Deformation Evolution And Parameter Inversion Study Of Weak Surrounding Rock Tunnel

With the continuous development of highway construction in China,the number of tunnel construction continues to increase,and more and more tunnels pass through the weak surrounding rock strata.The stability of weak surrounding rock is poor and deformation evolution during excavation is one of the most concerned problems in engineering.At the same time,it is an important basis for tunnel design and construction to accurately obtain the mechanical parameters of surrounding rock during excavation.Therefore,it is of great theoretical and engineering significance to carry out research on the deformation evolution and parameter inversion of soft and weak surrounding rock tunnels.The main work of this paper is as follows.Indoor similar model experiments were established based on actual engineering geological conditions.Using digital scatter correlation method and pressure capsules as the measurement means,the study on the influence of vertical load on the deformation evolution of soft surrounding rock was carried out.The displacement field,strain field and internal stress of the surrounding rock are analyzed,and the evolution process and law of displacement,strain and internal stress of the weak surrounding rock with the change of vertical load are obtained.It is found that: with the increase of vertical load,both horizontal and vertical displacements of the tunnel surrounding rock gradually increase,and the deformation rate of the surrounding rock is faster in the plastic phase compared with the elastic phase.The vertical strain field of surrounding rock presents overall compression,while the tensile zone of horizontal strain field mainly presents an X-shaped distribution centered on the cavern.From the cavern to the deep part of the surrounding rock,the effect of increasing vertical load on the tangential stress of the surrounding rock on both sides of the cavern level gradually decreases,and the effect on the radial stress gradually increases.From the loading surface to the top of the cavern,the influence of vertical load on the radial stress of surrounding rock decreases gradually.In order to keep abreast of the changes of material parameters such as surrounding rock strength,Poisson’s ratio,internal friction angle and cohesion during tunnel excavation,an inversion study of surrounding rock parameters was carried out based on the principle of displacement inverse analysis method.Firstly,a mechanical parameter inversion formula combining the digital speckle correlation method and the finite element method is constructed.Secondly,combining with the measurement data of the indoor similar model test,the mechanical parameters of the surrounding rock are inverse calculated through ABAQUS numerical simulation and MATLAB software programming.Finally,numerical simulations were performed using the inversion parameters,and the calculated results were compared and analyzed with the results of indoor similar model test.The feasibility of the inversion method and the accuracy of the inversion parameters are verified.The research results are useful for the design and construction of tunnels in weak surrounding rocks.