## 7 Conclusions  
The slide surface of the shallow buried loess tunnel may diagonally develop from the surrounding rock near the arch foot or the arch waist to the ground surface. Under the bias of stratum, the slide surface only exists on one side of the tunnel. The slide surface is a channel for water infiltration. Surface water can quickly infiltrate to the lining periphery through the slide surface, resulting in the deterioration of the mechanical property of loess as well as the deformation and cracking of the lining structure in varying degrees. Based on the above background, the effect of water immersion of different slide surfaces is simulated with the change of lining load. The cracking characteristics and internal force of secondary lining are studied in detail with a multi-point independent loading test system for tunnel lining. The main conclusions are as follows. (1) The type of slide surface of the shallow buried loess tunnel is closely related to tunnel excavation methods and stratum bias. The failure point of surrounding rock around the tunnel may be located at  
Figure 22: Curve of the allowable load ratio of cracked lining with the crack number. the arch foot or arch waist, the shape of the slide surface is an oblique straight line, and the sliding surface only exists on one side of the tunnel under the biased stratum. Four types of slide surfaces of shallow buried loess tunnel are proposed. (2) The immersion of the slide surface has the most significant effect on the deformation of the lining vault and arch waist. The cracking of the arch foot and the inverted arch has no apparent effect on the lining deformation, while the cracking of the vault and arch waist may change the lining deformation rate. The lining cracks are symmetrically distributed under the immersion of the bilateral slide surface, and the cracks are concentrated on the immersion side of the unilateral slide surface. The appearance of compressive cracks can be regarded as a precursor of lining instability. (3) In the bilateral slide surface immersion cases, the axial force of the lining arch always increases with fluctuating bending moment, whose cracking affects the change rate of the internal force. In unilateral slide surface immersion cases, when the failure point is the arch foot, the axial force of the lower section of the sidewall is higher than that of the upper section. When the failure point is the arch waist, the axial force of the lower section of the sidewall is smaller than that of the upper section. The lining bending moment of the unilateral slide surface immersion is significantly higher than that of the bilateral slide surface immersion. (4) In the thickness direction, lining cracks will always begin to develop with I-type initial cracks, then develop into L-type medium-term cracks, and finally develop into Y-type late-term cracks. The proportion of cracks in the medium-term is relatively large, and the initial and late-term cracks account for a relatively small proportion. (5) After the lining has cracked for the first time, the cracked linings under different slide surface immersion cases that can continue to bear the load ratio are all less than 40%. With the increase of cracks, the allowable load ratio of cracked lining decreases linearly. Among them, the allowable load ratio under unilateral arch waist slide surface immersion cases decayed fastest, and the decay rate of allowable load ratio under the other three slide surface immersion cases was basically the same. Conceptualization, H.L. ; formal analysis, Y.L. ; project administration, H.L. ; validation, Y.L. ; writing--original draft, Y.L. ; and writing--review & editing, H.L. All authors have read and agreed to the published version of the manuscript. This work was supported by the National Natural Science Foundation of China (Grant Nos. 51978064, 51908051), the Open Fund of State Key Laboratory of Structural Mechanics Behavior and System Safety of Traffic Engineering (Grant No.