Research On Cracking And Bearing Performance Of Shield Segment Structure Based On XFEM

The common failure form of shield segment is cracking,and concrete,as a typical heterogeneous composite material,its fracture failure is between brittleness and ductility.The fracture process is very complicated,and the development of cracks will cause the concrete segment to be durable.The performance and safety are seriously reduced.The traditional finite element method is difficult to simulate reliable results,and the extended finite element method can solve this problem.This article will take the extended finite element method according to the theory of fracture mechanics,and focus on the shield The main research contents of the failure mechanism of tunnel segment structure under initial crack conditions,surrounding rock loads and under bias conditions are as follows:(1)Introduction to the system The basic idea of the extended finite element(XFEM)method,and a basic overview of the basic content of the XFEM module in the ABAQUS software.At the same time,two classic crack problems are calculated using the XFEM module.It verifies the accuracy and convenience of the XFEM module in calculating cracks.(2)The concrete segment is taken as the research object separately,and the crack tip stress intensity factor(K)is used to reflect the stress characteristics.By analyzing the influence of different calculation methods,mesh density and crack depth on the K value,a reasonable mesh density and calculation method are determined,which provides a reference for the study of concrete segment cracking.(3)Based on the fracture criterion,determine the location where the shield tunnel segment structure is prone to crack initiation under different conditions of complete surrounding rock load and eccentric load.On this basis,using the theory of fracture mechanics and the extended finite element(XFEM)method,a finite element calculation model for the cracked shield concrete segment structure was established at the location of the crack initiation.(4)Using the theory of fracture mechanics and the extended finite element(XFEM)method,analyze the characteristic parameters of a single crack and the propagation path of the crack under complete surrounding rock load conditions and bias conditions.Select cracks at representative locations in different periods,analyze their stress distributions,compare the stress distributions of different types of cracks,and analyze the types of cracks in different periods.For the surrounding rock load conditions,the early stage of crack propagation is an open-type propagation.The crack propagation in the middle and late stages belongs to the compound form of open type and sliding type cracks.That is,I-II composite cracks.For the condition of the bias load,the crack growth belongs to the open type.(5)The ultimate bearing capacity of the complete segment is obtained by adopting the plastic damage model.And compared with the ultimate bearing capacity of cracked segments.By comparing the ultimate load-bearing capacity of the segment with different depth cracks and the ultimate load-bearing capacity of the complete segment,it can be found that the deeper the initial crack depth,the more the ultimate load-bearing capacity of the segment decreases,that is,the more serious the loss of bearing capacity.Under bias load conditions,the greater the bias range,the greater the bearing capacity loss.