Research On The Stability Of Surrounding Rock For NATM Tunnel With Different Construction Method

In recent years,with the development of economy,the transportation infrastructure has been accelerating gradually.Especially with the implementation of western development strategy and the construction of the high-speed railway, tunnel construction has been pushed to a new peak. The stability of surrounding rock is the basic condition for tunnel construction safe,and how to keep the stability of surrounding rock is one of the basic questions for tunnel engineering.Therefore scholars both at home and abroad have done a lot of research on the stability of surrounding rock with various research methods.This article set in Hulushan tunnel of the high-speed railway from Tianjin to Qinhuangdao, and it studied the influence on stability of surrounding rock from the construction technology of three-step method, two-step method, and full section method. The research contents and conclusions is:Firstly, the sections with larger deformation have been selected as the typical section, and the reason for larger deformation has been find out. The research conclusion is:The surrounding rock has experienced four stages. They are advanced displacement release stage, the sharp deformation stage, the slow deformation stage, and the stable stage. Among all stages,sharp deformation stage have the largest deformation, and it most probably be destroyed.Secondly,the general cross sections(all sections that have complete data)have been studied.The research includes statistical analysis of convergence of surrounding rock,arc crown and the duration of the sharp deformation stage.using the method of normal distribution fitting.The applicability of three-step method,two-step method and full section method has been demonstrated.And the article also concludes most sections will finish the sharp deformation and enter the slow deformation stage. So one month after the excavation will be the best time of construct secondary lining.Thirdly,the deformation law of surrounding rock of three-step method,two-step method and full section method have been studied by numerical simulation.The numerical simulation results were compared with the measured data,and the conclusion are:the deformation law of surrounding rock is mainly for the vault subsidence down, the bottom upward uplift,and the surrounding rock converge to the inside.The impact on the surrounding rock from tunnel excavation is mainly within4to5times of tunnel diameter.The maximum displacement occurs in the vault, arch shoulder and arch foot. Finally, the simulation results of three-step method were compared with the simulation results of two-step method with short steps and short footage,under the condition of V-level surrounding rock.The applicability of two-step method under the condition of V-level surrounding rock has been demonstrated.This provides useful basis for similar tunnel engineering.