Soft Ground Step Seven-step Construction Of Tunnel Surrounding Rock Stability And Deformation Characteristics Of Excavation

With the development of roads, railways and municipal tunnel, increasing number of large section tunnels are being invested, and the excavation methods became more and more varied and mature.The entrance area of Yunyang Mountain Tunnel on Hengyang-Yanling Highway was widely distributed with mild clay, and it has poor rock stability and almost with no self-stabilizing capacity. Considering various factors, the seven-step excavation method was choosed and used.Although the application of this method was widely used in our country, but only few field tests were conducted.So the force and deformation characteristics of surroundingrock and supporting structure during the tunnel construction process, especially the stage of each excavation division need to be further studied.In this paper, the implementation effects of the seven-step excavation method was analyzed based on the perspective of mechanical mechanism and field tests, then numerical analysis tools was used to analyze the stability and deformation characteristics when tunneling in soft ground by the seven-step excavation method, the main contents are:(1)By collecting large number of domestic and foreign literature, the results of previous studies was fully understood and summarized, tunnel excavation methods for large section was mastered,and its advantages and disadvantages,applicability were studied;Methods for studying the rock stability and their characteristics and status were summarized.(2) The seven-step excavation method was analyzed from the perspective of the mechanical mechanism, and the applying effects of this method in mild clay&soft ground of Yunyang Mountain Tunnel was verified by field measurement.(3) FLAC3D software was used to simulate and analyze the seven-step method used in the Yunyang Mountain Tunnel,concrete analysis was carried out for the deformation of surrounding rock, internal forces of supporting structure and the plastic zone when tunneling in soft ground, also the stability of the tunnel was evaluated.(4) The role of the core soil,the effects of the core soil size for controlling ground and vaultings settlement, the changes of parameters for different construction measures were studied using numerical simulation method.Also, parameter optimization was carried out for the seven-step excavation method, and with the practice of the construction, parameter values were proposed for the excavation method.