Cracking performance of asymmetric double-arch tunnels due to the voids behind linings

Voids behind linings are a typical problem in the majority of operational tunnels. Previous researches had pointed out a high correlation between the voids and tunnel damages. However, mainly single tunnels have been investigated so far. In fact, few studies focused on the cracking performance of asymmetric double-arch tunnels originating from the relative radial displacements around the void. Herein, by combining numerical simulation and model test, the real three-dimensional response of the asymmetric double-arch tunnel structures caused by the voids is reproduced. Results reveal that crack patterns around the void can be classified into three main types. Transverse cracks are clearly the typical cracks and the spatial distributions are closely associated with void dimensions. Moreover, the localized voids imply uneven earth pressure distribution near the void, producing an asymmetric radial relative displacement and local bidirectional internal forces. It is found that the axial force is much higher in the circumferential direction in comparison with the longitudinal force. Consequently, the longitudinal bending moment plays a decisive role in the cracking performance, and the tensile stress in longitudinal direction becomes higher, changing the usual mechanism of cracking of the linings. For the tunnel opposite to the voids, a slight growth of the earth pressure is observed at the connection between the vault and the middle wall, accelerating the overall cracking of the linings.