Analysis Of Shallow Tunnel Excavation And Reliability Considering The Spatial Variability Of Surrounding Rock

In the design and analysis of most tunnel projects at present,rock and soil are regarded as homogeneous,such an approach often ignores an inherent characteristic of rock and soil,that is,spatial variability.The existence of spatial variability of rock and soil will greatly affect the tunnel excavation process.Tunnel design and analysis that do not consider the spatial variability of rock and soil may be conservative or unsafe.With the development of tunnel engineering,the research on the spatial variability of surrounding rock has become a research hotspot in tunnel engineering.In order to study the tunnel excavation deformation and the reliability of tunnel under the spatial variability of surrounding rock,this paper established a two-dimensional random field model of tunnel excavation,and through a large number of numerical simulation experiments,the tunnel excavation under the random field of surrounding rock parameters has been studied.In this article,the main work and conclusions are as follows:(1)According to the principle of Latin hypercube sampling and covariance decomposition method,the program to realize the random field of geotechnical parameters is written in MATLAB,and the parameter random field data is mapped to the FLAC3 D numerical grid through the Fish language,and a process for quickly realizing the analysis of the stochastic finite difference model has been established.(2)A two-dimensional tunnel stochastic finite difference model was established by determining the model parameters.Based on the Mohr-Coulomb model,a total of 30 random field conditions were designed for the different spatial variability of elastic modulus,cohesion and friction.The parameter random field is sampled and calculated500 times.Through the summary and analysis of the results of the random field numerical experiment,the surrounding rock deformation,ground settlement and surrounding rock failure mechanism after tunnel excavation under the parameter spatial variability are studied.The results show that the deformation range of the tunnel surrounding rock increases with the increase of the spatial variability of the parameters,and the spatial variability of each parameter has different effects on the deformation.For the vault settlement: friction>elastic modulus>cohesion,For the horizontal convergence: friction >cohesion> elastic modulus.Under the parameter spatial variability,the failure of tunnel surrounding rock is different from the formation of a symmetrical shear failure surface of homogeneous surrounding rock,but will develop along the weak area with smaller values of surrounding rock parameters.As the parameter spatial variability increases,the surrounding rock shear strain zone gradually widens and becomes larger,and the shear failure area increases.By analyzing the surface settlement curves of tunnel excavation under different parameter spatial variability,four different forms of the surface settlement curve under the parameter random field relative to the deterministic parameter are put forward,namely the curve moves up and down,and the maximum settlement offsets left and right.,the one-sided settlement of the curve is large and the curve has multiple extreme points.(3)The stress relaxation method was used to solve the critical surrounding rock characteristic curve in the convergence constraint method,and the influence of the spatial variability of each parameter on the surrounding rock characteristic curve was studied.,The results show that the spatial variability of geotechnical parameters will cause the surrounding rock characteristic curve to move up relative to the deterministic result,which means that the surrounding rock supporting structure needs to bear greater supporting pressure under the same supporting time,or in other words,the surrounding rock and supporting structure will produce greater displacement under the same supporting pressure.(4)Four functional functions for solving tunnel reliability are established based on the convergence constraint method,and the influence of spatial variability of various parameters on tunnel reliability is studied.The results show that the increase of the spatial variability of various parameters will reduce the tunnel reliability,The degree of influence of the spatial variability of each parameter on the tunnel reliability is: friction >elastic modulus>cohesion.(5)Taking the subway tunnel in the backfill section as the background,a random field model considering the spatial variability of the backfill was established.The tunnel excavation deformation and ground settlement were analyzed through numerical simulation,and the reliability of the tunnel under the design parameters was verified according to the function function.