Study On Collapse Arch Of Surrounding Rock During Tunnel Excavation Based On Particle Flow Analysis

In recent years,with the rapid development of subway construction and transportation in China,the construction conditions of underground projects have become increasingly stringent,and tunnel collapse and other accidents are inevitable in the construction process.Therefore,it is particularly important to study the deformation process and instability mechanism of surrounding rock during tunnel construction.This paper focuses on the surrounding rock collapse arch after tunnel excavation.Firstly,the particle flow numerical simulation method is used to study the progressive failure mechanism and evolution law of surrounding rock after single-line and double-line tunnel excavation.Then,the theoretical calculation formula of surrounding rock pressure of deep-buried tunnel is derived by theoretical analysis.The main research results obtained in this paper are as follows:(1)The particle flow discrete element software is used to establish a two-dimensional biaxial test numerical model.The influence of five mesoscopic parameters in the parallel bond model:particle contact modulus,parallel bond modulus,parallel bond stiffness ratio,friction coefficient and parallel bond tangential strength ratio on macroscopic parameters is calculated respectively.The corresponding relationship between macroscopic and mesoscopic parameters is established,which provides a certain reference for the calibration of mesoscopic parameters of engineering scale models.(2)The two-dimensional numerical model of particle flow in single-line tunnel is established,and the excavation simulation of single-line tunnel under different buried depths is carried out.The collapse arch form of surrounding rock after single-line tunnel excavation is obtained.The dynamic change process of surrounding rock,force chain diagram and stress field change law after single-line tunnel excavation are studied.The results show that the tunnel is prone to collapse when the buried depth is shallow.When the depth is deeper,the tunnel is prone to arch collapse.On this basis,a two-dimensional numerical model of particle flow of double-track tunnel was established to study the progressive deformation and failure process of surrounding rock under different tunnel distances and different tunnel depths,and the collapse arch shape of surrounding rock after double-track tunnel excavation was obtained:The collapse arch morphology of surrounding rock after double-line tunnel excavation is obtained:when D/R≤1.0,the surrounding rock after double-line tunnel excavation finally forms a combined collapse arch;when D/R>1.0,collapse arches are formed independently.In the case of the same diameter ratio between tunnels,when the buried depth of the tunnel is small,the collapse is finally formed;when the buried depth is large,the double holes eventually form a combined collapse arch.Subsequently,the collapse failure deformation law of surrounding rock of double-track tunnel under different tunnel diameters and different surrounding rock grades was further discussed.(3)Summarizes the existing calculation theory and specification for deep buried tunnel surrounding rock pressure,combined with the results of particle flow numerical simulation,fitting the function relationship between the height and the diameter ratio of the small spacing tunnel collapse arch under the condition of Ⅲ～Ⅴ surrounding rock.According to the static equilibrium theory,the calculation formula of the surrounding rock pressure under the condition of deep buried tunnel is further deduced.Then the results obtained in this paper are compared with the Pu’s theory and the current specification method,and the rationality of the calculation results in this paper is verified.