Analysis of Rock Load for Tunnel Lining Design

Rock load relaxed by surrounding ground due to a tunnel excavation is one of the most important parameters in support system design of underground structures. There are three different methods for estimating rock load, namely, empirical solutions, convergence-confinement method (CCM), and numerical techniques. In the present study, rock loads acting on the final support system of Bazi-Deraz water conveyance tunnel at its different sections are estimated using aforementioned methods. Results show that, in a hydrostatic stress field, empirical and plastic zone-based numerical methods provide maximum and minimum rock load estimates, respectively, and numerical technique which is based on local safety factor obtains a more accurate rock load than the method based on plastic zone. Comparing empirical and analytical methods, rock load estimation using Goel-Jethwa's method obtains the closest values to analytical results in hydrostatic stress field. It is, however, observed that these methods cannot be used in non-hydrostatic stress fields. Therefore, it is proposed to utilize a coupled numerical-CCM method to estimate rock load when stress coefficient K is larger than 1.