Study On Construction Mechanical Effect Of Large Cross Section Highway Tunnel In Red Bed Geology Considering Variation Of Water Content

Relying on the Shanchongqing Tunnel Project of Yishi Expressway,this paper uses a method of combining numerical simulation and construction monitoring to study the construction mechanics effects of the red-bed geological large-section highway tunnel under the condition of changing water content and determines the red-bed the safe and feasible construction plan of the geological large-section tunnel guides the tunnel construction.The main work and research results of this paper are as follows:(1)Based on the test data of relevant literature,statistical analysis of the relationship between the water content of red sandstone and silty mudstone with immersion time and the changes of mechanical parameters such as internal friction angle,cohesion,elastic modulus with the change of water content Law.On this basis,with the water content as an intermediate variable,the relationship expression of the mechanical parameters of red sandstone and silty mudstone with the immersion time is obtained by statistics.(2)Using the method of numerical simulation,the construction mechanics effects of the Shanchongqing Tunnel’s Class IV and Class V surrounding rock sections with and without water content changes are studied.Numerical simulation results show that,compared with the working conditions that do not consider the change of water content,the increase of the water content of the surrounding rock increases the deformation of the surrounding rock and the internal force of the supporting structure,and the duration of the deformation of the surrounding rock is gradually extended,and the stability of the surrounding rock Deterioration,which fully demonstrates the necessity of considering changes in water content of surrounding rock.(3)According to the three-step method construction plan of the class IV surrounding rock section,four groups of different step lengths(4m,6m,8m,10m)were formulated to optimize the excavation parameters;for the class V surrounding rock CRD method construction plan,four groups of working conditions with different excavation steps(3m,4m,5m,6m)were formulated to optimize the excavation parameters.A comprehensive comparison is made from the deformation of surrounding rock,the stress and bending moment of the sprayed concrete structure,the axial force of the bolt and the range of the plastic zone and taking into account the construction efficiency and engineering cost,it is recommended that the step length of the three-step method for the class IV surrounding rock section is 8m,the excavation step distance of the CRD method for the class V surrounding rock section is taken as 5m.(4)Construction monitoring was carried out on the class IV and V surrounding rock sections of Shanchongqing Tunnel.Based on the monitoring data,the changes over time of vault settlement,horizontal convergence,and bolt axial force are analyzed;on this basis,the numerical simulation results and monitoring will consider the changes in the water content of the surrounding rock and the changes in the water content of the surrounding rock.The results are compared,and the results show that the numerical calculation results considering the change of the water content of the surrounding rock are more consistent with the monitoring results.