Numerical analysis of the rock mass conditions for rock burst occurrences in deep underground caverns

Abstract

Structural properties of rock masses are the material basis and main factors for rock burst occurrences. In deep tunnels, most rock bursts occur in hard surrounding rock characterized by elasto-friability. Sound conditions for rock masses, such as high strength, fewer original joint fissures and good integrality, are conducive to e-lastic strain energy accumulation in rock masses. In order to quantitatively analyze the influence of rock mass conditions on the possibility of rock bursts in surrounding rocks, and using the deep tunnel of the Jinping II hy-dropower station as an example, the uniaxial compressive strength of a rock mass is selected to represent the strength of the surrounding rock and the geological strength index (GST) is selected to represent the integrality of the surrounding rock mass. With an unchanged surrounding rock geo-stress, different uniaxial compressive strengths and various geological strength indexes, the stress behaviors and ultimate stress state at the stress concentration zones during tunnel construction are calculated by a numerical simulation. The numerical calculation results indicate that intense rock bursts mostly occur in surrounding rock masses of Class II characterized by high strength (uniaxial compressive strength>120 MPa) and good integrality (geological strength index>55). ©, 2015, Editorial Office of Modern Tunnelling Technology. All right reserved.