Inversion Of The Mechanical Parameters Of The Surrounding Rock And Stability Analysis Of The Shallow-buried And Biased Pressure Section Of The Dalu No.2 Tunnel

In order to promote economic development,China has invested in the construction of a large number of highways,and the number of road tunnels has increased dramatically.A large number of highway tunnels are subject to topographical conditions and line selection conditions,the cavity exists shallow buried bias situation,shallow buried bias tunnel surrounding rock and lining structure stress complex,to the construction process brings serious impact,a slight inadvertence will lead to collapse accidents,resulting in casualties and serious economic losses,so carry out shallow buried bias tunnel construction process stability analysis,engineering construction guidance,has important practical Engineering significance.This paper relies on the Benji Expressway No.2 tunnel project,using the obtained deformation monitoring data,on the basis of the analysis of the sensitivity of different surrounding rock mechanical parameters to tunnel deformation,using a comprehensive algorithm model combining particle swarm algorithm,simulated annealing algorithm and BP neural network algorithm,inversion of the surrounding rock mechanical parameters,and using the mechanical parameters obtained from the inversion to analyze the surrounding rock deformation and support force situation during the construction of this tunnel,to make an accurate evaluation of its stability,through the study of the following conclusions:(1)The analysis of the monitoring results of the shallowly buried deflected section of Tunnel No.2 shows that: the overall change trend of surface settlement deformation,horizontal convergence deformation and vault settlement deformation is the same,the initial deformation is faster,the maximum deformation rate reaches 1.6mm/d,the later slowly increases,and finally stabilises,influenced by the topographic deflection,the settlement on the left side of the vault is slightly larger than the settlement on the right side of the vault,due to the supporting effect of the palm face,the deformation of the monitoring section near the palm face The deformation of the monitoring section near the palm face is smaller than that of the monitoring section far from the palm face.(2)The results of the analysis of the degree of sensitivity of the ground mechanics parameters affecting the tunnel deformation show that the modulus of elasticity and Poisson’s ratio of the strongly weathered granite have a significant effect on all indicators of tunnel envelope deformation with a confidence level greater than 99%,and the cohesion of the strongly weathered granite has a significant effect on horizontal convergence with a confidence level greater than 99%.(3)A comprehensive algorithm based on the traditional neural network algorithm(BP)introducing particle swarm algorithm(PSO)and simulated annealing algorithm(SA)was used to invert the mechanical parameters of the highly sensitive surrounding rock,which was verified to reflect the mapping relationship between mechanical parameters and deformation relatively well.99.5k Pa.(4)The stress analysis of the shallow burial bias section of Tunnel 2 shows that the plastic zone of the surrounding rock reaches 6m during the upper-step excavation stage,with a maximum initial lining moment of 21 k N·m,a maximum anchor rod tension of 50 k N,and a maximum bending moment of 110N·m for the small advance guide pipe.During the lower-step excavation stage,the plastic zone of the surrounding rock extends to a depth of 10 m,with a maximum initial lining moment of 26 k N·m,a maximum anchor rod tension of 77 k N,and a maximum bending moment of 70N·m for the small advance guide pipe.The plastic zone during the arch excavation stage finally develops to a depth of 15 m,with a maximum initial lining moment of 31 k N·m,a maximum anchor rod tension of 79 k N,and a maximum bending moment of 40 N.m for the small guide pipe.The stepped construction method is used for the shallow burial bias section of Tunnel2 to maintain stability,but the arch foot and shoulder are weak points of the surrounding rock and initial lining that require special attention during actual construction.