IN-SITU MEASUREMENT OF LATERAL PRESSURES IN CLAY

Abstract

THIS PAPER DEALS WITH A SIMPLE METHOD OF IN-SITU MEASUREMENT OF THE LATERAL EARTH PRESSURE IN NORMALLY CONSOLIDATED CLAYS. THE METHOD DEVELOPED IS BASED ON THE PRINCIPALS OF HYDRAULIC FRACTURING. A VERTICLE CRACK IS INITIATED IN THE SOIL AROUND A PIEZOMETER TIP. THE WATER PRESSURE AT WHICH THE CRACK CLOSES IS MEASURED, AND THIS PRESSURE IS BELIEVED TO BE IDENTICAL TO THE TOTAL STRESS ACROSS THE CRACK. FROM THIS THE COEFFICIENT OF EARTH PRESSURE AT REST (K SUB 0 VALUE) CAN BE CALCULATED. THE METHOD IS USED K SUB 0 VALUES AT SIX SITES. AT TWO OF THESE THE CLAY IS QUICK, AND AT THE OTHER FOUR NON-QUICK LEAN OR PLASTIC. THE K SUB 0 VALUES ARE FOUND TO BE IN THE RANGE 0.40-0.50 FOR THE QUICK AND 0.50-0.60 FOR THE NON-QUICK CLAYS. BENEATH A FILL AN INCREASE IN THE HORIZONTAL STRESSES IS MEASURED. A COMPARISON OF THE K SUB 0 VALUES OBSERVED IN THE FIELD WITH THOSE MEASURED IN THE LABORATORY INDICATES THAT IN A CLAY DEPOSIT K SUB 0 INCREASES WITH TIME. /AUTHOR/