## 3 Results and Discussion
### Weathering Transition Zone Stability Monitoring Criterion  
The analysis shows that the axial force and pore water pressure have similar evolution laws. Therefore, based on the data of anchor bolt axial force and pore water pressure during rainfall infiltration and hydraulic fluctuation, the stability monitoring criterion for the weathering transition zone under cyclonic rainfall is established. The moving average method was used to reduce the noise of the data:  
\[y(n)=\frac{1}{5}\,\times\sum_{i=n-2}^{n+2}x(i), \tag{2}\]  
Figure 10: Variation of axial force at monitoring points ITS-7, ITS-8, and ITS-9 and slope failure characteristics: (**a**) Slope surface erosion characteristic; (**b**) Tension crack caused by block slide; (**c**) Variation of axial force. where \(y(n)\) is the data point after the moving average, and \(x(i)\) is the original data set. The pore water pressure at measuring point P-3, which showed obvious changes, was selected to fit the axial force of the bolt. In the rainfall infiltration stage, the pore water pressure increased in a gradient, and the axial force of the bolt continued to decrease. The scatter diagram was drawn with the pore water pressure as the abscissa. It was found that the axial force of the bolt tended to a lower limit when the pore water pressure was large. The asymptotic function with a similar variation law was selected, and the allometric function was fitted with the Logistic function. Figure 11a shows the scatter plot and fitting curve of the axial force of the bolt at ITS-1 and the pore water pressure at P-3. The Logistic function with gradient characteristics is better, and the fitting parameters of the remaining monitoring points are summarized in Table 5.  
The slope stability criterion formula based on the Logistic function is:  
\[A=\frac{C_{1}-C_{2}}{1+\left(P/P_{0}\right)^{n}}+C_{2}, \tag{3}\]  
where \(A\) is the anchor bolt axial force; \(P\) is the pore water pressure in the weathering transition zone; \(P_{0}\) is an undetermined parameter related to the extreme point of the first derivative of the axial force of the bolt; \(C_{1}\), \(C_{2}\), \(C_{3}\) and \(n\) are undetermined coefficients. In the hydraulic fluctuation stage, the pore water pressure at measuring point P-3 increases rapidly and then fluctuates continuously. The axial force gradient of the bolt increases during the overall slip period of the broken rock block, and the axial force of the bolt at some monitoring points shows the unloading response characteristics of ITS. The scatter diagram drawn by using the pore water pressure as the abscissa is shown in  
Figure 11: Different function model fitting results: (**a**) Fitting analysis of rainfall infiltration stage; (**b**) Fitting analysis of hydraulic fluctuation stage. \begin{table}
\begin{tabular}{c c c c c c c} \hline \multicolumn{2}{c}{**Variable**} & \multicolumn{4}{c}{**Constant**} & \multirow{2}{*}{\(\mathbf{R^{2}}\)} \\ \hline
**A Data Set From** & **P Data Set From** & \(C_{1}\) & \(C_{2}\) & \(P_{0}\) & \(n\) & \\ \hline ITS-1 & P-3 & 17.41 & 15.50 & 0.29 & 11.34 & 0.92 \\ ITS-2 & P-3 & 18.51 & 16.72 & 0.24 & 7.81 & 0.95 \\ ITS-3 & P-3 & 17.34 & 13.56 & 0.22 & 4.40 & 0.99 \\ ITS-4 & P-3 & 16.43 & 12.27 & 0.32 & 17.38 & 0.93 \\ ITS-5 & P-3 & 7.18 & 0.33 & 0.42 & 1.82 & 0.94 \\ ITS-6 & P-3 & 14.72 & 10.37 & 0.34 & 3.76 & 0.94 \\ \hline \end{tabular}
\end{table} 
Table 5: Fitting parameter during rainfall infiltration period. Figure 11b, which is the scatter diagram of the axial force of the bolt at measuring point ITS-2 and the pore water pressure at P-3. It can be seen that the axial force of the bolt shows a gradient change pattern.