## 3 Experimental Results
### Deformation Analysis of Main Rupture Zone  
In the soil rupture test of the slope crest, the MRZ formed by bedrock dislocation had a width of approximately 25 cm and a displacement difference of 8.5 cm (see Figure 8a). In the soil rupture test of the slope toe, the MRZ formed by bedrock dislocation had a width of approximately 15 cm and a maximum displacement difference of 5.5 cm (see Figure 8b).  
As shown in Figure 9, during Stage I, the depth of the MRZ (main shear zone) in the slope crest and toe soil rupture tests was approximately 3 cm and 20 cm, respectively, with slight variations observed, indicating early signs of slope instability and the onset of soil rupture. In Stage II, the maximum MRZ depth in the slope crest soil rupture test reached 92 cm, with a maximum width of 25 cm. With the depth of the MRZ increasing rapidly at first and then leveling off. This suggests that the soil rupture penetrates and fully develops, with minimal changes thereafter. In contrast, the MRZ depth in the slope toe soil rupture test reached a maximum of 60 cm, with a maximum width of 15 cm. The depth of the MRZ increased steadily, indicating that the soil rupture did not fully develop. In both the tests, the width of the MRZ experienced a sudden change on entering Stage III, marking an intensification of slope instability. During Stage III, The maximum width and depth of  
Figure 7: Failure process diagram of sandy soil slope during soil body rupture at the slope toe (T2): (**a–j**) refers the bedrock dislocation ranging from 10 mm to 100 mm.  
the MRZ during slope crest soil rupture were 35 cm and 95 cm, respectively, while during slope toe soil rupture, the maximum width and depth of the MRZ were 15 cm and 70 cm. The width and depth of the MRZ in both the tests tended to stabilize with minimal changes, indicating that the slope had fully lost its stability.  
During the stage of MRZ penetration and development, the damage caused by the slope crest soil rupture test was more severe. In the slope crest soil rupture test, by the time Stage II was reached, the soil in the slope underwent a thorough rupture, resulting in the formation of small overhanging faces. In Stage III, these overhanging faces become more pronounced, leading to the formation of a double-sided slope. Due to the steepness of the overhanging faces, there is a risk of secondary landslides under seismic activity and other conditions. In the slope toe soil rupture test, after reaching Stage II, the ruptured shear rupture zone near the slope toe caused the upper slope body to lose support. This can trigger secondary landslides under the influence of self-weight and other forces such as seismic activity. This process is more likely to occur after Stage III. Therefore, regardless of whether it is the slope crest or slope toe soil rupture test, secondary landslides are likely to occur once the slope soil undergoes thorough rupture. The slope crest soil rupture test required a greater amount of bedrock dislocation to reach Stage III, resulting in a wider and deeper MRZ and a greater extent of damage.  
Figure 8: Slope surface deformation under soil slope cross-bedrock fault. Slope surface deformation of sandy soil slope during soil body rupture at (**a**) slope crest (T1) and (**b**) slope toe (T2). The base figs show the on-site damage photos of the bedrock after a dislocation of 80 mm.  
The MRZ developed from small cracks in Stage I to a sliding surface (rupture zone) in Stage II, ultimately forming a zone that penetrated the soil to the slope surface. During this process, the formation of the MRZ was influenced by the width and depth of the rupture zone, the uneven deformation zone on the surface, and the internal slope rupture.