Mechanism of evolution of stress-structure controlled collapse of surrounding rock in caverns: A case study from the Baihetan hydropower station in China

During the excavation of the underground powerhouse in the Baihetan hydropower station, which is currently still under construction, stress-structure controlled collapse has occurred frequently. In order to study the mechanism behind the evolution of this kind of collapse, an in situ experiment involving microseismic (MS) monitoring was carried out in the left main/auxiliary powerhouse. In this paper, the spatiotemporal characteristics of stress-structure controlled collapse are summarized and presented. A field survey, scanning electron microscopy and MS monitoring have been used to investigate a typical stress-structure controlled collapse that occurred during the monitoring period. These methods provided a consistent set of results, namely, that tensile fracturing is the rock-mass fracturing mechanism that is most active during the process of evolution of stress-structure controlled collapse. In addition, the evolution of the microseismicity during the development of the studied collapse was also obtained. The results provide a direct case history that will assist the prediction and support of stress-structure controlled collapse disasters and contribute to excavation of deeply-buried caverns in the field. (C) 2015 Elsevier Ltd. All rights reserved.