Investigation of progressive failure mechanism of tunnel lining with material defects using discrete element method

Abstract

Material defects in the concrete lining are common due to factors such as poor construction quality and environmental erosion. Material defects can exacerbate the stress status, give rise to microcracks accumulation and may bring out a failure of the concrete lining. Thus, investigating the performance of concrete lining with material defects is essential for evaluating the safety of operating tunnels. In this paper, the discrete element method (DEM) is adopted to investigate the influence of material defects on the mechanical performance of the concrete and the progressive failure process of the lining structure. For this purpose, a numerical approach is adopted for modeling concrete with randomly distributed defects. After that, the mechanical performance and micro-fracturing evolution process of concrete specimens influenced by material defects are examined. Then, a numerical model of lining concrete structure containing aggregate and mortar is established to investigate the impact of material defects on the progressive failure mechanism and bearing capacity of the concrete lining structure. Findings show that the stress concentration caused by material defects damages concrete when the load is much lower than its strength. Macroscopic fracture bands formed from the interconnection of microcracks among defect sites, which not only accelerates the damage process but also changes the failure model of concrete specimens. These characteristics of defective concrete decrease its macroscopic mechanics, such as compressive strength and elastic modulus. At the structure level, material defects degrade the stress state of the lining structure, causing localized damage to the lining structure and dramatically lowering the safety of tunnels. The distribution of material defects has a prominent influence on the failure model of concrete lining structures, where the content of material defects significantly impacts the bearing capacity of the concrete lining structure.