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

Experimental studies were undertaken to investigate the vertical load versus displacement behavior of single model piles in sand (i.e., Unimin 7030 sand) under both saturated and unsaturated conditions. Stainless steel model piles with three different diameters (i.e., 19.25, 31.75, and 38.3 mm) with a length of 350 mm were used to conduct the pile load tests. Semiempirical methods were proposed to successfully predict the variation of end- and shaft-bearing capacities of single piles with respect to matric suction by modifying three conventional end-bearing capacity equations (Terzaghi 1943; Hansen 1970; Janbu 1976) and the β-method (Burland 1973), respectively. In addition, finite element analyses were also carried out to simulate vertical load versus settlement behaviors of model pile tests using a commercial finite element software, SIGMA/W (GeoStudio 2007).

Experimental and Simple Semiempirical Methods for Interpreting the Axial Load Versus Settlement Behaviors of Single Model Piles in Unsaturated Sands

Triaxial compression and oedometer consolidation tests are commonly performed to evaluate the strength and deformation behavior of soils. However, in the field, the stress paths imposed by various engineering works may deviate from the stress paths conventionally used in laboratory tests. Moreover, the stress-paths followed by different soil elements under a foundation are different. To obtain representative soil parameters, the laboratory stress path should be similar to that followed in the field. In this study, a significant number of stress-path triaxial tests, with stress probes in various directions, have been conducted to study the stress-path dependent behavior of an overconsolidated weathered crust of Champlain clay in Eastern Ontario. Both undrained and drained tests have been conducted for samples isotropically consolidated to the in situ vertical stress and anisotropically consolidated to in situ state of stress. The yield locus of the clay crust has been defined. It has been observed that the strength-deformation and yielding behavior of this weathered clay crust highly depends on the stress-path as well as on the in situ stress history.

Stress-path dependent behavior of a weathered clay crust

Two simple techniques are proposed in this Technical Note to estimate suction values over a range of 0 to 60,000 kPa on compacted glacial till specimens. The first technique uses a conventional pocket penetrometer in the estimation of matric suction values lower than 300 kPa. This technique is developed based on the assumption that there is a strong relationship between matric suction and the compressive strength measured using a pocket penetrometer. The second technique uses conventional tensiometer to estimate relatively high suction values in the range of 1200 to 60,000 kPa. In this technique, the tensiometer response versus time (TRT) behavior for a suction range of 0 to 50 kPa is used in a hyperbolic model to estimate the high suction value. This technique is proposed based on the assumption that each suction value has a unique initial tangent of TRT behavior. The equilibrium suction values of the compacted glacial till specimens are respectively measured using axis-translation technique and a psychrometer for low and high suction values and compared with those estimated using the techniques proposed in this study. There is a reasonably good comparison between the measured and estimated suction values both in the low and high suction range.

Simple Techniques for the Estimation of Suction in Compacted Soils in the Range of 0 to 60,000 kPa

The soil-water characteristic curve is conventionally measured using a pressure plate apparatus or a Tempe cell. Considerably long periods of time are required to measure the soil-water characteristic curves using the conventional equipment. A new test procedure is proposed, using a small-scale medical centrifuge to measure the soil-water characteristic curves for compacted, fine-grained soil specimens. Soil specimen holders were designed for the small-scale centrifuge. The soil-water characteristic curves of statically compacted specimens for three different fine-grained soils with varying percentages of clay were measured using the centrifuge for a suction range between 0 to 500 kPa. There is good comparison between the soil-water characteristic curves measured using the small-scale centrifuge and the conventional laboratory equipment. The results of this study are encouraging as soil-water characteristic curves can be measured in a shorter period of time, resulting in considerable savings.

/pdf/a-new-test-procedure-to-measure-the-soil-water-28iyflopls.pdf

A new test procedure to measure the soil-water characteristic curves using a small-scale centrifuge.

Several pipeline projects have been proposed in the world in recent years owing to the rapid growth of the petroleum industry. Onshore pipeline systems are usually buried above the natural groundwa...

Sai K. Vanapalli

Papers

Experimental and Simple Semiempirical Methods for Interpreting the Axial Load Versus Settlement Behaviors of Single Model Piles in Unsaturated Sands

Stress-path dependent behavior of a weathered clay crust

Simple Techniques for the Estimation of Suction in Compacted Soils in the Range of 0 to 60,000 kPa

A new test procedure to measure the soil-water characteristic curves using a small-scale centrifuge.

Axial force–displacement behaviour of a buried pipeline in saturated and unsaturated sand