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Article

Research on the Law of Top Coal Movement and Influence Factors of Coal Caving Ratio for Fully Mechanized Top Coal Caving Working Face

1
CCTEG Coal Mining Research Institute, Beijing 100013, China
2
CCTEG Tiandi Science & Technology Co., Ltd., Beijing 100013, China
3
School of Mining Safety, North China Institute of Science and Technology, Beijing 101601, China
*
Author to whom correspondence should be addressed.
Energies 2025, 18(16), 4312; https://doi.org/10.3390/en18164312
Submission received: 21 July 2025 / Revised: 8 August 2025 / Accepted: 12 August 2025 / Published: 13 August 2025
(This article belongs to the Special Issue Coal, Oil and Gas: Lastest Advances and Propects)

Abstract

To investigate the movement law of top coal and the influencing factors of coal caving ratio in fully mechanized top coal caving faces, this study adopts the theory of dispersoid mechanics. First, a top coal flow model was established without considering the influence of the support. Then, the effect of the support was analyzed, and it was found that the sliding resistance of the top coal body increases with the square of both the support width and the top coal thickness. Furthermore, the positive stress on the coal particles was derived through a microelement force analysis, and a theoretical formula for arching probability was proposed. The mobility of top coal was evaluated using a flow factor, and the influence of lump size on arching tendency was quantitatively analyzed. Based on these insights, several measures to improve top coal flowability and recovery rate were proposed, including increasing mining height, enlarging the coal caving opening, enhancing the initial support force, extending the caving step, and applying multiple alternating loads to pre-break top coal. These strategies provide a theoretical basis and practical guidance for enhancing top coal caving efficiency.

1. Introduction

Coal resources are an important part of China’s energy structure, and ensuring safe and efficient mining is of great strategic significance for supporting China’s energy security while promoting sustainable and stable economic development [1,2,3,4]. However, with the increasing depth of China’s coal resource mining and the increasingly complex mining conditions [5,6,7,8], traditional coal mining technology has had difficulty adapting to the new production requirements [9,10,11,12]. Therefore, accelerating the innovation of coal mining technology, especially the research and development of high-efficiency mining technology for thick and extra-thick coal seams, has become an important issue for the current coal industry [13,14,15].
The evolution of hydraulic support frames reflects advancements in integrated mining technology and marks significant progress in the optimization and innovation of coal mining processes [16,17,18]. In particular, the emergence of comprehensive hydraulic support breaks through the bottleneck of traditional thick and extra-thick coal seam mining and provides key technical support for its efficient and safe development [19,20,21]. In recent years, with the development of coal mining to deep and complex geological conditions, the mining of thick and extra-thick coal seams is faced with the problems of poor top coal mobility and low recovery rate, which urgently requires more in-depth research on top coal crushing movement law and the coal caving process [22,23,24,25].
The mobility of top coal is one of the important factors determining the success or failure of fully mechanized caving mining, which is directly related to the efficiency and economic benefits of top coal mining [26]. During the process of top coal caving, it is easy for the structure of the support and the physical properties of the coal rock to have an effect, leading to the coal arch phenomenon in top coal caving, which seriously restricts the efficiency of coal caving [27,28,29]. At present, scholars at home and abroad have conducted a large number of studies on the law of movement of top coal, the formation mechanism of top coal caving and its control measures, such as the influence of bracket parameters on coal caving performance, the particle size distribution law of top coal, and the optimal design of coal caving opening size, which have led to improvements in caving efficiency and coal–gangue separation [30,31,32,33]. Wang et al. [34] used similar simulation experiments and numerical simulations to study the top coal caving ratio of fully mechanized mining, and established a unified research system to study the four elements: the coal–rock interface, top coal caving body, top coal caving ratio, and gangue ratio. The morphology of the coal–rock interface and the influence of the bracket and shifting bracket on it were analyzed, and it was proposed that the coal–rock interface could be fitted by a parabola. Wu et al. [35] simulated the transportation law of the top coal particles in the working face by PFC numerical simulation software, and obtained the transportation of the coal gangue flow field and the evolution law of the coal gangue interface. The results show that when a low-level roof coal holder is used, the top coal can easily form an arch at the beginning of mining, and with an increase in the cumulative coal caving step, the long axis of the coal caving funnel formed by the top coal falling or slipping is gradually deflected to the mining area, and the interface of the coal gangue gradually becomes fuzzy and tends to be smooth. Bai et al. [36] established a discrete element numerical simulation model of top coal caving. The arching mechanism of top coal after racking is discussed in terms of two aspects: the motion characteristics of the coal rock mass and the evolution law of the contact force field. Zhang et al. [37] considered the complex geological conditions of large-angle thick coal seams, analyzed the influence of the coal caving ratio on the top coal caving ratio under the condition of a large-angle thick coal seam through a laboratory dispersoid experiment, and obtained the top coal caving ratio and gangue ratio of different coal caving scenarios. The top coal caving ratio of two mines and one coal caving scenario was the highest and the gangue ratio was the lowest, and the top coal caving ratios of different comprehensive caving and mining methods in a large-angle thick coal seam was investigated with PFC numerical software. Jiang et al. [38] provided a simulation method for the dynamics of a dispersoid system based on discrete units for a dispersoid system composed of polyhedral particles, and realized an efficient numerical simulation of the contact collision dynamics of the dispersoid system. This method has important theoretical value, and can be applied to the simulation of dispersoid particle system stacking and collision dynamics in many engineering fields. Zhang et al. [39] used PFC2D to simulate top coal discharge patterns with different particle sizes and analyzed their impact on the caving ratio based on dispersoid mechanics theory. The relationship between top coal lumpiness and top coal caving rate is thus derived.
Although previous studies have explored various aspects of top coal caving—such as bracket structure, particle size distribution, and flow field evolution—most of them focus on isolated factors or rely heavily on empirical observations. Few studies have established a comprehensive theoretical framework to quantify top coal arching behavior and evaluate mobility under complex geological and support conditions. In particular, there is a lack of unified criteria to identify critical parameters (e.g., arching rate, flow factor) that influence caving efficiency, as well as a shortage of targeted control strategies derived from mechanical modeling.
To address these gaps, this study develops a theoretical model based on dispersoid mechanics to analyze the flow characteristics of top coal and the formation mechanisms of arching. The proposed model quantifies the relationship between coal particle properties, support parameters, and flow conditions. It introduces a flow factor for mobility evaluation and derives formulas for critical arching probability and caving opening size. The key innovations of this research include introducing a mechanical model that couples particle-scale properties with the macroscopic flow behavior of top coal; establishing a criterion system for top coal mobility based on flow factor and arching rate; and proposing targeted engineering measures to improve top coal recovery. These contributions aim to fill theoretical and technical gaps in current top coal caving research and provide practical guidance for high-efficiency mining in thick and extra-thick seams.
Based on the theory of dispersoid mechanics, this study researches the movement law and influencing factors of the dispersoid medium of top coal in comprehensive discharge, determines the controllable factors to improve top coal mobility and top coal caving ratio, and formulates measures to prevent and control the arching of the top coal dispersoid medium, which can provide effective guidance for the production of a comprehensive discharge working face. The results of this study can not only further enrich the theoretical system of top coal dispersoid movement, but also have direct technical guidance significance for improving the efficiency of top coal caving in actual production, and provide an important theoretical basis and technical support for promoting the safe and efficient mining of thick and extra-thick coal seams.

2. Top Coal Dispersoid Media Flow Law and Mobility Evaluation

The top coal mobility and top coal recovery rate of the fully mechanized top coal caving working face are the key factors determining the success or failure of comprehensive discharge. Good top coal mobility is one of the indispensable conditions to ensure the high recovery rate of top coal. In the early stage of top coal caving, the caving body is composed of pure top coal, but with the coal caving process and the breakage and movement of the overlying rock layer, part of the crushed direct top coal gangue will be mixed into the caving body, forming a coal–gangue mixture. Coal gangue mixing will lead to ambiguity and uncertainty over when to stop the coal caving. During the caving process, a conflict arises between maximizing recovery and minimizing gangue contamination. This is further complicated by the formation of arch structures that trap top coal [35].

2.1. Top Coal Dispersoid Flow Characteristics and Types of Top Coal Arching

After the lower part of the coal is extracted from the fully mechanized top coal caving working face, the upper top coal is gradually fractured and broken under the mine pressure, presenting a loose and broken state, which can be regarded as a dispersoid body for analyzing and researching according to the theory of dispersoid medium mechanics on the flow and caving characteristics of top coal [38]. According to its block size, the dispersoid of top coal can be divided into the categories of large block, medium block, small block, and loose granular body. Among them, large block refers to a size larger than the coal discharge opening that can not be caved; medium block refers to a block size that can not pass the coal discharge opening after the combination of 2~3 blocks, and small block refers to a block size that can be caved smoothly when it does not form an arch; large, medium, and small blocks can be approximated as a collection of dispersoid particles.
Top coal arching is a major factor contributing to reduced recovery rates. These arches can be classified by medium into pure coal arches and coal–gangue arches, and by position into low arches (located near the coal discharge opening) and high arches (formed above the bracket cover beam). Collectively, these are referred to as coal discharge arches [39].

2.2. Flow Model of Top Coal Dispersoid

2.2.1. Top Coal Flow Without Support Influence

According to the theory of the dispersoid body flow process, because the top coal dispersoid body is in a non-equilibrium state, the coal caving arch will periodically collapse and later re-form. The caving of dispersoid particles is repeated by the formation and collapse of dynamic coal caving arch. According to the Brown–Richard theory, dispersoid particles are automatically caved from the horizontal discharge opening, and the free-flowing material near the discharge opening can be divided into five flow zones. It is assumed that when there is no hewing stand in the hewing face to influence the top coal to be automatically caved from a horizontal opening, the top coal caving has some similarity with the above flow model. In Figure 1: E1 is the top coal pre-cracking zone in front of and above the stent which has not entered the movement zone; E2 is the impingement zone composed of already impeached gangue and coal left in the air-mining area; A1 and A2 are the movement zones of the maximal height layer that can be caved, where A1 is the area in front of the discharge opening and A2 is the area at the rear of the discharge opening; B1 and B2 are the particle replenishment zones; C is the dispersal vertical movement zone; and D is the free-movement zone.

2.2.2. Top Coal Flow Considering Bracket Influence

There are two major differences between the actual coal caving process of the comprehensive discharge working face and the caving of dispersoid particles from the discharge opening: firstly, the coal caving opening in comprehensive discharge mining is located in the tail part of the comprehensive discharge stent, and the existence of the smooth cover beam of the comprehensive discharge stent has a greater impact on the movement of the dispersoid top coal; secondly, the comprehensive discharge working face is constantly advancing, and the boundary conditions and the state of force are changing, making theoretical modeling of top coal movement in the working face more complex. This increases the difficulty of theoretically analyzing the movement of the top coal discharge body in the face.
Wang et al. [40] analyzed dispersoid top coal top with a three-dimensional caving law test and PFC3D numerical simulation test, and concluded that the difference in friction factor between the bracket cover beam–dispersoid top coal and the top coal–top coal causes the dispersoid particle flow velocity at the junction of the E1 area and the B1 area at the bracket cover beam to be significantly larger than that in the state when there is no influence of the bracket, so the caving body develops over the bracket front.
Below, theoretical analysis will be used to analyze the force on the flow ellipsoid to determine its flow-influencing factors.
The resistance F of the top coal sliding along the cover beam is mainly composed of two parts:
F = F + 2 F ,
where F is the resistance to the upward movement of the sliding body along the shear plane (slip plane) of the sliding body by the gravity F G of the shear portion of the top coal above the stent; and 2 F is the frictional resistance of the two side surfaces of the top coal body in the top coal.
The resistance to motion F is shown in the following equation.
F = F G tan θ + φ ,
where θ is the mass force of the sliding body in the shear portion of the top coal, θ = 45 o φ 2 ; and φ is the slip angle of the passive limit equilibrium state and the internal friction angle of the top coal body.
F G = b h 2 γ g 2 cot θ ,
where b is the width of the support; h is the thickness of the top coal; g is the acceleration of gravity; and γ is the density of the top coal.
Then there is
F = b h 2 γ g 2 tan 45 ° + φ 2 tan 45 ° φ 2 ,
In Equation (4), γ represents the bulk density of the top coal body. For typical bituminous or anthracite coal under caving conditions, the density generally ranges from 1.2 to 1.5 g/cm3 (i.e., 1200–1500 kg/m3) depending on compaction and moisture content.
From Equation (4), it can be seen that for external factors, the top coal body sliding surface resistance is proportional to the square of the bracket width and the top coal thickness, considering that the bracket width is mainly determined by the bracket working resistance, bracket stability, and other factors, so reducing the top coal thickness in a controllable range will be an effective method of reducing the resistance of coal caving.
And so on to find the lateral resistance F :
2 F = b h 2 γ g 2 cot θ tan 45 ° + φ 2 tan φ ,

2.3. Mobility Analysis of Top Coal Dispersoid

There are two main components in this part: the coal caving arch free face force analysis and the top coal mobility evaluation.
Because the top coal can not flow freely after the arch is formed, there is a free surface in the coal discharge arch, and there is no positive stress or shear stress on the free surface. According to the principle of shear stress complementarity, there is only positive stress and no shear stress on the surface perpendicular to the free surface. Taking the coal discharge arch containing a free surface (not at the boundary) of a microcell as shown in Figure 2, it can be seen that this positive stress is the maximum positive stress that damages the coal discharge arch. This maximum positive stress is the physical property of the dispersoid body and is called the unconfined yield strength of the object σ c .
According to the stress characteristics of the free surface of the coal discharge arch, the stress distribution when the arch is in the critical stress state can be obtained as shown in Figure 3. According to the Mohr–Coulomb failure criterion, shear failure of a granular material occurs when the Mohr stress circle becomes tangent to the material’s failure envelope (i.e., the Coulomb line). In the context of top coal arching, this condition represents the onset of collapse or flow of the arch. The unconfined yield strength refers to the maximum axial (positive) stress that a dispersoid particle assembly can withstand without lateral confinement. It corresponds to the point where the Mohr circle touches the failure envelope, indicating the limit of material stability.
From the geometric relations in Figure 3:
O A + 1 2 σ c = σ c 2 sin φ ,
O A = c tan φ ,
where c is the cohesive force of the particles; φ is the angle of internal friction of the particles.
From Equation (7), the unconfined yield strength of the dispersoid particle is given as
σ c = 2 cos φ 1 sin φ c ,
The following is the top coal mobility evaluation.
Define the flow condition of the top coal dispersoid itself using the flow factor λ as
λ = σ σ c = σ 1 sin φ 2 c cos φ ,
where σ is the positive stress on the particle.
When the flow factor λ is used as the criterion, when λ ≥ 1, the dispersoid particles can be caved freely, and the top coal mobility is better; when λ < 1, the dispersoid particles will be arched, and the smaller λ is, the worse the top coal mobility is.

3. Analysis of the Influence of Lumpiness on the Caving Rate of Top Coal and Arch Formation

3.1. Influence of Lumpiness on Top Coal Caving Rate

The arching of top coal is an extreme poor liquidity condition of top coal. From the expression of flow factor λ , it can be seen that the arching of top coal is mainly affected by two factors: one is the physical and mechanical properties of the top coal body itself, such as cohesion and the angle of internal friction; and the other is the positive stress σ of the top coal. In the actual production process, the physical and mechanical properties of the top coal body are basically the same and are not easy to change, so it can be seen that for the same working face, the chances of the top coal arching are directly proportional to the positive stress. Therefore, it can be known that for the same working face, the chance of top coal arching is directly proportional to the positive stress. According to the theory of particle matter mechanics, the relationship between positive stress σ and lump size K d is as follows:
σ = E K d 3 ( 1 μ 2 ) ξ 3 2 ,
where E is the modulus of elasticity; μ is Poisson’s ratio; and ξ is the normal overlap of particles in contact.
It should be noted that Equation (10) is derived based on the contact mechanics theory of discrete particles, where the normal stress is a function of particle overlap under elastic deformation. Therefore, this relationship is applicable primarily under conditions where the particle size distribution falls within a moderate gradation range and where the top coal dispersoid exhibits a relatively stable porosity. In highly compacted or loosely packed conditions—i.e., when porosity deviates significantly—the stress transmission path and contact overlap may not conform to the assumptions embedded in this model. As such, the applicability of Equation (10) should be confined to cases where the particle assembly remains within the quasi-static and elastic interaction regime.
From Equation (10), it can be seen that for a particular coal body in the same working face, E and μ are known, and the positive stress σ will increase with the increase in the top coal block degree K d . Equation (10) can be substituted into Equation (9) to obtain the arching rate of the top coal:
λ = E K d 3 ( 1 μ 2 ) ξ 3 2 1 sin φ 2 c cos φ ,

3.2. Judgment of Arch Formation of Top Coal Dispersoid

The mobility of the dispersoid of top coal is determined by the nature of the dispersoid and the parameters of the hydraulic support in contact with it, such as the size of the cover beam, the size of the tail beam, the size of the coal discharge opening, and the characteristics of the wall.
In order to avoid the formation of a coal caving arch in the process of releasing top coal, it is necessary to determine the influence of each parameter on the arch formation conditions, and the following section derives the critical size of the coal caving opening through theoretical analysis.
Coal discharge arch force analysis [41] is shown in Figure 4, where a is the distance from the top coal to the compacted gangue; and Δ h is the thickness of the coal discharge arch. Set the separation of the body plane AB and CD on the combined stress as σ 0 . Decompose σ 0 into tangential stress τ b and positive stress σ b , and the separation weight force G is:
G = a 0 Δ h γ g ,
where a 0 is the distance from the top coal to the compacted gangue in the critical state. When the coal discharge arch is in the critical state of destruction, the downward force of gravity and the upward vertical force of the compression force σ 0 in the arch are equal, and τ b has the equilibrium relation equation
G = 2 Δ h τ b ,
a 0 = 2 τ b γ g ,
The extreme value of the shear stress τ b in the critical state is
τ b = τ 0 ( 1 + sin φ ) ,
For the shear stress of particles, the following relation is given:
τ 0 = σ tan φ + c ,
This can be obtained by substituting Equation (16) into Equation (15) and then into Equation (14):
a 0 = 2 σ tan φ + c 1 + sin φ γ g ,
From Equation (17), it can be seen that the critical minimum size of the coal caving opening is related to the properties of the top coal itself, such as dispersoid weight, angle of internal friction, and cohesion, as well as being positively correlated with the positive stresses exerted on the dispersoid of the top coal.
When the size of coal discharge opening l a 0 , the dispersoid of top coal can cave freely without arching; when l < a 0 , the smaller l is, the greater the possibility of arching.

4. Discussion of Measures and Practices for Preventing Arching of Dispersoid Medium of Top Coal

The principle of enhancing the fluidity and caving rate of top coal dispersoid media to avoid arching should be based on eliminating or weakening the compressive stress on the surface of the dispersoid body, the friction between dispersoid body particles, and the friction between top coal and the comprehensive discharge support. Through the above theoretical research combined with the author’s research in recent years, measures to improve the top coal mobility and enhance the top coal discharge rate are mainly formulated in the following aspects.

4.1. Extra-Large-Height Fully Mechanized Top Coal Caving

According to the definition, extra-thick coal seams refer to coal seams with a thickness of more than 6 m [42,43,44]. At present, the ZY21000/38/82D hydraulic support with the world’s largest primary mining height designed by the Mining Design Division of Tiandi Science & Technology Co., Ltd. (Beijing, China) has been put into use in Yankuang Jintjitan Coal Mine, which indicates that extra-thick seams with a thickness of 6–8 m can be realized by using a primary mining height. For extra-thick coal seams above 8 m, only integrated mining can realize high yield and high efficiency, and the current integrated mining height is generally not higher than 4.5 m. However, for 15–25 m extra-thick coal seams with high hardness and good integrity, the problems of the large thickness of the top coal, poor mobility, high arching rate, and low recovery rate are prominent. According to Equation (4), reducing the thickness of top coal within the controllable range can reduce the resistance to coal caving and thus improve the liquidity and caving rate of top coal. Accordingly, the ZFY21000/34/63D and ZFY21000/35.5/70D (came from Tiandi Science & Technology Co., Ltd., Beijing, China) series of two-pillar powerful oversize height hydraulic releasing supports are designed to adapt to hard and extra-thick coal seams. Compared with the traditional secondary coal caving mechanism (Figure 5 and Figure 6), this support innovatively adopts a strong-disturbance three-level high-efficiency coal caving mechanism (Figure 7 and Figure 8). This increases the angle between the cover beam and insert plate by 13° compared with the traditional design, and increases the size of the coal caving opening by about 25%, reduces the arching probability of large coals, and improves the caving rate and efficiency of top coal caving.

4.2. Pre-Rupturing Top Coal by Multiple Alternating Loads

According to Equations (9) and (11), reducing the positive stress on the top coal and the lumpiness of the top coal after its destruction can significantly improve top coal mobility and caving rate, so on the basis of determining the reasonable support strength, we suggest increasing the active support force of the bracket, and at the same time, increasing the coal caving step distance, utilizing many alternating load times to pre-break the top coal to reduce its lumpiness, reduce the arching rate, and increase the rate of top coal mining back.

4.3. Limitations and Future Research Directions

Although this study provides a theoretical framework for understanding top coal movement and arching mechanisms based on dispersoid mechanics, several limitations should be acknowledged. First, the analytical model was developed under simplified assumptions, such as uniform stress distribution and idealized particle behavior, which may not fully represent the heterogeneous and dynamic conditions encountered in actual mining environments. In addition, the current work is based primarily on theoretical derivation and lacks validation through large-scale physical modeling or discrete element simulations [45,46,47,48]. Moreover, time-dependent effects, dynamic interactions between supports and coal bodies, and real-time monitoring feedback are not considered, which may influence the applicability of the proposed measures in field operations.
Future research should focus on improving model fidelity and extending practical application. In particular, the use of discrete element simulations can provide deeper insights into the spatial–temporal evolution of coal arching and granular flow behavior under different support configurations. Techniques for identifying the coal–rock interface through intelligent sensing, such as machine vision or acoustic analysis [49,50,51,52,53], would enhance boundary recognition and enable more precise control strategies. Furthermore, automated coal–gangue identification systems based on deep learning and real-time image classification hold promise for improving caving efficiency while minimizing gangue contamination. Finally, integrating field monitoring data with intelligent control systems could enable adaptive support adjustment and dynamic decision-making in fully mechanized top coal caving operations. These future efforts will help bridge the gap between theoretical modeling and engineering applications, thus enhancing mining performance under complex geological conditions.

5. Conclusions

Based on the theory of dispersoid mechanics, this study investigates the flow behavior of top coal and the mechanisms of arching in fully mechanized top coal caving. The following conclusions can be drawn:
(1)
Coal gangue arching is an important influencing factor on poor top coal mobility and low top coal recovery rate. Using dispersoid mechanics theory can provide the influencing factors of the top coal body sliding surface resistance and reduction measures; that is, increase the height of coal cutting to reduce the thickness of the top coal, and design hydraulic support for large-height top coal caving to improve the mobility of the top coal.
(2)
The formula for calculating the arching rate of top coal is given; the larger the top coal lump size is, the lower the top coal caving rate is. Combined with the analysis of the balance mechanics of the coal caving arch, the critical coal caving opening size is obtained, and the design adopts a three-stage coal caving device to increase the size of the coal caving opening and reduce the arching rate of the top coal.
(3)
The oversize height comprehensive caving stent provides a new effective method for mining hard and 15~25 m extra-thick coal seams, and offers practical guidance for improving mining efficiency and recovery in similar thick seam conditions.

Author Contributions

Writing—original draft preparation, J.Z. and Z.C.; writing—review and editing, Z.C.; conceptualization, S.L.; formal analysis, K.G.; investigation, L.C.; methodology, Z.Z.; investigation, resources, J.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Key R&D Program of China, grant number 2023YFC2907503, National Natural Science Foundation of China (NSFC) Young Fund, grant number 52204133, and Hebei Provincial Natural Science Foundation General Project, grant number E2024508055.

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Conflicts of Interest

Authors Jinhu Zhang and Sheng Lei were employed by the company CCTEG Tiandi Science & Technology Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. Granular flow model based on Brown–Richard theory, illustrating the flow zones of top coal during caving (the schematic reflects typical behavior of granular materials in the absence of bracket constraints).
Figure 1. Granular flow model based on Brown–Richard theory, illustrating the flow zones of top coal during caving (the schematic reflects typical behavior of granular materials in the absence of bracket constraints).
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Figure 2. Schematic diagram of microelement on free surface of coal drawing arch.
Figure 2. Schematic diagram of microelement on free surface of coal drawing arch.
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Figure 3. Stress distribution of coal drawing arch in critical stress state.
Figure 3. Stress distribution of coal drawing arch in critical stress state.
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Figure 4. Stress analysis of coal drawing arch.
Figure 4. Stress analysis of coal drawing arch.
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Figure 5. Physical demonstration of traditional secondary coal drawing mechanism.
Figure 5. Physical demonstration of traditional secondary coal drawing mechanism.
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Figure 6. Schematic representation of traditional secondary coal drawing mechanism.
Figure 6. Schematic representation of traditional secondary coal drawing mechanism.
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Figure 7. Physical demonstration of strong-disturbance three-level high-efficiency coal drawing mechanism.
Figure 7. Physical demonstration of strong-disturbance three-level high-efficiency coal drawing mechanism.
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Figure 8. Schematic representation of strong-disturbance three-level high-efficiency coal drawing mechanism.
Figure 8. Schematic representation of strong-disturbance three-level high-efficiency coal drawing mechanism.
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MDPI and ACS Style

Zhang, J.; Cheng, Z.; Lei, S.; Guo, K.; Chen, L.; Zhang, Z.; Chen, J. Research on the Law of Top Coal Movement and Influence Factors of Coal Caving Ratio for Fully Mechanized Top Coal Caving Working Face. Energies 2025, 18, 4312. https://doi.org/10.3390/en18164312

AMA Style

Zhang J, Cheng Z, Lei S, Guo K, Chen L, Zhang Z, Chen J. Research on the Law of Top Coal Movement and Influence Factors of Coal Caving Ratio for Fully Mechanized Top Coal Caving Working Face. Energies. 2025; 18(16):4312. https://doi.org/10.3390/en18164312

Chicago/Turabian Style

Zhang, Jinhu, Zhiheng Cheng, Sheng Lei, Kai Guo, Liang Chen, Zherui Zhang, and Jiahui Chen. 2025. "Research on the Law of Top Coal Movement and Influence Factors of Coal Caving Ratio for Fully Mechanized Top Coal Caving Working Face" Energies 18, no. 16: 4312. https://doi.org/10.3390/en18164312

APA Style

Zhang, J., Cheng, Z., Lei, S., Guo, K., Chen, L., Zhang, Z., & Chen, J. (2025). Research on the Law of Top Coal Movement and Influence Factors of Coal Caving Ratio for Fully Mechanized Top Coal Caving Working Face. Energies, 18(16), 4312. https://doi.org/10.3390/en18164312

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