Analysis of bending deflection of tunnel segment under load- and corrosion-induced cracks by improved XFEM

Load-and corrosion-induced cracks are generated in the segment concrete of a shield tunnel during the operation period, and will reduce the bending performance of the tunnel segment. In this paper, an improved extended finite element method (XFEM) is proposed for calculating the cracks of a segment under the effects of an external load and reinforcement corrosion. A new fracture energy conversion equation is constructed to improve the calculation accuracy and is verified by a full-scale test, and a high-order function of the crack diffusion coefficient is used to optimise the calculation efficiency of the crack propagation. The characteristics of the corrosion -induced cracks of the segment and its relationship with the segment bending deflection are investigated based on the improved XFEM. The numerical calculation results show that: (1) the morphology of the tunnel segment corrosion-induced cracks can be described as multiple con-nected ellipses; (2) the span length and angle of the corrosion-induced cracks are affected by the load-induced cracks on the surface of the segment, and an increase in the bending moment will enlarge the crack span length and reduce the crack angle; and (3) when the corrosion time reaches 9 years, the deflection of the segment is increased by 24% to 58% from that of a non-corroded segment under bending moments of 220 kN.m to 260 kN.m, respectively. The relevant results can provide a theoretical basis for the analysis and treatment of shield tunnel structural diseases.

Automated summary

An improved XFEM method is proposed in this paper to calculate the cracks of a segment under the effects of an external load and reinforcement corrosion. The study shows that the morphology of the corrosion-induced cracks can be described as multiple connected ellipses, and the load-induced cracks on the surface of the segment affect the span length and angle of the corrosion-induced cracks. With longer corrosion time, the deflection of the segment increases more significantly under certain bending moments.