Study On Stress Calculation And Construction Mechanics Of Surrounding Rock Of Large Section And Shallow Buried Tunnel With Complex Bias And Small Clear Distance

At present,the construction of urban transportation infrastructure in southwest China has entered a vigorous development stage.In order to ensure the effective use of urban space,various types of small clearance tunnels have been designed and constructed.In order to supplement the theoretical research of special biased small clearance tunnels,Based on the special bias mode of shallow-buried complex biased small-clearance tunnels with large cross-sections,this paper relies on the actual tunnel engineering to comprehensively apply research methods such as theoretical analysis,field monitoring,and numerical simulation to small-buried complex biased small-clearances with large cross-section.The research on the calculation method of the surrounding rock pressure of the tunnel,the optimization of the net distance,the space-time effect of construction mechanics and the optimization of the construction scheme are carried out.The main contents are as follows:(1)Based on the existing theory of tunnel surrounding rock pressure calculation,considering the structural stress characteristics of a large cross-section shallow-buried complex biased small-clearance tunnel,the surrounding rock stress of a large cross-section shallow-buried complex biased small-clearance tunnel is analyzed.The force model is used to derive the formula for calculating the surrounding rock pressure of a large-section shallow-buried tunnel with complex bias and small clearances.Combining numerical simulation and comparing the simulated value with the theoretical calculation value,the reliability of the theoretical calculation formula is verified.(2)With the help of numerical simulation method,two-dimensional numerical models are established for different working conditions of tunnel,such as different clear distance,surrounding rock level,minimum buried depth of overburden soil and surface slope,and the evolution law of surrounding rock pressure and the stress state of support structure of large section shallow buried tunnel with complex bias and small clear distance are deeply analyzed in combination with theoretical calculation method;under the reasonable clear distance standard specified in the design code of highway tunnel The paper analyzes the construction mechanical effect of tunnels with different clear distance under different surrounding rock levels,compares various mechanical indexes,and optimizes the double line reasonable clear distance of tunnels with large section and shallow buried,complex bias and small clear distance under different surrounding rock levels.(3)Combined with the actual engineering of the tunnel,analyze the changes in the field monitoring of the tunnel's displacement and deformation(arch settlement settlement,horizontal convergence displacement),and use elastoplastic theory and finite element software to establish a three-dimensional finite element numerical model based on the actual excavation scheme and analyze the tunnel opening Spatial-temporal mechanical effects of excavation construction.Comparing simulated and measured data to verify the feasibility of the model,and studying the mechanical effects of excavation construction of large-section shallow-buried tunnels with complex bias and small clearances.(4)Combined with the three-dimensional numerical model of a large cross-section shallow-buried complex biased small-clearance tunnel,the simulation of the excavation sequence of the tunnel's leading and trailing tunnels,and the two-line construction conditions of the leading and trailing tunnels,this research was conducted Spatial-temporal mechanical effects of tunnels under different construction excavation orders.The fuzzy gray theory is used to establish the correlation matrix and expand the program optimization analysis to obtain the optimal construction plan for large-section,complex bias,and small-clearance tunnels.Tunnel engineering provides valuable lessons.