Analysis of Surrounding Rock Stability and Seismic Response in an Extra-Large Surge Chamber Crossing a Fault Zone

Wei Zhou¹Wu Chen²Yanan Lv²Yongxiao Qu³Bo Li³Qingrong Xiong^3*LiGe Wang^4*

• ¹CHN Energy Zhongyu Branch of Xizang Power Co., Ltd., Lhasa, China
• ²Changjiang Institute of Survey Planning Design and Research Co Ltd, Wuhan, China
• ³Shandong University, Jinan, China
• ⁴State Key Laboratory of Intelligent Manufacturing of Advanced Construction, Jinan, China

This study presents a comprehensive investigation of the static-dynamic stability of an extra-large surge chamber intersecting an active fault zone—a critical engineering challenge in modern hydropower infrastructure. Through three-dimensional numerical modeling (FLAC3D), we systematically quantified excavation-induced instability mechanisms and evaluated a deep-surface synergistic support system. Unsupported excavation simulations revealed severe instability with radial displacements up to 0.475 m, a 20 m plastic zone, and tangential stress loss of 65–75%. The deep-surface synergistic support system—comprising prestressed anchor cables, systematic bolts, and shotcrete—reduced displacement by 94.5%, confined the plastic zone to ≤5 m, and restored tangential stresses to 70–85% of in-situ values. Under the design earthquake (0.175 g horizontal, 0.1167 g vertical), displacement and stress increments remained <10% and <5% of static values, respectively. Plastic zone growth was limited to 3.8%, with all support elements operating within safe limits. This research validates a methodology for designing resilient underground infrastructure in fault-affected environments, providing critical insights for underground chamber design in complex geological settings previously considered unsuitable for large-scale development, with direct applications to hydropower engineering in tectonically active regions.