Experimental And Numerical Study On The Combined Pressure Arch Of Surrounding Rock In The Near Circular Twin Tunnels

In the process of tunnel excavation,the surrounding rock is disturbed and the stress redistribution occurs.Pressure arch will be formed above the tunnel,which is the embodiment of the self-stability of the surrounding rock.While the construction of two adjacent tunnels,because of the mutual influence of construction,the pressure arch form generated above it is more complex.Especially when the distance between two tunnels is small,the joint pressure arch will be formed above the tunnel after excavation.Based on laboratory model test and numerical calculation,the formation principle and shape of the joint pressure arch in the surrounding rock of the adjacent double-hole tunnel are studied,as well as its variation law under the influence of tunnel burial depth,tunnel spacing and surrounding rock conditions.In addition,based on the changing law of the joint pressure arch shape with various influencing factors,a method for defining the depth and depth of the adjacent double-hole tunnel is proposed.The main research contents are as follows:(1)based on the existing research results of pressure arch,a specific definition method for the shape of pressure arch generated after the excavation of single-hole tunnel was proposed.In addition,the specific functional expressions of each boundary of pressure arch were obtained through numerical calculation and function curve fitting.(2)on the basis of the research on the pressure arch of surrounding rock of single-hole tunnel,the specific form of the joint pressure arch of surrounding rock of adjacent double-hole tunnel was obtained through stress analysis,and three specific indexes were proposed to characterize the change of the pressure arch form.(3)a homemade indoor model box was used to simulate the excavation of a nearby double-hole circular tunnel and observe the shape of its collapse arch.By changing the relevant experimental parameters,the influence law and degree of the internal boundary shape of the joint pressure arch of the adjacent double-hole tunnel with the buried depth and spacing of the tunnel are obtained.(4)the two-dimensional numerical model of the adjacent double-hole tunnel was established,and through stress analysis,the change rules of the forming conditions and morphology of the joint pressure arch of the adjacent double-hole tunnel with tunnel spacing,surrounding rock conditions and tunnel burial depth were obtained.(5)based on the analysis of the variation law of the adjacent dual-hole tunnel surrounding rock joint pressure arch with various influencing factors,the critical burial depth and critical spacing of the adjacent double-hole tunnel surrounding rock joint pressure arch were proposed,and the critical burial depth was further used to define the depth and shallow burial of the adjacent double-hole tunnel under different surrounding rock conditions and different spacing.