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

Influence of freeze-thaw cycles on microstructure and hydraulic conductivity of saline intact loess

Influence of rain infiltration on the stability of compacted soil slopes

The shear strength of unsaturated soils can be computed using the soil-water characteristic curve and the saturated shear strength parameters of the soil. Closed-form solutions for the prediction of unsaturated shear strength are developed in this paper using simple soil-water characteristic curve equations available in the literature. These closed-form solutions are not suitable for all types of soils and large ranges of suction. A general form for the shear strength equation of unsaturated soils using a rigorous soil-water characteristic curve equation is also developed in this paper. The proposed models make use of the soil-water characteristic curve and the saturated shear strength parameters to predict the variation of shear strength with respect to suction. (A) For the covering abstract see IRRD 881647.

Predicting the shear strength function for unsaturated soils using the soil-water characteristic curve

Expansive soils are typically in a state of unsaturated condition and are widely found in semi-arid and arid regions of the world. The engineering properties of these soils are highly sensitive to changes in water content and suction in the active zone depth. One of the key problems associated with expansive soils is their swelling characteristics due to an increase in their natural water content. Practicing geotechnical engineers consider reliable prediction of the heave behavior of expansive soils and understanding its impact on the structures as one of their greatest challenges. Several researchers and practitioners from all around the world have made significant contributions over the past 60 years to better understand these problematic soils. This paper synthesizes information of various techniques available in literature for estimating the swelling pressure and the 1-D heave behavior of expansive soils. In addition, the limitations of using them in geotechnical engineering practice ar...

A state-of-the art review of 1-D heave prediction methods for expansive soils

Many studies are reported in the literature for estimating the potential heave of expansive soils; however, limited efforts have been directed towards estimating the heave with respect to time. In this Technical Note, a simple approach is proposed for estimation of the one-dimensional (1-D) heave of expansive soils over time. The approach involves integrating semi-empirical and numerical techniques into a unified method to estimate heave in response to the net changes in soil suction within the active zone. The information of the variation of modulus of elasticity with respect to suction is introduced into the soil structure constitutive equation proposed by Fredlund and Morgenstern (1976) to estimate the soil heave over time. The commercial software VADOSE/W, a product of Geo-Studio, is used as a tool to estimate the net changes in the soil suction. The approach is tested using the published results by Vu and Fredlund (2006) for Regina expansive clay. The estimated results of the proposed approac...

Sai K. Vanapalli

Papers

Influence of freeze-thaw cycles on microstructure and hydraulic conductivity of saline intact loess

Influence of rain infiltration on the stability of compacted soil slopes

Predicting the shear strength function for unsaturated soils using the soil-water characteristic curve

A state-of-the art review of 1-D heave prediction methods for expansive soils

Constitutive modeling approach for estimating 1-D heave with respect to time for expansive soils