## 2 Experimental Conditions and Experimental Programme Design
### Experimental Programme  
We have taken deep mining as an example. When the work face advances along the strike direction, the distribution of the upper roof rock support pressure near the work face is shown in Figure 3.  
Figure 1: Triaxial rock multi-field coupling test platform.  
Figure 2: Principle of experimental equipment.  
In the vicinity of the work face, stress-raising and stress-reducing zones are formed within a certain range. As the work face advances and the hydraulic support of the roadway top plate is \"supporting and shifting\", the rock layer of the roadway top plate will be subjected to the cyclic alternating action of \"loading and unloading\". The interior of the top rock layer at a point then exhibits repeated changes in stress in the vertical direction. In order to analyse the change pattern of the mechanical properties of the top rock layer at this point of the process, high-strength sandstone samples were investigated using triaxial graded cyclic loading and unloading. In order to investigate the mechanical and energetic characteristics of sandstone after thorough disturbance, the number of loading cycles per stage is 12. According to the experimental purpose and experimental equipment specifications in the triaxial multistage cyclic loading and unloading test, the stress-controlled loading method is adopted, in which the surrounding pressure is first loaded to a predetermined value and then the axial load is applied. The surrounding pressures were 0 MPa, 5 MPa, 10 MPa, 15 MPa, and 20 MPa with a loading rate of 0.1 MPa/s. The axial cyclic loading is divided into three stages of 0.45\(\sigma\) to 0.55\(\sigma\), 0.55\(\sigma\) to 0.65\(\sigma\), and 0.65\(\sigma\) to 0.75\(\sigma\), where \(\sigma\) is the average of the peak stresses of the samples obtained from the conventional triaxial compression test at the corresponding surrounding pressure. The axial cyclic loading and unloading rates were both 0.1 MPa/s. After completing the corresponding cycle, loading and unloading continue to load at a rate of 0.1 MPa/s until the sample is destroyed, and the stress loading path is shown in Figure 4. In order to obtain the peak strength of the sample at different surrounding pressures, a conventional triaxial compression test at the corresponding surrounding pressure should also be carried out. After the sample reaches the peak strength, the residual strength of the sample is obtained by displacement loading in a controlled manner at a rate of 0.02 mm/min. The details of the experimental programme are shown in Table 1.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Test Loading Method** & **Surrounding Pressure** & **Surrounding Pressure** & **Cyclic Loading and** & **Axial Pressure Loading** & **Samples No.** \\  & \(\sigma_{2}\)**, \(\sigma_{3}\)/MPa** & **Loading Rate/MPa/s** & **Pressure \(\sigma_{1}\)/MPa** & **Rate/MPa/s** & \\ \hline Conventional triaxial & & & & / & S1–S15 \\ loading & 0,5,10,15,20 & 0.1 & 0.45\(\sigma\)–0.55\(\sigma\), & & \\ Triaxial cyclic loading & & & 0.55\(\sigma\)–0.65\(\sigma\), & 0.1 & SC1–SC15 \\ and unloading & & & 0.65\(\sigma\)–0.75\(\sigma\) & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Experimental programme and parameters.  
Figure 3: Upper rock support pressure distribution.