The determination of the shear-strength parameters along natural slip surfaces encountered during the Sevenoaks By-pass investigations

THE SAMPLING AND TESTING TECHNIQUES ARE DESCRIBED WHICH ARE USED BY THE ROAD RESEARCH LABORATORY TO DETERMINE THE SHEAR STRENGTH PARAMETERS ON NATURAL SLIP SURFACES ENCOUNTERED DURING THE INVESTIGATION OF MAJOR INSTABILITY OF SIDELONG GROUND EXPERIENCED DURING THE CONSTRUCTION OF THE SEVENOAKS BY-PASS. CONSOLIDATED DRAINED TRIAXIAL TESTS WERE CARRIED OUT ON SAMPLES CONTAINING NATURAL SLIP PLANES. SIX BATCHES OF SAMPLES, OBTAINED FROM DIFFERENT LOCATIONS WITHIN THE UNSTABLE AREAS, WERE TESTED. DETAILS ARE GIVEN OF THE MODE OF FAILURE, AND EXPRESSIONS ARE PRESENTED WHICH ENABLE THE SHEARING AND NORMAL STRESSES ACTING ON THE INCLINED SLIP PLANE TO BE DETERMINED FOR ANY DEGREE OF AXIAL STRAIN. THE RESULTS SHOW THAT THE ANGLES OF SHEARING RESISTANCE (9) WERE AT THEIR RESIDUAL VALUES. HOWEVER A SIGNIFICANT COHESION INTERCEPT WAS MEASURED ON FIVE OF THE BATCHES TESTED AND AT PRESENT NO RIGOROUS EXPLANATION CAN BE OFFERED TO ACCOUNT FOR THIS. THE VALUE OF THE COHESION INTERCEPT MEASURED ON FOUR OF THE BATCHES TESTED WAS SMALL AND IT IS THOUGHT THAT THIS MAY HAVE RESULTED FROM INACCURACY IN THE APPROXIMATE CORRECTION APPLIED TO THE MEASURED LOAD. /A/RRL/ FROM INACCURACY IN THE APPROXIMATE CORRECTION APPLIED TO THE MEASURED LOAD TO TAKE ACCOUNT OF THE RESTRAINT PROVIDED BY THE RUBBER MEMBRANE AND PAPER FILTER DRAIN. /RRL/