Deformation characteristics of sidewall and anchorage mechanisms of prestressed cables in layered rock strata dipping steeply into the inner space of underground powerhouse cavern

Abstract

Local stability of underground powerhouse cavern subject to low to moderate geo-stresses, is frequently threatened by the unpredictable displacements of high sidewall in layered rock masses dipping into cavern space. Further understanding these displacements and the anchoring behaviours helps provide effective measures for ensuring the safe, rapid construction of major projects. This study investigates the deformation features of sidewall and anchoring mechanisms of long prestressed cables in layered strata steeply inclined toward the inner space of underground powerhouse, using field tests and numerical tools. First, the development characteristics of sidewall in layered strata steeply dipping into cavern space are analysed based on the deformation monitoring data. Time-dependent relationships between those displacements and depths from the excavation surface distinguished from that in other typical underground caverns in layered rock masses, are critically discussed. Second, damage characteristics of these strata caused by excavating activities are presented based on the microseismic (MS) monitoring data. Effects of damage zone on the evolution of deep deformations distinctively involved, are described in detail. Then, the calculation platform coupling MS data and continuum modelling, suitable for simulating progressive damage of layered rock masses, is introduced to reveal new insights into the mechanisms behind those distinctive deformations. Finally, the modified models properly capturing the mechanical responses of prestressed anchor cables, are integrated into such a calculation platform. Anchoring mechanisms of long prestressed cables associated with those deformations of layered strata dipping into the cavern are thus further investigated. This can explain why the prestressed anchor cables provide less effective control effects on deep deformations mainly induced by shear dislocations on bedding planes.