Investigation on the fire spalling behavior of underground structures in varied situations by global–local phase field modeling

Abstract

The fire response of concrete underground structures and the near vicinity is not well understood yet, partly due to a lack of an effective and efficient fracture model for spalling of concrete, especially when the large-scale stratum-structure model is involved. In this paper, the spalling behavior is numerically reproduced by a global–local phase field method in light of the s-version finite element method. Only the mesh for the potential spalling zone is refined, which contributes to lowering the computational effort. Numerical models for different cases were constructed and studied to account for several influential factors, including the shape, size, buried depth of the tunnel, the fire scenario, and the ground conditions. These models were expected to show the fire-induced spalling behavior of tunnel linings and the induced disturbance to the nearby ground in varied situations. The comparative analysis indicates that the fire-induced spalling pattern on the tunnel lining is highly related to the fire scenario and the structural shape. Severe damage occurs at the position where there exists a high temperature gradient or concentrated stress. The heated surface of the vault/roof experiences settlement after a transitory upheaval, while the ground above the tunnel is constantly uplifted. The disturbance the ground suffered from the fire accident is relatively slight.