Study On Deformation Characteristics And Control Technique Of Large Deformation In Extremely High Geostress And Soft Rock Tunnel

With the increasing number of tunnels, the large deformation such as lining’s large deformation or cracking when tunnel crosses soft surrounding rock has became an acute problem. This paper,based on the Guanyazi tunnel, by using field investigation, laboratory testing, theoetical analyses, site monitoring and numercial simulation method, studied the large deformation mechanism of sericite phyllites under high stress and identified the best construction method. The main conclusions are as follows:1. Analysed mineral composition of Guanyazi tunnel surrounding rock and determined the mechanical parameters of the phyllite by mechanical properties test, and judged this tunnel was under extreme-high stress.2.Combined with the site monitoring data, this paper analysed the rule of the tunnel segments with large deformation, this tunnel has obvious radial and asymmetry deformation, slow convergence, fast speed deformation and wide range of deformation. Though geological structure and lithology, in-situ stress of surrounding rocks, underground water and construction method, this paper discussed the mechanism of the tunnel deformation.3.By using numerical simulation methods, this paper determined the ADECO-RS is the best method of this tunnel by comparing the three-bench seven-step excavation method, performed core-soil sidesteps, CRD, double side drift method and ADECO-RS method, and then optimized ADECO-RS method from the deformation control, supporting structure and safety factor, that the length of the reinforced area is 15 m and the excavation footage is 1 m is the best excavation method when using the ADECO-RS and excavated on different steps.