Research on stress state variables of unsaturated soil

2014 ◽  
pp. 151-157
Author(s):  
B Qin ◽  
Z Chen
Keyword(s):  
Stress State ◽  
Unsaturated Soil ◽  
State Variables

scholarly journals State Variables in Saturated-Unsaturated Soil Mechanics

2016 ◽  
pp. 3-17
Author(s):  
Delwyn G. Fredlund
Keyword(s):  
Stress State ◽  
Continuum Mechanics ◽  
Unsaturated Soil ◽  
Material Properties ◽  
Soil Mechanics ◽  
Constitutive Relations ◽  
Saturated Soil ◽  
Clear Distinction ◽  
State Variables ◽  
Unsaturated Soil Mechanics

The description of the stress state in soils is the foundational point around which an applied science should be built for engineering practice. The stress state description has proven to be pivotal for saturated soil mechanics and the same should be true for unsaturated soil mechanics. Continuum mechanics sets forth a series of principles upon which a common science base can be developed for a wide range of materials. The principles require that there be a clear distinction between state variables and constitutive relations. Constitutive relations relate state variables and incorporate material properties. State variables, on the other hand, are independent of the material properties. It has been possible to maintain a clear distinction between variables of state and constitutive relations in the development of saturated soil mechanics and the same should be true for unsaturated soil mechanics. This paper presents a description of the source and character of stress state variables for saturated and unsaturated soils. The descriptions are consistent with the principles of multiphase continuum mechanics and provide an understanding of the source and importance of stress state variables.

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.

Influence of stress history on the strength parameters of an unsaturated statically compacted soil

1999 ◽  
Vol 36 (2) ◽  
pp. 251-261 ◽  
Author(s):  
Tomoyoshi Nishimura ◽  
Yasunari Hirabayashi ◽  
Delwyn G Fredlund ◽  
Julian K-M Gan
Keyword(s):  
Shear Strength ◽  
Unsaturated Soil ◽  
Stress Ratio ◽  
Matric Suction ◽  
Strength Parameter ◽  
Direct Shear ◽  
State Variables ◽  
Total Stress ◽  
Stress History ◽  
Compacted Soil

Unsaturated soils are generally near the ground surface and are commonly overconsolidated due to environmental effects. The stress state variables for an unsaturated, in situ profile consist of the net total stress, (σ - ua), and matric suction, (ua - uw), where σ is the total stress (in three directions), ua is the pore-air pressure, and uw is the pore-water pressure. These stress state variables control the behavior of the unsaturated soil. A total stress ratio, TSR, was used in this study as a measure of the stress history. The total stress ratio is defined as the ratio of the compaction pressure to the current confining pressure. Shear tests were conducted using a modified direct shear apparatus on a statically compacted unsaturated soil subjected to various total stress ratios with controlled matric suction. The shear strength parameters (i.e., ϕ', ϕb, and c') for an unsaturated soil were measured using the modified direct shear apparatus. The total stress ratio influences the shear strength parameter ϕb of a compacted soil. The shear strength parameter ϕb decreases with matric suction regardless of the loading history. For a compacted soil with a total stress ratio of 1.0, ϕb was higher than that for the soil tested at a total stress ratio greater than 1.0, regardless of increase in matric suction, and was shown to be influenced by loading history.Key words: unsaturated soil, shear strength, stress history, compacted soil, direct shear test, matric suction.

Stress State Variables for Unsaturated Soils

1977 ◽  
Vol 103 (5) ◽  
pp. 447-466 ◽  
Author(s):  
Delwyn G. Fredlund ◽  
Norbert R. Morgenstern
Keyword(s):  
Stress State ◽  
Unsaturated Soils ◽  
State Variables
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