Rockburst Mechanism Research Articles

Unified Mechanism of Rock Burst Induced by Coal Mine Earthquake and Its Activity and Response Characteristics

The occurrence regularity of the coal mine earthquake under the influence of hard roof, fault, and mining was studied by theoretical analysis, field investigation, and monitoring data analysis for the phenomenon of rock burst induced by coal mine earthquakes. The dissipation characteristics of coal mine earthquake energy propagation considering a hypocenter scale were described, and the coal mine earthquake response characteristics were analyzed. The two principles of rock burst induced by hard rock fractured type coal mine earthquakes and the three principle of rock burst induced by fault were described. Based on this, the unified mechanism rock burst induced by different types of coal mine earthquakes was proposed. The results show that the microseismic energy increases sharply and decreases sharply when mining in the fault area. The amplitude and frequency of support resistance increased before and after the heavy coal mine earthquake occurred. The periodic characteristics of the coal mine earthquake in the 43upper 13 working face of the Dongtan coal mine show that there are 50 m small periods within 100 m large periods. The multiparameter field monitoring can make it possible for instantaneous capture of the coal mine earthquake dynamic responses. The unified rock burst mechanism induced different types of coal mine earthquake and is the difference energy between the superposition energy of the rock burst source region and the energy consumed by coal-rock instability increases suddenly under the action of coal mine earthquakes. Meanwhile, the violent rock burst accident occurs when the stiffness condition is satisfied.

Mechanism and Control Technology of Rockburst Induced by Thick Hard Roof and Residual Coal Pillar: A Case Study

Rockburst caused by the fracture of thick hard roof and the instantaneous instability of residual coal pillar seriously jeopardize the deep coal mining safety. This study takes Boertai Coal Mine, Shendong, China, as the engineering background, in which dynamic instability mechanisms of the gob-side roadway surrounding rock are analyzed by integrating field research, theoretical analysis, and numerical simulation. The results show that the overlying residual coal pillar, side abutment pressures, and front abutment pressures together induce high static stresses in the surrounding rock of the gob side roadway, with peak values exceeding the in situ stress by one order of magnitude. High stresses accumulated in the goaf-side roadway surrounding rock can easily induce dynamic disaster. With the working face advanced, overburdens are caved in succession, resulting in a continuously decreasing of the overlying residual coal pillar width, once the working face entered the influence area of the residual coal pillar. As the morphology of abutment pressure in the residual coal pillar changes from “unimodal distribution” to “bimodal distribution,” the residual coal pillar gradually changes from elastic state to plastic state. When the width of the overlying residual coal pillar is less than the critical width, the thick hard roof and residual coal pillar structure (THRRCPS) lose stability suddenly, resulting in strong dynamic load on the surrounding rock of gob-side roadway. In order to prevent the rockburst of the gob-side roadway under the influence of THRRCPS, regional and local prevention measures are adopted to mitigate the accumulation of stress in the thick hard roof and gob-side roadway surrounding rock by hydraulic fracturing technology and large diameter pressure relief drilling hole.

Characterization of true triaxial rock bursts in sandstones with different water contents

The rockburst phenomenon occurs in dry red sandstone under high in situ stress, and the rockburst effect is weaker for a water-bearing rock. The rockburst effect on red sandstone with different water contents is analyzed in this paper. A true triaxial testing machine is used to conduct the loading, and acoustic emission recording equipment and a high-speed camera are used to monitor the acoustic signal inside the rock and the rock-caving situation throughout the entire process in order to analyze the characteristics of the acoustic emissions and the ejection form of the rockburst. The results show that rockburst occurs in dry red sandstone and 50% saturated red sandstone but not in saturated red sandstone. The phrase characteristics of the stress–strain curve of the dry rock vary more significantly than those of the water-bearing rock, and the elastic strain energy inside the rock decreases gradually as the water content increases. The double peak of the acoustic emissions curve occurs during the failure process of the dry rock and gradually transitions to a stepped pattern as the water content increases. The ejected fragments of dry red sandstone during the rockburst are abundant and large. The true triaxial test results illustrate the characteristic effect of the rockburst on red sandstone with different water contents, reveal the failure mode and ejection characteristics of red sandstone with different water contents, and demonstrate the influence of the water content on the rockburst characteristics of red sandstone. The results of this study provide a theoretical reference for the study of the rockburst mechanisms of similar hard rocks.

Characteristics of Ground Pressure Disaster and Rockburst Proneness in Deep Gold Mine

Abstract To obtain rockburst characteristics at rock engineering, the rockburst event, in situ stress characteristics, and rockburst proneness are studied in a deep gold mine. The severity of rockburst increases with cover depth at the mine. The main locations of spalling and rockburst events include roof and sidewall. The in situ stress measurement results show this area that is controlled by horizontal constructional pressure, and the self-weight stress also has an important influence. The rockburst mechanism is analyzed from the principal stress and tangential stress. When the maximum tangential stress (MTS) does not exceed 0.4 times UCS of surrounding rock, no obvious disaster in tunnel is found. When the MTS of tunnel is between about 0.4 ~ 0.55 times UCS of rock, the tunnel may suffer spalling. When the MTS of tunnel exceeds 0.55 times UCS of rock, serious failure may occur in tunnel, such as rockburst and large roof collapse. When surrounding rock is relatively hard and complete (high impact energy index, elastic strain energy index, linear elastic energy index, and RQD index), the tangential stress plays a very important role in the rockburst at the mine.

Study on the dynamic response and the hazard of rock burst under the influence of fault slip

In the process of coal mine production, rock burst accidents near faults occur frequently. In order to further reveal the induced mechanism of fault slip rock burst, a numerical simulation method for dynamic calculation of fault slip under the influence of mining is proposed, and the law of fault slip and dynamic response characteristics of the stope are studied. The study shows that with the working face getting closer to the fault, the fault activity and the number of high-energy microseismic events increase significantly, and the fault slip dynamic load has a significant impact on the vibration velocity and abutment stress of coal and rock mass near the stope. Under the effect of a strong fault slip dynamic load, the coal and rock mass in the area with peak abutment stress undergo plastic failure and release a large amount of energy, and the potential of fault slip rock burst is high. The evaluation index Icd of rock burst hazard under fault slip dynamic load is proposed, and the rock burst hazard of working face passing through the fault is analyzed. The research results provide a theoretical basis for further revealing the induced mechanism and hazard assessment of fault slip rock bursts.

Application of Data Analysis Techniques to Identify Rockburst Mechanisms, Triggers, and Contributing Factors in Cave Mining

Application of Data Analysis Techniques to Identify Rockburst Mechanisms, Triggers, and Contributing Factors in Cave Mining

Evaluation of Rock Burst Propensity and Rock Burst Mechanism in Deep Phosphate Mines: A Case Study of Sujiapo Phosphate Mine, Hubei Province, China

Rockburst is one of the major problems in rock underground engineering and mechanics. To make a risk assessment of rockburst and improve the mine safety index, some evaluation systems for rockburst propensity have been proposed and applied, and progress has been made in the study of high-value mines and single evaluation systems, but these evaluation systems are still immature for deep low and medium grade phosphate mines with more complex influencing factors. Therefore, to solve this problem, this study takes the phosphate mining area of the Sujiapo phosphate mine as the main research object, and combines the characteristics of the deep rockburst of the phosphate mine and its physical and mechanical properties; the evaluation system combines fuzzy mathematical method and multiple evaluation methods to determine the propensity of rockburst of deep mining of Sujiapo phosphate mine. The JSM-500LV SEM and acoustic emission results are used to analyze the microscopic mechanism of rockburst from the morphology and composition of the rocks, and the rationality of the evaluation system is further demonstrated. The study shows that dolomite and phosphorite in the study area are moderate rockburst, and shale has a weak rockburst tendency; because the roof dolomite and phosphorite crystallization degree are higher, the elastic modulus is large. Under the action of external load, the roof dolomite stored more elastic strain energy. Deformation damage consumes less energy. The energy released to the outside world after the damage is large, more likely to occur brittle damage, and the rockburst tendency is high. Therefore, the evaluation system combining multiple evaluation methods can comprehensively determine rockburst in phosphate mines.

The Revealed Mechanism of Rock Burst Based on an Innovative Calculation Method of Rock Mass Released Energy.

It is very necessary to study the mechanism of rock burst, which is related to the safe construction of many geotechnical projects. Previous studies have shown that small trigger stress will lead to large energy release, but the specific conditions that cause the release and how to quantify the energy are urgent problems to be solved. In this study, an innovative calculation method of rock mass energy release is proposed, and the calculated release energy is consistent with the monitoring results of field monitoring equipment. The revealed mechanism of rock burst reflected is that under the condition of a large-ratio pre-state stress field (mostly > 2.5), a small trigger stress field will lead to a large amount of energy release under "late butterfly shape" or "final butterfly shape" of the plastic zone. This study reveals the key factor of rock burst, which plays an important reference role for the mechanism research, subsequent monitoring and treatment method of rock burst.

Development mechanism of radial chain rockbursts in a deep tunnel excavated by TBM

In this work, the concept of radial chain rockbursts (RCRs) was proposed for the first time. As a case study, RCRs that occurred in a deep tunnel excavated by TBM was analyzed. The occurrence process and geological characteristics of the RCRs were described. Though analyzing the microseismic (MS) temporal and spatial evolution characteristics, stress and energy evolution characteristics and fracturing mechanism of the RCRs, the development mechanism of the RCRs was revealed. The following results were obtained: (1) The RCRs is prone to occur under geological conditions with alteration zone and lithologic interface. (2) The time interval of adjacent rockbursts gradually increased, and RCRs exhibited the characteristics of time and space delay. The time interval of adjacent rockbursts was mainly affected by the adjustment of the excavation and support measures, and the stress gradually developed to the deep surrounding rock mass. (3) The stress and energy in the development stage were distributed in the deep surrounding rock mass and were released in the surface layer of surrounding rock mass in the occurrence stage. The apparent stress of the rock mass in the occurrence stage was higher than that in the development stage, and the stress gradually developed to the deeper zone during both the occurrence stage and the development stage. The repeated occurrence of RCRs was mainly controlled by three factors: the mechanical properties of the surrounding rock, stress conditions and multiple local shear slips in the rock mass near the alteration zone that are caused by TBM excavation disturbance. (4) The first two rockbursts were strain rockburst, and the latter two rockbursts were strain-structure slip rockburst that occurred along the alteration zone. The research has a guiding role for construction under similar engineering geological conditions, and provides a basis for the research on warning and mitigation of RCRs.

Formation mechanism of rockburst in deep tunnel adjacent to faults: Implication from numerical simulation and microseismic monitoring

Formation mechanism of rockburst in deep tunnel adjacent to faults: Implication from numerical simulation and microseismic monitoring

Energy Evolution Law during Failure Process of Coal–Rock Combination and Roadway Surrounding Rock

The deformation and failure of a coal–rock system in a deep environment is affected by its own mechanical properties, natural endowments, and geological structures; it is very important to study the energy evolution law of coal–rock systems. For this purpose, a Particle Flow Code in 2 Dimensions (PFC2D) simulation was conducted to assess the coal–rock structure and roadway surrounding rock. The hard roof would produce a rebound “energy supply” phenomenon when the coal was destroyed, and the influence of rock strength on the energy evolution of the coal–rock combination was analyzed. In addition, the energy evolution law of roadway surrounding rock with different roof strength is studied; the energy evolution process of roof and coal seam and deep and shallow coal mass are compared, according to the energy storage characteristics of roadway surrounding rock in different areas; the partition energy storage model of roadway surrounding rock is established preliminarily and the concepts of energy storage area and energy supply area of roadway surrounding rock are proposed; the prevention and control methods of near-field rock burst in deep roadways are discussed, and the research conclusions can provide theoretical reference for the research on the mechanism of rock burst in deep coal mines.

Study on Occurrence Mechanism and Prevention Technology of Rock Burst in Narrow Coal Pillar Working Face under Large Mining Depth

This paper presents a collaborative control scheme involving “unloading-solidifying” to prevent rock bursts during narrow pillar recovery at large mining depths. In this study, the stress distribution rule of coal rock mass during the excavation and mining process is studied, and the energy accumulation characteristics of the overlying hard and thick roof structure are investigated. In this way, the rock burst inducing mechanism of the narrow coal pillar working face under complex conditions is investigated. The results show that the peak lateral bearing pressure of the goaf and the maximum horizontal principal stress provide the static load condition for the occurrence of rock burst during roadway excavation. Affected by the superposition of “near-field high static load + far-field dynamic load”, it is extremely easy to reach the critical destabilization value during the mining period at the narrow coal pillar working face. According to the monitoring results, the developed coordinated control scheme, which focuses on the strong pressure relief and strong support in near-field high-bearing pressure coal mass and the pressure relief in far-field high-level hard roof with an advanced pre-cracking roof, can effectively avoid the occurrence of rock burst accidents on narrow coal pillar working face.

Particle Flow Analysis of Acoustic Emission Features of Rock under Rock Burst Stress Path

The AE (acoustic emission) features could reflect the process of fracture initiation and propagation in rocks. Taking Lalin railway tunnel granite as an example, a three-dimensional particle flow numerical model of rock was established based on the PFC (particle flow code). The mechanical properties between particles were simulated using parallel bond. The rock burst stress path was simulated using the movement of the wall in the particle flow model. The results of uniaxial compression tests in a laboratory were used to calibrate the mesoscale mechanical parameters of the particle flow model. AE features of rock deformation and failure under different confining pressures were then studied. It shows that the unloading direction of rock may produce strong dilatation deformation during rock burst; with the increase of confining pressure, the more obvious dilatation deformation and the more possibility of serious rock burst to occur; the unloading failure of rock reveals that rock burst is a mixed failure of tensile and shear, and the tensile cracks account for about 70%; the number of AE events of rock unloading failure occur at the top and bottom of the rock first and then expand rapidly to the middle part until the rock is completely destroyed; in the process of rock burst, AE rupture strength is relatively concentrated, the number of AE events surge obviously, and the number of AE events in surge period account for more than 80% of all AE events. The results presented herein may be referable in analyzing the mechanism of rock burst.

Mechanism of Rock Burst and Its Dynamic Control Measures in Extra-Thick Coal Seam Mining from below the Residual Coal Seam to below the Gob

Abstract In this paper, aiming at the mechanism and regulation of overburden breakage induced by mining from the residual coal seam to the mined-out area, taking Kuangou Coal Mine as the background, the mechanism of rock burst from the residual coal seam to the mined-out area was revealed through the laws of overburden breakage and its structural evolution, ground pressure appearance, and energy release. The impact risk area is determined by the comprehensive evaluation results of multimethod face impact risk. A roof pressure relief and impact prevention control method using large-diameter empty hole combined with advanced deep hole blasting was formed, and the field verification was completed. The research results show that an obvious inverted trapezoid structure is formed when the residual coal seam of the W1123 working face is mined to the working face under the gob, which is related to the energy release caused by the occurrence of periodic pressure and the rupture of the critical layer. The shock ground pressure of the working face predicted by the neural network is mainly weak shock and medium shock risk; the numerical simulation analysis shows that the shock hazard area of the W1123 face below the solid coal is mainly located in the lower part of the working face near the transportation roadway and the shock below the W1145 gob. The dangerous area is about 32~72 m away from the return air alley. Through the plastic zone distribution and the orthogonal test, the optimal pressure relief scheme for large-diameter holes is 12 m in depth, 300 mm in diameter, and 2 m in spacing. When the blasting angle is consistent with the overlying rock fracture angle obtained from the simulation experiment, a better pressure relief can be achieved. When the bursting angle is consistent with the simulated overburden rupture angle, it has a better pressure relief effect. The pressure relief and anti-scour control method of large-diameter holes combined with advanced deep hole blasting reduce the daily average vibration frequency, energy, incoming pressure, and step distance of working face mining. The safe and efficient mining has a certain reference effect.

Investigation on Rockburst Mechanism Due to Inclined Coal Seam Combined Mining and its Control by Reducing Stress Concentration

Investigation on Rockburst Mechanism Due to Inclined Coal Seam Combined Mining and its Control by Reducing Stress Concentration

Mechanism Study and Tendency Judgement of Rockburst in Deep-Buried Underground Engineering

Rockburst is a type of dynamic instability failure phenomenon and frequently brings huge losses to underground engineering projects such as mines and tunnels. In order to explore rockburst mechanisms and predict rockbursts better, relying on the background of Wulaofeng deep-buried highway tunnel, in situ stress measurement was performed using new wireless devices, and mechanics tests of surrounding rock samples taken from different burial depths were carried out. The rockburst mechanism was explored from the microscopic perspective based on the analysis of scanning electron microscopy (SEM). Rockburst tendency was judged comprehensively by a tendency analysis, grade prediction and numerical simulation. The result showed that the mechanical parameters of granite rocks in the deep-buried section were larger than those in the entrance section, and the fractured morphology mainly comprised sheet and monolithic block, corresponding to transgranular fracture and intergranular fracture. Rocks with few types of mineral cementation, good crystallization and small particle size differences had better energy storage and release characteristics. There was little difference in the rockburst tendency of rocks with different buried depths, but there were obvious differences in the rockburst grade. In the deep-buried section of the tunnel, the rockburst grade was of a moderate–heavy level and the rockburst risk at the vault and right spandrel of the cross section was more severe, which was basically consistent with the situation at the tunnel site. This study can provide a theoretical basis for the prevention and control of rockbursts in Wulaofeng tunnel and other similar engineering projects.

Unstable Pillar Failure under Soft Loading Condition

Abstract Pillar rockburst is an unstable pillar failure and one of the most hazardous problems in the underground mining engineering of deep hard-rock mines. In order to study the mechanism of unstable pillar failure, laboratory tests, numerical simulation, and theoretical analysis are adopted. The disc spring group was used to realize the soft loading function of testing machine, where loading stiffness of testing machine can be adjusted by changing the number and combination mode of disc springs. The results show that the loading stiffness of testing machine has major effect on the post-peak failure behavior of rock specimen, which means that the elastic rebound of disc spring group determines the unstable failure characteristics of rock specimen. The sudden jump Δd of rock specimen deformation and the elastic energy release ΔW of disc spring group all increase with the decreased loading stiffness of testing machine, resulting in more severe rock unstable failure (pillar rockburst). The soft loading condition has buffering and delaying effects on rock failure, but it increases the unstable failure intensity of rock specimen. The numerical simulation reproduced the rock unstable failure and the elastic rebound behavior of disc spring group, which also illustrated the damage evolution process of rock unstable failure. The necessary condition of rock unstable failure and the analytical solution of sudden jump Δd and elastic energy release ΔW were derived based on catastrophe theory, which further verified the experimental results. This study reveals the physical essence of unstable pillar failure, which may help to under the mechanism of pillar rockburst and provide references for underground mining.

Mechanism and Safety Mining Technology of Overall Instability-Induced Rockbursts of Multi-Coal Seam Spatially Isolated Working Face

The isolated working face has always been the hardest hit area for the occurrence of rockburst, and the spatially isolated working face with multiple coal seams is often easily overlooked due to its hidden nature, which leads to the occurrence of rockburst accidents. This paper takes the Liuhuanggou coal mine (9–15) 08 isolated working face as the engineering background, used field research, theoretical analysis, numerical simulation, and field monitoring, investigated the coal body stress evolution law during mining, and revealed the overall instability rockburst mechanism of the working face and deduced the limit advance distance when the working face was in a state of boundary instability. The research results show the following: (1) with the increase of advancement, the overlying strata on the working face are dynamically transformed from the “C” spatial structure with hollowing on both sides to the “θ” spatial structure with coal body support in the middle; (2) when the dynamic load stress on the coal body of the working face exceeds 1.5 times its integrated compressive strength, there is a risk of overall instability rockburst; (3) when the working face advances to 430 m from the open cutting, the superimposed stress on the coal body exceeds its comprehensive compressive strength and reaches a critical instability state, which is verified by numerical simulation. Based on the analysis of the mechanics and mechanism of the overall instability rockburst of the working face, this paper proposes a set of targeted safe mining solutions: (1) The joint monitoring system of microseism-stress-drilling cutting is adopted to monitor and warn the dangerous rockburst areas. (2) The “rockburst-gas” drilling technique is used to unload the pressure on both sides of the working face and the coal wall. (3) The mining speed shall not exceed 3.2 m/d when the working face is mined before 350 m, and shall not exceed 2.4 m/d when the working face enters the influence area of mined-out LW(4-5)02 (350∼550 m). The microseismic monitoring results and field practice confirmed the reasonableness and effectiveness of the safe mining technology plan.

Rockburst mechanism and the law of energy accumulation and release in mining roadway: a case study

The rockburst dynamic disasters in the process of deep coal mining become more and more serious. Taking the rockburst occurred in the 23130 working face of Yuejin Coal Mine as the engineering background, we study the characteristics of mining stress field around roadway, the plastic failure morphological characteristics of surrounding rock and the accumulation/release law of elastic energy before and after burst. An analysis model quantitatively describing the physical process of rockburst in the mining roadway is established, and the calculation method of dynamic release of elastic energy in the physical process of rockburst is educed. The mechanism of rockburst in mining roadway is revealed. The results show that an “L-shaped” stress concentration zone is formed within 100 m of the 23130 working face, and the principal stress ratio of the surrounding rock of the transportation roadway is 2.59–4.26. The change of the direction of the maximum principal stress has a significant effect on the burst appearance characteristics. The failure strength of different sections of the mining roadway is characterized by the elastic energy release value. With the increase of the working face distance, the elastic energy released by burst failure and the expansion variation of failure boundary radius show a nonlinear variation law that tends to decrease steadily after sharp fluctuation. The closer to the working face, the higher the burst risk. At a distance of 10 m from the working surface, the maximum principal stress reaches its maximum value. The butterfly-shaped failure system generated by the surrounding rock of the roadway has energy self-sustainability, and the elastic energy released by the sudden expansion of the butterfly leaf is enough to cause a burst damage of 1.9 magnitude. This work could provide theoretical support for the prediction and prevention of rockburst.

Determination of Width of Sectional Coal Pillars in the Working Face of Burst-prone Inclined Thick Coal Seams

In coal mines, a reasonable design of the widths of coal pillars is critically important, particularly for rockburst mines. This is because the frequent occurrence of rock burst in coal mines often arises from the inappropriate widths of the coal pillars. To address this problem, we first review two recent incidents of rockburst occurring and thus present a theoretical calculation of lateral bearing pressure distribution in goaf of inclined thick coal seam to illuminate the occurrence mechanism of rockburst induced by inappropriate width of sectional coal pillars. Based on the mechanism model, we then propose a design criterion for sectional coal pillar widths in inclined thick coal seams that can effectively reduce the risk of the induced rock burst. Our theoretical calculations, field stress monitoring, numerical simulation and field investigation all demonstrate the validity of the proposed design criterion in preventing the induced rock burst and large deformation of surrounding rock. The results from this paper may be used as a theoretical guidance of sectional coal pillar designs in inclined thick coal seams.