| Xiaolangdi water diversion tunnel is an essential component of the water diversion project in the north bank of Xiaolangdi irrigation region.The geological conditions of the tunnel envelope are complex,and the tunnel side walls are deformed and the steel arches are fractured during the excavation process,which poses a hidden risk to the safety of the project.This paper relies on Xiaolangdi diversion tunnel project,and analyzes the deformation features and deformation mechanism of the tunnel in depth.Based on the on-site large deformation monitoring data,FLAC3 D finite difference software is used to establish a 3D numerical model of the dynamic excavation of the tunnel and to invert the physical and mechanical parameters of the tunnel surrounding rock.Combined with the engineering construction principle of "weak excavation,strong support",we propose support control measures such as improving arch type,shortening steel arch spacing,non-isotropic anchor placement,and pre-reinforcement of small conduits in advance,to study the deformation control effect and support force characteristics of the surrounding rock.The main research contents and results of this paper are as follows.(1)Analyze the engineering geology,hydrological conditions and construction process of the diversion tunnel,and analyze the deformation and damage mechanism of the tunnel surrounding rock based on the deformation characteristics of the tunnel surrounding rock.The lithology of the surrounding rock in the large deformation cavern section is poor,easily softened by water,easily disintegrated by disturbance,and with fracture water seepage.Research shows that excavation disturbance,rock deterioration and fracture water during construction are the main influencing factors leading to large deformation of tunnel surrounding rock.(2)Combined with the deformation data of the monitored sections during excavation,FLAC3 D is used to establish a 3D numerical model of the tunnel dynamic excavation and to perform parameter inversion of the tunnel surrounding rock parameters to obtain the surrounding rock parameters in line with the actual site engineering.(3)Based on the established 3D numerical model,analyze the type of steel arch,shorten the spacing of steel arch and other measures,and study the deformation control effect of surrounding rock and the force characteristics of steel arch;analyze the force characteristics of anchor rods,lay anchor rods with non-equal parameters,and study the deformation control effect of anchor rods with non-equal parameters;take pre-reinforcement measures of overrunning small conduit grouting,and study its suppression of extrusion deformation of palm face and horizontal convergence of side wall.control effect.The results show that improving the steel frame type can effectively control the large deformation of the tunnel side wall,and the axial stress of the steel arch pillar is reduced.The effect of shortening the spacing between steel arches on the control of deformation of the surrounding rock is limited.The horizontal convergence of the tunnel side wall can be suppressed by the non-isoparametric deployment of anchor rods;the extrusion deformation of the palm face can be suppressed and the horizontal convergence displacement of the side wall can be reduced by the pre-reinforcement of small conduits in advance,and the stability of the palm face can be improved and the risk of collapse of the palm face can be reduced by the pre-reinforcement of small conduits in advance.(4)Based on the research results,three support schemes are preset.In comparative analysis,the support scheme of 18 models of steel frame,steel frame spacing of 1m,non-equal parameter layout of bolts,and pre-reinforcement of advanced small conduits was taken as the final support scheme. |
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