Analysis of the response characteristics of a roadway wall under the impact of gas explosion

Mine gas explosion causes serious failure (damage) to the roadway, but the research on the response characteristics of the impact load of gas explosion to the roadway wall are still very limited. In view of the shortcomings of the existing research, the LS‐DYNA software is used to establish the physical and mathematical models of gas explosion in a roadway, and the validation results show that the model is effective and reliable. Based on the model, changes of pressure, velocity, displacement of roadway walls and equivalent stress under the impact of gas explosions are measured. The response characteristics of the end and wall of roadway under the thermal impact of gas explosion are analyzed. The results show that the pressure on the closed end wall, the center and edge of the roadway is relatively large, and the wall failure is also relatively more serious. With the propagation of gas explosion, the overpressure on the closed end wall gradually attenuates, and the maximum overpressure region also retracts to the center. At the closed end, the explosion pressure is first loaded on the inner wall and gradually transferred to the outer wall. During the transfer, the pressure decays step by step, and the velocity of the measuring point at the closed end decays continuously. With the propagation of gas explosion, the displacement of each measuring point in the Z direction increases continuously. In the axial direction, the displacement near the center of the roadway is large, and then the displacement decreases in the form of regular rings. The impact load produced by the gas explosion is first loaded onto the closed end wall, resulting in wall deformation and equivalent stress. The study results can provide some theoretical basis and data support for the roadway wall design, and reduction of the wall failure.


| INTRODUCTION
The gas explosion accident in a coal mine causes many casualties, huge property losses and serious failure (damage) to roadway facilities and equipment. [1][2][3] The failure effect of the gas explosion is mainly reflected in the propagation stage of the gas explosion. To master the failure and response characteristics of gas explosion, many scholars have done a lot of research on gas explosion, [4][5][6][7][8][9] and achieved fruitful research results. For example, Yuan summarized the commonly used research methods about the study of dynamic response characteristics of surrounding rock of underground caverns, such as on-site blasting vibration test, theoretical calculation and numerical simulation. 10 Gao et al. studied the distribution law of vibration velocity, stress and bending moment of mountain tunnel lining under bottom dynamic load, which obtained that under the action of blasting dynamic load at the bottom, the peak vibration velocity at the bottom of the tunnel lining arch is the largest, followed by the two sides, and the peak vibration velocity in vault is the smallest. 11 Tianyuan et al. used FLAC3D software to establish an underground roadway model, and analyzed the variation characteristics of the velocity and displacement of the underground roadway under the action of blasting vibration. 12 Liu Bowen et al. studied the propagation and influence of vibration signals in the blasting excavation process of deep tunnels, as well as the difference of blasting vibration response characteristics between internal surrounding rock and surface rock. The results showed that the distance between rock mass particles and the excavation surface is an important factor, and the spatial relationship between them is also an important factor affecting the maximum vibration velocity of particles. 13 Zhang simulated the construction process of tunnel blasting, the numerical results found that the exponential load waveform can more completely show the spatial variability characteristics of surrounding rock than the smooth curve load waveform and the triangular load waveform, and the deformation size is consistent with the actual working condition. 14 He et al. studied the variation law of explosion load and transient unloading stress field of in-situ stress caused by multi-stage blasting on the excavation surface. The research results found that when the local stress continues to increase, the contribution of transient unloading of geostress to the damaged region will become more and more obvious. 15 Yang et al. studied the problem of rock fragmentation under the action of coupled static stress and spherical charge explosion, 16 and found that uniaxial static stress loading can change the rock failure surface from circular to elliptical, and increase the failure region. Under the action of biaxial equal stress, the shape of the failure surface is circular. Guo et al. established numerical simulation model of a rock blasting mechanics based on discontinuous deformation analysis (DDA) method, 17 and carried out numerical simulation of single-hole blasting of homogeneous rock under the conditions of two-way equivalent and unequal geostress. The results showed that under the condition of bidirectional equivalent stress, the blasting crack region is approximately circular, and its region decreases with the increase of initial geostress, in the condition of two-way unequal stress, the blasting crack expands deeper in the direction of larger geostress.
At present, the research on the structural response and structural failures caused by explosion impact loads are mostly reflected in explosions of solid explosives. However, research on the response characteristics of impact loads in underground gas explosions to roadway walls is still very limited. In most research, laboratory pipes are mainly used to simulate underground roadways to analyze the wall response of roadways, but the limitations of explosion experiments make it impossible to get the detailed information of explosion process, however, numerical simulation can well reproduce the whole explosion process. Research shows that numerical simulations can better simulate the explosion impact problem. 1,7 In view of the shortcomings of the existing research, the LS-DYNA software is used to establish the physical and mathematical models of gas explosion in roadways. The response characteristics of roadways under the thermal impact of gas explosions are analyzed by measuring the changes in pressure, velocity, displacement and equivalent stress of roadway walls under the impact of gas explosions. It is expected that the study results can provide some help for the reduction of roadway wall damage. To simplify the calculation, some basic assumptions are made for the model as follows: (1) There is only one thermal source of gas explosion in the roadway.
(2) Roadway wall is smooth, the turbulence caused by the wall is not considered. (3) The boundary is set as non reflective boundary condition. (4) Under normal temperature and pressure, the initial state of gas is evenly distributed, the initial temperature T 0 is 25°C and the initial pressure P 0 is 0.1 MPa. (5) There are no obstacles inside the roadway. (6) The thermal effect of roadway wall is not considered. (7) Only one step reaction of gas explosion is considered. Namely, in reaction, CH 4 + O 2 = CO 2 + H 2 O is only considered. The intermediate process of chemical reaction is ignored; intermediates and instantaneous products are also not considered.

| Basic governing equation
ANSYS/LS-DYNA software mainly adopts the Lagrangian description increment method. The particle position at the initial time is taken as X i ( = 1, 2, 3) i . At any time t, the particle position is The motion equation of the particle is as follows 18,19 : When t = 0, the initial condition is as follows: where, V i is the initial velocity.

Momentum conservation equation
where, σ ij is Cauchy stress, f i is volume force per unit mass, xï is acceleration.

Mass conservation equation
where, ρ is the current mass density, ρ 0 is the initial mass density,

Energy conservation equation
where, ε is the strain rate, q is volume viscous resistance, S is deviator stress, p is pressure, δ is Kronecker symbol.  (9) where, n j ( = 1, 2, 3) j is the cosine of the outer normal direction of the boundary, t i ( = 1, 2, 3) i is the surface force load.
2. Displacement boundary condition where, K t ( ) i is the Shift function for a given location i 3. Displacement condition at geometric discontinuity of sliding contact surface In the process of solving the cycle, the new time step is the minimum value of the time step of all elements, namely.
where, N is the number of units. The limit time step of the element can be calculated by the following equation: which is premixed gas with 9.5% of methane concentration. The premixed gas is separated from the inner space of the roadway by a film, and the air filling length is 5 m. The ignition position is (0, 0, 2).

| Grid division
The unified system of units (kg/m/s) is adopted in this model and material parameters. The roadway model is shown in Figure 2. The mapping grid division is selected for this model, the hexahedral element grid division is selected for the gas in the roadway, Euler grid division is used for air, and Lagrange grid division is selected for roadway wall. The unit length is 0.05 m. The finite element model after grid division is shown in Figure 3. The physical model of the gas explosion in the roadway is divided into 171700 units. After preliminary simulation, the grid generation can meet the needs of this study.

| Unit type and material model
Air constitutive model Initial state parameters of air in the standard state are as follows: P is 0.1 MPa, ρ is 1.29 kg/m³, T is 298 K, the thermal exchange during propagation and the friction between shock wave and roadway wall is ignored. Assuming that the expansion process of shock wave of gas explosion is an adiabatic process, according to Gama criterion, it can be expressed as follows: where P a is the gas pressure, γ is the specific thermal ratio, ρ is the current density of air, ρ a is the air density at the initial time, and E a is the internal energy per unit volume of gas.

Air material model and state equation
The *MAT_NULL is adopted in air material model, and is generally described by *EOS_LINEAR_POLYNOMIAL state equation. 20 A linear-polynomial state equation is as follows: where, P is the explosion pressure, E is the internal energy per unit volume. μ ρ ρ = / 0−1 , ρ is current density, ρ 0 is the initial density, μ is the relative density, C C equation is used to describe the relationship between explosion pressure and volume. 21 The JWL state equation is as follows: Where p is unit pressure, V is relative volume, E 0 is initial internal energy density, Parameters A and B are material constants. R 1 and R 2 are dimensionless constant. ω is Gruneisen constant, namely, the change rate of pressure relative to internal energy under constant volume condition, and the parameters of JWL state equation are shown in Table 2. 22 Material parameters of roadway wall Due to the automatic disappearance of the unit after the damage and destruction of the roadway wall, it is not conducive to monitoring the relevant parameters of the roadway wall. Therefore, a rigid material model is adopted in the wall surface of the basic roadway model, 23 and the key word for this model in LS-DYNA is * MAT_ RIGID. The selected materials are shown in Table 3.

Hourglass control
If the full integration algorithm is used, it will consume a lot of CPU time. CPU time can be effectively saved by using single point integration in the model. However, it is easy to cause the zero energy mode of the hourglass, so it is necessary to control the hourglass. For the entity unit solid164 hourglass control, the K file settings are shown in Table 4. 22

Ignition position
In the K file, the ignition position of the model is set as Table 5.

Time control
The solution termination time is set to 0.05 s and the time step is controlled to 0.67, which is shown in Table 6.

| ANALYSIS ON NUMERICAL SIMULATION RESULTS
Gas explosions can produce thermal impact on the roadway wall. After the roadway wall bears the thermal impact load, the temperature field and thermal stress field inside the roadway will also change, and the wall F I G U R E 3 The finite element model after grid division.
T A B L E 1 Air material equation of state parameters.  The results obtained are compared with the literature 1,7 and experimental results, and the validation results show that the model is effective and reliable(due to space limitation, simulation diagram and measured comparison diagrams are not elaborated this time). In many studies on wall failure, researchers often focus on the wall of the explosive body, and often ignore the failure of the gas explosion in end face, therefore, the overall failure state of the exploded object cannot be obtained. To comprehensively study the dynamic response of the inner wall of the roadway under gas explosion, the corresponding measuring points are set at the closed end and the axial wall in this paper to conduct a relatively complete response analysis of the roadway failure.

| Analysis on wall pressure
The measuring points set on the closed end wall of the roadway are shown in Figure 4A, In the X direction, measuring points (A-E) are set at an interval of 0.2 m from the center to the side wall of the closed end wall of the roadway, among them, measuring point A is unit 41605, measuring point B is unit 41557, measuring point C is unit 41497, measuring point D is unit 430, and measuring point E is unit 425. The measuring points in the Y direction are as follows: measuring point F is unit 41609, measuring point G is unit 41613, measuring point H is unit 20893, and measuring point I is unit 20968.
The measuring points set on the axial wall of the roadway are shown in Figure 4B, and the measuring points (1)(2)(3)(4) are set at an interval of 2 m from the closed end to the open end along the axial wall of the roadway. Among them, measuring point 1 is unit 4168, measuring point 2 is unit 8344, measuring point 3 is unit 12376, and measuring point 4 is unit 16552. Figure 5 is the pressure time history curve of the gas explosion in the closed end wall. To facilitate the analysis of the corresponding measuring points and conditions, some measuring points are selected as shown in Figure 6. It can be found from Figure 6 that the measured values and development trends of measuring point 425 and measuring point 20965 are almost the same, and the measured values and development trends of measuring point 41497 and measuring point 41613 are also basically the same. Because the roadway is circular and symmetrical, the shock wave front is loaded on the closed end wall with spherical waves at the initial stage of gas explosion, so the measured values of the corresponding measuring points on the closed end wall are basically consistent with the development trend. Therefore, in the follow-up study, only measuring points in X direction (named as measuring points A-E) are taken at the closed end for related response research. pressure process is that the pressure rises rapidly, reaches the peak value of pressure instantly, and the rising process tends to be linear and gradually shows nonlinear attenuation. With the propagation of gas explosion, it shows nonlinear attenuation and eventually tends to be stable.

| Pressure analysis of closed end wall
From the peak value of pressure, the peak value of pressure at measuring points A-D decreases successively, and the maximum pressure of measuring point A reaches 6.92 MPa. As the measuring point E is close to the  interface between the two walls, the pressure is constrained by the wall, and the pressure cannot be sufficiently relieved, resulting in a large pressure of 5.98 MPa. The results show that the pressure at the center and edge of the roadway is relatively large, and the wall failure will be relatively more serious.

| Pressure nephogram at closed end
In LS-PREPOST, the S plane control function is used to slice the end face of the closed end of the roadway, and the slice position is shown in Figure 8. Figure 9 shows the pressure nephogram of the end face at different times. From Figure 9, IT can be seen that the positions with high end face pressure are the center position and the inner edge position. When t is 0.0005 s, the maximum pressure at the wall junction reaches 6.11 MPa, and the maximum pressure at the center of the wall also reaches 3.95 MPa. Subsequently, the pressure region on the wall continues to expand, as shown at the closed end, when t is 0.01 s. As the gas explosion continues, the pressure on the closed end wall gradually decreases, and the maximum pressure region also retracts to the center. At 0.04 s, it basically tended to be consistent, and then due to the reciprocating expansion of the pressure region reflected by the shock wave, the response state of nephogram in the closed end wall is consistent with the pressure conclusion at the measuring point of the closed end wall. Figure 10A shows the pressure time history of measuring points (1)(2)(3)(4). To facilitate the analysis, the pressure time history curves of each measuring point are extracted respectively, as shown in Figure 10B-E. It can be seen from Figure 10B-E that after the gas explosion in the roadway, the shock wave propagates in all directions at the same time. Due to the rigid wall constraint of the roadway and the existence of the closed end, the positive reflection shock wave in Z direction is generated at the closed end face. The measured value of pressure at measuring points 1 and 2 show an overall attenuation trend, and gradually tend to 0 with the depletion of gas. It can be seen from Figure 10B-E that the peak pressure at measuring point 1 is 5.9 MPa, and the peak pressure at measuring point 2 is 5.0 MPa. The measured value of pressure at measuring points 3 and 4 shows a trend of first increasing and then decreasing. The measured value of pressure is also lower than that of measuring points 1 and 2. The reason is that measuring points 3 and 4 are located in the air region, and the instantaneous shock wave of gas explosion does not reach the measuring point in the air region, but is disturbed to a certain extent.  Figure 11 is the schematic diagram of the axial wall slice of the roadway. Figure 12 shows the dynamic development process of pressure from the inner wall to the outer wall of the roadway in the process of gas explosion. It can be seen from Figure 12 that the explosion pressure at the closed end is first loaded on the inner wall. Due to the continuity of the medium, it is gradually transmitted to the outer wall, and the pressure decays step by step in the transmission process. In the axial direction, at the moment of the gas explosion, the wall presents a high pressure state. At this time, the pressure load on the wall of the air region is relatively small, and the pressure decays step by step from the inner wall to the outer wall. Figure 13 shows the velocity time history change law of each measuring point on the closed end wall. From Figure 13A, the velocity change of each measuring point shows a consistent law, namely, with the progress of gas explosion, the velocity of measuring point in the closed end decreases continuously and basically tends to 0 at 0.05 s. It can be clearly seen from Figure 13B maximum measured value of velocity at each measuring point is different, the difference is not large. Figure 14 shows the velocity time history change law of each measuring point on the axial wall. It can be seen from Figure 14A that the velocity change of each measuring point is relatively disordered, and there is no obvious law. Because the impact load is irregularly reflected on the roadway wall many times, the velocity distribution of measuring points on the axial wall is irregular. According to Figure 14B-E, the measured velocity of each measuring point on the axial wall is about 0.1 m/s. On the whole, the measured values of velocity at measuring points 1 and 2 show an attenuation trend. The measured values of velocity at measuring points 3 and 4 oscillate significantly, but the oscillation frequency is lower than that at measuring points 1 and 2. Figure 15 shows the vector nephogram of threedimensional roadway wall velocity under the impact load of gas explosion, in which Figure 15A shows the velocity vector nephogram of roadway wall in Z direction at different times, and Figure 15B shows the velocity vector nephogram of roadway wall in XY directions at different times. It can be seen from   Figure 15A that the velocity distribution at the closed end of the roadway at the initial stage of gas explosion is convex. When t is 0.00049 s, the maximum velocity in Z direction at node 4489 is 0.29 m/s. With the continuous progress of gas explosion, the velocity distribution of roadway wall also changes constantly. When t is 0.05 s, the maximum velocity at node 3073 is 0.014 m/s. The wall velocity gradually decreases from the closed end to the open end. Near the closed end of the roadway, because the impact load converges and overlaps at the corner, the junction is loaded in multiple directions at the same time, resulting in serious deformation, so the velocity is large, and the failure is more serious. As can be seen from Figure 15B, when t is 0.00049 s, the maximum velocity in XY directions at node 17427 is 0.0687 m/s. As the gas explosion continues, the velocity distribution on the roadway wall presents irregular changes. When t is 0.05 s, the maximum velocity at node 49888 is 0.0734 m/s. Figure 16A shows the time history change law of wall displacement at each measuring point on the closed end wall. According to Figure 16A, the displacement of each measuring point in Z direction increases continuously with the progress of gas explosion. In 0-0.01 s, the displacement variation reaches about 0.6E−03 m, the displacement increment is about 0.4E−03 m in the following 0.02 s, and the displacement increment was only about 0.2E−03 m in 0.03-0.05 s. It shows that at the initial stage of gas explosion, the displacements of measuring points increase rapidly, which is reflected in the large slope of the curve. Through the displacement time history curve, it can be obtained that the initial pressure relief of gas explosion is very important, and the explosion energy is fully diffused, so that the F I G U R E 12 Pressure nephogram on axial wall. displacement of the exploded object will not continue to increase. As the gas is exhausted, the explosion energy is gradually reduced, and the displacement change of the measuring point is also gentle. Figure 16 shows that the displacement of each measuring point on the wall is relatively similar, because the shock wave of gas explosion mainly propagates in the axial direction, the intensity difference on the wave front is small, and the region of the closed end wall is limited. Therefore, the displacement of each measuring point is relatively similar, and finally the displacement of each measuring point reaches about 0.0012 m. Figure 16B shows the time history change law of wall displacement at each measuring point on the circumferential wall. According to Figure 16B, the displacement of measuring points 1 and 2 in the gas region is large within 0.01 s, reaching 0.0445E−03 m. After 0.01 s, the circumferential wall displacement in the air region increases, but it is far less than the maximum displacement of the wall measurement point in the gas region. Figure 17 shows the vector displacement nephogram of the closed end of the roadway at the initial time t = 0.00049 s and the end time t = 0.05 s. Figure 17 not only includes the change nephogram of displacement time history in axial roadway, but also shows the displacement vector nephogram of the roadway in the XY directions, the vector arrow represents the magnitude and direction of displacement. It can be seen from Figure 17 that in the axial direction, the displacement near the center of the roadway is large, and then the displacement decreases in the form of a regular ring. As it is a circular roadway, the gas explosion propagates to the closed end wall with spherical (convex) shock wave, and the shock wave at the front end is intense. Therefore, the displacement on each circular belt from the center of the roadway to the roadway wall is relatively uniform, which can also be obtained from the relatively neat circular arrangement and distribution of the displacement vector. On the circumferential (XY) wall, the longer the arrow is, the larger the displacement is, which indicates the larger the deformation is, the denser the arrows are, the more concentrated the displacement is, and the more serious the failure is. Figure 18 is the displacement vector nephogram of three-dimensional roadway wall in Z direction. From Figure 18, the displacement law of the roadway wall under the impact load of gas explosion can be found more intuitively. At the moment of gas explosion, the displacement change of the closed end wall is obvious, and the displacement in Z direction is seriously protruding. The displacement of the center of the closed end wall is the largest, and the maximum displacement at node 4490 reaches 8.489E−05 m. The axial wall displacement of the roadway is smaller in the Z direction as a whole. When t is 0.05 s, the displacement of the closed end in Z direction reaches 1.216E−03 m, namely, within 0.05 s, the impact load continues to load the closed end wall, and the displacement continues to increase. At this time, the axial wall has a certain displacement in the Z direction, and the displacement from the closed end to the open end shows a decreasing trend. Figure 19 shows the circumferential displacement vector nephogram of three-dimensional roadway wall. The circular wall displacement law of the roadway under the impact load of gas explosion can be obtained from Figure 19. At the initial stage of gas explosion, the circumferential displacement of the wall in the gas region is significantly larger than that in the air region, and the circumferential displacement of the wall at the node 21826 in the gas region reaches 4.454E−05 m. As the explosion propagates towards the open direction, the fourth of the maximum displacement in the gas region.

| Displacement nephogram
In general, the overall displacement of the closed end wall is large, and the displacement of the gas region in the axial direction is larger than that of the air region. Figure 20 shows the time history curve of equivalent stress at each measuring point on the axial wall. In Figure 20A, the equivalent stress generally shows an attenuation trend. Within 0-0.02 s at each measuring point, the peak value and frequency of equivalent stress are relatively high, which indicates that the loading times of wall stress are frequent and the roadway fatigue damage is serious. It can be obtained from Figure 20B-E that the equivalent stress of measuring points 1 and 2 is similar, and the maximum peak value of stress exceeds 10E6 Pa. The peak stress of measuring points 3 and 4 in the air region is reduced compared with the peak stress of measuring points 1 and 2 in the gas region. Although the stress of measuring points 1 and 2 is large, the attenuation is relatively rapid, and the fluctuation amplitude of the stress of measuring points 3 and 4 is relatively uniform. According to the equivalent stress of the closed end wall in Figure 21 (A), the equivalent stress generally shows an attenuation trend. At the moment of gas explosion, the relationship of peak stress is E > A > B > C > D. Reason is that the explosion energy ZHENZHEN and QING | 2499 converges at the junction of the closed end of the roadway, and the junction is subjected to axial and circumferential loads at the same time. Serious deformation occurs at the junction of the roadway, and the maximum equivalent stress appears locally. Therefore, the peak stress of measuring point E is larger than that of other measuring points. After 0.01 s, the stress at each measuring point at the closed end decreases significantly.

| Analysis on wall equivalent stress
It can be obtained from Figure 21B-F that the maximum stress peak at measuring points A,B,C,D and E are 9.2, 8.6, 6.4, 4.9 and 9.9 MPa, respectively. All the maximum measured values occur at the moment of gas explosion, which indicates that the most serious failure to the wall surface of the closed end is caused by the initial stress of the wall surface. Figure 22 shows the distribution of equivalent stress nephograms of roadway walls with time. It can be found from Figure 22 that the impact load generated by the gas explosion is first loaded onto the closed end wall, resulting in wall deformation and equivalent stress. At the closed end, the equivalent stress at the center of the roadway and the junction of the roadway is relatively large. As the explosion continues, the load produced by the gas explosion continues to load on the roadway wall in the open direction, but the loading stress continues to decrease. It can be seen from Figure 22 that the stress loading is not completely uniform, and the stress is relatively concentrated in some wall regions, and these stress concentration regions are often regions with serious failure.

| CONCLUSIONS
To completely reflect the response characteristics of the roadway wall by gas explosion, the LS-DYNA is used to establish the simulation models of gas explosion in roadway, the parameters of pressure change, velocity change, displacement change and other stress changes of roadway wall under the gas explosion impact are measured, and the gas explosion impact and the response characteristics of the roadway wall is analyzed and the following conclusions are obtained.
1. At the closed end of the roadway, the pressure in the center and edge of the roadway is relatively large and the wall failure is relatively more serious. 2. With the propagation of gas explosion, the pressure on the closed end wall gradually attenuates and the maximum pressure region also retracts to the center, which basically tends to be consistent at 0.04 s, and then the pressure region expands back and forth due to the reflection of shock wave. 3. After the gas explosion in the roadway, the shock wave propagates in all directions at the same time.
Due to the rigid wall constraint of the roadway and the existence of the closed end, the total reflections also appear on the closed end face and the axial inner wall. 4. At the closed end, the explosion pressure is first loaded on the inner wall and gradually transferred to the outer wall, and the pressure decays step by step in the transfer process. At the moment of gas explosion, the pressure load on the wall of the air region is relatively small, and the pressure also decays step by step from the inner wall to the outer wall. 5. With the propagation of gas explosion, the velocity of measuring point in the closed end decreases continuously. Because the impact load is reflected irregularly on the roadway wall many times, the distribution of velocity values of measurement points on the axial wall is irregular. 6. With the continuous progress of gas explosion, the velocity distribution of the roadway wall also changes constantly, and the wall velocity gradually decreases from the closed end to the open end. 7. With the propagation of gas explosion, the displacement of each measuring point in Z direction increases continuously. For the axial direction, the displacement near the roadway center is large, and then the displacement decreases in the form of a regular ring. The displacement on each circular belt from the center of the roadway to the roadway wall is relatively uniform. 8. The impact load produced by the gas explosion is first loaded on the closed end wall, resulting in wall deformation and equivalent stress. As the explosion continues, the load produced by gas explosion continues to load the roadway wall in the open direction, but the loading stress continues to decrease.
In this study, many assumptions have been adopted. To improve the research results, in future research, assumptions can be further reduced to make the simulation conditions closer to the real situation. At the same time, it is possible to conduct further research on explosive gas action, temperature field, stress field, material property and their mutual coupling effects, as well as in-depth analysis on energy transfer, transformation during impact action, and its' energy impact loss process.