Stability study of an underground power cavern in sandstone

An underground power cavern with a span of 26.2 m is currently under construction in China. It is situated in flat dipping sedimentary rocks such as sandstone, siltstone, etc. The rock mass is of good or fair quality based on both the RMR system and the Q system. Numerical study with the Universal Distinct Element Code (UDEC) has been conducted to assess the stability of the power cavern. The study reveals: (i) The displacements at the crown are small, but those at the sidewalls are much larger; (ii) Larger loosening zones are identified at both the downstream and the upstream sidewalls, where both the maximum and the minimum principal stresses are small. Displacement measurements in several excavated underground caverns indicate that displacements at sidewalls are larger than those at crowns, which is consistent with the finding from this UDEC analysis.