Study on failure mechanism and treatment measures of inverted arch under asymmetric immersion of loess tunnel basement

Recently, the issue of inverted arch cracking caused by water immersion is more prominent. Nevertheless, the evidence for this remains inconclusive. This paper addressed the failure of the inverted arch caused by asymmetric immersion of base in a loess highway tunnel. Firstly, the distribution characteristics of inverted arch cracks are studied. Then, the mechanical response of the inverted arch in the process of tunnel basement immersed was investigated. Subsequently, the deformation and stress characteristics of the inverted arch under the influence of different immersed positions were analyzed. Finally, the corresponding treatment measures are put forward. The findings show that cracks are mainly concentrated in the center of inverted arch and the water immersion arch foot area under asymmetrical water immersion. Furthermore, after tunnel base immersed in water, the pressure on the vault and sidewall of the lining structure increase, and the inverted arch tensile stress continues widening, the differential settlement between the arch foot in the immersed area and the invert structure in the un-immersed area aggrandizes, leading to the formation of longitudinal cracks in the inverted arch. Numerical simulation showed that the water immersion position has significant influence on the crack propagation process and damage degree of inverted arch, especially when the water immersion position at the arch feet. The distribution of stress and deformation of tunnel supporting structure were significantly influenced by changes of the water immersion range. When the water infiltration depth between 3 ∼ 6 m, the deformation and stress of inverted arch were significant. The combined treatment measure of “reinforcing arch foot with steel pipe piles + optimizing tunnel drainage system” is proposed. The vertical displacement of the inverted arch structure is significantly decreased by 76.2 % following treatment, demonstrating a substantial improvement in structural stability, and the research results can provide a certain reference for the treatment of similar tunnel diseases.