Probabilistic Estimation of Rock Load Acting on Tunnels Considering Uncertainty in Peak and Post-peak Strength Parameters

This paper deals with estimation of loads relaxed by surrounding rocks on underground excavations that might be a problematic issue because of uncertainties in different aspects of geotechnical characterization of a project. A probabilistic procedure has been proposed to estimate the rock load value considering peak and post-peak strength parameters of rock mass in the generalized Hoek–Brown model, which in turn assumes the uncertainties available in the parameters as well. Assigning single random variables (SRV) for geomechanical properties from their distribution functions, many numerical models have been analyzed to estimate statistics of response parameters (i.e. plastic zone thickness and rock load) using different failure criteria including the conventional Hoek–Brown and Mohr–Coulomb models and these models considering effects of residual strength parameters. Results show that plastic zone thicknesses/rock loads obtained using the Hoek–Brown strength drop model are completely close to the values obtained using the analytical method while the other models are not able to predict the response parameters’ range accurately. Moreover, in contrast to the Hoek–Brown model, strength drop consideration does not affect Mohr–Coulomb model results significantly.