Rockburst evaluation in complex geological environment in deep hydropower tunnels

Rockburst is the most dangerous phenomenon in deep underground excavation. It is inevitable when stresses are very high in hard rock mass. During deep hydropower tunnel excavation large faults are usually avoided in design but small scale joints, shear zones and structural planes are common which are very difficult to avoid. These structures sometimes become barriers to accumulate tangential stresses in underground which result in abnormal stress concentration which finally released in the form of huge rockburst energy. Additionally, the presence of geological structures like anticline and syncline can worsen the situation because the stresses are usually concentrated in synclines. Rockburst under these different conditions are really studied. In this paper two extreme rockburst events in recently completed Neelum-Jhelum and Jinping II hydropower projects, are discussed. The FLAC3D numerical simulation results show that stresses are concentrated near structure planes which result in displacement and itense rock-burst.