In order to improve the impact resistance mechanical properties of bolt, the requirements of rock burst roadway support must be met. Based on the requirements that the anchor should have a reasonable deformation load threshold, high stroke efficiency, constant reaction force and stable repeatable deformation damage mode. A constant resistance anti-impact device was designed, and a new constant resistance energy-absorbing impact anchor rod was designed in combination with a conventional anchor rod, and the working principle of a constant resistance energy-absorbing impact anchor rod was given. ABAQUS finite element software was used to analyze the mechanical properties of bolt and the results showed that the constant resistance energy-absorbing anti-shock anchor has a stable and repeatable deformation damage mode under both static and impact loads, and the three indexes of the constant resistance energy-absorbing anti-shock anchor, such as yield distance, impact resistance time and energy absorption, are significantly better than those of the conventional anchor. The impact energy and impact velocity have less influence on the load-bearing capacity and stroke efficiency of the impact device. The impact velocity has less influence on the indices of the rod yield load, breaking load, absorbed energy and the yield distance of a conventional anchor and constant resistance energy-absorbing anti-stroke anchor, and the impact resistance time decreases non-linearly with the increase in the impact velocity.
Conventional FRP anchor rods have low elongation and poor impact resistance, both of which do not meet the support requirements of rock burst roadways. Therefore, a pressure energy-absorbing FRP anchor rod composed of an FRP rod body, tray, energy-absorbing sleeve and round table nut was designed. Numerical simulations were carried out to study the mechanical properties of the FRP anchor rod in static tension and impact tension, and to compare its mechanical properties with those of conventional FRP anchor rods. The results show that the pressure energy-absorbing FRP anchor rod is stretched in four stages: the front-elastic stage, constant resistance to compression, the back-elastic stage and damage, with an additional constant resistance to compression stage compared with conventional FRP anchors. The elongation, energy absorption and impact resistance time of the pressure energy-absorbing FRP anchor rods are greater than those of conventional FRP anchor rods, and the mechanical properties of the pressure energy-absorbing FRP anchor rods are better than those of conventional FRP anchor rods. As the impact velocity increases, the energy absorption rate of the pressure energy-absorbing FRP anchor increases non-linearly. The impact energy and impact velocity have less influence on the breaking load, elongation and energy absorption of pressure energy-absorbing FRP anchor rods. The research results can provide a theoretical basis for the application and parameter design of the pressure energy-absorbing FRP anchor rod, and provide support for the safe and efficient mining of the mine.
In order to enhance the anti-impact mechanical properties of the roadway support system, an automatic anchoring pre-tightening energy absorbing anchor composed of rod body, tray, constant resistance energy absorber, energy-absorbing casing bulging block, pre-tightening force warning washer, and nut and anchorage force warning stopper was designed and developed for the special requirements of rock burst roadway support. The anchor can automatically judge the anchoring force and pre-tightening force of the anchor, and also has the functions of energy absorption and early warning. The static load tensile test and impact test are used to study the mechanical properties of the energy absorbing anchor, such as the displacement distance, energy absorption, and impact time, and they are then compared with the mechanical properties of the conventional anchor. It is concluded that under static load, the yielding distance of the energy absorbing anchor is 1.67 times that of conventional anchor. The absorbed energy is 1.61 times that of the conventional anchor. Under the impact load, the displacement distance of the energy absorbing anchor is 2.02 times that of the conventional anchor. The absorbed energy is 1.85 times that of the conventional anchor, and the anti-impact time is 1.47 times that of the conventional anchor. The energy absorbing anchor increases the constant resistance deformation stage of the energy absorber during the deformation process, so that the anchor has better deformation ability, energy absorption, and anti-impact ability than the conventional anchor, and it can thus effectively guide and control the release and transformation of surrounding rock deformation energy.
In practice, constant-resistance, energy-absorbing, and anti-scouring bolts inevitably deflect at an angle from the coal wall and other bearing surfaces, eventually giving way and losing their energy-absorbing function. The aim of this study was to determine the applicable range of deflection angles for constant-resistance, energy-absorbing, and anti-scouring bolts and to provide a reference design for bolt construction. The principle of application of bolts under various deflection angles was proposed, and the numerical simulation of use of constant-resistance, energy-absorbing, and anti-scouring bolts was carried out using ABAQUS finite element software. The effects of deflection angle, impact energy, and impact velocity on the deformation performance, load-bearing performance, and energy absorption performance of the bolts were investigated. The deformation process of the bolt based on deflection angle was found to change from axial stretching to “stretching and bending”. As the deflection angle increased, the load bearing capacity of the anti-punching device increased, and the bolt’s breaking force increased after decreasing, and then decreased again while absorption energy decreased non-linearly. The bolt yield distance decreased while the displacement of bolts remained essentially the same and the deflection distance of the anti-punching device decreased. The stroke efficiency of bolts decreased and, based on the design principles of constant-resistance, energy-absorbing, and anti-scouring bolts, it was determined that the bolt was still applicable within a deflection angle of 0–17°. The impact energy had a minor effect on the bolt indicators of yield force, breaking force, and energy absorption, and the bolt’s impact resistance time decreased non-linearly with increasing impact energy. Impact velocity had less effect on bolt yield force and breaking force. Both yielding time and anti-punching load capacity of the bolt decreased with increased impact velocity. As the impact velocity increased, yield distance, anti-punching deflection distance, and stroke efficiency all increased. The absorption energy increased linearly with increasing impact velocity. The results of this study provide a reference for similar anchor angle studies and a guide for the design of field construction.
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