*3.1.2 Relationship between the cohesion increment and the strength-stress ratio and plant span*

According to the 29 underground plants in **Table 2**, the cohesion increment Δ*Cb* of the surrounding rock is fitted to the plant span *B* and the strength-stress ratio *Kσ* by least squares surface fitting, and the equation is as follows:

$$(\Delta \text{C}\_{\text{b}}) = 0.01481(2K\_{\sigma}{}^{-2} + 0.405)B \tag{5}$$


#### **Table 2.**

*Relevant data of the powerhouse and calculation of the cohesion incrementally reinforced by the anchor bar.*

In **Figure 6**, the cohesion increment provided by the anchor is approximately linearly related to plant span *B*, which increases with an increase in plant span. In addition, the cohesion increment Δ*Cb* and strength-stress ratio still show 2 times nonlinearity.

### **3.2 Incremental cohesion of the surrounding rock for anchor cable reinforcement**

The anchor cable support parameters for 12 large and medium-sized hydropower plants are shown in **Table 3**, and the cohesion increment in the surrounding rock is calculated by Eq. (3), where *η* = 3.5.
