Progressive failure process of secondary lining of a tunnel under creep effect of surrounding rock
During the operation of tunnels, a problem that is encountered often is the cracking of secondary lining caused by the time-dependent deformation of weak surrounding rocks. In this article, the Dujia mountain tunnel, which is situated in a weak and crushing phyllite stratum, was taken as an example to study this issue. First, we conducted a field investigation of the cracking situation of the secondary lining. Then, the similarity model test and particle-discrete-element numerical approach were used to study the failure process of the secondary lining. The results showed that the similarity model test and the results of numerical simulation were consistent with respect to the order in which cracks occurred and the final failure pattern. The progressive failure process can be divided into four stages, i.e., (1) the elastic stage, (2) the initial damage stage, (3) the ultimate limit stage, and (4) the instability stage. For a lateral pressure coefficient (λ) > 1, cracks initially appeared at the left haunch, the right haunch, and the spandrel due to bending damage caused by large-eccentricity compression. For λ = 1, cracks appeared first at the left arch springing because of the compressive and shear damage. For λ < 1, the bending damage first occurred at the spandrel. For the secondary lining with pre-existing cracks, micro-cracks were first generated where pre-existing cracks initially existed, and one or two hinges appeared at the location of the pre-existing cracks when the structure was in its ultimate limit stage. A void behind lining influenced the cracking pattern of the secondary lining in three different ways, i.e., (1) no effect; (2) the order in which cracks emerged was affected, but the final fracture pattern was not; and (3) the order in which cracks emerged and the final fracture pattern were affected.
Keywords: Creep, Secondary lining, Progressive failure, Discrete element method,