ON THE GENERALIZED STRESS-STRAIN BEHAVIOUR OF WET CLAY

THE BASIC CAMBRIDGE THEORY OF THE STRESS-STRAIN BEHAVIOUR OF WET CLAYS, AS DEVELOPED FOR 'TRIAXIAL' (AXI-SYMMETRIC) COMPRESSION TEST CONDITIONS, IS EXTENDED TO INCLUDE GENERALIZED THREE-DIMENSIONAL STRESS AND STRAIN CONDITIONS. THE THEORY IS DEVELOPED IN THE LIGHT OF A NEW WORK EQUATION PROPOSED BY BURLAND. TWO OTHER NEW CONCEPTS ARE INTRODUCED. FIRST, A NEW YIELD LOCUS TO TAKE ACCOUNT OF THE SHEAR DISTORTION THAT OCCURS, WITHOUT PLASTIC VOLUME CHANGE, FOR STATE PATHS BENEATH THE STATE BOUNDARY SURFACE. SECONDLY, THE MOHR-COULOMB CRITERION IS INCORPORATED IN THE THEORY TO PREDICT RUPTURE WHEN WET CLAYS ARE SUBJECTED TO STRESS PATHS IN THREE-DIMENSIONAL STRESS SPACE. THE MECHANICAL BEHAVIOUR OF A GIVEN WET CLAY UNDER SUCH A GENERAL SYSTEM IS PREDICTED FROM THE THREE SOIL CONSTANTS, M, LAMBDA AND KAPPA OBTAINED FROM TRIAXIAL COMPRESSION TESTS. AFTER SHOWING THAT TRIAXIAL EXTENSION TEST RESULTS CAN BE SATISFACTORILY PREDICTED FROM TRIAXIAL COMPRESSION DATA, PARTICULAR ATTENTION IS PAID TO PLANE STRAIN WHICH IS SO FREQUENTLY RELEVANT IN PRACTICAL PROBLEMS. THE PLANE-STRAIN BEHAVIOUR AS PREDICTED FROM TRIAXIAL DATA IS COMPARED WITH OBSERVATIONS IN A PLANE-STRAIN APPARATUS, AND A SIMPLE-SHEAR APPARATUS. EXCELLENT AGREEMENT IS OBTAINED, AND CONFIRMS THE PREDICTION THAT FOR WET CLAYS THE ANGLE OF INTERNAL FRICTION IN DIRECT SHEAR TESTS IS LESS THAN THE TRIAXIAL VALUE. TO ILLUSTRATE THE POWER AND PRACTICAL SIGNIFICANCE OF THE THEORY, IT IS USED TO PREDICT THE STRAINS THAT ARE REQUIRED TO DEVELOP THE ACTIVE AND PASSIVE RANKINE STATES IN A MASS OF WET CLAY. THESE PREDICITIONS ARE IN AGREEMENT WITH EXPERIENCE. /RRL/A/