Loess is a kind of special soil with structure and hydrocollapse behavior; due to the particularity of loess, the deformation\nregularity of the tunnel in loess shows different characteristics from those in rock. To ensure the safety of construction, crown\nsettlement (CS) and horizontal convergence (HC) are widely used to assess the stability of the tunnel structural system. Based on\nstatistical analysis, this study focused on analyzing the influence of cover depth on the deformation of surrounding rock of loess\ntunnels by ANOVA, and relationships between them were presented by regression analysis. The achieved results indicated that the\ninfluence of cover depth on deformation was not obvious in shallow tunnels, while the cover depth had a significant effect on\ndeformation in deep tunnels. Based on the difference of influence of cover depth on deformation between shallow tunnels and\ndeep tunnels, a method for determining the cover depth threshold (CDT) in the tunnel by statistical analysis was proposed. The\nhorizontal and vertical deformations in shallow tunnels were discrete and obeyed the positive distribution, mainly concentrated\nwithin 200 mm. The deformation allowance in shallow tunnels was recommended to be 200 mm. In deep tunnels, as the cover\ndepth increased, the deformation increased linearly, while the CS/HC decreased.
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