The concept of the suction stress characteristic curve (SSCC) for unsaturated soil is presented. Particle-scale equilibrium analyses are employed to distinguish three types of interparticle forces: (1) active forces transmitted through the soil grains; (2) active forces at or near interparticle contacts; and (3) passive, or counterbalancing, forces at or near interparticle contacts. It is proposed that the second type of force, which includes physicochemical forces, cementation forces, surface tension forces, and the force arising from negative pore-water pressure, may be conceptually combined into a macroscopic stress called suction stress. Suction stress characteristically depends on degree of saturation, water content, or matric suction through the SSCC, thus paralleling well-established concepts of the soil–water characteristic curve and hydraulic conductivity function for unsaturated soils. The existence and behavior of the SSCC are experimentally validated by considering unsaturated shear strength data for a variety of soil types in the literature. Its characteristic nature and a methodology for its determination are demonstrated. The experimental evidence shows that both Mohr–Coulomb failure and critical state failure can be well represented by the SSCC concept. The SSCC provides a potentially simple and practical way to describe the state of stress in unsaturated soil.

Suction Stress Characteristic Curve for Unsaturated Soil

A unique relationship for X for the determination of the shear strength of unsaturated soils

In this note, a unique relationship between the effective stress parameter chi and the ratio of suction over the air entry value (suction ratio) is proposed, based on the shear strength data reported in the literature. Comparisons are made between the measured and the calculated shear strengths for two laboratory prepared unsaturated soils. Extremely good agreement has been obtained between the measured and the calculated values using the proposed relationship. (A)

A unique relationship for χ for the determination of the shear strength of unsaturated soils

http://www.saetaequina.com/files/1-s2_0-S0950061811006763-main.pdf

A simple review of soil reinforcement by using natural and synthetic fibers

Unsaturated soil mechanics has rapidly become a part of geotechnical engineering practice as a result of solutions that have emerged to a number of key problems (or challenges). The solutions have emerged from numerous research studies focusing on issues that have a hindrance to the usage of unsaturated soil mechanics. The primary challenges to the implementation of unsaturated soil mechanics can be stated as follows: (1) The need to understand the fundamental, theoretical behavior of an unsaturated soil; (2) the formulation of suitable constitutive equations and the testing for uniqueness of proposed constitutive relationships; (3) the ability to formulate and solve one or more nonlinear partial differential equations using numerical methods; (4) the determination of indirect techniques for the estimation of unsaturated soil property functions, and (5) in situ and laboratory devices for the measurement of a wide range of soil suctions. This paper explains the nature of each of the previous challenges and...

http://keshavarz.persiangig.com/document/Fredlund2006.pdf

Unsaturated Soil Mechanics in Engineering Practice

Design of Retaining Wall and Single Pile in Expansive Soils Using Unsaturated Soil Mechanics as a Tool

This Technical Note presents the design detail of a combined air trap and volume gauge burette used for flushing air bubbles from under ceramic disks in axis translation systems that are used to measure or apply matric suction to unsaturated soil specimens. Axis translation systems are commonly used in the testing of unsaturated soils to subject soil specimens to matric suction values greater than 1 atm. Diffused air may come out of solution and accumulate below the ceramic disk of the axis translation system, prompting to provide a flushing system to remove them. An apparatus consisting of two concentric glass tubes, alongside a graduated scale, two water vessels permitting the isolation of the water phase to reduce moisture exchange with the surrounding atmosphere, and connected to the flushing groove below the ceramic disk of the axis translation system through two plastic tubes was developed. The apparatus described permits an accurate measurement of the volume of water expelled from the specimen and can allow for the volume of diffused air flushed out.

Integrated Air Trap and Volume Gauge for Axis Translation Systems

At-Rest Lateral Earth Pressure of Compacted Expansive Soils: Experimental Investigations and Prediction Approach

The development of theoretical and semi-empirical models to study capillary mechanisms and predict the soil-water characteristic curve (SWCC) generally requires the idealization of pore space and pore water, considering simplifying hypotheses. The study of ideal materials comprised of particles with controlled shape and size allows the evaluation of such simplifying hypotheses and the subsequent generalization to actual soils. In this paper, four theoretical and semi-empirical models for the prediction of the SWCC are applied to the prediction of artificial materials comprised of spherical particles. Nineteen grain-size distribution curves, with varying coefficients of uniformity are considered. The dataset is comprised of materials previously published and additional tests carried out by the authors, under highly controlled conditions. The analyses allowed the evaluation of the effect of grain-size distribution curve and shape of the particles. The limitations and advantages of each prediction model was investigated, and a detailed comparison is presented, guiding future implementations of improved models.

/pdf/evaluation-of-prediction-models-applied-to-the-soil-water-1aolae8brp.pdf

Evaluation of prediction models applied to the soil-water characteristic curve of ideal materials

In this paper, numerical study results that highlight the capability of using pond ash as a cover material in covers with capillary barrier effects are succinctly summarized. A model was exclusively developed and calibrated using commercial software SEEP/W for this study. After calibration, the efficiency of pond ash as a coarse-grained layer (CGL), fine-grained layer (FGL), unsaturated drainage layer (UDL), and seepage control layer (SCL) was investigated using various combinations. The CCBE made of pond ash obtained from the output and input points of an ash pond as alternate fine- and coarse-grained layers were observed to perform well. The performance of pond ash as UDL and SCL was also observed to be good. The approach presented in this study is valuable in assessing likely slope failures of coal ash storage facilities that may be triggered by rainfall events. The study aids in significantly reducing rainfall infiltration, improving the overall stability of the slopes, and promoting sustainability by utilising the concept of “waste covering waste”. The approaches used in this study can be extended in the rational design of slopes to address the future challenges anticipated with unprecedent rainfall events and its negative impacts associated with climate change effects.

https://www.e3s-conferences.org/articles/e3sconf/pdf/2023/19/e3sconf_unsat2023_21004.pdf

Sai K. Vanapalli

Papers

Design of Retaining Wall and Single Pile in Expansive Soils Using Unsaturated Soil Mechanics as a Tool

Integrated Air Trap and Volume Gauge for Axis Translation Systems

At-Rest Lateral Earth Pressure of Compacted Expansive Soils: Experimental Investigations and Prediction Approach

Evaluation of prediction models applied to the soil-water characteristic curve of ideal materials

Efficacy of Pond Ash as a Cover Material in Single and Dual Capillary Barriers