## 2 Test Overview
### Test Flow  
The specific test flow is shown in Figure 4.  
(1) Laboratory mechanical test  
Considering the established stress environment of slope rock mass with excavation disturbance, in situ stress of 18 MPa obtained from borehole data in the field is taken as the upper limit of lateral stress and as the boundary condition for simulating lateral stress of slope. Based on the above considerations, the saturated sandstone samples were subjected to triaxial compression tests with confining pressures of 0, 9, 12, and 15 MPa and triaxial unloading tests with corresponding confining pressures, respectively. The maximum axial pressure of the triaxial unloading test was 70% of the peak strength of the sample under the corresponding confining pressure [35], and the triaxial loading and unloading test results of the samples were obtained as shown in Table 2. The formula in brackets represents the calculation process of 70% of the triaxial peak strength under corresponding confining pressure, and it is used as a reference for unloading amount. (2) Preparation of unloaded samples  
Based on the results of conventional triaxial loading and unloading tests in the laboratory, three confining pressures of 9, 12, and 15 MPa with the magnitude of 80% unloading [33] were selected, and the stress-strain curves of the proposed confining pressure of the unloaded samples were obtained as shown in Figure 5, and the corresponding stages were referred to in Figure 2. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Test Types** & **Maximum Axial Pressure/(MPa)** & **Confining Pressure during Unloading Failure/(MPa)** \\ \hline Uniaxial Compression Test & 48 & — \\ Triaxial Compression Test (Confining pressure 9 MPa) & 115 & — \\ Triaxial Compression Test (Confining pressure 12 MPa) & 127 & — \\ Triaxial Compression Test (Confining pressure 15 MPa) & 140 & — \\ Triaxial Unloading Test (Confining pressure 9 MPa) & 81 (115 \(\times\) 0.7) & 2.5 \\ Triaxial Unloading Test (Confining pressure 12 MPa) & 89 (127 \(\times\) 0.7) & 4 \\ Triaxial Unloading Test (Confining pressure 15 MPa) & 98 (140 \(\times\) 0.7) & 5.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of laboratory conventional mechanical tests. Figure 4: Test flow chart. It can be seen from Figure 5 that there is a large overlap of hysteresis loops under different upper limit stress conditions, which depends on the initial confining pressure and is mainly reflected in stage 2. With the increase of initial confining pressure, the area of the hysteresis loop increases gradually, and the corresponding area increase ratio shows an accelerating trend. Compared with the lateral strain, the axial strain changes relatively evenly and approximately linearly in each stage. The lateral strain expansion includes linear and nonlinear stages. In unloading stages, the strains are quite different and show a significant nonlinear trend. Compared with stage 1, the lateral strain variation of stage 5 decreases significantly, and the maximum is only about 40% of stage 1. The main reason is that during the process of confining pressure grading unloading, the activity of microcracks increases rapidly, the volume of the sample increases, and part of the deformation caused is irrecoverable. It is reflected from the side that the confining pressure unloading stage is the main stage of the load-induced damage of the sample. (3) Dry-wet cycle test  
Taking the number of dry-wet cycles as the grouping standard, the unloaded samples were divided into five groups. The test was set to dry in the oven at 105 \({}^{\circ}\)C for 12 h and fill with water for 12 h as a dry-wet cycle. The mass and wave velocity of each sample after each dry-wet cycle were measured, respectively, and the variation of mass and wave velocity of unloaded samples with dry-wet cycles was analyzed. (4) NMR  
An NMR spectrometer (MesoMR23-060H-I) was used to carry out the test. The pore size distribution was determined by analyzing the relaxation characteristics of hydrogen-containing fluids (such as water) in rock pores.