## 3 Discussion of the Reinforcement Mechanism of Prestressed Anchor Cables
### The Reinforcement Mechanism of Prestressed Anchor Cables on the Slope  
According to the aforementioned analysis, it can be seen that reinforcing the slope by using prestressed anchor cables increased the safety factor. Based on the previous understanding on the reinforcement of prestressed anchor cables on the slope, it was generally thought that on the one hand, prestressed anchor cables provided a certain sliding resistance. On the other hand, it imposed a large compressive stress on the sliding surface, thus enhancing the shear resistance thereof (Figure 10). It can be seen from the figure that cable prestress was decomposed into sliding resistance and compressive stress, with the latter being much greater than the former: however, according to previous research [11; 32] prestressed anchor cables show a finite transmission range (mainly in the range of 0 to 2 m from the surface to the interior of a slope) within the slope rock and soil masses. Generally, high and steep slopes have a deep sliding surface, so using prestressed anchor cables cannot directly improve the compressive stress on the sliding surface and its shear strength cannot be strengthened as a result. As a result, this is not a reasonable explanation for any increase of safety factor of the slope caused by prestress anchor cables. Figure 9: Variation of force with different strength reduction factors in certain cables. (**a**) Cable 1; (**b**) Cable 3; (**c**) Cable 5; (**d**) Cable 8; (**e**) Cable 10; (**f**) Cable 12; (**g**) Cable 13; (**h**) Cble 15. Additionally, the reinforcement mechanism of a prestressed anchor cable on slopes is generally discussed from the perspective of improving the stress state. It is thought that the function of prestressed anchor cables is to improve, and even recover, the stress state of slope rock and soil masses, thus increasing the safety of slopes. Based on this understanding, some scholars have proposed some design methods. For example, [PERSON] et al [14] proposed a design method for reinforcing slopes by recovering the stress state of sliding surfaces. [PERSON] et al. [15; 16; 17] proposed a design method for reinforcing slopes by analysing the stress and deformation fields. However, according to the stress distribution in surrounding rocks reinforced by prestressed anchor cables, it can be seen that prestressed anchor cables only can improve or recover the stress state within a finite range of soil depths. Especially for high and steep slopes with a deep sliding surface, this understanding fails to explain the true reinforcement mechanism of prestressed anchor cables on slopes. By exploring the reinforcement effect of cables on high slopes in Three Gorges Shiplock, [PERSON] et al. [11] proposed the concept of an anchored rock wall. They suggested that the degradation of the mechanical properties of rock mass within the anchored walls is mitigated, thus inhibiting the deformation of slope rock and soil masses and improving slope stability. To some extent, this partially explains why the stability of excavated high and steep slopes is strengthened after installation of prestressed anchor cables. However, the reinforcement effect of prestressed anchor cables is not only mitigating the degradation of mechanical properties of rock and soil masses within the compression zone on the surface of slopes. After all, whether a potential sliding surface slides or not is the dominant factor governing slope stability. Through aforementioned analysis, by comparing displacements of the slope without and with prestressed anchor cables (Figure 6), with increasing strength reduction factor, cables effectively restricted the sliding of potential sliding masses in the slope. As shown in Figure 8, as the strength reduction factor increased and even exceeded the safety factor of the slope, the incremental force on the cables increased, indicating that the slope started to slide while prestressed anchor cables began to play a restrictive effect on the sliding of the slope.