Geomechanical model test for mechanical properties and cracking features of Large-section tunnel lining under periodic temperature

The stress state of tunnel linings is complex and variable because of the repeated climate changes and deterioration of surrounding rock. In the long run, the cracking of the lining and the weakening of the bearing capacity will be aggravated. Thus, the bearing capacity and cracking mechanism of tunnel linings under thermal stress should be explored. Here, a tunnel geomechanical model test system is independently developed to simulate the thermal stress and the pressure of surrounding rock on a large-section lining of a tunnel during operation . Air cooling circulation and active loading are applied. Then, the deformation, internal force variation and crack characteristics of the lining under temperature-load coupling are investigated. Results show that, the cracks generated in the lining structure are mainly in the form of bending tension cracks and compression shear cracks. Bending tension cracks occur at the vault and inverted arch, whereas compression shear cracks occur at both side walls of the tunnel. The deformation of the tunnel lining entails vertical extrusion and lateral expansion. When compression shear cracks occur on the side walls, the inverted arch clearly rises. The crack width increases under repeated temperature changes, but no new crack occurs. The axial force distribution of the lining structure is symmetrical, and the bending moment distribution is similar to that of a horn. When the second compression shear crack occurs on both side walls, the lining structure is destabilised. The bearing capacity of lining decreases, and the ultimate bearing capacity decreases by 4%.