Effect of the longitudinal local wetting-induced collapse on tunnel structure in loess strata

•The longitudinal local collapse in loess tunnel is studied by model test.•The response modes of tunnel structure to local collapse are revealed.•The disposal strategies of local collapse are suggested based on the findings. The wetting-induced collapse poses a threat to the safety of tunnels and underground buildings in loess strata, which has attracted wide attention of researchers. In this paper, based on the cracking behaviors of Guoqi tunnel lining, the response of tunnel structure to the longitudinal local wetting-induced collapse of foundation was studied by virtue of indoor model tests. Through analysis of the vertical vault displacement, surrounding rock pressure and lining strain, the location and size of wetting area were proved to be the significant influencing factors of the above characteristics. The size of wetting area was relevant to both the maximum value and the distribution of values of the monitored indexes in the model tests. When the longitudinal local collapse happened near the tunnel face, the tunnel structure approached to behave like “cantilever beam”; when the longitudinal local collapse was located behind the tunnel face, the characteristics of tunnel structure were similar to the “simply supported beam”. Based on the current findings, the surrounding non-collapsible area was also suggested to be carefully treated during the treatment of the longitudinal local wetting-induced collapse of loess tunnels.