ALTERNATIVE APPROACH FOR PREDICTING MODULUS OF DEFORMATION USING FEM

Abstract

Modulus of deformation is an important parameter which defines the engineering behaviour of rock mass. It is generally determined by in-situ methods like Plate Loading Test, Plate Jacking Test etc. Due to difficulties encountered while conducting in-situ tests, modulus of deformation is often estimated by design engineers on basis of empirical correlations developed for the purpose on the basis of available field test data. For the interpretation of in-situ test data, the rock mass behaviour is assumed to be elastic which does not represent the actual behaviour of rock mass in nature. In the present work, simulation of plate jacking test conditions has been carried out for five different dam sites for which field data was readily available in the literature (Mehrotra, 1992). The analysis considers the elasto-plastic response of the rock mass through Drucker-Prager yield criterion and the theory of cyclic plasticity. The analysis has been performed using the finite element method with the help of ANSYS 10.0. The modulus of deformation of rock mass has been determined from load intensity versus strain response of rock mass corresponding to different loading and unloading cycles for various stress ranges. It has been observed that modulus of deformation is greatly affected by geological conditions and the geotechnical properties of rock mass and its degree of saturation. The analySis also provides an alternate means for predicting the modulus of deformation, which would be useful in situations where it is difficult to conduct such tests.