Average Soil Skeleton Stress for Unsaturated Soils and Discussion on Effective Stress

Author(s):  
Chenggang Zhao ◽  
Zhenzhen Liu ◽  
Peixin Shi ◽  
Jian Li ◽  
Guoqing Cai ◽  
...  
2015 ◽  
Vol 52 (12) ◽  
pp. 2067-2076 ◽  
Author(s):  
Jean-Marie Konrad ◽  
Marc Lebeau

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.


2020 ◽  
Vol 195 ◽  
pp. 02027
Author(s):  
Stefano Muraro ◽  
Cristina Jommi

The paper assesses fully coupled hydro-mechanical numerical approaches developed for unsaturated soils to model the effect of free gas overpressure on the response of peat layers. A simple linear model is used for the soil skeleton, however, the global response is non-linear due to changes over time of the compressibility of the solid skeleton over the compressibility of the fluid, and solubility of gas in water. The overpressure generated in foundation peat layers by barometric pressure oscillations is modelled, and the results are compared to literature data. The development of pore overpressure upon unloading is analysed as a function of the soil skeleton compressibility, and the consequences on the average stress acting on the soil skeleton are discussed.


Geosciences ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 428 ◽  
Author(s):  
Shashank Menon ◽  
Xiaoyu Song

The formation of desiccation cracks in unsaturated soils as a discontinuity phenomenon can compromise the integrity of civil infrastructure on unsaturated soils. Because of the singularity at such discontinuities, the mathematical modeling of desiccation cracking is challenging. In this study, we apply a coupled nonlocal peridynamic poroelastic framework to model desiccation cracking in unsaturated soils. The soil skeleton is modeled by a nonlocal peridynamic elastic solid. A peridynamic equivalence of the generalized Darcy’s law is utilized to model unsaturated fluid flow. Cracking is determined by a critical stretch criterion between material points as well as an energy criterion. We present numerical simulations of desiccation cracking in soil bars and thin soil discs for one-dimensional cracking and two-dimensional cracking networks, respectively. The numerical results have demonstrated that the proposed nonlocal mathematical framework is a promising and robust method for modeling desiccation cracking in unsaturated soils.


2014 ◽  
Vol 580-583 ◽  
pp. 123-128
Author(s):  
Issam Hanafi ◽  
Fouad Dimane ◽  
Francisco Mata Cabrera ◽  
José Tejero Manzanares

In this work, one-dimensional problem has a well-known linear solution and, thus, provides a simple verification of the consolidation capability using numerical solution. The coupling is approximated by the effective stress principle, which treats the saturated soil as a continuum, assuming that the total stress at each point is the sum of an effective stress carried by the soil skeleton and a pore pressure in the fluid permeating the soil. This fluid pore pressure can change with, and the gradient of the pressure through the soil that is not balanced by the weight of fluid between the points in question will cause the fluid to flow: the flow velocity is proportional to the pressure gradient in the fluid according to Darcy's law. A typical case is a consolidation problem. Here the addition of a load to a body of soil causes pore pressure to raise initially; then, as the soil skeleton takes up the extra stress, the pore pressures decay as the soil consolidates. The Terzaghi problem is the simplest example of such a process. For illustration purposes, the problem is treated with and without finite-strain effects. The numerical solution agrees reasonably well with the analytical solution, with some loss of accuracy at later times.


1994 ◽  
Vol 31 (2) ◽  
pp. 311-317 ◽  
Author(s):  
Hans H. Vaziri ◽  
Harold A. Christian

Terzaghi's one-dimensional consolidation theory is modified to account for the compressibility of fluid and solid phases. The proposed modified equations can be used to analyze the consolidation response of unsaturated soils over the saturation range where the gases remain in an occluded form (generally within a range between 80 and 100aturation); however, such applications are subject to the same limitations and idealizations implicit in Terzaghi's classical consolidation theory. The purpose of this note, therefore, is to offer a simple solution and not to unravel the complexities involved in general analysis of flow and deformation response of unsaturated soils. The proposed approach involves defining the consolidation coefficient, and hence the time factor, in terms of an equivalent fluid compressibility. This equivalent fluid is assumed to represent the compressibility characteristics of all the compressible phases that constitute the soil skeleton. The proposed generalized form of Terzaghi's consolidation equations is shown to qualitatively capture the consolidation behaviour of unsaturated soils. To test the validity of the formulations presented, one-dimensional oedometer tests were performed on specimens of Lantz clay that had been prepared at different saturation levels; satisfactory agreement was achieved between the theoretical and measured data at two states of saturation. Key words : consolidation, theoretical solutions, oedometer test, compressible fluid, occluded gas.


2012 ◽  
Vol 256-259 ◽  
pp. 108-111
Author(s):  
Seboong Oh ◽  
Ki Hun Park ◽  
Oh Kyun Kwon ◽  
Woo Jung Chung ◽  
Kyung Joon Shin

The hypothesis on effective stress of unsaturated soils is validated by consolidation strength results of triaxial tests for the compacted residual soil. The effective stress can describe the unsaturated soil behavior, which was defined from shear strength or from soil water characteristic curves. Since the effective stress from consolidation agrees with that from the shear strength, the effective stress from soil water retention curve could describe the unsaturated behavior consistently on both consolidation path and stress at failure. The effective stress can describe the entire unsaturated behavior from consolidation to failure.


2016 ◽  
Vol 9 ◽  
pp. 17006
Author(s):  
Hiram Arroyo ◽  
Eduardo Rojas ◽  
José Arroyo

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