New Concept of Effective Stress in Unsaturated Soil and Its Proving Test

    Published: Jan 1988

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    Triaxial compression tests, including anisotropic consolidation tests, were performed on compacted kaolin clay by an automatically controlled apparatus. Test results were analyzed in terms of suction and (σ − ua), where σ is total normal stress and ua is pore air pressure, recognizing that when soil is saturated, ua becomes equal to uw, pore water pressure.

    When suction is kept constant, the relationships among the observed shear strength, stress-strain, and stress-water content change can be formulated in equations similar to those of saturated soil, in which suction can be regarded as a factor contributing to soil constants. When both suction and all-around pressure are varied, the plastic volumetric strain can be expressed by an equation in which (σ − ua) is multiplied by a function of suction. Therefore suction can be regarded as a factor contributing to soil constants in this case too. These facts mean that the suction need not be regarded as one of the principal stress components such as (σ − ua) in the stress-strain equations of unsaturated soil.


    unsaturated soil, kaolin, suction, effective stress, triaxial compression test, stress-strain relationship

    Author Information:

    Karube, D
    Associate professor, Kobe University, Kobe,

    Committee/Subcommittee: D18.05

    DOI: 10.1520/STP29097S

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