ENERGY CONSIDERATIONS OF STRAIN ROCKBURSTS IN JOINTED ROCK MASSES
As a typical phenomenon of deep excavations, strain rockbursts often occur in a sudden manner, violently releasing a large amount of accumulated elastic strain energy. The high stored strain energy in the rock mass cannot be dissipated entirely by shear sliding along joints, and part of the released strain energy may be converted into instantaneous kinetic energy that triggers strong shock which at times is coupled with block ejections. We study these complex interactions by investigating energy transfers and kinematics of ejected key blocks. We argue that in discontinuous rock masses removable key block ejection from the rock mass into the excavation space will precede fracture initiation in intact rock elements because of the much lower shear strength of discontinuities when compared to the shear strength of intact rock. We use linear elasticity to analyze the affected domain due to tunneling and the numerical discontinuous deformation analysis (DDA) method to study the energy of the ejected key blocks. Considering local energy concentrations, we delineate the rockbursting prone zone (RPZ), found to extend to an annulus of 0.5D thickness from the opening boundary. We combine theoretically obtained analytical expressions and modified version of DDA modelling to explore an in-depth understanding of the intrinsic physical mechanism which controls rock bursts by utilizing the energy budget. For a specific case associated with excavation at the design stage, the methodology proposed here can be capable of calculating quantitatively the mutual transformation of energy components, i.e., energy dissipation, kinetic energy of the entire block system and the strain energy. We find that with increasing initial stresses and decreasing frictional resistance of the preexisting discontinuities the sudden release of strain energy due to tunneling is increased, as well as the kinetic energy of ejected key blocks, resulting in stronger instantaneous shock thus increasing the risk of strain rockbursts. Finally, we use DDA to analyze how to mitigate strain rockbursts using top heading and bench excavation methodology based on data from the Jinping hydroelectric project to support our conclusions.
Strain rockbursts linear elasticity energy conversion key block theory DDA
Yossef H. Hatzor Xia-Ting Feng
Dept. of Geological and Environmental Sciences Ben-Gurion University of the Negev Beer Sheva, Israel State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil Mechani
国际会议
西安
英文
321-334
2016-05-25（万方平台首次上网日期，不代表论文的发表时间）