Stability Analysis Of Shield Tunnel Face Considering Spatial Variability Of Hydraulic Parameters

With the deepening of the urbanization process,more and more people flow into the urban economic center,a large number of population caused traffic jams,and urban ground traffic resources are becoming increasingly saturated.In order to alleviate traffic pressure and make full use of space resources,more and more cities begin to build underground rail transit.Shield method is favored by engineers for its advantages of small risk,weak interference and rapid progress.The stability of shield tunnel excavation face is very important to ensure the safety of tunnel construction.When constructing a tunnel under water or in water rich stratum,the seepage force is a key factor to determine the support force of the excavation face.The uncertainty of the hydraulic parameters of natural rock and soil has a great influence on the seepage force near the excavation face.In view of this problem,this paper establishes a stochastic numerical limit analysis method for the stability analysis of the excavation face under the influence of seepage,considering the spatial variability of hydraulic parameters,and conducts an in-depth study on the stability of the excavation face of the shield tunnel under the condition of rich water,so as to provide an important theoretical basis and reference for the engineering practice,The main contents are as follows:(1)Combined with Latin hypercube sampling,K-L series expansion,Nataf transformation and equal probability transformation criteria,a random field discretization program considering multi parameter correlation is compiled,which lays a foundation for determining the seepage field near the excavation face of shield tunnel when considering the spatial variability of hydraulic parameters.(2)The second development of the finite element analysis software ABAQUS is carried out by using Python language to write post-processing script.The MATLAB toolbox is used to make the three interact effectively and automatically complete the seepage field analysis of multiple groups of tunnel excavation models.The influence of the random field control parameters of permeability coefficient and external factors on the seepage field of tunnel excavation is studied.The results show that the influence scope of the seepage field increases with the increase of the coefficient of variation of permeability coefficient;The autocorrelation distance of permeability coefficient tends to be very large or very small in both horizontal and vertical directions,and the influence range of autocorrelation distance on tunnel excavation seepage field is small.When the autocorrelation distance in one direction increases,the influence range will increase in the same direction with the increasing direction;When the ratio of vertical and horizontal permeability coefficient is 2,the influence range of the seepagefield in the vertical direction increases with the increase of the correlation number of permeability coefficient anisotropy;with the increase of the ratio of vertical and horizontal permeability coefficient anisotropy,the influence range of tunnel excavation on the seepage field in the vertical direction increases.(3)Based on the dual form of classical limit analysis upper limit theorem,combined with conic programming and related non Gaussian parameter random fields,a stochastic upper limit analysis method considering the spatial variability of hydraulic parameters is established,and the related calculation program is compiled.Numerical examples are calculated and the correctness of the algorithm is verified.The results show that the random numerical limit analysis method can effectively analyze the stability of excavation surface under the influence of seepage,and has a high calculation efficiency.(4)Based on the stochastic numerical limit analysis method,the influence of spatial variability of permeability coefficient on the stability of the excavation face of shield tunnel in water rich stratum is studied.The results show that,With the increase of permeability coefficient variation coefficient,anisotropic correlation coefficient and anisotropic ratio,the ultimate support force of tunnel excavation face will increase;The ultimate support force of excavation face decreases with the increase of horizontal autocorrelation distance,and increases with the increase of vertical autocorrelation distance;The damage range of excavation surface increases with the coefficient of variation,the correlation coefficient and the ratio of anisotropies.