Research on Deformation and Loose Zone Characteristics of Large Cross Section Tunnel in High Geo-Stress Soft Rock

In constructing high-geo-stress soft rock tunnels, the major deformation disaster of the surrounding rock has always been the main problem faced during construction. The research on the deformation and loose zone characteristics of large deformation tunnels has positive significance for the safe and rapid construction of tunnels. Therefore, based on the Yuntunpu large deformation tunnel, this article first analyzes the geological and deformation characteristics of the tunnel site area in response to the problem of high-geo-stress soft rock large deformation. Subsequently, on-site testing and analysis were conducted on the loose zone characteristics of four tunnel sections. Finally, based on the comprehensive analysis of tunnel deformation and loose zone characteristics, the causes of large deformation in the tunnel are analyzed. The results indicate that the large deformation characteristics of the Yuntunpu Tunnel are mainly manifested as a large initial deformation rate of the surrounding rock, a short self-stabilization time of the surrounding rock, a large cumulative deformation amount, and a long deformation duration. The Yuntunpu Tunnel is influenced by the grade and structure of the surrounding rock, with a loosening zone ranging from 12 to 14 m, and the wave velocity variation characteristics exhibited by different grades of surrounding rock vary greatly. Adopting collaborative active control of long and short anchor rods is recommended to limit the continued development of loose zones and the deformation of surrounding rocks. The large deformation of tunnels is mainly affected by high geo-stress, formation lithology, geological structure, engineering disturbance, and groundwater. Among them, high geo-stress and formation lithology are the decisive and important factors for the occurrence of major deformation disasters in the tunnel.