Mechanical effect of hydraulic expansion bolt reinforcement of roadway surrounding rock

Since the bolt was used in Coal Mine Support in the 1940s, bolt support has developed very rapidly due to its safety, high efficiency, and low cost, and has become the preferred main support method for coal mine roadways. However, when the coal seam group is mined at a very close distance, the integrity of the roof before the mining of the lower coal seam has been affected by the mining damage of the upper coal seam. Rock roadway, the use of traditional resin bolts to support such complex roadways can no longer control the overall stability of the roadway. Force) hydraulic expansion bolt support system, and has been successfully applied in the underground, effectively controlling the deformation and damage of the surrounding rock of the roadway. However, the research on the supporting mechanism of the hydraulic expansion bolt is not mature. In this paper, a reasonable numerical calculation and mechanical model are established according to the supporting method of the full-length anchoring of the hydraulic expansion bolt to study the mechanism of its reinforcement of the surrounding rock, and the research results are put into Xinrui Coal Mine is used for engineering practice.

1. The mechanism and structure of the hydraulic expansion bolt

The hydraulic expansion bolt is composed of end sleeves, retaining rings, liquid injection ends, trays and other accessories. As shown in Figure 1. The hydraulic expansion bolt is put into the bolt hole and expanded with high-pressure water. During the expansion process, the hydraulic expansion bolt is permanently deformed, making it firmly embedded in the surrounding rock and generating great friction; When the rod body expands, the anchor rod exerts a large pressure on the surrounding rock mass, forcing the surrounding rock to produce strain and increasing the stress of the surrounding rock. In the process of water expansion, because the diameter changes from thin to thick, there is a certain amount of shrinkage in the longitudinal direction, so that the tray of the anchor rod is tightly pressed to the surface of the surrounding rock, and an axial extrusion force is generated, so as to realize the prestressing of the surrounding rock. . The hydraulic expansion bolt generates friction and pressure in the whole length range, cooperates with the mechanical interlocking force generated at the tray, and is tightly embedded on the rock wall, which has a strong extrusion effect on the surrounding rock, resulting in a larger impact. The radial pressure and friction force can obtain effective anchoring force and realize the reinforcement of surrounding rock. The mechanism of action is shown in Figure 2.

2. Mechanical effect analysis of hydraulic expansion bolt action mechanism

2.1 Numerical simulation of the action mechanism of the hydraulic expansion bolt

2.2 Influence of anchorage length on the stress field of surrounding rock of roadway

2.3 Analysis of mechanical effect of hydraulic expansion bolt

2.4 Application conditions of hydraulic expansion bolt

3. Engineering application

According to the analysis of observation data, it can be seen that the hydraulic expansion bolt support technology has been successfully applied to the broken roof roadway, the strong deformation of the surrounding rock has been effectively controlled, the labor intensity of the workers is reduced, the working environment of the workers is improved, the safety of the working face is improved, and the safety of the working face is improved. The smooth progress of the mining work has created favorable conditions for the mine construction.

4. Summary

1) Hydraulic expansion bolts are suitable for loose, broken and weak rock formations, and have strong adaptability to surrounding rocks.

2) Within a certain range, the anchoring force of the hydraulic expansion bolt increases with the increase of the filling pressure, the greater the pressure of the rod on the hole wall, the more sufficient the deformation of the rod body, the larger the anchoring range, and the greater the friction. The anchoring force will also be greater.

3) With the increase of the anchoring range of the bolt, the area of the compressive stress area of the bolt gradually increases, the compressive stress field interacting with the bolt forms a dense network area, and the range of the tensile stress area at the top of the bolt increases gradually. The surrounding rock forms an integral bearing structure.

4) Numerical calculation shows that the friction force is distributed as a hyperbolic function under different pulling forces. When the hydraulic filling pressure is 30MPa, it is calculated that the supporting force (pre-tightening force) of the hydraulic expansion bolt is equal to 126ư 9kN. The calculation formula of the anchor force is consistent with the field test data.

5) The hydraulic expansion bolt support technology has been successfully applied in Xinrui Coal Mine, which can effectively control the deformation of the surrounding rock of the broken roadway, reduce the labor intensity and improve the working environment of the workers, and achieve good social benefits.

(From COAL ENGINEERING)