## 2 Test Overview
### Test Program  
To study the freeze-thaw deterioration characteristics of excavation unloaded rock masses on steep and high bank slopes in cold regions, an integrated indoor test considering the interaction between excavation disturbance and freeze-thaw cycles was carried out. The specific test protocol is as follows:  
1. Triaxial compression tests were carried out at three confining pressures (10 MPa, 15 MPa, and 20 MPa), and compressive strengths were obtained at specific circumferential pressures (130.25 MPa, 152.67 MPa, and 172.11 MPa);
2. The excavation unloading stress path of the slope rock in cold regions was simulated and triaxial unloading tests with constant axial pressure unloading of the confining pressure were performed in which the axial stress was loaded to 70% of the compressive strength at a specific surrounding pressure [19]. The confining pressure was then unloaded until the specimen was damaged. To investigate the evolution of the unloading damage process of the enclosing pressure and to obtain unloaded-damaged rock samples that still have a certain load-bearing capacity, the unloaded-damaged sample was prepared by using a stress path with constant unloading of the confining pressure to the target value;
3. The cold region bank slope excavation unloaded rock body is in a three-way force state, and the slope support causes the surface rock body to be affected by the restraint effect, and the freezing and thawing environment triggers the freezing and swelling force caused by the internal water-ice phase change of the rock body in the form of extended development and misalignment slip toward the internal fissures of the rock body. Using the unloaded-damaged sample rock sample as the object, a homemade rock freeze-thaw jig was used (as shown in Figure 2) and combined with the characteristics of the field temperature environment to perform an indoor freeze-thaw cycle test. The freezing temperature was set to \(-\)30 \({}^{\circ}\)C, the ablation temperature was set to 25 \({}^{\circ}\)C, and the sample experienced low-temperature freezing for 12 h followed by room-temperature ablation for 12 h (as shown in Figure 3). A freezing-thawing cycle pre-test was carried out on the unloaded-damaged sample until obvious macroscopic cracks appeared in the rock sample and the rock sample would be broken after the next freezing-thawing cycle. The maximum number of freezing-thawing cycles was measured to be eight times. Therefore, the number of freezing-thawing cycles was finally selected to be zero, two, four, six, and eight times.
4. The unloaded-damaged samples were removed after each freeze-thaw cycle, and the mass, height, diameter, and porosity were recorded. After reaching the target number of freeze-thaw cycles, all rock samples were removed for uniaxial and triaxial reloading tests, in which the values of confining pressure for the triaxial reloading mechanics test were selected as the target values of confining pressure unloading in the preparation of the unloaded-damaged sample, which reflected the stress state after unloading and could better facilitate the investigation of the relationship between the stress state of excavation unloaded rock masses and freeze-thaw erosion.