Numerical evaluation of photoelastic data from discontinuous models

Abstract

Equations are developed which allow the solution to the photoelastic problem of obtaining the boundary loads causing the internal stress pattern on a block of material when the isoclinics and isochromatics from within the block are known. The method uses the well known line integral theory and Flamant's solution for the stress distribution in a semi-infinite plane due to a point load. The problem is solved without having to start at a boundary of known loading, which is the approach generally used in evaluating photoelastic data. This new method offers great facility and reliability when examining discontinuous models, such as rock or soil systems. Data which have been obtained from carefully controlled experiments on blocks of various sizes are analysed by a numerical method using the developed equations. The calculated boundary loads are then compared with the average applied boundary loads, which are imposed by contact. It is found that the distributions of the applied loads on the boundary are affected by local stress concentrations. In general, the average values agree well with the computed boundary loads, except, however, for the case of applied boundary shear. After examining the relatively large single blocks, some typical results of boundary loads on specific blocks within blocky models are examined. Here the results of the numerical method described in this paper are compared with results obtained from the shear difference method.