Pressure Calculation And Stability Analysis Of Shallow Buried Bias Tunnel Surrounding Rock Under Variable Slope Conditions

Tunneling is an essential part of transportation construction in mountainous and hill y areas.Irre gular topograph y is a common situation in tunnel construction,and shallow buried bias tunnels with variable slope conditions are a special case of bias tunnels.Due to the existence of variable slope conditions in biased tunnels,the irregularit y of the original topographic features of biased tunnels is enhanced,thus changing the distribution characteristics of the pressure in the surrounding rock of biased tunnels.The traditional method of calculating the pressure in the surrounding rock of shallow buried biased tunnels will not be sufficient to support the calculation of the pressure in the surrounding rock of shallow buried biased tunnels under variable slope conditions,and the stabilit y of the surrounding rock of tunnels is also changed accordingl y.Therefore,this paper will explore the shallow buried biased tunnel envelope pressure calculation,envelope pressure influence factor analysis and envelope rock stabilit y analysis under variable slope conditions through theoretical derivation,theoretical analysis,numerical simulation and practical monitoring methods.The main research contents and results are as follows:（1）To summarize the tunnel damage model obtained from previous studies and the existing equations for calculating the envelope pressure in shallow buried biased tunnels.Based on the original shallow buried biased tunnel envelope pressure calculation method,a shallow buried biased tunnel damage model under variable slope conditions is constructed,and the limit equilibrium principle is applied to derive the shallow buried biased tunnel envelope pressure calculation formula under variable slope conditions.The intermediate variableβ’is introduced as the basis for selecting the pressure calculation method of biased tunnel envelope under variable slope conditions,and the normative formula and the existing formulae in literature are compared with the formulae in this paper to verif y the reasonableness and applicabilit y of the formulae in this paper.（2）The formula for calculating the surrounding rock pressure of shallow buried biased tunnel under var ying slope conditions is derived,and the influence law of physical and mechanical parameters of friction Angleφand cohesion force c,as well as natural slope Angleα₁and variable slope Angleα₂ on the tunnel surrounding rock pressure is anal yz ed.The results show that when the friction Angleφ=25°and the cohesion force c=0.4MPa,the horiz ontal pressure coefficientλ₂ and the sliding resistance T₂ are the maximum.The natural slope Angleα₁is positivel y proportional to the horiz ontal pressure coefficientλ₁ and sliding resistance T₁,and inversely proportional to the horiz ontal pressure coefficientλ₂and sliding resistance T₂.The slope Angleα₂ is inversel y proportional to the lateral pressure coefficientλ₂ and the sliding resistance T₂.（3）Combined with the actual tunnel project,the excavation of shallow buried bias tunnel under different envelope rock levels,different natural slope angles and different variable slope angles were numerically simulated,and the tunnel monitoring and measurement data were collected to anal yz e the stress and displacement stability of the ex cavated tunnel envelope rock.The anal ysis shows that the vertical displacement of the deep buried side of the vault is large due to the topographic bias,and the lateral displacement of the side of the variable slope section is large due to the variable slope conditions.The actual monitoring and measurement work of the tunnel should pay more attention to the settlement of the arch on the deepl y buried side of the tunnel,the change of displacement convergence changes around the arch waist on the variable slope side,and make timel y preventive reinforcement measures.