Study on Reservoir and Water Inrush Characteristic in Nibashan Tunnel, Sichuan Province, China

The Nibashan tunnel is a major project mountain tunnel on Ya’an to Lugu lake expressway in Sichuan province. The tunnel relative elevation of about 2,100 m and the maximum depth of 1,701 m, belongs to the deep buried and extra-long tunnel. The tunnel’s strata are mainly igneous rock of Suxiong Formation, Lower Sinian. The rock type belongs to rhyolite (69 %), andesite (21 %) and a small amount of pyroclastic rocks, dykes and terrigenous clastic rocks. Based on the field investigation and drilling data of Nibashan tunnel, analysis of igneous rock reservoir space and performance factor by the lithology, lithofacies, fractures, structure and diagenesis of igneous rock. It considered that the igneous rock reservoir water storability was mainly affected by tectonism, and the reservoir site is located in the tectonic fracture zone. Finally, through the high pressure water pressure test and pumping test of drilling on Nibashan tunnel, obtaining the water reservoir and water inrush characteristic of igneous rock and geological flaws in tunnel, and providing a theoretical basis to construct safely and smoothly the tunnel.