STP740

    The Critical-State Pore Pressure Parameter from Consolidated-Undrained Shear Tests

    Published: Jan 1981


      Format Pages Price  
    PDF Version (340K) 21 $25   ADD TO CART
    Complete Source PDF (12M) 21 $61   ADD TO CART


    Abstract

    The results of isotropic and anisotropic consolidated-undrained shear tests (CIU, CK0, U) are used to determine the critical-state pore pressure parameter (Λo). The relative advantages of using the critical-state parameter (Λo) over Skempton's pore pressure parameter (A) and Henkel's parameter (a) are discussed. The effects of over-consolidation ratio (OCR) and initial stress state (K0) on both Henkel's and Skempton's pore pressure parameters can significantly alter effective stress predictions of undrained strength. The critical-state parameter is independent of OCR, K0, and level of shear to failure, thus requiring only two basic soil constants in order to predict undrained strength: (1) the effective stress friction angle (φ'), and (2) the critical-state pore pressure parameter (Λo).

    An “extended” critical-state model is developed using the equivalent pressure concept for overconsolidated states. The method then provides a simple analytical representation of undrained stress-strain behavior and pore pressure response for clays with different values of OCR. One additional soil constant (Cc: the virgin compression index) is required in order to model stress-strain behavior.

    The validity of the critical-state theory is substantiated by data from over ninety different clay and silt soils reported in the geotechnical literature. Furthermore, the critical-state concepts are shown to encompass both total stress and effective stress methods under one unified theory.

    Keywords:

    clays, effective stresses, overconsolidation, pore pressure, shear strength, strain, total stresses, triaxial shear tests


    Author Information:

    Mayne, PW
    Geotechnical engineer and senior geotechnical engineer, Law Engineering Testing Company, Washington, D.C.

    Swanson, PG
    Geotechnical engineer and senior geotechnical engineer, Law Engineering Testing Company, Washington, D.C.


    Paper ID: STP28763S

    Committee/Subcommittee: D18.05

    DOI: 10.1520/STP28763S


    CrossRef ASTM International is a member of CrossRef.