Analysis of block deformation characteristics and its stability under high in-situ stress

摘要

Laxiwa powerhouse is a lager cavern located in high in-situ stress region with stresses ranging from 10MPa to 30MPa. Faults f10, f12 and f24 are revealed in region A of cavern upstream wall. By lower hemisphere joint plane projection, Faults f10, f12 and f24 can form key blocks with excavation face. The block volume is 2103m3, area of excavation face is 468m2. During cavern excavation, block deformation keeps increasing slowly under action of excavation. The maximum rate of rock deformation reaches 1.22mm/d in a monitoring cycle (7 days). By analysis with theory of block movement, the sliding type is two-face slide (they are f10 and f12). Under cohesion force C=0.0 and friction angle φ =21.8 °, the factor of safety is 1.30;based on block deformation monitoring andstability analysis, only conventional support to block is necessary. After monitoring for 598 days, the block deformation attains 38.9mm. The present average rate of rock deformation is 0.0018mm/d, and it is convergent s, which shows the block is stable. From this example, if the factor of safety for the block is satisfied, and block deformation does not influence other structure, block deformation during excavation may be allowable, and no special reinforcement measures are necessary for blocks.