Seismic Stability Analysis Of Jointed Rock Surrounding Underground Caverns In Hydropower Projects

In recent years, many large underground hydroelectric caverns have been started constructing or designing in Southwest and Northwest China. The weakness plane in the surrounding rock has a relatively weak mechanical strength, which leads to the discontinuity, heterogeneity and anisotropy of the mechanical properties of rock mass, and plays a significant controlling role in the stability of the caverns. In addition, China is one of the most damaged countries where earthquake takes place, locating in the joint zone of earthquake cinctures that are the Pacific Ocean and the South Mediterranean in the world. Therefore, it is great important to conduct research on the dynamic responses and the engineering safety about jointed rock.Based on the entire simulation process of underground caverns'comprehensive responses under static and dynamic loads, this paper mainly focused on the influence of material parameters of the joint, and the fracture and degradation characteristics of the intermittent joint under dynamic earthquake action. Finally, an assessment about the seismic stability of the underground caverns of Xiluodu hydropower project in rock layers was carried out. Using Strength Reduction Method the safety factor was obtained. Main contents of this paper are shown as follows:(1) Described the geometrical and mechanical characteristics of general joints, especially on the fracture properties of intermittent joints.(2) Based on the mechanical properties of joint, the method for selecting normal and tangential stiffness of interface was improved in the finite difference method software FLAC3D. The parameters sensitivities of joints were first defined, and then the joint parameters that have more great influence on seismic responses of rock surrounding caverns were discussed, which can be a reference to parameter selection for dynamic stability analysis of underground caverns with jointed rock.(3) Using the fracture mechanics, the fracture and degradation properties about intermittent joints were discussed based on the modified Jennings strength criteria. Then the modified strength criteria was coded using the built-in language FISH provided by the discrete element Software UDEC and applied to a real project to verified the necessity of correctly selecting strength criteria for joints. (4) Taking the underground caverns in rock layers in the left bank of Xiluodu hydropower project as an example, the seismic stability analysis was performed, and the safety factor was calculated using Strength Reduction Method, which is a reference to other similar projects in the research of seismic stability analysis.