Study On Stability Of Large Section Tunnel Face

In the process of tunnel construction,the deformation of a large section tunnel face not only controls the stability of the tunnel face,and also directly influences the convergence of its surrounding rock.In this paper,the stability of tunnel face of a large section tunnel has been studied based on the Wu Fengshan Tunnel in Enshi city of Hubei Province.The main research work and achievements include:1)Based on the theory of elastic-plastic,the response of surrounding rock in excavation of large section tunnel is analyzed.Some theory on the radial stability of the tunnel is extended to the study on the longitudinal stability of a tunnel,then explore the forms of deformation,failure mechanism and stability control theory of the large section tunnel face.2)This paper establishes numerical model of Wu Fengshan Tunnel,Wan Xinglu tunnel and Han Jialing tunnel by using FLAC3 D.The Origin software was adopted for nonlinear data fitting to the maximums of extrusion displacement of large cross section tunnels face in different surrounding rock grade,different buried depth,different span and different water level,finding out some change rules of the maximums of extrusion displacement of large cross section tunnels face.3)The deformation of the large section tunnel face mainly includes three kinds of: first is that the maximum deformation position centralizes at the upper 0.69 H of tunnel face,second is at the center 0.55 H of tunnel face,third is at the lower 0.35 H of tunnel face.This paper verifies that the pre convergence of core soil in front of tunnel face can effect the stability of tunnel by numerical simulation.4)The deformation of tunnel face in Grade I and Grade II rock mass is small,where no plastic zone or only local plastic zone.The plastic zone in Grade III and Grade IV rock mass centralizes is about 1/2D(D tunnel span)in the front of the core soil.The groundwater can expand the plastic zone in Grade IV rock mass to 1/2D~1D.The plastic zone in Grade V and Grade VI rock mass centralizes is about 1/2D~1D in the front of the core soil.5)The paper classifies the steady state of large cross-section tunnels face into stable,less stable,understable and unstable four levels by combining with the calculation results and engineering practice to provide the basis for stability classification of the large section tunnel face.