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

A critical review of soil moisture measurement

A review of the methods available for estimating soil moisture and its implications for water resource management

Experimental data from different testing methodologies on different compacted clayey soils, with dominant bimodal pore size distribution, are presented and analysed, to provide a comprehensive picture of the evolution of the aggregated fabric along hydraulic and mechanical paths. Fabric changes are analysed both from the porous network viewpoint, by means of careful mercury intrusion porosimetry investigation, and from the soil skeleton viewpoint, by quantifying swelling and shrinkage of the aggregates in an environmental scanning electron microscopy study. The consequences of the aggregated fabric evolution on the water retention properties of compacted soils are analysed and discussed. A new model for water retention domain is proposed, which introduces a dependence of the intra-aggregate pore volume on water content. The model succeeds in tracking correctly the evolution of the hydraulic state of the different soils investigated along generalised hydromechanical paths. The proposed approach brings to l...

An insight into the water retention properties of compacted clayey soils

Expansive clay soils—those that change significantly in volume with changes in water content—are the cause of distortions to structures that cost taxpayers several billion dollars annually in the United States. Much has been learned about their behavior over the past 60 years, and relatively successful methods have been developed to modify and stabilize them. This paper reviews some of the key advances developed over the past 60 years in improving our understanding of the nature and methods of modifying and stabilizing expansive clay soils. The state of the practice in stabilization is presented, and practical and research needs to help improve the state of the practice are discussed.

Review of Stabilization of Clays and Expansive Soils in Pavements and Lightly Loaded Structures—History, Practice, and Future

Current methods of determining soil moisture suction are outlined and their shortcomings identified. A new instrument is then described which will overcome a number of these problems by the use of a miniature pressure transducer, and minimum volume of water between the active face of the transducer and the porous stone. The instrument uses an Entran EPX-500 stainless steel miniature pore water pressure transducer, with a working range up to 3500 kPa, shrouded by a stainless steel sheath fitted with a porous stone. The mechanics of the instrument and its evaluation against known values of suction are outlined. Reliable measurements of suction were achieved up to 1500 kPa.

A new instrument for the measurement of soil moisture suction

The influence of fabric on mechanical behaviour is explicitly considered in some of the current constitutive models for unsaturated soils. These are based on assumptions regarding the interaction b...

/pdf/evolution-of-microstructure-in-compacted-london-clay-during-5d04w1536f.pdf

Evolution of microstructure in compacted London Clay during wetting and loading

This paper describes a novel method of controlling suction by means of air circulation in combination with independent suction measurement. The technique has been incorporated in a standard triaxial stress path cell, and could easily be incorporated in other standard apparatus such as the direct shear box and oedometer. The application of the technique is demonstrated by means of an exploratory testing programme in which samples of a reconstituted saturated clayey silt were progressively dried to various predetermined suctions, which were then maintained constant during isotropic compression followed by shearing to failure. In this way the drying and stress history of the soil was carefully controlled in a way that could be made representative of the genesis of natural unsaturated soils. Though exploratory, the experimental investigation described in this paper has provided some interesting and thought-provoking results. Prior to desaturation the clayey silt behaves in accordance with the classical critic...

The mechanical behaviour of a reconstituted unsaturated silty clay

Soil matrix suction is assuming an increasing importance in geotechnical engineering. It is now recognised that soil suction is not confined to arid or semi-arid regions of the world. It is frequently encountered in a great many geotechnical problems in temperate climates. For example, all fills and compacted soils have an inherent suction when they are formed; many slopes, both natural and man-made, have in-situ suctions; and all samples that are removed from the ground during a site investigation possess a soil suction in their unconfined state. Measurements of soil matrix suction can be used to: (a) identify disturbance and/or desiccation in samples removed from the ground; (b) estimate the average in-situ effective stress once the effect of disturbance and/or desiccation has been quantified; (c) apply more rigorous controls to the compaction of fill materials where swelling is likely to cause problems; and (d) assess the stability in natural and engineered slopes. This paper describes and compares thr...

Soil matrix suction: some examples of its measurement and application in geotechnical engineering

This paper presents a review of techniques for field measurement of suction, water content, and water hydraulic conductivity (permeability). Main problems in the use of field tensiometers are addressed and hints on how to improve tensiometer performance are given. Advantages and limitations of instruments for indirect measurement of suction including electrical conductivity sensors, thermal conductivity sensors, dielectric permittivity sensors, filter paper, and psychrometer are discussed. Techniques for water content measurement based on dielectric methods are then presented. These include time and amplitude domain reflectometry and capacitance. Finally, a brief overview of methods for measurement of water permeability in the field is presented.

Field measurement of suction, water content, and water permeability

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