Research on Roof Structure and Determination of Working Resistance of Shallow Buried Single Key Stratum Based on Grid Drillhole Field Method

In the process of underground coal mining, controlling overburden movement is the primary issue. Only by grasping the possible formation structure and its activity law after the rock mass is destroyed can the relationship of “support-surrounding rock” be reasonably used, controlling the safety of the stope economically and ensuring the safety of personnel and equipment [1–4]. The overburden structure is not an artificial structure. Expecting to obtain the morphological characteristics of overburden failure, filed observation drillhole, and peeking [2, 5], advanced testing methods are employed at the filed research, such as electromagnetic seismic [6, 7], microseismic [8–10], and optical fibers [11]. In the laboratory, physical simulation [12–16] and numerical simulation [17–19] are applied to simulate the overlying strata movements. The roof structure is analyzed and deduced through the acquisition, analysis, and processing of characteristic data. The commonly used test methods for field measurement of surrounding rock deformation are shown in Table 1.

Roof weighting is the performance of roof structure movement. Mastering the movement law of the roof structure and establishing the mechanical model of the roof structure are important bases to reveal the mechanism of weighting and determine reasonable support resistance. The “voussoir beam” theory and the key stratum theory in stope ground control are proposed, which both came from the drillhole field measurement of roof breaking movement [1–3]. The key stratum refers to the strata that plays a decisive role on the rock mass in whole or in part when there are multiple layers of hard strata in the overburden of the stope. The former can be called the key stratum of strata movement, and the latter is critical stratum [1]. The breakage of the key stratum will cause the breakage of all or part of the overburden strata and causes a large range of strata movement. If the rock structure is satisfied with the “S-R” stability after the break, it will form “voussoir beam” structure and continue to be the main carrier. Based on the “voussoir beam” theory, the overhanging “slab” mechanical model is established, which lays a theoretical foundation for the prediction of roof weighting. Meanwhile, the relationship and the monitoring principle of “support-surrounding rock” as well as the concept of green mining in coal mines are proposed [20, 21], which will made great contribution to ensure the safety of mining work.

The “voussoir beam” theory and key stratum theory also have great guiding significance in the field of shallow coal seam. Based on the key strata, load ratio, and burial depth as indicators, the definition of shallow coal seam is given [4], and the structure model of “step voussoir beam” of main roof is put forward [22–24]. According to field measurement and theoretical analysis, shallow coal seams can be divided into two types: (1) Typical shallow coal seams are characterized by shallow burial, small base load ratio, and single key stratum (SKS) structure. (2) Nearly shallow coal seams manifest as large bedrock thickness and small loose load layer thickness, which generally show two groups of key stratum with slight step subsidence. Researchers have proposed different roof structures according to different mining conditions, which effectively solves the problems of mining practice in shallow coal seam, for example, concentrated coal pillars [25–27], surface subsidence [28, 29], and water protection mining [30–32]. To solve the large deformation problem of gob-side entry retained mining, a negative Poisson’s ratio (NPR) anchor cable supporting solution was designed based on the principle of energy coupling support and field tests were carried out [33–36]. However, the roof structure is mainly based on theoretical models proposed by support load measurement, physical simulation, and numerical calculation. There is no systematic study of roof structure field measurement in shallow coal seam. The field measurement of the movement of the roof rock layer is mostly based on vertical drillhole observations on the ground surface of the working face; this method is mainly to observe the heights of the fractured zone and the caved zone, but the cost is expensive and the observation time is long [37–39]. The location and intensity of the broken zone of the working face can be more accurately grasped by using of the indirect observation method, but it is difficult to seize the true situation of the roof breakage and structural movement.

The Shenfu Dongsheng coal field in China is one of the largest coal fields in the world. The main coal seam in this area is a shallow seam of Jurassic age. The thickness of coal seam is 3.5~8 m, and the depth is less than 250 m [4, 12]. The 2^-2 coal seams have wide occurrence in the Shenfu mining area, which are shallowly buried and have large recoverable thickness. Besides, the overburden bedrock is thin and the thickness of the loose layer is large, which is manifested as a single key stratum structure [30]. Shallow coal seam causes strong roof pressure and threat to the fragile environment during period weighting [2–4], as shown in Figure 1. At present, the roof structure of shallow buried working faces is mainly based on the theoretical models proposed by the measurement of support load, physical simulation, and numerical calculation [40–45]. With the continuous mining of 2-2 coal seam, the safety of stope and determination of working resistance in SBSKS have become a technical problem to be solved in the mining area. Therefore, in order to avoid the accidents in the roof caused by the large-scale weighting on the working face and ensure the safety during mining on the working face, the roof structure and determination of working resistance of SBSKS have important theoretical and practical guiding significance.

In order to reveal the roof structure shape during the mining process under the condition of SBSKS, the authors use multiple drillhole displacements and drilling peek in conjunction with the field measurement of the support load on the working face, which provides a scientific basis for the roof control of SBSKS mining. The authors have invented a field measurement method of grid drillhole. This method is suitable for three gateways arranged along the working faces. For example, there is 20~25 m section pillar between the auxiliary headgate gateway (AHG) and headgate gateway (HG). While ensuring the observation effect of the roof, the cost and construction volume of the drill site construction are considered, as shown in Figure 2.

The method includes setting multiple fixed stations in the AHG. The drillholes in the TA are divided into displacement inclined drillhole (DID) $An$⁠, displacement vertical drillhole (DVD) $Bn$⁠, and peek incline drillhole (POD) $Cn$⁠; $Bn$ and $An$ are located on the same plane, and they intersect into mesh, while $Cn$ is arranged parallel to the largest displacement incline drillhole. According to the drillhole and the inclination of the working face, the drillholes are divided into vertical drillholes and inclined drillholes in the tailgate airway (TA), as shown in Figure 3. Advanced drillholes in the TA are important sources to obtain advance fracture or movement information of the roof, which can accurately realize to early warning and forecast in mining.

Drillholes in the AHG can achieve the real-time monitoring of the whole process from before mining to after mining on the working face and satisfy the existing observation requirements for caved zones and fractured zones of roof overburden. Setting many fixed stations of measuring the AHG, the drillhole of each fixed measuring station includes displacement drillholes $Dn$⁠, $En$⁠, and $Fn$ and peep drillhole, which are arranged parallel to the displacement drillhole $Fn$⁠, as shown in Figure 4, where $n=1,2,3⋯i$⁠.

Due to the limitation of the underground mining and the working environment, we must consider the factors such as observation cost and quantity of observation works; the number of grid drillholes is not limited. The observation site and quantity are determined by the observation purpose.

Firstly, we must determine the level of the roof structure to be studied, that is, the vertical height of the drillhole. The maximum vertical height of the drillhole must exceed the main roof boundary of the key stratum, which can form the main roof structure, for example, $H1,H2,H3⋯Hn$ in Figure 2. The determining principle is mainly considered from the following aspects: depth, mining height, thickness, and lithology of immediate roof and main roof. The observing horizon height of the roof structure is determined through combining with engineering practice analogy and theoretical analysis.

At present, according to research experience for stope in shallow coal seam [4, 42], the vertical height of the drillhole generally takes 4-6 times of the mining height. Among them, the equivalent immediate roof is 2~3 times, and the main roof is 3~6 times. The observation horizon can be divided into 2~3 horizons.

Secondly, the distance of the initial drillhole or station from the setup entry to the working face is $L0$/m. According to the results of theoretical research, engineering practice, etc., the range of the first weighting intervals are obtained, so $L0$ should be smaller than it. Meanwhile, we should select the same $L0$ of the AHG and TA.

Thirdly, $l$/m is the horizontal distance of the adjacent drillholes in the TA, as shown in Figure 2. We refer to the results of engineering practice and theoretical research; $l$ is smaller than $lz$ (⁠$lz$/m is the periodic weighting interval of the roof). For the fixed station of the AHG, the distance between two adjacent stations is $nl$⁠, generally $n=1−3$⁠. The fixed measuring station must be arranged in the AHG, because it can meet the whole process of monitoring, while it cannot be observed when the working face is extracted in the TA. The drillholes of the fixed station include displacement drillholes and peek drillholes. The displacement drillholes need to be determined through the observation of the structure layer of the roof stratum. However, a vertical drillhole is usually arranged in the same position as the maximum displacement drillhole. The schematic of the drillholes of the fixed stations are shown in Figure 3.

According to the inclination of the drillhole and the working face, the designed drillholes in the TA are divided into vertical drillholes and inclined drillholes, and they are also divided into displacement vertical (inclined) drillholes and peek vertical (inclined) drillholes through their function. The vertical drillholes and inclined drillholes are in the same plane. The three-dimensional schematic of the drillhole are shown in Figure 3. The vertical drillholes and the inclined drillholes cross into a mesh. The angle between the inclined drillholes (⁠$A1,A2,A3⋯Ai$⁠) and the axial direction of the roadway is $α$/°; the elevation angle is $β$/°. The angle between the vertical drillholes (⁠$B1,B2,B3⋯Bi$⁠) and the axial direction of the roadway is 90°, while $a/m$ is the horizontal distance between the DOD and the displacement incline drillhole. Combining the engineering practice with situation of construction safety, $a$ is generally taken 0.5 m. Similarly, the elevation angle between the vertical drillhole and the horizontal plane can be calculated. The distance from the openings of the drillhole $A$⁠, $B$⁠, and $C$ to the floor is determined by the specific section size of the roadway and the construction conditions of the drillhole.

The machine of YCJ90/360 drillhole peek was used to observe the broken position of internal drillhole, which can collect video, depth, inclination angle, etc. Besides, the postprocessing software can calculate the vertical layer height of the broken roof and overhang distance (horizontal distance from the side of the pillar). According to comprehensive analysis, the broken structure of roof in strike and the broken structure of roof in inclination on the working face are obtained, as shown in Figure 7.

The meter of multipoint displacement is installed to observe the roof displacement. The displacement of the different roof layers is based on the initial value through the fixed point of floor corresponding to the displacement counterweight, and we used measuring rod for reading, as shown in Figure 8. A positive value indicates that the steel wire is pulled in, while a negative value indicates that the steel wire is spit out.

Through installing displacement monitoring devices in each displacement drillhole in the drillhole field of the AHG and TA, the displacement change of roof in the drillhole can be monitored. The proposed method for the grid drillhole field in SBSKS is a coupling analysis method, which combines “field monitor of drillhole displacement, drillhole peek, and physical simulation.” Compared with the current method and technology, this method can acquire a large amount of characteristic data from the roof movement and a wide observation range, which includes both the spatial position of the roof breakage and the displacement of the roof subsidence as well as the strength and the range of the damage. Therefore, it can fully reveal the structural characteristics of the roof movement in SBSKS, in order to realize the analysis of the roof structure shape and the movement process, including the height of the caving zone, the articulation layer of the roof, and the evolution of the broken angle.

During the process of mining on the working face, the drillhole peeker was employed to observe the drillhole continuously, so as to obtain the location of cracks, delamination, or cavings in the drillhole, and record the drillhole depth of each position (depth $dij$⁠, where $i$ is the number of the drillholes and $j$ is the number of observations). Until the roof movement in the goaf of the working face is relatively stable, the final position of the break corresponding to each drillhole will be obtained.

The horizontal distance $lij$ from the orifice and the corresponding vertical height $hij$ can be obtained by combining the drillhole angle $α$ and the drillhole depth $dij$ while solving different peek positions. By calculating all points of the broken position at each observation, the points in the drawing software were depicted to draw the evolution map of the broken position of the roof at different layers.

Drillholes can realize the real-time monitoring of the whole process of mining on the working face, revealing the relationship of the space and time between the movement and the weighting of the roof and verifying the size and the shape of the tip area on the working face that is inclined breakage. The advanced drillholes can monitor the overtime breakage or movement information of the roof and apply it to warn and forecast the weighting on the working face.

The quantitative calculation parameters of the roof structure were obtained, which provide important data to support the theoretical calculation. The conclusions include the determination of the broken expansion coefficient, the height of equivalent immediate roof.

By observing the breakage of the roof in each drillhole and collecting data to obtain the broken depth, then the vertical horizon height and lateral overhang distance of the broken roof are calculated, that is, the horizontal distance from the side of the coal pillar. Broken roof structure in working direction and in inclined direction according to comprehensive analysis.

According to the above-mentioned design principles, 31 drillholes crossed into a mesh at the 22201 working face of Zhangjiamao Coal Mine in Shennan Mining Area of China. The average thickness of coal seam at 22201 working face is 8.0 m, the mining height was 6 m, the inclination angle was 1~2°, and the average buried depth was 76 m [41, 42]. The drillhole was continuously observed for about 60 days; meanwhile, the data of multipoint displacement meter and drillhole peek video for the first weighting and 5 times period weightings at 22201 working face were recorded totally. Based on the analysis of the measured data on field, the law of subsidence of the roof for the first weighting and the period weighting were obtained. The arrangement of drillhole in the AHG is shown in Figure 9. Among them Figure 6(a) expresses the section of inclination on the working face (AHG), while Figure 6(b) represents the section of strike on the working face (setup entry).

A total of 19 drillholes are arranged in the TA, which includes 11 inclined drillholes (including 3 peek drillholes) and 8 vertical drillholes, and the vertical drillholes and the inclined drillholes are on the same plane. The specific parameters are shown in Table 2.

Observing the whole process of advance breakage, rotation, and continuously weighting of the roof and combining the field measurement of weighting on the working face revealed the structural form and movement law of the roof with large mining height in SBSKS. According to the roof displacement and its peek of the grid drillhole, the formation and the movement process of the roof structure were obtained during the first weighting and period weighting on the working face.

Through the field measurement of the drillhole and support pressure, during the first weighting, the roof movement obviously increased (up to 0.9 m) in the horizon of 8-10 m ahead of the working face, as shown in Figure 10(a). When the working face occurred the period weighting, the roof movement was ahead of the coal wall, as shown in Figures 10(b) and 10(c). In Figure 10, when the working face is advanced to the observation station, the multipoint displacement meter can obtain the displacement of the different horizon of the roof. The results show that the field measurement result of the advanced breaking position of the 22201 working face is 5~10m, and the roof movement and the roof advanced breaking are ahead of the roof pressure.

The 15~20 m horizon of the roof moved at the large range of 5~10 m behind the working face, and the roof falling and separation zone are mainly concentrated in the 15~20 m horizon of the roof, as shown in Figure 11. It indicates that the hinged layer is in 15~20 m horizon of the roof.

The experiment takes the 22201 large mining height working face of Zhangjiamao Coal Mine as the background. The simulation experiment has a geometric similarity ratio of 1 : 100. The model size is $200cmlength×20cmwidth×84cmheight$⁠. Select river sand as the aggregate, gypsum and white powder as the cementing material, and mica powder as the layered fissure material. According to the physical and mechanical parameters of coal and rock mass [41], according to similar conditions to determine the similar ratio of each rock layer, the experimental ratio table has a geometric similarity ratio of 1 : 100; see Table 3 for details.

When the working face advances to 31 m, the immediate roof caving, the caving height is 2.4 m. When the working face advances to 37 m, the immediate roof fully caving, the collapse height is 4.2 m, as shown in Figures 12(a) and 12(b).

When the working face advances to 48 m, the main roof first weighting, the caving height reaches 17 m, and the roof forms an asymmetrical three-hinged arch structure, as shown in Figure 12(c). When the working face is advanced to 60 m, the main roof first periodic weighting, the periodic weighting interval is 12 m, and the height of the roof caving zone reaches 17~19 m, as shown in Figure 12(d).

When the working face advances to 75 m, the main roof second periodic weighting, the periodic weighting interval 15 m, and the height of the roof caving zone is 28 m. The height of the roof caving zone which is originally 10~16 m is raised to 16~28 m, as shown in Figure 12(e). When the working face advances to 88 m, the main roof third periodic weighting, the periodic weighting interval is 13 m, the height of the roof fractured zone is 42 m, and the roof separation layer further develops upwards, as shown in Figure 12(f).

When the working face advances to 103 m, the main roof fourth periodic weighting, the periodic weighting interval is 15 m, the height of the roof fractured zone is 54 m, and the roof separation layer develops upward to the soil layer, as shown in Figure 12(g). When the working face advances to 119 m, the main roof fifth periodic weighting, the periodic weighting interval is 16 m, the roof fractured zone to the surface, the roof breaking angle behind the working face is 64°, and the loess roof breaking angle is 67°, as shown in Figure 12(h).

When the working face advances to 133 m, the main roof sixth periodic weighting, the periodic weighting interval is 14 m, and the overburden cracks develop to the surface, as shown in Figure 12(i). When the working face advances to 149 m, the main roof seventh periodic weighting, the periodic weighting interval is 16 m, and the surface form a sinking basin, as shown in Figure 12(j).

Through physical simulation, the first weighting interval of 22201 working face is 49 m, and the main roof breaks to form an asymmetrical three-hinged arch structure at the first time. The main roof forms a stepped rock beam hinged structure at the 18~26 m horizon, and the average periodic weighting interval is 14 m. Combined with the field measurement and analysis of the mining pressure law of the 22201 working face, the periodic weighting interval is 10~15.8 m, with an average of 13 m, indicating that the physical simulation experiment is basically consistent with the actual measurement results.

Based on the analysis of the floor’s sensor, the distribution law of the front abutment pressure of working face is obtained, as shown in Figure 13. When the working face occurred in first weighting, the front abutment pressure peaks at 10~12 m before the work face, the maximum value is 2.90 MPa, and the peak factor is 1.61; during the period of periodic weighting, the front abutment pressure peaks at 8~15m ahead of the work face, and the peak coefficient is 1.74~1.86. The actual measured front abutment pressure peak is 8~10 m ahead the coal wall of the working face, and the peak coefficient is 1.7. The physical simulation results are consistent with the actual measurement results, indicating that the physical simulation is accurate and reliable.

The movement is stable after the working face is advanced to the fracture line, and the weighting is covered. The articulation layer of roof was gradually moved from 10~20 m to 16~30 m, as shown in Figure 14. According to the field results [41], similar results have been obtained through numerical simulation and physical similarity. It can explain the above phenomenon more intuitively, and make up for the shortcomings of discontinuous observation in the field.

The periodical weighting of the working face is divided into three stages: the front roof breaks before the weighting comes, the roof structure rotates when the weighting comes, and the roof structure slides after the weighting, as shown in Figure 15, providing a basis for building a roof structure model.

According to statistics on the locations where cracks, separation zone, or caving zone occur in the D, E, and F drillholes of the fixed station, the broken law in inclination of the roof on the working face would be obtained. The 10 m, 20 m, and 30 m layers of the roof collapsed layer by layer from the bottom to the top, forming an arched breaking shape at the end area, as shown in Figure 16(a). Based on the peeping results after the overburden are stabilized, as shown in Figure 16(b), the trigonometric function is used to convert the breaking angles of the three stations from 10~30 m to 65°, 66°, and 67.7°.

The results of comprehensive drilling peek showed that the height of the overburden caving zone was about 16 m, the articulated rock stratum is 16~30 m, and the roof occurred step subsidence, which could form the structure model of step voussoir beam. Meanwhile, the height of step sinking is about 1.7 m, the maximum width of the crack is 260 mm, and the distance between periodic cracks is 9~13 m, as shown in Figure 17.

Therefore, the range of θ₁ is $33.7°<θ1<38.3°$⁠.

Combining the values of various parameters, the roof breaking angle of shallow coal seam in Shenfu mining area ranges from 56.2° to 69.3°. Because there is a small internal friction angle of the soil layer, the breaking angle is larger than that of the bedrock.

Through the continuous peeping of the peep holes of the I station in AHG, when the working face advances to 66 m (the third periodic weighting was 63 m), it is ahead of the I station by 38 m, and the movement of the roof overburden tends to be stable; the peep results of D₁ and E₁ and peep holes of station I (as shown in Figure 18) can sketch the shape of the breaking angle of the roof.

According to the peek result in Figure 18, the corresponding horizontal distance can be calculated using mathematical knowledge. Therefore, based on the locations of the collapsed holes observed at different horizontal distances, it is calculated that when the mining height of the I station is 4.8 m, the bedrock breaking angle of the 10 m~20 m horizon is 71.5°, and the breaking angle of the 10 m~30 m horizon is 71.5°, and the average bedrock breaking angle is 65°.

In the same way, according to the analysis of the observation results in Figure 19. At the II station, when the mining height is 5.8 m, the bedrock breaking angle of the 10 m~30 m horizon is 74.4°~76.6°; at the III station, the bedrock breaking angle from 10 m~30 m levels is 67.7°.

By analyzing the influence of the thickness of the key stratum and the thickness of the load layer on the breaking angle, in the mining conditions of the 22201 working face, the thickness of the key stratum is in the range of 10 m~20 m, the roof breaking angle is 66°~68°, and the measured average breaking angle is about 68°, and the theoretically calculated breaking angle of the roof is 62.3°, which is basically consistent.

For the general filling type of large mining height in the working face, the key stratum of the main roof has a higher hinge horizon and exists a step subsidence. Therefore, the “high position step voussoir beam” structure model of roof is established in high mining height working face in SBSKS. Figure 20 shows that $m$ is the mining height, m; $h1$ is the thickness of $KS$⁠, m; $∑hi$ is the thickness of the EIR, m; $h2$ is the thickness of EIR “short cantilever beam,” m; $h3$ is the thickness of easily caving EIR, m; $M$ and $N$ are the key blocks of “high position step voussoir beam” structure; $R1$ is the force acting on the EIR from key block M, kN/f; $R2$ is the weight of “short cantilever beam” EIR, kN/f;$R3$ is the weight of easily caving EIR, kN/f; $Pm$ is the support load, kN/f; $A$⁠, $B$⁠, and $C$ are the hinge point of key blocks; $d$ is the step height of rock blocks $M$ and $N$⁠, m; $W$ is the amount of rotation subsidence of rock block $N$⁠, m; and θ is the rotation angle of rock block $M$⁠, °.

According to the “step voussoir beam” theory [4], the mechanical model of “high position step voussoir beam” key blocks can be established as Figure 21. The key block $N$ falls completely on the caving rocks, and the key block $M$ is supported by the key block $N$ at point $C$⁠. At this point, the key block $N$ is basically compacted, desirable $RN≈P2$⁠, $QB≈0$⁠.

As the mining height increases, the proportion of EIR load in the working resistance continues to increase. During the weighting, the EIR weight $R2+R3$ accounts for 60%-65% of the rated working resistance, and the key stratum structure load R₁ accounts for 35%-40% of the rated working resistance. The weighting pressure load is caused by the movement of the key stratum structure, and it is caused by an increased pressure on the support. According to the structural mechanics model of the “high step rock beam” roof of large mining height face, the support resistance during nonpressure is the sum of the EIR weight $R2+R3$ and the force during the noncompression of the key stratum.

According to the analysis, the height of the key block of the high position step voussoir beam is 13 m, and the load layer above the key stratum has weathered bedrock (⁠$hZF=13$ m) and loose sand soil layer (⁠$hZT=29$ m), whose bulk densities are $γZF=21$ kN/m³ and $γZT=17$ kN/m³.

With the above parameters, the calculation is $R1=6844.7kN/f$⁠.

Then the working resistance of support is $P=Pm/0.9=R1+R2+R3/0.9=12752.6kN/f$⁠.

According to the field measurement, the average working resistance of the support is 10343 kN/f during the period weighting, the maximum working resistance of the support at the middle of the working face is 12049 kN during the weighting, and the opening rate of the safety valve is less than 8%. According to the established theoretical model of the roof structure, the maximum working resistance of the support is 12752.6 kN/f. The theoretical calculation is consistent with the actual and reliable basis. In summary, the utilization rate of support resistance is high, and the operation is safe and the support adaptability is better.

• (1)

  In this paper, the field measurement technology of grid drillhole is developed, and the roof breaking process and its movement track were detected, and then, the calculation formula of roof breaking angle was given. The broken law of the EIR was measured in practice, and then, the load and the bearing effects of the thick EIR were analyzed. Besides, the phenomenon of “step subsidence “ of the roof with large mining height working face was field proved. Meanwhile, the phenomenon of the upward movement for the hinged layer of the main roof and the movement process of the roof structure on the working face with large mining height in SBSKS was proved

• (2)

  Based on the innovative methods and comprehensive analysis methods such as field measurement of drillholes, the form and the evolution process of the roof structure on the working face with large mining height in SBSKS were revealed. In terms of large mining height, the “asymmetry arch with three articulation structures” during the first weighting and the “high position step voussoir beam” during the period weighting were verified practically

• (3)

  The space-time relationship was established between the movement of the roof structure and the weighting of the working face. The three-stage division of roof breaking movement and the behavior of the weighting are proposed, and then, the most dangerous state of roof was determined, which provided reliable basis for establishing roof structure model and determining reasonable support resistance

• (4)

  According to the field measurement and theoretical analysis, the “high position step voussoir beam” structure model of large mining height in SBSKS is proposed, and the reasonable working resistance calculation equation for large mining height working face is given. During the field measurement, the maximum working resistance of the support during the period of weighting pressure is 12049 kN/f. The theoretical calculation of the maximum working resistance is 12752.6 kN/f, indicating that the theoretical model is reasonable and the calculation results are reliable

The data are available and explained in this article; readers can access the data supporting the conclusions of this study.

The authors declare no conflict of interest.

Q.H. conceptualized the study; Q.H. and Y.H. designed the experiments; Q.H. and Y.H. validated the study; Y.H. was responsible for data curation; Q.H. supervised the study; Y.H. wrote the original draft; Q.H. and Y.H. wrote, reviewed, and edited the study; Q.H. supervised the study; Q.H. was responsible for project administration; Q.H was responsible for funding acquisition.

This research was funded by the National Natural Science Foundation of China, grant numbers 52074211 and 51674190, Natural Science Basic Research Program of Shaanxi, program no. 2019JLP-08, and 2019 Excellent Doctoral Dissertation Program of University, program no. PY19001.