽

Vicente Navarro ◽

Laura Asensio ◽

Domenico Gallipoli

Keyword(s):

Water Retention ◽

Double Porosity ◽

Degree Of Saturation ◽

Retention Model ◽

Boom Clay ◽

Retention Behaviour ◽

Pore Size Distributions ◽

New Formulation ◽

Clay Aggregates ◽

Porosity Model

AbstractThis paper presents a constitutive model that predicts the water retention behaviour of compacted clays with evolving bimodal pore size distributions. In line with previous research, the model differentiates between the water present inside the saturated pores of the clay aggregates (the microstructure) and the water present inside the pores between clay aggregates (the macrostructure). A new formulation is then introduced to account for the effect of the macrostructural porosity changes on the retention behaviour of the soil, which results in a consistent evolution of the air-entry value of suction with volumetric deformations. Data from wetting tests on three different active clays (i.e. MX-80 bentonite, FEBEX bentonite, and Boom clay), subjected to distinct mechanical restraints, were used to formulate, calibrate, and validate the proposed model. Results from free swelling tests were also modelled by using both the proposed double porosity model and a published single porosity model, which confirmed the improvement in the predictions of degree of saturation by the present approach. The proposed retention model might be applied, for example, to the simulation of the hydromechanical behaviour of engineered bentonite barriers in underground nuclear waste repositories, where compacted active clays are subjected to changes of both suction and porosity structure under restrained volume conditions.

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Competing effects of volume change and water uptake on the water retention behaviour of a compacted MX-80 bentonite/sand mixture

Applied Clay Science ◽

10.1016/j.clay.2015.12.019 ◽

2016 ◽

Vol 121-122 ◽

pp. 57-62 ◽

Cited By ~ 23

Author(s):

Claude Gatabin ◽

Jean Talandier ◽

Frédéric Collin ◽

Robert Charlier ◽

Anne-Catherine Dieudonné

Keyword(s):

Water Uptake ◽

Volume Change ◽

Water Retention ◽

Sand Mixture ◽

Retention Behaviour ◽

Water Retention Behaviour

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Interpretation of unsaturated soil behaviour in the stress – Saturation space, I: Volume change and water retention behaviour

Computers and Geotechnics ◽

10.1016/j.compgeo.2012.04.010 ◽

2012 ◽

Vol 43 ◽

pp. 178-187 ◽

Cited By ~ 92

Author(s):

An-Nan Zhou ◽

Daichao Sheng ◽

Scott W. Sloan ◽

Antonio Gens

Keyword(s):

Volume Change ◽

Unsaturated Soil ◽

Water Retention ◽

Retention Behaviour ◽

Soil Behaviour ◽

Water Retention Behaviour

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A general mathematical framework for modelling soil-water retention behaviour

MATEC Web of Conferences ◽

10.1051/matecconf/202133702006 ◽

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.

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Effects of pyrolysis temperature, feedstock type and compaction on water retention of biochar amended soil

Scientific Reports ◽

10.1038/s41598-021-86701-5 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

He Huang ◽

Narala Gangadhara Reddy ◽

Xilong Huang ◽

Peinan Chen ◽

Peiying Wang ◽

...

Keyword(s):

Water Retention ◽

Pyrolysis Temperature ◽

Chemical Properties ◽

Bare Soil ◽

Chicken Manure ◽

Soil Water Retention ◽

Amended Soils ◽

Retention Behaviour ◽

Water Retention Behaviour ◽

Amended Soil

AbstractRecent studies on water retention behaviour of biochar amended soil rarely considers the effect of pyrolysis temperature and also feedstock type into account. It is well known that pyrolysis temperature and feedstock type influences the physical and chemical properties of biochar due to stagewise decomposition of structure and chemical bonds. Further, soil density, which is in a loose state (in agricultural applications) and dense (in geo-environmental engineering applications) can also influence water retention behaviour of biochar amended soils. The major objective of this study is to investigate the water retention properties of soil amended with three different biochars in both loose and dense state. The biochars, i.e. water hyacinth biochar (WHB), chicken manure biochar (CMB) and wood biochar (WB) were produced in-house at different pyrolysis temperature. After then, biochars at 5% and 10% (w/w%) were amended to the soil. Water retention behaviour (soil suction and gravimetric water content) was studied under drying and wetting cycle simulated by varying relative humidity (RH, 50–90%). Results show that 10% WHB produced at 300 °C were found to possess highest water retention. CMB is found to possess higher water retention than WB for 10% amendment ratio. In general, the addition of three biochars (at both 300 °C and 600 °C) at 10% (w/w) significantly improved the water retention at all suction ranges in both loose and dense compaction state as compared to that of the bare soil. The adsorption (wetting) and desorption (drying) capacity of biochar amended soils is constant at corresponding RH.

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

Canadian Geotechnical Journal ◽

10.1139/cgj-2014-0300 ◽

2015 ◽

Vol 52 (12) ◽

pp. 2067-2076 ◽

Cited By ~ 32

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.

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