Abstract
Compacted soils constitute most engineering projects such as earth dams, embankments, pavements, and engineered slopes because of their high shear strength and low compressibility. The shear strength of compacted soils is a key soil parameter in the design of earth structures but it is seldom determined correctly due to their unsaturated state. The shear strength of compacted soils can be better evaluated under the framework of unsaturated soil mechanics. Saturated and unsaturated tests were conducted on compacted specimens using conventional direct shear apparatus under constant water content condition. Tests were conducted at different water contents and net normal stresses. The main objective of this study is to develop a shear strength model for compacted soils. Initial matric suction was measured before the test using the filter paper method. The two-stress state variables together with the extended Mohr-Coulomb failure criterion for unsaturated soils were used to obtain a lower bound model of the shear strength. The model was demonstrated using published data.
Highlights
Compacted soils constitute most engineering projects such as earth dams, embankments, pavements, and engineered slopes because of their high precompression stresses and shear strength
Research shows that there exists a close relationship between the soil-moisture state and shear strength of unsaturated soils [1,2,3,4]
It is widely accepted that the shear strength of unsaturated soils can be expressed in terms of: (i) the effective stress principle or single stress state variable, similar to saturated soils [5,6,7] or, (ii) the two stress state variable principle [8]
Summary
Compacted soils constitute most engineering projects such as earth dams, embankments, pavements, and engineered slopes because of their high precompression stresses and shear strength. Equations 1 and 2 are the most commonly modified shear strength equations for unsaturated soils for single and two stress state variables, respectively. Parameters ua uw tan ¢ and ua uw tan b in Equations 1 and 2, respectively, are the shear strength as a result of matric suction (ua-uw). Experimental results show that there is no unique relationship between χ (used in the single stress variable framework) and the degree of saturation but rather χ depends on soil type and degree of saturation. It is reported in the literature that matric suction is due to pore water existing in the meniscus form between soil particles. In the constant water content test, the pore-air pressure is drained to reflect the field conditions
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