ASSESSMENT OF RHEOLOGICAL CONSTANTS OF CLAY

Abstract

The loading of the soil mass below the foundation of the structure is inevitable. This soil mass adjusts itself to the imposed stress in many ways. - The technique of "rheological modelling" is resorted to predict this behaviour of the soil mass with time under any generalised stress system. The strain in the soil mass depends, alongwith a host of other factors on the drainage conditions permitted in the soil mass. In a drained condition (long term stability problems) both the hydrostatic and the deviatoric strain components .are present. Therefore it is needed to evaluate the rheological constants under two different stress conditions namely, hydrostatic and deviatorid stress conditions. Two approaches one based on the Consolidation test data on saturated undisturbed soil sample and other based on Triaxial test data on saturated undisturbed soil sample have been attempted here , test data presented and results discussed. The Triaxial test approach is more general in nature as it takes into account the non linear visco elastic behaviour of the soil mass based on a non linear Kelvin 'model. The variation of spring and dashpot constants (under both stress conditions) is obtained with the degree of consolidation that has occured in the soil mass. Thus these constants are functions of stress level, current strain level, the strain rate and time . These constants will be independent of the structure type or foundation area shape or its depth and hence more aptly be called as "fundamental rheological constants". The approaches presented are very easy to follow in the laboratory and do'away with any field test to predict the rheological behaviour of the soil. The use of such an approach is, therefore highly called for in a realistic analysis of Soil Structure interaction.