## 4 Discussion
### Influence of the Cavity Depth Variation on the Deformation of the Baseplate of the Yuanjue Grottos  
As mentioned above, the influence of the weathering cavity on the Yuanjue Grottos is controlled by the fissures [19; 20]. Therefore, displacement monitoring stations were set up at the intersection of the fissures in order to further ascertain the influence degree of the  
Figure 7: Displacement vector diagrams of wallrock of the Yuanjue Grottos under different cavity depths. (**a–j**) denote cavity depths of 0–10 m, respectively. weathering cave on the Yuanjue Grottos, where the aim was to explore the deformation regularity of the baseplate of the Yuanjue Grottos. There were two fissures in the bottom of the Yuanjue Grottos, named Fissures J10 and L8, which are almost vertically crossed (Figure 8). The baseplate of the Yuanjue Grottos is divided into four areas, and two displacement monitoring points were selected in each area. This was performed to analyze the vertical displacement of each area that occurred due to the change in cavity depth, and the curve of vertical displacement change with the depth of cavity was drawn (Figure 9). As can be seen from Figure 9, with increases in the cavity depth, the baseplate of the Yuanjue Grottos produced a certain uplift, indicating that the front area of the entrance of the Yuanjue Grottos presents an overall forward trend in the early stage of cavity development. This is a typical elastic rebound phenomenon, suggesting that the rock strata of the baseplate are in the stage of elastic deformation [8] ([PERSON] et al., 1993). The rock strata of the baseplate absorbed a certain amount of potential energy due to gravity. The gravity of the lower particles was relieved with increases in the cave depth; this potential energy causes an uplift in the above-rock strata of the baseplate. The uplift heights of the displacement monitoring of Points 1 and 4 were found to be greater than that of Points 2 and 3, which also proves the above conclusion. The evolution processes of the vertical displacement of Points 1 and 2 can be subdivided into three stages. Stage 1 represents when the cavity depth is less than 4 m, where vertical displacement changes slowly. Stage 2 represents when the cavity depth is between 4 m and 7 m, where the vertical displacement of Points 1 and 2 has entered an accelerated change stage along with increases in the cavity depth. Stage 3 represents when the cavity depth is more than 7 m, where the vertical displacement of Points 1 and 2 tends to gently change along with increases in the cavity depth. Stages 1 and 2 belong to the elastic defor  
Figure 8: Diagram of the baseplate area division of the Yuanjue Grottos. Figure 9: The vertical displacement variation curves of the measuring points in the different areas of the baseplate with increases in the cavity depth. (**a**) The vertical displacement variation curves of the measuring points in the right area of the baseplate, (**b**) The vertical displacement variation curves of the measuring points in the left area of the baseplate. mation stage, while Stage 3 indicates where the rock strata of the baseplate transform into the plastic and brittle deformation stage [22]. The evolution processes of the vertical displacement of Points 3 and 4 can be subdivided into two stages (Figure 9b). Stage 1 represents when the cavity depth is less than 5 m, where the vertical displacement of Points 3 and 4 increases with increases in the depth and the two areas are constantly uplifted. Stage 2 represents when the cavity depth is more than 5 m, where the vertical displacement of Points 3 and 4 has a reverse steep drop, where the uplift of the two areas continuously decreases, and where the vertical settlement occurs in Point 4. Stages 1 and 2 belong to the elastic and brittle deformation stages, respectively.