# The Deformation Law of a Soft-Rock Cavern by Step Excavation in a Pumped Storage Power Station
## 3 Results
### The Influence of Support Measures on the Stability of the Surrounding Rock in Underground Caverns
According to Figures 22 and 23, it can be observed that, regardless of whether there were support measures or not, the development of deformation in the surrounding rock of the underground caverns was concentrated in the exposed areas of the soft-rock strata, and the displacement of the left wall was greater than that of the right wall. This was because the soft rock was exposed in the middle of the left wall and the lower part of the right wall. The strength of the soft rock was relatively lower compared to the sandstone layer, and the stress release degree was strong. The soft-rock layer on the left wall was in a forward inclined state, while the soft-rock layer on the right wall was in a reverse inclined state. Therefore, the soft-rock layer was a displacement concentration area, and the left wall was more prone to instability compared to the right wall, with a deformation range of the surrounding rock greater than the right wall. Figure 23: Displacement cloud map of the walls under different support conditions: (**a**) displacement cloud map of the left-side wall under unsupported conditions; (**b**) displacement cloud map of the right-side wall under unsupported conditions; (**c**) displacement cloud map of the left-side wall under supported conditions; (**d**) displacement cloud map of the right-side wall under supported conditions. Figure 22: Displacement cloud map of y = \(-\)79.4 m section under different support conditions: (**a**) displacement cloud map of y = \(-\)79.4 m section under unsupported conditions; (**b**) displacement cloud map of y = \(-\)79.4 m section under supported conditions. Based on the simulation results and displacement cloud map, the maximum displacement of the left and right walls, the maximum displacement of this section, and the corresponding increment could be obtained. At the same time, the maximum displacement and the increment of the displacement of the whole underground cavern under the conditions with or without support measures could be obtained. The specific displacement values and increments of each part are shown in Table 7.  
According to the Table 7, it can be observed that, whether the specific section or the whole underground cavern, the maximum displacement under support measures could be effectively reduced. Therefore, the support measure could limit the deformation of the soft rock effectively, reduce the displacement of the surrounding rock efficiently, and improve the stability of the surrounding rock greatly. In order to understand the influence of the support measures on the displacement of the left- and right-side walls of the underground cavern, three sections were selected from the front, middle, and rear sections (y = \(-\)156 m, y = \(-\)76 m, y = \(-\)30 m) in the excavation direction of the underground cavern, and the maximum horizontal displacement before and after the support of the left- and right-side walls of each section and increments were compared. The maximum horizontal displacement values before and after the support of each section and increments are shown in Table 8, and the displacement cloud diagram is shown in Figure 24.  
According to Figure 24 and Table 8, it can be observed that the displacement of the left-side wall of the cavern under the unsupported condition is greater than that of the right-side wall. However, the displacement of the left-side wall in the front and rear sections of the cavern is still greater than that of the right-side wall, while the displacement of the right-side wall is greater than that of the left-side wall in the midspan of the tunnel. This phenomenon occurred under the influence of the reinforcement effect of anchor rods after support and the stress conduction of the lining.