The Seismic Fracture Study Of Large Diameter TBM Tunnel Based On The Fine Lining Numerical Model

Nowadays shield technology is more and more mature,becoming the preferred method for underground tunnel and underground pipeline construction.The total length of railway tunnels in China is now about 20,000 km,and the length of highway tunnels has increased by more than 1,100 km annually in recent years.By 2030,the total length of urban pipe corridors planned will reach 4,443.3 km.There are three trends in the development of shield tunnel: larger and larger diameter,complex strata crossing and longer mileage,which have higher requirements for the safety performance of tunnel from construction to operation.The kobe earthquake in Japan in 1995,the Duzce earthquake in Turkey in 1999,and the Wenchuan earthquake in China in 2008 all show that underground structures can still be seriously damaged by earthquakes.The damage forms of tunnel under earthquake include shear failure,crack loss,concrete spalling,water leakage and so on.In order to explore the seismic cracking mode of shield tunnel more comprehensively,numerical simulation method is adopted in this paper to establish the refined model of pipe ring and the refined model of local segment.The constitutive model of CDP(Concrete Damage Plastic)and Extended Finite Element Method XFEM(Extended Finite Element Method)were considered,and the model was verified by combining existing tests.A free field model was established to obtain the boundary conditions of seismic displacement time history around the pipe ring.The seismic cracking characteristics of shield tunnel are studied by applying seismic loads of different directions and intensities to pipe rings and local segments.The main content and research results of this paper are as follows:(1)Based on the existing full-ring lining loading test and segment joint test,the refined finite element model of the ring and the finite element model of the local segment were established respectively to verify the model and determine the optimal parameters of different materials.(2)A free field soil model was established,and the viscoelastic boundary was used to absorb the boundary effect to obtain the seismic time history data of the outer boundary of the pipe ring.Based on the reaction displacement method,an equal layer method is proposed to replace the spring layer.The damage modes and joint opening of segment were studied by applying seismic action in different directions and intensities to the fine pipe ring model.It was found that the damage of the pipe ring was mainly concentrated in the vault,the bottom of the arch,the inside of the waist and the upper and lower 45° shoulder.The time of damage development and joint opening mutation coincides with the time of peak acceleration and peak displacement.(3)The refined local segment model and segment joint model are established.By applying the maximum positive and negative bending moments under earthquake intensity and different bolt pretightening forces,the effect of bolt pretightening forces on the crack loss mode of segment under earthquake intensity was studied by using the pseudo-static method.It was found that the bolt pretightening force was 360 k N and the crack loss degree was the minimum.Then,the ultimate fracture loss mode,fracture location,fracture depth and fracture loss development law of the local segment model were investigated by applying the limit positive and negative bending moment.