Study on the Support Effect of Energy-Absorbing Support Structure in the Coal Mine Roadway and the Synergic Effect with Wall Rock

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Introduction
In recent years, China's coal mining industry has shifted to deep mining due to the depletion of shallow coal resources, resulting in more complex formation conditions and an increased risk of rock burst accidents [1]. Most rock burst incidents occur in roadway, causing signifcant damage to the wall rock and posing a serious threat to the safety of personnel and equipment [2]. Rock support in burst-prone grounds needs to address a few additional designs [3]. Te use of yielding support is a key component when designing a rock burst support system. To prevent and mitigate these disasters, energy-absorbing technology has become a research area in roadway rock burst prevention and reduction [4].
Various studies have been conducted to improve roadway stability and prevent rock burst accidents [5][6][7][8], including the use of high-strength support systems such as single hydraulic columns and portal hydraulic supports. Te yielding cable bolt has also been studied [9,10]. Coal pore structure will also be afected by other factors [11][12][13]. Tose mentioned above follow the rock support guiding principles. Tere are also some new support theories [14,15]. Tere are some prevention and control methods for mining working face [16][17][18]. While these supports can reduce the probability of rock burst incidents, they may not be efective in mitigating the large impact energy associated with some rock burst disasters. To address this issue, Jiang et al. [19] proposed the use of energy-absorbing materials [20], energy absorption, and anti-impact coupling support [21], which have been shown to be efective in preventing rock burst accidents. Based on the theory of support systems and the analysis of roadway wall rock [22], a design principle for anti-impact support has been proposed, and the energy absorption anti-impact hydraulic support [23] has been developed and successfully applied in the feld. In addition, a folded thin-walled device [24] has been proposed as an energy absorption core device and yielding hydraulic support, and its mechanical properties have been studied.
Tis paper proposes that the use of a roadway energy absorption anti-impact support structure can signifcantly improve the prevention and control of rock burst in coal mines. Te support structure works in synergy with the wall rock to enhance its efectiveness. To establish a system model between the energy absorption anti-impact support and the wall rock, a numerical calculation method is used. Te mechanical state of the support and wall rock combination system is analyzed under both static and impact loads, based on the vertical and horizontal deformation of the roadway, equivalent plastic strain, plastic property, and damage range. Tese research indicators are used to study the support efect of the energyabsorbing support and its synergistic efect with the wall rock in coal mine roadway.

Energy Absorption Anti-Impact Support in Coal Mine
Roadway. Te roadway, which is supported by anchor mesh, anchor rods, anchor cables, hydraulic lifting sheds, and hydraulic support for rock burst prevention, adopts a semicircular arch section. Te roadway anti-impact hydraulic support is installed within the range of 40 m-260 m of the advanced coal mining face and the support is implemented at a spacing of 3 m. Te support base is buried in the foor, and tracks and belts are laid on the base. Te hydraulic support adopts an energy absorption anti-impact device, which is shown in Figure 1. Tere was a mining earthquake event in 2016 which caused the mechanical pressure gauge on the column in the two hydraulic supports for rock burst prevention to burst and damage, but the wall rock supported by the anti-impact structure did not have obvious deformation and showed no signs of damage. Tis event had a certain impact on the roadway in the support area, but the energy absorption anti-impact structure effectively resisted the dynamic process of the wall rock triggered by this mining earthquake.

Geological Background.
Te tectonics is a westward inclined monoclinic structure without faults. Te dip angle of the coal seam is 1-3°, with an average thickness of 4.72 m and a burial depth of approximately 680 m. Te surface water system in the mine feld is not developed, and there are no surface water bodies such as reservoirs and lakes.
According to the test results of the mechanical properties of the top and bottom slates of the coal seams, the top and bottom slates of each coal seam are mainly mudstone, sandy mudstone, and siltstone, followed by fne and medium sandstone. Te compressive strength of coal samples is the lowest among all rock types, belonging to soft rock and fractured rock mass.
Te compressive strength of the coal seam roof is between 3.20 MPa and 77.42 MPa, and the compressive strength of the coal sample belongs to soft rock with broken rock mass.

Energy-Absorbing Device.
Te crucial component of the energy absorption and anti-impact support is a structural member with special geometry [25,26]. Te mechanical properties and energy absorption efect of this member play a critical role in the anti-impact performance of the entire support. Te main structure of this component is depicted in Figure 2.
Te support function of the energy absorption antiimpact support depends on the deformation of the energy-absorbing device. After the deformation of the device, the support still has sufcient working resistance while allowing the limited deformation of the wall rock to continue to release energy, which can not only adapt to the deformation of the wall rock but also control the deformation of the wall rock, giving full play to the support efect of the support. Based on the abovementioned engineering applications, this paper studies the deformation synergy of the roadway wall rock support model.

Simulation
Model. Te fnite element model for this study was constructed using ABAQUS software, and the calculation model is depicted in Figure 3. Te roadway has a width of 4.88 m. To minimize the boundary efects on the model calculation process, a range of 3-5 times the tunnel diameter is selected around the roadway and the model size is 30 m × 30 m × 0.5 m. Te wall rock adopts the Mohr-Coulomb constitutive relationship, and the mechanical parameters are presented in Table 1.
Te energy absorption anti-impact support is composed of Q550 steel with a yield strength of 550 MPa, a density of 7850 kg/m 3 , an elastic modulus of 206 GPa, and Poisson's ratio of 0.3. Te simulation process adopts an ideal elastoplastic constitutive model, without considering the hardening properties of the steel. Te entire model uses  universal contact, with normal behavior defned as "hard contact," tangential behavior defned as a penalty function, and a friction coefcient of 0.3. Te wall rock element type is C3D8R, with a total of 8288 elements, while the rack unit type is S4R, with a total of 14456 units. Infnite elements are used around and at the bottom of the model, and the element type is CIN3D8. Te method of coupling the fnite element and infnite element is used to simulate the surrounding infnite space.

Calculation Condition.
To investigate the diference in support efectiveness between the energy-absorption antiimpact support and ordinary support without an energyabsorbing device, a comparison working condition was established. Vertical stress is simulated for the upper part of the wall rock, while horizontal stress adopts diferent lateral pressure coefcients.
Two stress ratios were applied to load the wall rock, and the specifc calculation working conditions are presented in Table 2.

Support Deformation.
Te support deformation in the roadway for each working condition is shown in Figure 4, while the maximum value of support deformation is presented in Table 3.
Based on the results shown in Figure 4 and Table 3, it can be observed that the energy absorption support deformation increased by 20.40% compared to the ordinary support, with the maximum deformation occurring at the upper right column. In addition, the anti-impact support exhibits the characteristic of deformation giving way to the overall deformation compared to the ordinary support. When the ordinary support is subjected to external impact, the deformation is biased to one side, and the column displacement is larger when the load increases. Although the deformation of the top beam down and bottom beam up of the energy absorption anti-impact support is larger than that of the ordinary support, the integrity is better, and the column part is close to the overall translation to ensure a "strong column" [27]. Terefore, to further compare the support deformation in the vertical direction under diferent working conditions, the vertical support deformation is analyzed. Figure 5 illustrates the vertical deformation of the supports. With the energy-absorbing device added at the bottom of the hydraulic column, the vertical displacement of the entire energy-absorption anti-impact support is primarily the rigid displacement of the bottom beam. In contrast, the vertical displacement of the column is small. Tis demonstrates that the energy-absorbing device plays a crucial role in protecting the column and preventing it from bending damage.   Shock and Vibration

Support Stress and Damage Range.
Te stress of the support is shown in Figure 6. Te maximum value of stress is shown in Table 4. For ordinary supports, the stress is mainly concentrated in the upper part of the three columns and the connection between the middle column and the top beam. When the vertical load increases to 20 MPa, the stress is mainly concentrated in the upper part of the three columns and the variable cross section of the left and right columns. For the energy absorption anti-impact support, the stress compared with the ordinary support stress, it increased by 4.74%, mainly concentrated in the upper part of the left and right columns. Compared with the ordinary support stress, energy absorption devices are mainly concentrated in the bottom beam which increased by 9.09%. Te upper left and right column strengths of both brackets are low, and there is a risk of yielding during application. After the energy-absorbing device is applied to the support, the stress in the upper part of the center column is obviously reduced, the overall stress distribution is more uniform, the stress concentration parts are reduced, and the support is more reasonably stressed.
Te equivalent plastic strain of the supports is shown in Figure 7. Te maximum values of the equivalent plastic strain are shown in Table 5.
Te energy absorption anti-impact support is adopted, and the overall stress of the support is diferent from the position of the maximum equivalent plastic strain of the ordinary support. Te maximum equivalent plastic strain of the ordinary support occurs at the location of the midcolumn variable cross section, whose place is more dangerous. Te maximum equivalent plastic strain of the energy absorption anti-impact support occurs at the position of the limit hinge of the bottom beam, and compared with the ordinary support, the plastic strain decreased by 66.67%. In the actual production and application process, there is thickening treatment at the position of the limit hinge, and it      can be considered that the position meets the safety requirements.
Te plastic strain distribution of the support is shown in Figure 8. Plastic deformation occurs in the upper part of the three columns of the ordinary support, while the columns of energy absorption anti-impact support are still within the elastic range of the line. Terefore, it can be considered that the energy-absorbing device applied in the support can play a good role in protecting the support, making the force of the whole support more uniform and reasonable, and favorably reducing the risk of damage to the support.

Support Energy.
Te energy nephogram of the three columns of the support under each working condition is shown in Figure 9. Te energy absorbed is shown in Table 6. It can be observed that the energy absorption is more than twice that of ordinary support. Te energy absorption of the three columns is not equal, and the most energy absorbed place is the left column. Te energy absorption of the middle column is the average of the left and right columns. When the entire support is impacted, due to the close distance between the left two columns, it bears more energy absorption function, while the right column absorbs less energy. Te support structure can be optimized in the future. Figure 10. Compared with the ordinary support, when the wall rock is with the energy absorption support, its deformation is improved by 3.59% and 2.91%, respectively. It can be considered that the energy absorption      anti-impact support is used to give way frst and then resist to the wall rock, which can also ensure the overall deformation of the wall rock.

Wall Rock Deformation. Te deformation of the wall rock is shown in
Te energy absorption anti-impact support calculated in this paper has a yielding efect in the vertical direction. From the vertical deformation of the wall rock in Figure 11,       +1.191e+00 +1.000e-09 +9.167e-10 +8.333e-10 +7.500e-10 +6.667e-10 +5.833e-10 +5.000e-10 +4.167e-10 +3.333e-10 +2.500e-10 +1.667e-10 +8.333e-11 +0.000e+00 Max: +1.  because the energy absorption anti-impact support leaves a deformation space of about 120 mm in the vertical direction, when the external force acts on the support, the allowable deformation is larger compared to the ordinary support. Finally, the deformation in the vertical direction of the wall rock increases when the wall rock is supported by the energy absorption anti-impact support, and the maximum value only increases by 0.85 mm. Tat means the energy-absorbing device applied in the roadway, the wall rock, and the energy absorption anti-impact support can deform together. Te support frst gives way, the wall rock resists the external impact, and then the support and the wall rock resist the pressure together to achieve synergy.

Wall Rock Stress and Damage
Range. Te stress distribution in the wall rock is shown in Figure 12. In the process of deformation of the energy absorption anti-impact support giving way, the wall rock stress has a certain degree of release, making the secondary stress redistribution process also increase the scope of infuence. Compared with the ordinary support, the maximum stress of the wall rock is increased when the energy absorption anti-impact device supports the wall rock; when σ H � 10 MPa and σ V � 10 MPa, the maximum stress is 67.05 MPa and the maximum value is increased by 10.19%, and when σ H � 10 MPa and σ V � 20 MPa, the maximum stress is 55.52 MPa and the maximum value is increased by 16.42%. Te equivalent plastic strain distribution of the wall rock for each working condition is shown in Figure 13. Te plastic zone of the wall rock is increased when the energy-absorbing device is used, making full use of the wall rock itself to resist external dynamic loads.

Conclusion
(1) After the energy-absorbing support mentioned in this article was used in a certain project, a mining earthquake occurred in a coal mine. Te mechanical part of the hydraulic support column was damaged due to excessive pressure, but the deformation of the wall rock roadway was not signifcant, and the support structure did not show any damage. Te energy-absorbing and anti-impact support efectively resisted the dynamic damage of the wall rock caused by the mining earthquake. (2) Te addition of the energy-absorbing device in the support has signifcant advantages. Te stress concentration area is reduced, and the overall stress distribution becomes more uniform. Tis results in a more reasonable stress distribution on the support and reduces the risk of damage. Te energy-absorbing device also allows for deformation giving way to the overall deformation, making the force of the whole support more uniform and reasonable. Terefore, the energy-absorbing device applied in the support plays a signifcant role in protecting the support. (3) Te energy absorption anti-impact support can effectively absorb more energy compared to ordinary support. Tis means that it can reduce the plastic damage caused by the impact load on the hydraulic support. Tis feature is particularly useful in environments where impact loads are high, as it can help prevent structural damage and ensure the long-term stability of the support. (4) Te energy absorption anti-impact support can deform together with the wall rock. Tis means that the support frst gives way, and then the wall rock resists external shocks, and fnally, the support and the wall rock resist pressure together. Tis process achieves synergy between the support and the wall rock, ensuring the overall deformation of the wall rock. Te energy absorption anti-impact support's ability to give way frst and then resist the wall rock makes it an excellent choice for supporting the tunnel structure in environments where impact loads are high.

Data Availability
Te data used to support the fndings of this study are included within the article.

Conflicts of Interest
Te authors declare that there are no conficts of interest.