## 4 Experiment Procedure
### Test Cases and Lining Loads  
Because the lining cracking of shallow buried loess tunnel is closely related to the slide surface and immersion, the design of the test cases considered the slide surface types and the flooded range of loess around the slide surface. As shown in Table 5, the test cases were divided into four cases according to the types of slide surfaces. The slide surfaces in case 1 and 3 were distributed on both sides of the tunnel. The failure points were at the arch foot and arch waist, respectively. The slide surfaces in case 1 were No. 1 and No. 2, and the slide surfaces in case 3 were No. 3 and No. 4. It should be noted that the slide surfaces in case 3 were the same as the slide surfaces in the sections K1841 + 475-K1841 + 495 of the above tunnel engineering (Figure 7). In cases 2 and 4, the slide surface was distributed on one side of the tunnel. The slide surface in case 2 was No. 1, and the failure point was at the arch foot. The slide surface in case 4 was No. 3, and the failure point was at the arch waist. According to the loess field immersion test [34], the total width of the immersion on both sides of the loess crack can reach 4.54 m after immersion for three days. Based on this result, the immersion width B around the crack in each case was set to 0 m, 1 m, 2 m, 3 m, 4 m, and 5 m.  
The combined effect of different slide surfaces and different immersion width around the crack has a strong influence on a load of tunnel secondary lining. The authors of this paper have calculated the secondary lining load value of the immersion slide surface with a numerical simulation method that is verified with on-site monitoring results [19]. This paper is a follow-up research of the reference [19]. The two studies have the same research background, which is the immersion of the slide surface in shallow buried loess tunnel, but different research focuses. Reference [19] focus on the loads on the secondary lining caused by the immersion of the slide surface, and the loads on the lining was calculated by numerical simulation. This paper focus on the characteristics and laws of lining cracking under the effect of slide surface immersion, and a loading model test was carried out. In the model test, the loading value of lining model refers to the calculation results of the reference [19], so the Figure 14 of this paper is the same as the Figures 10-14 in reference [19]. The calculation cases are the same as the Table 5, and the degree of loess flooding is set as the saturated state. The buried depth and support parameters in the numerical simulation take from the sections K1841 + 475-K1841 + 495 of tunnel engineering in Section 2.3, so the buried depth is 30 m, and the thickness of secondary lining and primary support are 40 cm and 20 cm, respectively. The load values on the secondary lining of the shallow buried loess tunnel under the four cases are shown in Figure 14a-d. Figure 14e shows the load monitoring points corresponding to the abscissa of Figure 14a-d. The positions of load monitoring points are the loading positions of the hydraulic cylinders in the loading system of test equipment, and in the center of two adjacent monitoring sections. For better understanding, the monitoring sections in Figure 13a are marked in Figure 14e. It can be seen that the slide surface immersion caused the load on arch foot (Nos. 6 and 11) to increase. Comparing the load at the positions 6 and 11 in case 1 (Figure 14a), case 2 (Figure 14b), case 3 (Figure 14c), and case 4 (Figure 14d), it can be seen that the increased value caused by the immersion of the arch foot slide surface was higher than what caused by the immersion of the arch waist slide surface. For the arch of the tunnel, the lining load at the arch waist (Nos. 3 and 14) increased when the arch foot slide surface was flooded. The effect of the arch waist slide surface immersion mainly caused the load increase at the arch shoulder (Nos. 2 and 15), and the position of the increased load is closer to the vault. In addition,