Study On Calculation Method Of Loose Zone And Excavation Spatial Effect Of Small Spacing Tunnels

In recent years,with the continuous impr ovement of China’s economic level,people’s requirements for road access have become higher and higher.In order to ensure the smoot h passage of highways,the expectation for the traffic volume of tunnel roads has gradually increased.In some central areas,ordinary two-way four-lane tunnels cannot meet current driving requirements.The most economical and direct way to pass capacity is to expand existing tunnels to form small spacing tunnelBased on the theory of Compl ex Analysis and Rock Mechanics,this paper uses the unified strength theory and the broken line met hod to solve the problem of small spacing tunnel based on Damushan and Jingxi tunnels.The plastic zone and loose circle radius of the small clear distance tunnel were determi ned,.the influence of the intermediate principal stress,internal friction angle,cohesion and releasing zone of surrounding rock on t he theoretical solution is analyzed.At the same time,in-depth excavation was conducted on the monitoring data of Damaoshan Tunnel,and the relationship between tunnel space constraints and excavation distances during the expansion of CD method was analyzed.Finally,the theoretical results are compared with the results of the loosening circle detection by the Geological radar in Jingxi tunnel and the three-di mensional numerical simulation results of Abaqus to verify its correctness and provide analytical calculation support for the construction of the small clear distance tunnel.The following main conclusions have been obtained:1.The radius of the li mit plastic zone without overlapping the plastic zone in the small spacing tunnel is defined as connected radius of the rock plastic zone.Taking into account the infl uence of intermediate principal stress,we use the unified strength theory and Schwar z alternating method to analysis the small spacing tunnels’ elastic-plastic state and deduces the analytical expression of small spacing tunnels’ plastic zone.Through the example,the influence of the inter mediate principal stress,internal friction angle and cohesion on the theoretical solution is analyzed.2.There are some problems in using the double-hole tunneling loose ring determined by the classical theory of plasticity mechanics,which affects the rationality of doubl e-hole tunnel support design.Using plastic mechanics to solve the new system and the Schwarz alternating method,the exact solution of the loose ring of surrounding rock of double-hole tunnel is deduced.The research on the loose ring,the internal friction angle and the quality of the surrounding rock in the isotropic homogeneous strata are carried out,and the theoretical results are compared with the results of t he geophone detection loose ring,the two are in good agreement.3.Based on the site monitoring and measured data from the enlarged excavation of Damaoshan Tunnel,the paper discussed the influence law of the spatial constraint and the heading distance in the heading face of the enlarged excavation tunnel.The obtained fitting curve was compared with the three type LDC curves and the neighboring pilot tunnel affected to the enlarged excavation of the tunnel was analyzed.4.In order to explore the variation characteristics of the loose ring of surrounding rock of water inrush and mud tunnel,taking the Jingxi tunnel in Sanming as the engineering background,ground penetrating radar was used for on-site measurement.The main sections of rock loosening in the four main lithologic sections of Jingxi tunnel were obtained,It is found that the loose ring of surrounding rock corresponding to the site of water-bursting mud disasters is larger and affected by surrounding bypass guides.The maxi mum fluctuating zone of surrounding rock is transferred from the right shoulder to the arch waist.5.Based on the ABAQUS three-dimensional numerical simulation software,this paper studied the tunneling process of small clear distance tunnels,analyzed the mechanical properties of the surrounding rock caused by the construction of in-situ tunnels,determined the size of theloose zone,analyzed the excavation steps on the vertical deformation curve of the surrounding rock,and the ground settlement.Impact.