A method for assessing the risk of rockburst based on coal-rock mechanical properties and In-Situ ground stress

Abstract

With the increase in mining depth and intensity, dynamic disasters such as rockburst in mines are becoming more severe. Deep resource extraction is characterized by a high in-situ stress geological environment, closely associated with geological dynamic disasters. However, there is currently no quantitative analysis method for the correlation between the two. In this study, an elastic energy density calculation method is employed, considering the dissipative effect of the self-weight stress field on the tectonic stress field. The remaining energy, referred to as impact energy, is used to classify the risk of coal seam impact, providing a computational method for rapid assessment of impact risk before mining production. The proposed calculation method is compared with 22 mine impact engineering practices in the literature, showing accurate predictions for 21 mines. Since measuring in-situ stress and coal seam physical and mechanical properties is a preliminary work in coal seam extraction, the comprehensive analysis of these data holds significant research and practical value.

Introduction

With the depletion of shallow resources, the coal mining industry has shifted towards deep mining. As the depth and intensity of mining increase, dynamic hazards such as rockburst become more pronounced. Rockburst, a powerful dynamic effect resulting from the rapid release of accumulated elastic deformation energy within coal and rock formations, is among the most severe dynamic hazards in coal mines¹.

Deep mining involves high ground stress geological conditions. The stress state of underground rocks or soil, known as ground stress, represents the stress environment for underground engineering structures. In its original form, the stress within underground rocks is defined as the initial ground stress. From a geological perspective, initial ground stress includes gravity stress, tectonic stress, expansion caused by water absorption, and stress induced by temperature changes. Gravity stress is derived from the rock’s own weight and Poisson’s effect, while tectonic stress is a result of crustal movements, both of them are major components of initial ground stress^2,3,4. Research on ground stress measurement and analysis in underground coal mines indicates that horizontal stress is dominant and serves as the primary force causing deformation and damage to underground mining structures^5,6,7.

Rockburst is the sudden release of elastic energy in coal and rock formations, making the accumulation and dissipation of energy during the deformation and failure process a fundamental study for identifying rockburst occurrences. Ground stress studies reveal that higher horizontal deviatoric stress leads to a higher risk of rockburst^8,9, this conclusion is supported by seismic wave CT inversion results¹⁰. Simultaneously, the direction of stress, being a vector, is also associated with rockburst risk. The highest risk occurs when the underground tunnel axis is perpendicular to the maximum horizontal stress and is lowest when parallel to the maximum principal stress¹¹. The application of grouting reinforcement technology in improving the stability and bearing capacity of fault crossing roadway provides a new idea for controlling energy release of coal and rock mass under complex geological conditions¹². According to the research of LI et al.¹³, the Energy composition model and static load anchoring characteristics of the new ACE Type Energy Release Bolt have been well applied in the energy release of geological engineering.

The stress field in the earth can be further divided into two types: static stress field and dynamic field, both of which are triggering factors for rockburst disasters⁸. For instance, the static load concentration generated by fault structures and the dynamic release of stress activation in faults have been proven to be important factors in tunnel rockbursts¹⁴. In folded mining areas, the maximum principal stress direction is perpendicular to the axis of folding, which is considered a primary controlling factor for rockburst occurrences^15,16. Additionally, parameters such as the maximum curvature and amplitude of folds are closely related to rockburst occurrences¹⁷. In summary, research on the stress field indicates that regional tectonic stress resulting from geological structural activities is a controlling factor for dynamic mining disasters such as rockbursts^18,19.

It’s widely agreed that regional stress fields are closely related to rockbursts. Yet, a quantifiable analysis method for this correlation is lacking. As measuring regional ground stress and surrounding rock properties is a preliminary task in coal mining, assessing rockburst risk with this data is crucial. The urgency lies in the growing threat of rockbursts to mining safety. This study aims to develop a rapid assessment method for rockburst risk before coal production. The core problem is the lack of a way to quantify the relationship. It uses the elastic energy density calculation method considering self-weight stress effects. The remaining energy classifies rockburst risk. The main contribution is providing a practical approach. Validated by 22 mining practices, it can aid in deep coal mining and rockburst prevention designs, enhancing mining safety.

Materials and methods

Calculation method for stress elastic deformation energy

Under natural geological conditions, the dynamic system of coal rock is considered stable, assuming it behaves like an elastic system. Assuming homogeneity and isotropy, the deformation energy density of coal rock can be calculated using stress-strain methods, stress-elastic methods, and strain-elastic methods²⁰.

The stress-strain method is primarily based on measured structural stress and resulting strain of coal rock, calculating the strain energy of the coal rock mass. The stress-elastic method relies on structural stress of the coal rock mass, as well as the elastic modulus and Poisson’s ratio of the coal rock, for the calculation. Meanwhile, the strain-elastic method involves calculating based on the strain of the coal rock mass and its elastic modulus and Poisson’s ratio parameters.

This study utilized the elastic stress method to calculate the strain energy density of coal-rock masses²¹, as follows:

$${E_\varepsilon }=\frac{1}{{2E}}\left[ {\left( {\sigma _{1}^{2}+\sigma _{2}^{2}+\sigma _{3}^{2}} \right) - 2\mu \left( {{\sigma _1}{\sigma _2}+{\sigma _2}{\sigma _3}+{\sigma _1}{\sigma _3}} \right)} \right]$$

(1)

Where:

${E_\varepsilon }$ is the strain energy density of the coal-rock mass in J/m³.

E is the elastic modulus of the coal in MPa.

${\sigma _1}$ is the maximum horizontal stress in MPa.

${\sigma _2}$ is the vertical stress in MPa.

${\sigma _3}$ is the minimum horizontal stress in MPa.

$\mu$ is the Poisson’s ratio.

This method calculates the strain energy density of coal rock mass based on empirical data and rock mechanics properties, thereby quantifying its energy conditions. By studying the distribution pattern of strain energy in coal rock mass, it aims to predict dynamic hazards such as rockburst in mines.

Constructing stress field coal rock dynamic system energy accumulation

The impact range of dynamic hazards in mines, such as rockburst, is limited. The energy provided by rockburst and the coal rock mass affected constitute a coal rock dynamic system^{22,23,24,25,26,27,28}. Without structural movement, there is no structural stress field or energy field, and the geological dynamic environment necessary for rockburst does not exist. As a result, the coal rock dynamic system does not form, and the energy conditions for mine dynamic hazards are not present. The “Relationship model between coal and rock dynamic system and rock burst development”²¹ is built to describe the relationship between the structural characteristics of coal and rock dynamic system and mine rock burst development, as shown in Fig. 1.

Figure 1

Model of the relationship between rockburst and coal-rock dynamic system.

In the context of constructing a stress field, the measured in-situ stress includes the stress induced by the self-weight. Therefore, the energy calculation under such conditions reflects the energy of the stress field induced by self-weight. In this scenario, the energy of the coal-rock dynamic system is equivalent to the energy of the constructed stress field. The accumulated energy in the coal-rock mass is directly related to the stresses in its three directions (σ₁, σ₂, σ₃), which can be obtained from the methods of measuring in-situ stress. Under the constructed stress field, the relationship between the coal-rock mass and the three-directional stress and self-weight stress can be described by Eq. (2) to (4). Then, by integrating Eq. (1) under the constructed stress field, the energy of the coal-rock dynamic system can be obtained, as shown in Eq. (5).

$${\sigma _1}={k_1}\gamma H$$

(2)

$${\sigma _2}={k_2}\gamma H$$

(3)

$${\sigma _3}={k_3}\gamma H$$

(4)

$${U_T}=\frac{1}{{2E}}\iiint {\left[ {\left( {\sigma _{1}^{2}+\sigma _{2}^{2}+\sigma _{3}^{2}} \right) - 2\mu \left( {{\sigma _1}{\sigma _2}+{\sigma _2}{\sigma _3}+{\sigma _1}{\sigma _3}} \right)} \right]}dV$$

(5)

In the given expressions,

${E_T}$ is the energy density for constructing the dynamic energy system of coal and rock under the stress field, measured in J/m³.

${U_T}$ is the energy for constructing the dynamic energy system of coal and rock under the stress field, measured in J.

${k_1}$ is set as the ratio of the maximum horizontal principal stress to the self-weight stress.

${k_2}$ is set as the ratio of the vertical stress to the self-weight stress.

${k_3}$ is set as the ratio of the minimum horizontal principal stress to the self-weight stress.

Under the conditions of constructing the stress field, when the dynamic energy system of coal and rock accumulated in the mine due to the rock burst is sufficient to cause ground pressure impact, it becomes the main source of energy.

Self-weight stress field and energy dissipation in coal-rock dynamic system

According to Jenike’s assumption, in the self-weight stress environment, considering only the influence of self-weight stress on the coal-rock dynamic system, the self-weight stress is directly proportional to the rock density and the burial depth of the rock unit. At the same time, the lateral stress can be regarded as the product of self-weight stress and the lateral pressure coefficient, as expressed in Eqs. (6) and (7).

$${\sigma _V}=\gamma H$$

(6)

$${\sigma _h}=\lambda {\sigma _V}$$

(7)

$$\lambda =\mu /(1 - \mu )$$

(8)

$${U_G}=\frac{1}{{2E}}\int {\int {\int {\left[ {\sigma _{V}^{2}+2\sigma _{h}^{2} - 2\mu \left( {2\sigma _{h}^{2}+{\sigma _V}{\sigma _h}} \right)} \right]} } } dV$$

(9)

In the given equations:

${\sigma _V}$ is the self-weight stress of the coal-rock mass, in MPa.

$\gamma$ is the average unit weight of overlying rock layers, in kN/m³.

H is the burial depth of the elemental volume, in meters.

${\sigma _h}$ is the lateral stress of the coal-rock mass, in MPa.

$\lambda$ is the lateral pressure coefficient.

The energy of the coal-rock dynamic system is established as the foundational energy under the self-weight stress field, with the energy density of the coal-rock dynamic system given in J/m³.

Method for discriminating impact energy of coal-rock dynamic system

If the released energy of the coal-rock dynamic system exceeds its critical energy level, it may trigger the phenomenon of dynamic ground pressure. In the natural geological environment, the total energy of the coal-rock dynamic system is equal to the energy of the coal-rock dynamic system under the tectonic stress field. Due to the effect of tectonic movement, the coal-rock mass undergoes deformation while accumulating elastic energy. If the stability of the coal-rock mass is disrupted, the previously accumulated energy will be released and perform external work²⁹. The released energy is the result of subtracting the basic energy from the total system energy, as shown in Eq. (10). Rock burst occurs only when the released energy exceeds the critical energy.

$$\Delta U={U_T} - {U_G}$$

(10)

In the given expression, $\Delta U$ represents the energy released by the coal-rock dynamic system, measured in joules J.

When the energy released by the coal-rock dynamic system exceeds the critical energy value for the occurrence of rock burst, the phenomenon of rock burst will occur. In China, this critical value is approximately 104 J to 106 J. The intensity of rock burst is directly proportional to the energy release of the system. Through in-depth research, it has been found that once the coal-rock dynamic system loses its stable state, the damaged coal-rock mass will be ejected to the surrounding area. The initial velocity of this ejection serves as a crucial factor in determining whether rock burst will occur: when the initial velocity of the ejected coal-rock mass is less than 1 m/s, rock burst almost does not occur. However, if the initial velocity is not less than 10 m/s, the risk of rock burst significantly increases³⁰. The initial velocity of the coal-rock mass can be measured and determined through mathematical modelling, laboratory testing, and other methods^{31,32,33,34,35}.

The conditions for the occurrence of rock burst are as follows: Assuming each cubic meter of coal rock as an independent unit, rock burst may occur when the cumulative elastic energy of the coal rock dynamic system can meet the energy loss requirements when the coal rock fractures, and also satisfies the critical kinetic energy requirements for the ejection of coal rock. Therefore, when the critical conditions for triggering rock burst are reached, the energy density of the released energy from the coal rock dynamic system can be expressed using Eq. (11). The energy density results of the released energy from the coal rock dynamic system can be described using formula (12).

In the equations:

$${E_{\hbox{min} }}=\frac{{\rho v_{0}^{2}}}{2}+\frac{{\sigma _{c}^{2}}}{{2E}}$$

(11)

$${U_S}=\int {\int {\int {\left( {\frac{{\rho v_{0}^{2}}}{2}+\frac{{\sigma _{c}^{2}}}{{2E}}} \right)} } } dV$$

(12)

${E_{\hbox{min} }}$ represents the energy density of the released energy when rock burst occurs, measured in J/m³.

ρ is the average density of the coal rock, measured in kg/m³.

${\nu _0}$ is the average initial velocity of the ejected coal rock, measured in m/s.

${\sigma _c}$ is the uniaxial compressive strength of the coal rock, measured in MPa.

In typical rockburst-prone mines, the energy generated by rockburst is derived from the difference between the structural stress field energy and the foundational energy. In summary, by substituting Formulas (5) and (7) into Formula (10) and simplifying, Formula (12) can be obtained, which serves as the basis for determining whether rockburst is likely to occur in typical rockburst-prone mines.

$$\frac{1}{{2E}}\left[ {\sigma _{1}^{2}+\sigma _{2}^{2}+\sigma _{3}^{2} - 2\mu \left( {{\sigma _1}{\sigma _2}+{\sigma _2}{\sigma _3}+{\sigma _1}{\sigma _3}} \right)} \right] - \frac{1}{{2E}}\left[ {\sigma _{V}^{2}+2\sigma _{h}^{2} - 2\mu \left( {2\sigma _{h}^{2}+{\sigma _V}{\sigma _h}} \right)} \right] \geqslant \frac{{\rho V_{0}^{2}}}{2}+\frac{{\sigma _{c}^{2}}}{{2E}}$$

(13)

Simplifying Formula (13) yields Formula (14). By substituting Formulas (2), (3), (4), (6), and (7) into Formula (13), Formula (14) is obtained. Expanding Formula (14) results in Formula (15), which, when further simplified, leads to Formula (18).

$$\sigma _{1}^{2}+\sigma _{2}^{2}+\sigma _{3}^{2} - 2\mu ({\sigma _1}{\sigma _2}+{\sigma _2}{\sigma _3}+{\sigma _3}{\sigma _1}) - \sigma _{V}^{2} - 2\sigma _{h}^{2}+2\mu (2\sigma _{h}^{2}+{\sigma _V}{\sigma _h}) \geqslant E\rho V_{0}^{2}+\sigma _{c}^{2}$$

(14)

$${\left( {{k_1}{\sigma _V}} \right)^2}+{\left( {{k_2}{\sigma _V}} \right)^2}+{\left( {{k_3}{\sigma _V}} \right)^2} - 2\mu \left( {{k_1}{k_2}\sigma _{V}^{2}+{k_2}{k_3}\sigma _{V}^{2}+{k_1}{k_3}\sigma _{V}^{2}} \right) - \sigma _{V}^{2} - 2{\lambda ^2}\sigma _{V}^{2}+4\mu {\lambda ^2}\sigma _{V}^{2}+2\mu \lambda \sigma _{V}^{2} \geqslant E\rho V_{0}^{2}+\sigma _{c}^{2}$$

(15)

$$k_{1}^{2}\sigma _{V}^{2}+k_{2}^{2}\sigma _{V}^{2}+k_{3}^{2}\sigma _{V}^{2} - 2\mu {k_1}{k_2}\sigma _{V}^{2} - 2\mu {k_2}{k_3}\sigma _{V}^{2} - 2\mu {k_1}{k_3}\sigma _{V}^{2} - \sigma _{V}^{2} - 2{\lambda ^2}\sigma _{V}^{2}+4\mu {\lambda ^2}\sigma _{V}^{2}+2\mu \lambda \sigma _{V}^{2} \geqslant E\rho V_{0}^{2}+\sigma _{c}^{2}$$

(16)

$$(k_{1}^{2}+k_{2}^{2}+k_{3}^{2}-2\mu {k_1}{k_2}-2\mu {k_2}{k_3}-2\mu {k_1}{k_3}-1-2{\lambda ^2}+4\mu {\lambda ^2}+2\mu \lambda )\sigma _{V}^{2} \geqslant E\rho V_{0}^{2}+\sigma _{c}^{2}$$

(17)

$$k_{{_{1}}}^{2}+k_{2}^{2}+k_{3}^{2}-2\mu {k_1}{k_2}-2\mu {k_2}{k_3}-2\mu {k_1}{k_3}-1-2{\lambda ^2}+4\mu {\lambda ^2}+2\mu \lambda \geqslant \frac{{E\rho V_{0}^{2}+\sigma _{c}^{2}}}{{{\gamma ^2}{H^2}}}$$

(18)

Substituting Formula (8) into Formula (18) yields Formula (19), and simplifying further gives (23):

$$k_{1}^{2}+k_{2}^{2}+k_{3}^{2} - 2\mu {k_1}{k_2} - 2\mu {k_2}{k_3} - 2\mu {k_1}{k_3} - 1 - 2{\left( {\frac{\mu }{{1 - \mu }}} \right)^2}+4\mu {\left( {\frac{\mu }{{1 - \mu }}} \right)^2}+2\mu \left( {\frac{\mu }{{1 - \mu }}} \right) \geqslant \frac{{E\rho V_{0}^{2}+\sigma _{c}^{2}}}{{{\gamma ^2}{H^2}}}$$

(19)

$$k_{1}^{2}+k_{2}^{2}+k_{3}^{2} - 2\mu ({k_1}{k_2}+{k_2}{k_3}+{k_1}{k_3}) - 1+\frac{{2{\mu ^3}}}{{{{\left( {1 - \mu } \right)}^2}}} \geqslant \frac{{E\rho V_{0}^{2}+\sigma _{c}^{2}}}{{{\gamma ^2}{H^2}}}$$

(20)

$$k_{1}^{2}+k_{2}^{2}+k_{3}^{2} - 2\mu ({k_1}{k_2}+{k_2}{k_3}+{k_1}{k_3})+\frac{{2{\mu ^3} - {\mu ^2}+2\mu - 1}}{{{{\left( {1 - \mu } \right)}^2}}} \geqslant \frac{{E\rho V_{0}^{2}+\sigma _{c}^{2}}}{{{\gamma ^2}{H^2}}}$$

(21)

$$k_{1}^{2}+k_{2}^{2}+k_{3}^{2} - 2\mu ({k_1}{k_2}+{k_2}{k_3}+{k_1}{k_3}) - \frac{{1+{\mu ^2} - 2{\mu ^3} - 2\mu }}{{{{\left( {1 - \mu } \right)}^2}}} \geqslant \frac{{E\rho V_{0}^{2}+\sigma _{c}^{2}}}{{{\gamma ^2}{H^2}}}$$

(22)

$$k_{1}^{2}+k_{2}^{2}+k_{3}^{2} - 2\mu ({k_1}{k_2}+{k_2}{k_3}+{k_1}{k_3}) \geqslant \frac{{E\rho V_{0}^{2}+\sigma _{c}^{2}}}{{{\gamma ^2}{H^2}}} - \frac{{2{\mu ^3} - {\mu ^2}+2\mu - 1}}{{{{\left( {1 - \mu } \right)}^2}}}$$

(23)

In Eq. (23), the ratio of vertical stress to self-weight stress is typically set to ${k_2}$= 1. Substituting ${k_2}$= 1 into Eq. (23) gives Eq. (24), which is the typical criterion formula for rockburst in mining induced by dynamic ground stress:

Simplifying Eq. (24) results in Eq. (25):

$$k_{1}^{2}+1+k_{3}^{2} - 2\mu ({k_1}+{k_3}+{k_1}{k_3}) \geqslant \frac{{E\rho V_{0}^{2}+\sigma _{c}^{2}}}{{{\gamma ^2}{H^2}}} - \frac{{2{\mu ^3} - {\mu ^2}+2\mu - 1}}{{{{\left( {1 - \mu } \right)}^2}}}$$

(24)

$$k_{1}^{2}+k_{3}^{2} - 2\mu ({k_1}+{k_3}+{k_1}{k_3}) \geqslant \frac{{E\rho V_{0}^{2}+\sigma _{c}^{2}}}{{{\gamma ^2}{H^2}}} - \frac{{2{\mu ^3}}}{{{{\left( {1 - \mu } \right)}^2}}}$$

(25)

To simplify the statement, let’s call $\frac{{E\rho V_{0}^{2}+\sigma _{c}^{2}}}{{{\gamma ^2}{H^2}}}$ part one, set $k_{1}^{2}+k_{3}^{2} - 2\mu ({k_1}+{k_3}+{k_1}{k_3})$ to part two, set $\frac{{2{\mu ^3}+2\mu -{\mu ^2}-1}}{{{{\left( {1-\mu } \right)}^2}}}$ to part three, set $\frac{{E\rho V_{0}^{2}+\sigma _{c}^{2}}}{{{\gamma ^2}{H^2}}}-\frac{{2{\mu ^3}+2\mu -{\mu ^2}-1}}{{{{\left( {1-\mu } \right)}^2}}}$ to part four.

In typical dynamic systems of coal-rock inrush ground pressure mines, the accumulated energy can support the occurrence of ground pressure during the mining process and is easily triggered. In contrast, non-typical ground pressure mines require additional energy from other engineering conditions before the possibility of ground pressure occurrence during mining¹⁹.

Results

To validate the accuracy of the discriminant formula for typical ground pressure mines, a combination of measured data from some mines was used for verification. The measured data are sourced from typical ground pressure mines, non-typical ground pressure mines, and mines with no ground pressure. The specific coal-rock physical and mechanical parameters for the selected mines are shown in Table 1, and the calculation results of the discriminant formula for typical ground pressure mines are presented in Table 2.

Table 1 Coal and Rock Mass Physico-mechanical parameters^{36,37,38,39,40,41,42,43,44,45,46,47,48,49,50}.

Table 2 Typical coal bump mine discrimination formula calculation results.

As shown in Table 1, where V₀, k₂, and γ are taken as the average values according to experience, while the remaining parameters are determined based on the actual conditions of different mines. Therefore, V₀ is set to 10 m/s, k₂ is equal to 1, and γ is taken as 27,000 kN/m³ or 25,000 kN/m³.

For typical rock burst mines, under natural geological conditions, the coal-rock dynamic system releases energy greater than the critical energy required for rock burst occurrence. For non-typical rock burst mines, under natural geological conditions, the coal-rock dynamic system releases energy less than the critical energy required for rock burst occurrence, requiring additional supplementation.

As shown in Table 2, Jixian Coal Mine, Laohutai Coal Mine, Wudong Coal Mine, Liangbaosi Coal Mine, Junde Coal Mine, Longjiapu Coal Mine, Tangshan Coal Mine, Hongyang Third Mine, Xinjulong Coal Mine, Dongrong Third Mine, Xingcun Coal Mine, Mengcun Coal Mine, Hengda Coal Mine, Ji’er Coal Mine, and Hongqinghe Coal Mine are identified as typical rock burst mines. Qianqiu Coal Mine, Hongqinghe Coal Mine, Hongqingliang Coal Mine, and Dongrong First Mine are identified as non-typical rock burst mines.

Discussion

Impact of mining on impact hazard

The genesis and occurrence of rock burst are the result of the combined effects of geological dynamic environmental factors^51,52 and human-engineered activities. It is also a dynamic process of energy accumulation and release within the coal-rock dynamic system²².

In the same geological dynamic environment yet under different mining conditions, there may be cases where intense explosive destructive events or other forms of large-scale disasters occur. However, in other mining scenarios, similar events may not take place. Hence, the stress redistribution caused by mining conditions has an influence on the manifestation of rock bursts. The essence of this study lies in the accumulation and release of energy within the coal-rock system, without considering the redistribution of energy after mining.

The energy conditions of the coal-rock dynamic system have a significant impact on the occurrence of dynamic ground pressure. The energy accumulated in the system forms the basis for the occurrence of dynamic ground pressure disasters. Three elements constitute the energy sources of the coal-rock dynamic system: firstly, in the natural geological environment, the energy is mainly generated under the action of tectonic stress (including self-weight stress); secondly, the influence caused by mining operations, which leads to an increase in energy due to the mining process; finally, it involves methods to mitigate dynamic ground pressure, namely, controlling the system’s energy through the implementation of mitigation measures.

Mining operations aim to improve the energy level of the coal-rock dynamic system and reduce the risk of dynamic ground pressure. This is achieved through activities such as excavation. Mitigation measures include various methods such as borehole stress relief and blasting unloading, aiming to control the system’s energy effectively and reduce the risk of dynamic ground pressure. However, in different mines and geological conditions, these activities may cause changes in the energy of the coal-rock dynamic system, and there is no fixed calculation model. Detailed analysis and calculation are required based on the actual situation.

Impact hazard geological dynamics analysis

The geological dynamic environment in mines is complex and diverse, with various factors such as structure, stress, and multiple combination modes collectively influencing the dynamic behavior of coal and rock geological bodies within the mining field⁵³.

The occurrence of dynamic ground pressure is determined by the coupling of geological dynamic conditions and engineering disturbances. The occurrence of dynamic ground pressure is related to the geological dynamic environment of the region, and geological dynamic environment assessment indicators include mining depth, stress, structure, coal pillar retention, etc. Using the geological dynamic environment assessment method, some coal mines in China are classified into different types, and the specific classification results are shown in Table 3. Among them, Jixian Coal Mine, Wudong Coal Mine, Laohutai Coal Mine, etc., are classified as typical dynamic ground pressure mines, while Hongqingliang Coal Mine is classified as a non-typical dynamic ground pressure mine, and Dongrong Mine is classified as a non-dynamic ground pressure mine.

Table 3 Mine classification using geological dynamic environment assessment method.

Article 225 of the “2022 Coal Mine Safety Regulations” stipulates that coal seams in the mining field where dynamic ground pressure phenomena have occurred or coal seams (or their roof and floor rock layers) identified with dynamic ground pressure tendencies and assessed for dynamic ground pressure risk are classified as dynamic ground pressure coal seams, and mines with dynamic ground pressure coal seams are classified as dynamic ground pressure mines. The results obtained from applying the typical dynamic ground pressure mine discrimination method are compared with the results of the geological dynamic environment assessment, as follows:

• (1) Out of 22 data sets, 15 sets of typical dynamic ground pressure mines are mutually validated successfully. Jixian Coal Mine, Laohutai Coal Mine, Wudong Coal Mine, Liangbaosi Coal Mine, Junde Coal Mine, Longjiapu Coal Mine, Tangshan Coal Mine, Hongyang San Mine, Xinjulong Coal Mine, Dongrong San Mine, Xingcun Coal Mine, Mengcun Coal Mine, Hengda Coal Mine, Ji’er Coal Mine, and Hongqinghe Coal Mine are all identified as typical dynamic ground pressure mines. The results of both methods are consistent.

• (2) Hongqingliang Coal Mine is identified as a non-typical dynamic ground pressure mine, and the results of both methods are consistent.

• (3) There is a difference in the results for Qianqiu Coal Mine and Hongqinghe Coal Mine. The reason is that the unconventional nature of the stress measurement results in Qianqiu Coal Mine and Hongqinghe Coal Mine, influenced by large geological structures such as the F16 fault and fault zones. Considering the differences in the distances between stress measurement points and geological structures, there may be variations in the readings of local stress measurement points, leading to differences in the discrimination results.

Based on a large number of instances, it is shown that different typical rock burst mines, despite differences in geographical locations and physical-mechanical parameters, all conform to the discriminant formula for the occurrence of rock bursts in typical rock burst mines. This implies that it is possible to predict and discriminate the occurrence of rock bursts in typical rock burst mines in advance. Further verification demonstrates the significant influence of modern geological structural movements, internal dynamics, and structural stress fields on the energy evolution and rock burst risk of coal-rock masses.

Conclusions

• (1) Taking the energy composition of the coal-rock dynamic system as a starting point, this study analyzed the evolution characteristics of coal body elastic residual energy under different stress and physical-mechanical parameter conditions in different typical rock burst mines. A new perspective on the relationship between self-weight stress, structural stress, and the deformation and failure energy of coal-rock masses is proposed.

• (2) This paper refines rock burst mines, establishes the relationship between the coal-rock dynamic system and rock burst mines, and proposes a theoretical calculation method for discriminating typical rock burst mines. This method can be used to classify mine types and determine the danger of rock bursts in typical rock burst mines.

• (3) Representative measured data from rock burst mines were selected to validate the accuracy of the discriminant formula for typical rock burst mines. The results show that the formula can be used to discriminate whether a mine is at risk of rock bursts.

• (4) For the coal-rock dynamic system of atypical rock burst mine, many supplementary factors need to be considered, such as mining disturbance, fault activation, emergency treatment methods, etc. The calculation method of rock burst in atypical rock burst mine will be discussed in depth in the follow-up study.