Stepwise excavation process of underground caverns of hydropower station using DDA

A process of continuum excavation has been simulated using discontinuous deformation analysis(DDA) which is introduced element birth and death method.Comparing the calculated result with finite element method,we prove that DDA method is effective in cavern's simulation.Based on the geological exploration data of Dagangshan hydropower station,DDA models of the underground cavern group with different combinations of joints are established.We analyze the failure modes of underground cavern group's excavation,and explain the failure mechanism briefly.Based on Monte Carlo method and excavation design of Dagangshan hydropower station,random distribution of joints is simulated;and developments of displacement and stress are researched in the sub-step excavation process.Studies show that: displacements of all the blocks around the cavern are pointing to the cavern when excavation is completed;deformations of tailrace surge chamber and underground main powerhouse's sidewall are relatively large;major principal stresses of the blocks around the cavern are parallel to the caverns' boundary line;stress of the tailrace surge chamber relieves obviously;and blocks of sidewalls have slid;the three caverns interact on each other in the excavation process;the effects of tailrace surge chamber and underground main powerhouse on the main-transformed cavern are more obvious.The study shows specific parts which are need to be reinforced in the excavation process;and it provides a basis for optimal support measure of the project.