Interpretation of plate load test data

Abstract

Abstract The International Society for Rock Mechanics (ISRM) has a suggested method for determining in situ the deformability of rock using a plate test. Previous studies using a method of data interpretation that is similar to that recommended by the ISRM show that there is a potential for significant error when interpreting plate load test data. In particular, the determined deformation modulus of a rock mass may be larger than Young's modulus of the intact rock, even where the rock mass is jointed and should intuitively have a deformation modulus that is less than that of the intact rock. Simulations of plate load tests in jointed and unjointed rocks were made using a finite element code to assess some of the effects of jointing and excavation geometry on the determination of the deformation modulus. The results of the simulations are also used to demonstrate a modification of the ISRM suggested method of interpreting plate load test data that should help in interpreting the sometimes apparently counterintuitive results. The proposed modification uses least squares to calculate Young's modulus of the rock mass and also allows Poisson's ratio to be calculated, which is in contrast to the ISRM suggested method that requires Poission's ratio to be known a priori.