## 4 Results and Discussion
### Major Cracks and Stress Variations
#### 4.2.2 Locations and Depths of the Major Cracks  
Three main parameters need to be analyzed during the formation and propagation of major cracks [14], namely the stress level, the crack initiation, and the direction and length of crack propagation. The first factor was discussed in Section 2. In practical terms, we are unlikely to investigate the stress change process of the soil unit point by point, and burying more sensors in the soil slope will also face the problem of high cost. The progressive failure process of a soil slope is also a process of stress transfer and redistribution in the soils. During the loading process of this test, \(\Delta\sigma_{z}\) changes linearly (shown in Table 2). Combined with Equation (8), the sudden change of the principal stress near the crack would inevitably lead to the sudden change in \(\Delta\sigma_{x}\). When investigating the stress changes in two adjacent measuring points under the same load step, the measuring points on both sides of the crack should show the phenomenon of discontinuous stress transfer. The stress analysis during the aforementioned loading process showed that for the progressive failure process of the clay slope, the changes in horizontal stresses were more sensitive than those of vertical stresses. When investigating the locations and depths of the cracks, horizontal stresses were adopted. The horizontal stress differences between two adjacent measuring points in the same layer of the soil slope are shown in Figure 6. Both the fourth and fifth layers were not analyzed because there was only one available stress monitoring point. Figure 6: Horizontal stress difference curves of lateral adjacent monitoring points. Using i and j to represent the measuring point, the difference curve i-j represents the horizontal stress at point j minus the horizontal stress at point i under the same load step. The difference curves were generally below the zero line, indicating that the distribution characteristics of the horizontal stresses in the soil slope were large in the rear part and small in the front part centered on the loading position. Curves 13-14, 23-24, and 33-34 basically remained linear in the 0-140 kN stage because the corresponding measuring points were in the nonyielding zone during the loading process, and the stress transfer process always follows the elastic or elastoplastic law. The difference curves basically stayed linear during 0-100 kN, possibly because the measuring points were not affected by cracks in this stage. In the first layer, there was an obvious turning point in the difference curve 11-12 at 100 kN, indicating that it was affected by the trailing edge crack. The difference curve 12-13 showed a linear transfer form before 120 kN, and deflection occurred at 120-140 kN, indicating that it was affected by the front edge crack. In the second layer, the difference curve 21-22 increased during the 100-120 kN period, certifying that no cracks appeared between the measuring points 21 and 22, and the trailing edge crack appeared on the left side of the measuring point 21. During the period of 100-120 kN, the horizontal stress differences between measuring points 23 and 22 changed from a positive value to a negative value, indicating that the front edge crack passed through the area between the two measuring points. In the third layer, the difference curve 31-32 was always negative, and the slopes of the curve did not change significantly during the period of 100-140 kN, demonstrating that there was no crack between the two measurement points. However, the differences between measuring points 33 and 32 changed from zero to an increasingly obvious negative value during the period of 0-100 kN, demonstrating that there was a crack passing between the two measuring points. As for curves 11-12 and 21-22, they remained level during 100-140 and 120-140 kN, respectively, which might have been affected by the plastic zones in the loading process.