Elastoplastic prediction of hydro-mechanical behaviour of unsaturated soils under undrained conditions

2008 ◽  
Vol 35 (6) ◽  
pp. 845-852 ◽  
Author(s):  
De’An Sun ◽  
Daichao Sheng ◽  
Li Xiang ◽  
Scott W. Sloan
Keyword(s):  
Mechanical Behaviour ◽  
Unsaturated Soils ◽  
Undrained Conditions

A framework for the behaviour of unsaturated expansive clays

1992 ◽  
Vol 29 (6) ◽  
pp. 1013-1032 ◽  
Author(s):  
A. Gens ◽  
E. E. Alonso
Keyword(s):  
Key Words ◽  
Mechanical Behaviour ◽  
Unsaturated Soils ◽  
Expansive Soils ◽  
Experimental Results ◽  
Structural Rearrangements ◽  
Expansive Clays ◽  
Clay Model ◽  
Model Predictions ◽  
Low Activity

The paper presents a framework for describing the mechanical behaviour of unsaturated expansive clays. It is an extension of an existing formulation developed for unsaturated soils of low activity. The extended framework is based on the distinction within the material of a microstructural level where the basic swelling of the active minerals takes place and a macrostructural level responsible for major structural rearrangements. By adopting simple assumptions concerning the coupling between the two levels, it is possible to reproduce major features of the behaviour of unsaturated expansive clays. Some selected qualitative comparisons between model predictions and experimental results reported in the literature are presented. Despite the simplified hypotheses made, a very encouraging agreement is obtained. Key words : capillarity, clay, model, unsaturation, suction, expansive soils.

Influence of loading path on the undrained behaviour of a medium loose sand

2004 ◽  
Vol 41 (1) ◽  
pp. 166-180 ◽  
Author(s):  
V De Gennaro ◽  
J Canou ◽  
J C Dupla ◽  
N Benahmed
Keyword(s):  
Mechanical Behaviour ◽  
Transverse Isotropy ◽  
Vertical Direction ◽  
Loading Path ◽  
Preparation Technique ◽  
Cyclic Mobility ◽  
Significant Difference ◽  
Soil Fabric ◽  
Undrained Conditions ◽  
Stress Reversals

The results of an experimental programme aimed at studying the undrained behaviour of Hostun sand are presented in this paper. Specific conditions concerning the initial relative density (medium loose arrangements) and the loading paths (compression and extension under monotonic and cyclic loadings) were considered in the test programme. Monotonic tests carried out in both drained and undrained conditions show a significant difference in behaviour between compression and extension. It is observed that, in undrained conditions, Hostun sand is weaker in extension than in compression. In compression, the material is stable (dilatant) and the phase-transformation state controls the mechanical behaviour. In extension, the experimental results show an unstable behaviour (contractant), with monotonic, liquefaction-induced instability in undrained conditions. The results of cyclic tests, carried out with one- and two-way stress reversals, show a good correlation with the results of monotonic tests. The loading path strongly influences the undrained mechanical behaviour of the sand, mainly by inducing liquefaction in extension. This situation suggests that differences in soil fabric, caused by the sample preparation technique (air pluviation), can influence the sand behaviour by inducing a significant contraction in extension. By further analysing the cyclic results, it is shown that, during unloading, the stress paths reflect the transverse isotropy (orthotropy) of the sand, with stiffer elastic characteristics in the vertical direction than in the horizontal direction.Key words: liquefaction, cyclic mobility, sands, triaxial test, anisotropy, loading path.

Modified state-surface approach to the study of unsaturated soil behavior. Part III: Modeling of coupled hydromechanical effect

2012 ◽  
Vol 49 (1) ◽  
pp. 98-120 ◽  
Author(s):  
Xiong Zhang ◽  
Robert L. Lytton
Keyword(s):  
Unsaturated Soils ◽  
Coupling Effect ◽  
Degree Of Saturation ◽  
Compression Tests ◽  
Soil Behavior ◽  
Volume Changes ◽  
Surface Approach ◽  
Soil Skeleton ◽  
Hydromechanical Behavior ◽  
Undrained Conditions

A modified state-surface approach (MSSA) was proposed in the authors’ previous study to investigate volume change of the soil skeleton for unsaturated soils. This paper discussed the coupling effect between volume changes of soil skeleton, water phase, and air phase for unsaturated soils based on the proposed MSSA and experimental results presented by other researchers. The MSSA was further extended to study the coupled hydromechanical behavior for unsaturated soils. Besides void ratio constitutive surface, conventional unique water content and degree of saturation constitutive surfaces were also divided into elastic and plastic regions by loading–collapse (LC) yield curves and simultaneously used to describe the coupled hydromechanical behavior for unsaturated soils. A general theoretic formulation was derived for the simultaneous use of the MSSA under isotropic conditions. Based on the derived formulation, existing elastoplastic models were reviewed, and compatibility and consistency in modeling the mechanical and hydraulic behavior of unsaturated soils were discussed. Afterwards, the results of a number of suction-controlled laboratory isotropic compression tests at different suctions were used to demonstrate the ability of the proposed approach to reproduce the observed soil behavior quantitatively and soil behavior under undrained conditions qualitatively.

scholarly journals Compression mechanisms of unsaturated clay under high stresses

2015 ◽  
Vol 52 (12) ◽  
pp. 2099-2112 ◽  
Author(s):  
Woongju Mun ◽  
John S. McCartney
Keyword(s):  
Unsaturated Soils ◽  
Water Pressure ◽  
High Stress ◽  
Control Mode ◽  
Gradual Transition ◽  
Compression Tests ◽  
Suction Control ◽  
Unsaturated Clay ◽  
Undrained Conditions ◽  
Drained And Undrained Conditions

This paper investigates the compression behavior of unsaturated clay under mean stresses up to 160 MPa and different drainage conditions. A new isotropic pressure cell was developed that incorporates matric suction control using the axis-translation technique, and a high-pressure syringe pump operated in displacement-control mode was used to control the total stress and track specimen volume changes. In addition to presenting results from characterization tests on the cell, results from a series of isotropic compression tests performed on compacted clay specimens under drained and undrained conditions are presented. These results permit evaluation of the hardening mechanisms and transition points in the compression curve with increasing effective stress. As expected, specimens tested under undrained conditions were much stiffer than those tested under drained conditions. In the drained tests, the rate of compression was sufficient to permit steady-state dissipation of excess pore-water pressure except under the highest stress ranges. Suction-induced hardening was observed when comparing saturated and unsaturated specimens tested in the drained compression tests. In both the drained and undrained compression tests, the range of applied stresses was sufficient to cause collapse or dissolution of the air voids (pressurized saturation) and convergence of the virgin compression lines for unsaturated specimens with that measured for saturated specimens. A gradual transition to full-void closure was observed at high stresses when the compression curves were plotted on a natural scale, but the shapes of the compression curves at high stresses were not consistent with conventional soil mechanics models when plotted on a semilogarithmic scale. The results from this study provide insight into how constitutive models for unsaturated soils can be extended to high stress conditions for drained and undrained conditions.

scholarly journals Application of single-board computers in experimental research on unsaturated soils

2020 ◽  
Vol 195 ◽  
pp. 02022
Author(s):  
Marius Milatz
Keyword(s):  
Uniaxial Compression ◽  
Mechanical Behaviour ◽  
Unsaturated Soils ◽  
Water Retention ◽  
University Teaching ◽  
Water Retention Curve ◽  
Raspberry Pi ◽  
Granular Soils ◽  
Compression Tests ◽  
Unsaturated Granular Soils

In this contribution, the application of single-board computers for the investigation of the hydro-mechanical behaviour of unsaturated granular soils is presented. Single-board computers, such as the Raspberry Pi or Arduino, have recently experienced a hype of applications in school and university teaching, in the maker scene, amongst hobbyists, but also in research. In combination with easy to learn and open programming languages, such as Python, individual experimental set-ups for research in unsaturated soil mechanics, using actuators and sensors can be easily developed with the help of different programmable hardware, such as stepper motors, analog-to-digital converters and other controller boards. For the experimental application in imaging of unsaturated granular soils by computed tomography (CT), we present a miniaturized uniaxial compression device for the measurement of unsaturated shear strength and capillary cohesion in CT-experiments. The device has already been applied for CT-imaging of the development of water distribution and capillary bridges in between different shear steps. Furthermore, a new fully programmable hydraulic experimental set-up for the automated investigation of transient hydraulic paths of the water retention curve of granular media is presented. Both devices have been developed in the framework of the Raspberry Pi single-board computer and Python programming language with simple and relatively inexpensive hardware components. In addition to the technical development of the testing devices, experimental results of the hydro-mechanical behaviour of unsaturated sand and glass beads, derived from uniaxial compression tests and water retention tests, will be presented.

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