# The Failure Law and Combined Support Technology of
## 4 Failure Mechanism and Control Technology of Roadway Surrounding Rock Support
### Support Technology Combined with Multi-Stage Strengthening of Surrounding Rock  
The above analysis shows that the mechanical properties of surrounding rock in fracture, plastic, and elastic zones are different, so the required supporting strength is also different. Moreover, the coupling of support and mechanical properties of surrounding rock can effectively improve the geological strength index (\(GSI_{\text{res}}\)) residual value and reduce the disturbance degrees (\(D_{\text{res}}\)). It also helps to give full play to the support resistances (\(P_{i}\)) of the support body. Based on this, we put forward the subsection reinforcement combined support technology with \"high-strength prestressed anchor bolt (cable) support as the core, deep and shallow hole grouting as the foundation, bottom angle and floor anchorage grouting reinforcement as the key,\" as shown in Figure 9. The principle is as follows:  
1. Prestressed bolts, steel mesh, and shotcrete support are preferred in the initial support. Among them, the density of bolt support should not be too small, as the \"pin effect\" of the bolt can transform the cataclastic structure into a cohesive whole structure, significantly improving the surrounding rock's bearing capacity. In addition, the length of the bolt should not be less than 2.6 m, which is conducive to each bolt exerting a force on the surrounding rock along the length of the bolt, forming a reinforcement zone. All the reinforcement zones are connected, forming a reinforcement ring with an arch effect inside the surrounding rock. It can not only improve its strength and have a self-supporting effect but also provide confining pressure and improve the stress environment of surrounding rock, thus limiting the tangential and radial deformation of surrounding rock. 2. High-prestressed long anchor cable should be the primary reinforcement support. The anchorage section of the long anchor cable can extend into the deep, stable surrounding rock with high confining pressure and then transmit the load of the fracture zone to the deep, stable rock layer through suspension. In the fracture zone, the plastic softening zone and elastic zone were connected into a region that expands the bearing range of the surrounding rock and fully mobilizes the overall bearing capacity of the surrounding rock. 3. The primary reinforcement support should be full-section multi-stage grouting. It is difficult to prevent the long-term rheology of surrounding rock only by supporting anchor rods and cables in the roadway with high stress and weak surrounding rock. The extensive development of cracks in surrounding rock provides a channel for cement grout to penetrate the surrounding rock. Low-pressure shallow hole grouting can bond and solidify the rock mass in the fractured area, forming a grouting reinforcement ring in the surrounding rock's shallow part, effectively preventing the grout leakage. The high-pressure deep hole grouting can close the micro-cracks, and the grout diffuses in the cracks in a \"network\" to form a high-strength skeleton structure, improving the surrounding rock's shear strength and integrity. At the same time, after the plastic energy of the surrounding rock is released, the key bearing area will move to the depth. The key bearing zone, strengthened by grouting, requires only a tiny compressive expansion force and supporting resistance to maintain roadway stability. (4) A high-strength anchorage bearing arch system is formed in broken surrounding rock by high prestressed anchor bolt (anchor cable) support, graded grouting reinforcement, and concrete spray layer. However, the stability of the bearing arch also depends on the strong bottom foundation [27]. The bottom foundation is used to bear the arch leg, and the deformation and malposition of the arch leg will cause instability in the supporting system. The natural strength of floor strata is improved, and the release of horizontal stress is blocked by anchoring reinforcement of the floor and bottom angle.