Predicted and measured rock mass moduli

Abstract

Plate bearing and rock bolt jacking tests are used to measure the in situ deformational response of four jointed rock masses, namely sandstone, limestone, shale and coal. Samples representing the intact rock and joint material were retrieved from the test sites and examined in the laboratory. While performing the joint shear strength tests, the joint normal and shear stiffnesses were also measured. The predicted values of the rock mass moduli were evaluated using composite theory and the laboratory determined joint stiffnesses and intact rock moduli. When evaluating the predicted rock mass moduli, lower bound composite formulations were used. These predicted rock mass moduli were then compared with the measured in situ deformational moduli. Joint shear stiffness is an order, that is 10 times, less than the joint normal stiffness and this has the important effect of disproportionally increasing the deformational response. The in situ measured moduli correlate reasonably well with the predicted moduli evaluated from the lower bound deformational formulations. However, good correlation is obtained when the lower values of joint stiffnesses are used in the lower bound deformational formulations.