Deformation mechanisms of sidewall in layered rock strata dipping steeply against the inner space of large underground powerhouse cavern

Abstract

In low to moderate stress regions, deformations of the high sidewall dominated by bedding planes dipping against the cavern space, often pose an unpredictable threat to local stability of underground powerhouse. In this study, detailed field surveys, in-situ tests, beam theory, and the discrete element method (DEM) are used to critically investigate the deformation mechanisms of high sidewall in layered rock strata steeply inclined against the inner space of the underground powerhouse cavern. First, an approach integrating in-situ surveys, deformation monitoring and acoustic wave tests, is adopted to analyse the evolutionary features of displacements of a high sidewall in layered strata steeply dipping against cavern space. Differences of deformation behaviours and their relationships with excavating activities in low to moderate and high geo-stress regions, were distinguished. Second, two zones with different deformation mechanisms in layered strata involved are presented, which could be evidenced by the presence of various displacement modes near the top area of a high sidewall. Then, based on the conceptual beam models, mechanisms of displacements controlled by bedding planes in two zones are investigated. Synergistic effects arising from two zones promoting the overall deformation profile are presented. Third, combining with DEM simulations, the mechanical influences of bedding thickness on the excessive deformation modes near the top of sidewall, are revealed. Displacements of a sidewall partly affected by an intersecting chamber are described in detail. Finally, suggestions for applicable supports of the high sidewall with bedding planes dipping steeply toward the internal area of surrounding rocks during cavern excavation are presented. The aforementioned investigations can provide valuable guidelines for the construction of similar underground powerhouse caverns.