Comparison Between Field Measured Indices of Different Stress Release Plans for High Geo-stress Soft Rock Tunnels

Abstract

Taking Maoyu Mountain Tunnel on the Lanzhou-Chongqing Railway as the object, this paper measures the surrounding rock pressure, initial support stress and other parameters in the tunnel of the pilot heading and space reservation, two popular methods for the stress release of high geo-stress soft rock tunnels. Then, the measured parameters of the two methods were compared and analyzed, aiming to select the stress release method suitable for the target tunnel. The comparative analysis shows that the maximum stress on the steel frame in initial support of pilot heading is 3.4 times that on the steel frame in initial support of space reservation, reaching the level of 340MPa. To release the stress of the said tunnel, it is recommended to reserve a large space (50cm) and add a flexible support net to deform with the surrounding rock. The flexible support net can withstand large deformation stress, thus reducing the stress on the initial support and that on the secondary lining. The research results show that the space reservation is an easy, efficient and economical way to release geo-stress before excavation.