Mitigating geotechnical challenges to improve safety during the excavation of ultra-deep shaft stations

Abstract

This thesis presents the geotechnical challenges encountered during the excavation of two shaft stations at depths of 2490 m and 2550 m in highly stressed grounds. It also outlines the engineering solutions implemented to effectively reduce exposure and mitigate risk, ultimately enhancing safety. Despite proactive measures, the 2490-level shaft station experienced adverse stress conditions, leading to significant issues. These included damage to the shaft’s concrete liner, elevated seismic activity, and significant floor overbreak. Drawing on detailed observations and data gathered during the 2490-level shaft station excavation, the 2550 station excavation methodology was modified. Key modifications include reinforcing the shaft liner, reducing the scale of initial blasting, and pre-sinking and supporting below the station floor. These changes resulted in a 50% reduction in seismicity, an intact shaft liner, and no floor overbreak. Findings from this work provide valuable insights into geotechnical challenges of shaft station construction and effective excavation strategies at extreme depths.