A Generalised Plastic Model for Gravelly Soils Considering Evolution of Void Ratio and Particle Breakage

Gravelly soils exhibit complicated mechanical behaviours closely related to particle breakage and relative density state. To better capture the mechanical responses of gravelly soils, a generalised plastic model considering evolution of void ratio and particle breakage was developed within the framework of critical state soil mechanics. In the model, particle breakage effect was described by incorporating breakage index to deviate the critical state line off the ideal position. A differential equation relating increment of void ratio to variation of volumetric strain was used to depict the evolution of current void ratio. It indirectly reflected the relative density state of gravelly soils. The model was applied to conducting numerical simulations for a series of triaxial tests on four types of gravelly soils. Comparisons between the test data and the modelling results indicated that considerations of void ratio evolution and particle breakage could better simulate the stress-dependent dilatation/contraction behaviours of gravelly soils.

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An updated skeleton void ratio for gravelly sand mixtures considering the effect of grain size distribution

Canadian Geotechnical Journal ◽

10.1139/cgj-2020-0570 ◽

2021 ◽

Author(s):

Tao Wang ◽

Sihong Liu ◽

Antoine Wautier ◽

François Nicot

Keyword(s):

Grain Size ◽

Size Distribution ◽

Grain Size Distribution ◽

Critical State ◽

Void Ratio ◽

Triaxial Tests ◽

Empirical Equations ◽

Test Results ◽

Density State ◽

Semi Empirical

Recent researches on the behavior of gravelly sands advocate for the use of skeleton void ratio to characterize their density state. Skeleton void ratio corresponds to the void ratio of grains constituting the stress-bearing skeleton. However, such a void ratio relies on parameters difficult to determine in practice, such as the fraction of fine grains that take part actively in the load bearing skeleton. Also, it fails to consider the effect of Grain Size Distribution (GSD) of gravel and sand grains. Therefore, the skeleton void ratio index introduced by Chang et al (2015) is revisited to account for the effect of GSD of both gravel and sand grains. Two semi-empirical equations are developed in this paper to connect GSD parameters with skeleton void ratio parameters. The validity of the proposed equations has been checked for a particular class of gravelly sand materials. A series of specially-designed drained triaxial tests on gravelly sands were then conducted. Test results show that it is essential to consider the effect of GSD when using skeleton void ratio index. It also verifies the effectiveness and applicability of the proposed updated skeleton void ratio, which shows advantages in characterizing critical state lines of gravelly sands.

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Non-orthogonal elastoplastic constitutive model with the critical state for clay

10.31224/osf.io/vpwq3 ◽

2021 ◽

Author(s):

Jingyu Liang ◽

Dechun Lu ◽

Xin Zhou ◽

Xiuli Du ◽

Wei Wu

Keyword(s):

Plastic Flow ◽

Critical State ◽

Flow Direction ◽

Volumetric Strain ◽

Yield Function ◽

Triaxial Tests ◽

Flow Rule ◽

Model Framework ◽

Plastic Strain Increment ◽

Plastic Flow Rule

A non-orthogonal elastoplastic model for clay is proposed by combining the non-orthogonal plastic flow rule with the critical state concept, and the model framework is presented from the perspective of the magnitude and direction of the plastic strain increment. The magnitude is obtained based on the improved elliptical yield function and the plastic volumetric strain dependent hardening parameter. The direction is determined by ap-plying the non-orthogonal plastic flow rule with the Riemann-Liouville fractional derivative to the yield function without the necessity of additional plastic potential function. The presented approach gives rise to a simple model for soil with five parameters. All parameters have clear physical meaning and can be easily identified by triaxial tests. The model performance is shown by analyzing the evolution process of the yield surface, the hardening rule and the plastic flow direction. The capability of the proposed model to capture the mechanical behaviours of clay with different stiffness is also confirmed by predicting test results from the literature.

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UNDRAINED SHEAR STRENGTH OF K0 CONSOLIDATED SOFT CLAYS UNDER TRIAXIAL AND PLANE STRAIN CONDITIONS

International Journal of Applied Mechanics ◽

10.1142/s175882511450032x ◽

2014 ◽

Vol 06 (03) ◽

pp. 1450032 ◽

Cited By ~ 2

Author(s):

QIUSHENG WANG ◽

XIULI DU ◽

QIUMING GONG

Keyword(s):

Shear Strength ◽

Plane Strain ◽

Yield Surface ◽

Critical State ◽

Volumetric Strain ◽

Stress Path ◽

Undrained Shear Strength ◽

Triaxial Tests ◽

Soft Clays ◽

Undrained Shear

Theoretical formulas for predicting the undrained shear strength of K0 consolidated soft clays under the stress path related to triaxial and plane strain tests are presented within the framework of critical state soil mechanics. An inclined elliptical yield surface is adopted to take account of the initial anisotropic stress state. The undrained strength is determined by combining the undrained stress path in the volumetric stress–strain space and the initial yield surface in the deviator-mean stress space. The derived mathematical expressions are functions of the critical state frictional angle, the plastic volumetric strain ratio and the overconsolidation ratio, which can be simplified into the solutions for isotropically consolidated clays under triaxial tests or under plane strain tests. The results calculated by using the theoretical formulas obtained in this paper are in good agreement with the available collected test results. It indicates that these new formulas are applicable to triaxial and plane strain tests on normally and lightly to moderately overconsolidated soft clays.

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A Strain-Based Percolation Model and Triaxial Tests to Investigate the Evolution of Permeability and Critical Dilatancy Behavior of Coal

Processes ◽

10.3390/pr6080127 ◽

2018 ◽

Vol 6 (8) ◽

pp. 127 ◽

Cited By ~ 6

Author(s):

Dongjie Xue ◽

Jie Zhou ◽

Yintong Liu ◽

Sishuai Zhang

Keyword(s):

Axial Strain ◽

Triaxial Compression ◽

Sudden Change ◽

Volumetric Strain ◽

Confining Pressure ◽

Percolation Model ◽

Triaxial Tests ◽

Transition Behavior ◽

Orthogonal Experiments ◽

Stress Dependent

Modeling the coupled evolution of strain and CH4 seepage under conventional triaxial compression is the key to understanding enhanced permeability in coal. An abrupt transition of gas-stress coupled behavior at the dilatancy boundary is studied by the strain-based percolation model. Based on orthogonal experiments of triaxial stress with CH4 seepage, a complete stress-strain relationship and the corresponding evolution of volumetric strain and permeability are obtained. At the dilatant boundary of volumetric strain, modeling of stress-dependent permeability is ineffective when considering the effective deviatoric stress influenced by confining pressure and pore pressure. The computed tomography (CT) analysis shows that coal can be a continuous medium of pore-based structure before the dilatant boundary, but a discontinuous medium of fracture-based structure. The multiscale pore structure geometry dominates the mechanical behavior transition and the sudden change in CH4 seepage. By the volume-covering method proposed, the linear relationship between the fractal dimension and porosity indicates that the multiscale network can be a fractal percolation structure. A percolation model of connectivity by the axial strain-permeability relationship is proposed to explain the transition behavior of volumetric strain and CH4 seepage. The volumetric strain on permeability is illustrated by axial strain controlling the trend of transition behavior and radical strain controlling the shift of behavior. A good correlation between the theoretical and experimental results shows that the strain-based percolation model is effective in describing the transition behavior of CH4 seepage in coal.

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Behaviour of Uniform Drava River Sand in Drained Condition—A Critical State Approach

Applied Sciences ◽

10.3390/app10175733 ◽

2020 ◽

Vol 10 (17) ◽

pp. 5733

Author(s):

Vedran Jagodnik ◽

Ivan Kraus ◽

Sandi Ivanda ◽

Željko Arbanas

Keyword(s):

Relative Density ◽

Critical State ◽

Constitutive Models ◽

Friction Angle ◽

State Theory ◽

Shear Behaviour ◽

Triaxial Tests ◽

River Sand ◽

Drava River ◽

The Difference

Numerous triaxial tests on sand and sand-like materials have been performed worldwide during the past several decades. Their results provided a development of the advanced soil constitutive models and laboratory testing devices, as well as the establishment of a worldwide database of different types of uniform sandy materials. From such research, the critical state and steady state theory has emerged as one of the most useful tool for the modelling of a soil behaviour. This paper presents the results of static drained tests performed on the uniform Drava River sand from the Osijek region in Croatia. The main aim was to determine the shear behaviour and critical state, given that these characteristics are mostly unknown for the tested sand material. A series of detail triaxial tests were performed in drained conditions for three different initial relative densities, DR, and two different loading directions; e.g., axial compression and axial extension. In total, 18 drained tests were performed. The study indicated that the value of 33.75∘ is the critical friction angle for the tested sand. The relative density of 57% is determined as the critical relative density. Additionally, the study confirmed the difference in critical state for compression and extension loading. In addition, the results indicate that the sample preparation procedure has an important impact on the critical state of loosely prepared sandy samples. These results give the first insights into the behaviour of the Drava River sand, which can generally contribute to the worldwide sand behaviour knowledge base.

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Observed and predicted behaviour of rail ballast under monotonic loading capturing particle breakage

Canadian Geotechnical Journal ◽

10.1139/cgj-2013-0361 ◽

2015 ◽

Vol 52 (1) ◽

pp. 73-86 ◽

Cited By ~ 48

Author(s):

Buddhima Indraratna ◽

Qi Deng Sun ◽

Sanjay Nimbalkar

Keyword(s):

Critical State ◽

Large Scale ◽

Soil Mechanics ◽

Confining Pressure ◽

Particle Breakage ◽

Shear Behaviour ◽

Triaxial Tests ◽

Triaxial Apparatus ◽

Elastoplastic Constitutive Model ◽

Constitutive Parameters

A substantial amount of experimental evidence suggests that the critical state envelope for ballast is nonlinear, especially at low confining pressure. To study the implications of this nonlinearity and the associated role of particle breakage, monotonically loaded drained triaxial tests were conducted using a large-scale cylindrical triaxial apparatus. A nonlinear critical state envelope is determined in the q–p′ and υ–lnp′ planes. Mathematical expressions for critical state stress ratio and specific volume are proposed to incorporate the evolution of particle breakage during monotonic shearing. In this paper, an elastoplastic constitutive model based on the critical state soil mechanics framework is presented to capture the salient aspects of stress–strain behaviour and degradation of ballast. Constitutive parameters were conveniently determined from large-scale laboratory tests. The model is able to predict the monotonic shear behaviour of ballast corroborating with the laboratory measurements. The proposed model is further validated using experimental results available from past independent studies.

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Inclusion of specific water volume within an elasto-plastic model for unsaturated soil

Canadian Geotechnical Journal ◽

10.1139/t96-023 ◽

1996 ◽

Vol 33 (1) ◽

pp. 42-57 ◽

Cited By ~ 87

Author(s):

S J Wheeler

Keyword(s):

Water Content ◽

Unsaturated Soil ◽

Critical State ◽

Constitutive Models ◽

Degree Of Saturation ◽

Triaxial Tests ◽

Water Volume ◽

Plastic Model ◽

Elasto Plasticity ◽

Soil Behaviour

Existing elasto-plastic critical state constitutive models for unsaturated soil provide no information on the variation of water content or degree of saturation. These models cannot therefore, for example, be used to predict unsaturated soil behaviour during undrained loading, when the variation of suction is determined by the requirement that water content remains constant. This problem has been tackled by extending an existing elasto-plastic model to include relationships describing the variation of specific water volume (the volume of water and solids in an element of soil containing unit volume of solids). The proposed form of the variation of specific water volume was based on consideration of the soil fabric, resulting in a coupled form of elasto-plastic behaviour. Predictions from the elasto-plastic model showed good agreement with the experimental results from suction-controlled triaxial tests on unsaturated samples of compacted speswhite kaolin. Normal compression lines for specific water volume at different values of suction were well predicted, as was the variation of specific water volume during wetting. Critical state values of specific water volume were slightly underestimated, but test paths for both drained and undrained shearing were predicted with reasonable success. Key words: compacted clays, constitutive model, critical state, elasto-plasticity, triaxial tests, unsaturated.

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Recommended Procedures to Assess Critical State Locus from Triaxial Tests in Cohesionless Remoulded Samples

Geotechnics ◽

10.3390/geotechnics1010006 ◽

2021 ◽

Vol 1 (1) ◽

pp. 95-127

Author(s):

António Viana da Fonseca ◽

Diana Cordeiro ◽

Fausto Molina-Gómez

Keyword(s):

Critical State ◽

Review Paper ◽

State Theory ◽

Soil Freezing ◽

Triaxial Tests ◽

Cohesionless Soils ◽

Saturation Condition ◽

Testing Procedures ◽

Laboratory Procedures ◽

Soil Behaviour

The critical state theory is a robust conceptual framework for the characterisation of soil behaviour. In the laboratory, triaxial tests are used to assess the critical state locus. In the last decades, the equipment and testing procedures for soil characterisation, within the critical state framework, have advanced to obtain accurate and reliable results. This review paper summarises and describes a series of recommended laboratory procedures to assess the critical state locus in cohesionless soils. For this purpose, results obtained in the laboratory from different cohesionless soils and triaxial equipment configurations are compiled, analysed and discussed in detail. The procedures presented in this paper reinforce the use of triaxial cells with lubricated end platens and an embedded connection piston into the top-cap, together with the verification of the full saturation condition and the measurement end-of-test water content—preferable using the soil freezing technique. The experimental evidence and comparison between equipment configurations provide relevant insights about the laboratory procedures for obtaining a reliable characterisation of the critical state locus of cohesionless geomaterials. All the procedures recommended herein can be easily implemented in academic and commercial geotechnical laboratories.

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