China has abundant reserves of ultra-thick coal seams, and the fully mechanised caving face mining of ultra-thick coal seams has the characteristics of high output, fast efficiency and significant economic benefits [1, 2]. The mining depth of most underground coal mines in our country is not more than 400–500 m, and the movement range of the roof is mainly 6–8 times the mining height above the coal seam, which is the traditional theory of rock pressure [3, 4]. Key parameters such as mining scale and intensity of longwall panels are constantly being refreshed. The movement range of the overlying rock at the working face increases dramatically, and the evolution law of the mining stress field presents complexity [5, 6]. In the height direction, it has far exceeded the ‘basic roof’ range, and in the horizontal direction, it has also exceeded the range of the upper and lower lanes on the working surface.
In recent years, domestic scholars have achieved a lot of research results on the characteristics of rock pressure in fully mechanised caving faces of extra-thick coal seams. In view of the research on the failure height of the top coal body in fully mechanised caving mining of extra-thick coal seams, a ‘three-zone’ structural model of the top coal body in fully mechanised caving mining of extra-thick coal seams is proposed, namely ‘scattered body zone’ and ‘block body zone’ from bottom to top ‘Cracked beam belt’ [7–9]. Based on the cantilever beam-masonry beam mechanical structure model of extra-thick coal seam, the mechanical model of the fracture of the cantilever beam structure with the central inclined crack is established, and the expression of the support load is given [10]. The ‘face contact block arch’ model of fully mechanised caving surface of extra-thick coal seam was proposed, the mechanism of top coal arching was studied, and the arching phenomenon that the top coal was easy to form blocking coal caving during the caving process was revealed [11]. Based on the BBR research system, the optimisation of the coal caving method for fully mechanised caving mining in extra-thick coal seams is carried out, and the segmented and large-interval coal caving method is proposed [12]. The research on the mechanism of shock composite dynamic disasters should be strengthened from the following aspects:
Make a more scientific classification of the combined dynamic disaster of mine shock and shock in thick and hard rock mines [13];
In-depth study of the quantitative mechanical model of shock composite dynamic disasters [14, 15];
Consider the research on the disaster mechanism of the mine-seismic composite system in the mine with thick hard rock layer under the stress path that is more in line with the actual conditions of the site [16];
Strengthen the role of deep learning and big data technology in the study of the nonlinear mechanism of disasters [17];
Continue to increase scientific and technological research efforts [18].
The movement state and stress distribution of the overlying hard rock layers in the stope are the main factors controlling the occurrence of dynamic disasters such as rockbursts. Scholars have carried out a lot of research in related fields [19, 20]. With the continuous depletion of superficial resources in our country and the continuous increase in the depth and intensity of coal mining [21], in recent years, rockburst disasters have occurred frequently, and rockburst has become a typical form of dynamic disasters that affect the safety of coal mine production in China and restrict the harmonious development of mining areas. Rockburst is an induced disaster [22]. The main reason for it is that the stratum structure is damaged or the stress is in an abnormal state in the mining influence range [23]. The motion state of the thick and hard rock layer determines the dynamic appearance and influence scope of the working face, and its buckling motion is the main reason for inducing strong rockbursts [24, 25]. Rockburst is usually regarded as a problem related to structural instability of coal and rock mass.
In summary, this paper proposes a study on the dynamic hazard system of seismic and shock loads in thick rock mines. The main outstanding work is as follows:
Detailed research and discussion on the analysis of the seismic and impact composite dynamics of the thick and hard rock layers;
A complete set of disaster prevention and control system is proposed under the combined influence of the combination of earthquake and shock in thick and hard rock layers;
Finally, the experimental comparison is carried out, and the experiments are carried out under different vibration degrees. The experimental analysis results show that the system proposed in this paper can pre-analyse disaster prevention and control.
During the fracture movement of the thick and hard rock layer, the bearing stress of the coal body in the working face also undergoes periodic stress changes. The periodic breaking motion of the overlying thick hard rock layer in the stope is the main reason for the concentration and transfer of the advanced bearing stress in the working face. According to the width of the coal pillar and its stress state, the fully elastic state mainly experienced by the coal pillar of the re-mining face during the continuous mining process is obtained [26]. Based on the spatial structure of the thick and hard rock layers and their boundary characteristics, the overhanging thick and hard rock layers are regarded as elastic rock beams, and the coal-rock mass at the stope boundary is regarded as the fixed support end of the stope. The basic morphological characteristics that may appear after the critical layer is broken are as follows:
The key layer cantilever beam structure and the masonry beam structure (or hinged structure) are the two types of key layer structures that determine the pressure of the working face and control the type and danger of disasters;
The main factor of the shape of the key layer in the stope is the mining height and the height of the key layer from the coal seam, that is, after the key layer is broken, whether the rotation amount of the broken rock block exceeds its maximum rotation amount to maintain a stable structure;
After the coal seam is mined, the low-level roof directly collapses layer by layer and fills the goaf, according to Qian Ming et al., as
Here, the rotation amount Δ
By analysing the thick and hard rock layer-coal pillar structural system and its stress state, the mechanical model of the thick and hard rock layer-coal pillar structure under static conditions is further simplified. In order to facilitate the analysis and calculation, the support force on the fixed end of the cantilever rock beam is approximated as the concentrated force
The overhang length of the cantilevered rock beam at the fixed end does not exceed the ultimate breaking step distance under the equilibrium condition of the hinged structure;
The stress on the coal pillar at the bottom of the fixed support end is lower than its comprehensive support strength.
The model is squeezed by the rock masses on both sides to form horizontal thrusts
Among them,
In the horizontal direction, the broken rock block squeezes with the adjacent rock beams during the rotational deformation process, thus forming a horizontal thrust. It is not difficult to conclude that
Here,
Finally, the expression of the concentrated force
The basic theory of flexural deformation of rock beam in elastic mechanics, the differential equation of flexural deformation of rock beam is:
First, according to the moment balance condition, the bending moment
Then, the maximum bending moment
Finally, if the ultimate tensile strength of the thick hard rock layer is σ
The magnitude of the additional concentrated force transmitted from the space hinge to the coal pillar in the thick and hard rock layer-coal pillar model can further analyse the instability criterion of the thick and hard rock layer-coal pillar model.
The shock wave generated by the mine earthquake is similar to the general shock wave. The shock wave can produce strain effects (deformation and vibration) and inertia effects (pressure and tension) on the surrounding medium and surface buildings during the propagation of the medium. Among them, the judgement basis (safe
Vibration damage judgement table
1 | ||||
2 | ||||
3 | ||||
4 |
It can be seen from the elastic mechanics reasoning that the additional force caused by the mine earthquake is related to the particle vibration velocity:
The equation of motion of an isotropic ideal elastic body is:
Aiming at the regular mechanism of shock composite dynamic disaster, the existing research can be summarised into qualitative and preliminary quantitative research as follows. The first category is to combine typical case studies and theoretical analysis to discuss the conditions and characteristics of disaster occurrence, and then to propose a qualitative explanation of the disaster occurrence mechanism. The second type is to use the experimental platform to carry out experimental research from the point of view of the damage and instability induced disasters of gas-bearing coal and rock mass, in order to grasp the occurrence mechanism of compound disasters. The process of composite dynamic disaster must be controlled by the damage and damage of objects and rock medium and its coupling effect with mechanics and seepage behaviour in coal.
Under the condition of deep high stress, rockburst disasters mainly occurred in the coal seam with strong shock tendency and developed into the coal seam with weak shock tendency. Similarly, the increase of stress, gas content and gas pressure led to coal and gas outburst from soft coal to medium hard coal. Coal development is shown in Figure 1. Therefore, many deep mining mines face the threat of rockburst and gas outburst dynamic disaster at the same time, and some mines even have a composite dynamic disaster in which the impact and outburst are mutually induced.
The use of microseismic monitoring technology to study composite dynamic disasters is an interdisciplinary subject, involving the knowledge of many basic disciplines such as geology, rock (damage, fracture) mechanics, dynamic signal testing and analysis. The essence of a microseismic event is the manifestation of a series of dynamic evolution processes such as stress, strain, deformation, cracking, instability and failure of the surrounding rock. Because the microseismic monitoring technology can describe the movement and failure of rock formations in an all-round way in space stress drop and its failure size and failure mode, so it has unique advantages over traditional methods.
At present, the main technical measures for pressure relief and outburst elimination of coal seam roadway excavation working face include mining protective layer, regional gas pre-drainage, advanced drilling, deep hole water injection, hydraulic punching, hydraulic cutting, deep hole loosening blasting and deep hole drilling controlled blasting and so on.
The rupture of thick and hard rock layers can induce strong mine earthquakes and cause different degrees of vibration damage to the ground. According to the conditions of strong mine shocks induced by the rupture of thick and hard rock layers, the idea of a shock composite dynamic disaster prevention and control system is proposed to change the conditions of mine shocks and reduce the energy released by mine shocks, as shown in Figure 2. Changing the conditions of mine shock can be based on mining technology, where the purpose is to reduce the height of the fracture of the thick hard rock layer and maintain the structural stability of the thick hard rock layer. Among these, reducing the energy released by the mine shock mainly controls the splitting scale of the thick and hard rock layers and the scale of the movement of the thick and hard rock layers.
Mining protective layer and regional gas pre-draining have been widely used in China and abroad as regional technologies for preventing and controlling mine gas dynamic disasters. In view of the characteristics of poor gas permeability and soft coal quality of prominent dangerous coal seams in China, enhanced drainage technologies such as hydraulic hole reaming, wind-driven slag discharge and other drilling construction technologies along the coal seam have been studied, and good application results have been achieved. However, the short-range lower protective layer mining technology and regional gas pre-extraction and anti-outburst affect the evaluation system as follows:
Mining of protective layers between coal groups in mines. At present, most mines adopt the downward mining sequence of coal groups. The mining practice of some mines has proved that the upward mining between groups has a good protective effect on the coal of the upper group.
Mining of protective layers within coal seam groups of mines. When mining within the group, give priority to mining the protective layer within the group and liberate other coal seams.
Preventive measures for excavation face. Under the condition of no protective layer mining, the gob-side roadway technology is preferentially used for the coal roadway driving face with the risk of composite dynamic disaster in each mine. The coal seam extraction measures shall be implemented in the gob-side roadway to protect the roadway excavation of the adjacent outburst coal seam.
Outburst prevention measures at coal mining face. The coal mining face generally adopts the measures of transportation, long-draining along the layer of the return air lane, shallow-draining in the working face, and drilling through the layer in the high (low) level roadway. After the effectiveness of the measures exceeds the standard, take supplementary measures for shallow hole pressure relief and drainage in the area exceeding the standard.
In the northwestern part of a mining area, the main mining thick hard rock layers are mines, with an average coal thickness of 9.43 m and a coal burial depth of 800–1000 m. Since the coal mine was opened in July 2019, the phenomenon of impact composite dynamic has occurred many times during the excavation of the main road and after the formation of the roadway with the thick and hard rock layers. During the period, the coal-rock mass fracture-induced shock composite dynamic appears in the coal pillar area of a typical deep-buried mine. This section selects 8 dynamic manifestation events and 58 mine earthquake events that occurred in the Northwest Mine Coal Mine from August to December 2019 as the research objects, and explores the mechanism law of mine earthquake and shock composite dynamic disaster prevention and control system in deep hard rock mines.
The width of the working face is first divided into 175 m, according to the actual mining experience in the west area. The three options are as follows:
When the working face is preferentially mined, the overlying thick hard rock can be broken, and the sum of the width of the working face and the adjacent goaf is about 545 m;
The sum of the width of adjacent goaf is about 535 m in priority;
The sum of the width of the joint working face and the adjacent goaf is about 715 m.
Here, the ratio of goaf width and rock thickness in different schemes is (535-715)/110 = 4.86–6.45. Therefore, referring to the research results of the thin plate theory, the rock fracture law is analysed as:
According to the mining geological data, the goaf width on one side of the incomplete mining area is 360 m. Take the average bulk density of the overlying rock as
Figure 3 shows that the average support strength of coal mines increases with the increase in working face width and tends to be stable. When the working face width is less than the limit width (about 80 m), there is a possibility of ‘static instability’. The theoretical estimate of the limit width of the working face is about 145 m. In order to meet the height safety requirements of rockburst working face, factors such as roadway, section coal pillar arrangement and safety factor are considered. The actual working face layout width should be greater than 175 m. According to the analysis, scheme 3 is the best for the prevention and control of rockburst.
In addition to considering the overall stability of the working face, there are important water conservancy facilities on the stope ground. Assess the vibration damage effect of mine earthquakes on water conservancy facilities. Find mining options that reduce vibration damage. According to the three schemes, the total lengths
Mine seismic analysis results
1 | 0.12 | 0.13 | 0.03 |
2 | 0.19 | 0.18 | 0.04 |
3 | 0.23 | 0.25 | 0.06 |
4 | 0.29 | 0.29 | 0.08 |
5 | 0.31 | 0.33 | 0.09 |
6 | 0.39 | 0.47 | 0.12 |
7 | 0.48 | 0.51 | 0.13 |
8 | 0.49 | 0.56 | 0.14 |
9 | 0.58 | 0.61 | 0.16 |
10 | 0.61 | 0.65 | 0.17 |
Table 2 shows that the vibration velocity
The motion state of the thick and hard rock strata determines the dynamic appearance degree and influence range of the working face, and its instability motion is the main reason for the strong rockburst disaster. Rockburst is usually regarded as a problem related to structural instability of coal and rock mass. This paper proposes a framework of a composite dynamic disaster prevention and control system framework for thick and hard rock mines. First, the gravity forms, extents and deformation characteristics of different rock layers of the structural model are analysed, and the expressions of concentrated force and periodic breaking step distance of rock beams in thick and hard rock layers at the fixed support end are deduced, based on this. Then, according to the cause of the shock composite dynamic disaster, finally, the specific testing and calculation methods of mine earthquakes in thick hard rock mines are designed. The regional and local measures to manage compound dynamic disasters are put forward. Experiments show that the system is successfully applied to the mining practice of working face, and the results of water conservancy and stress monitoring support the rationality of the system. However, the mines discussed are still relatively simple, and there are no comparative experiments with multiple mines. In the future work, the multidimensional mine seismic data will be compared horizontally.
Mine seismic analysis results
1 | 0.12 | 0.13 | 0.03 |
2 | 0.19 | 0.18 | 0.04 |
3 | 0.23 | 0.25 | 0.06 |
4 | 0.29 | 0.29 | 0.08 |
5 | 0.31 | 0.33 | 0.09 |
6 | 0.39 | 0.47 | 0.12 |
7 | 0.48 | 0.51 | 0.13 |
8 | 0.49 | 0.56 | 0.14 |
9 | 0.58 | 0.61 | 0.16 |
10 | 0.61 | 0.65 | 0.17 |
Vibration damage judgement table
1 | ||||
2 | ||||
3 | ||||
4 |
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Neural Network in Vibration Control of Civil Engineering Structure Optimal Model Combination of Cross-border E-commerce Platform Operation Based on Fractional Differential Equations The influence of accounting computer information processing technology on enterprise internal control under panel data simultaneous equation Research on Stability of Time-delay Force Feedback Teleoperation System Based on Scattering Matrix BIM Building HVAC Energy Saving Technology Based on Fractional Differential Equation Construction of comprehensive evaluation index system of water-saving irrigation project integrating penman Montei the quation Human Resource Management Model of Large Companies Based on Mathematical Statistics Equations Data Forecasting of Air-Conditioning Load in Large Shopping Malls Based on Multiple Nonlinear Regression Analysis of technical statistical indexes of college tennis players under the win-lose regression function equation Automatic extraction and discrimination of vocal main melody based on quadratic wave equation Analysis of wireless English multimedia communication based on spatial state model equation Optimization of Linear Algebra Core Function Framework on Multicore Processors Application of hybrid kernel function in economic benefit analysis and evaluation of enterprises Research on classification of e-commerce customers based on BP neural network The Control Relationship Between the Enterprise's Electrical Equipment and Mechanical Equipment Based on Graph Theory Mathematical Modeling and Forecasting of Economic Variables Based on Linear Regression Statistics Nonlinear Differential Equations in Cross-border E-commerce Controlling Return Rate 3D Mathematical Modeling Technology in Visualized Aerobics Dance Rehearsal System Fractional Differential Equations in Electronic Information Models BIM Engineering Management Oriented to Curve Equation Model Leakage control of urban water supply network and mathematical analysis and location of leakage points based on machine learning Analysis of higher education management strategy based on entropy and dissipative structure theory Prediction of corporate financial distress based on digital signal processing and multiple regression analysis Mathematical Method to Construct the Linear Programming of Football Training Multimedia sensor image detection based on constrained underdetermined equation The Size of Children's Strollers of Different Ages Based on Ergonomic Mathematics Design Application of Numerical Computation of Partial Differential Equations in Interactive Design of Virtual Reality Media Stiffness Calculation of Gear Hydraulic System Based on the Modeling of Nonlinear Dynamics Differential Equations in the Progressive Method Knowledge Analysis of Charged Particle Motion in Uniform Electromagnetic Field Based on Maxwell Equation Relationship Between Enterprise Talent Management and Performance Based on the Structural Equation Model Method Term structure of economic management rate based on parameter analysis of estimation model of ordinary differential equation Influence analysis of piano music immersion virtual reality cooperation based on mapping equation Chinese painting and calligraphy image recognition technology based on pseudo linear directional diffusion equation Label big data compression in Internet of things based on piecewise linear regression Animation character recognition and character intelligence analysis based on semantic ontology and Poisson equation Design of language assisted learning model and online learning system under the background of artificial intelligence Study on the influence of adolescent smoking on physical training vital capacity in eastern coastal areas Application of machine learning in stock selection Comparative analysis of CR of ideological and political education in different regions based on improved fuzzy clustering Action of Aut( G ) on the set of maximal subgroups ofp -groupsResearch on loyalty prediction of e-commerce customer based on data mining Algebraic Equations in Educational Model of College Physical Education Course Education Professional English Translation Corpus Under the Binomial Theorem Coefficient Geometric Tolerance Control Method for Precision Machinery Based on Image Modeling and Novel Saturation Function Retrieval and Characteristic Analysis of Multimedia Tester Based on Bragg Equation Semiparametric Spatial Econometric Analysis of Household Consumption Based on Ordinary Linear Regression Model Video adaptive watermark embedding and detection algorithm based on phase function equation English Learning Motivation of College Students Based on probability Distribution Scientific Model of Vocational Education Teaching Method in Differential Nonlinearity Research on mobile Awareness service and data privacy Protection based on Linear Equations computing protocol Vocal Music Teaching Model Based on Finite Element Differential Mathematical Equations Studying a matching method combining distance proximity and buffer constraints The trend and influence of media information Propagation based on nonlinear Differential equation Research on the construction of early warning model of customer churn on e-commerce platform Evaluation and prediction of regional human capital based on optimised BP neural network Study on inefficient land use determination method for cities and towns from a city examination perspective A study of local smoothness-informed convolutional neural network models for image inpainting Mathematical Calculus Modeling in Improving the Teaching Performance of Shot Put Application of Nonlinear Differential Equation in Electric Automation Control System Higher Mathematics Teaching Curriculum Model Based on Lagrangian Mathematical Model Computational Algorithm to Solve Two–Body Problem Using Power Series in Geocentric System Decisions of competing supply chain with altruistic retailer under risk aversion Optimization of Color Matching Technology in Cultural Industry by Fractional Differential Equations The Marketing of Cross-border E-commerce Enterprises in Foreign Trade Based on the Statistics of Mathematical Probability Theory Application of Linear Partial Differential Equation Theory in Guiding Football Scientific Training Nonlinear Channel Estimation for Internet of Vehicles Some Necessary Conditions for Feedback Functions of de Bruijn Sequences The Evolution Model of Regional Tourism Economic Development Difference Based on Spatial Variation Function System Model of Shipping Enterprise Safety Culture Based on Dynamic Calculation Matrix Model An empirical research on economic growth from industrial structure optimisation in the Three Gorges Reservoir area The Inner Relationship between Students' Psychological Factors and Physical Exercise Based on Structural Equation Model (SEM) Analysis and Research on Influencing Factors of Ideological and Political Education Teaching Effectiveness Based on Linear Equation Study of agricultural finance policy information extraction based on ELECTRA-BiLSTM-CRF Fractional Differential Equations in Sports Training in Universities Examination and Countermeasures of Network Education in Colleges and Universities Based on Ordinary Differential Equation Model Innovative research of vertical video creation under the background of mobile communication Higher Education Agglomeration Promoting Innovation and Entrepreneurship Based on Spatial Dubin Model Chinese-English Contrastive Translation System Based on Lagrangian Search Mathematical Algorithm Model Genetic algorithm-based congestion control optimisation for mobile data network