Rockburst Mechanism Research Articles

Test study on failure and energy supply characteristics of rock under different loading stiffness

Based on the stiffness theory, the stiffness difference and energy supply of surrounding rocks are important inducing factors for rock burst. However, due to the lack of multi-level low stiffness testing machine, there are few experimental studies on rock failure mechanism under the influence of loading stiffness. Aiming at the above problems, this paper improved the rock mechanics testing machine, and developed several sets of low stiffness flexible rings, which realized laboratory test under five different loading stiffness in the range of 0.07 ∼ 0.615GN/m. Based on low stiffness loading device, the mechanical behavior of sandstone specimens was studied. With the decrease of the loading stiffness, the post-peak stage of the stress–strain curve of the specimen changes from step shape to oblique linear shape, and the specimen changes from progressive shear failure to brittle splitting failure. There is a power function positive correlation between the specimen’s post-peak failure duration and stiffness ratio of the testing machine and the specimen, and a power function negative correlation between stress drop rate and stiffness ratio. When the specimen is damaged and the stress is dropped, the deformation of low stiffness testing machine rebounds with high-speed, resulting in an obvious dynamic load behavior. The loading stiffness has little effect on the energy storage and energy dissipation characteristics of the specimen, while the release energy of the testing machine increases as the stiffness ratio decreases, which is the key factor affecting the failure mode of the specimen. According to the test results, a rock burst mechanical model considering the stiffness is established, and the energy supply mechanism of rock burst is quantitatively explained.

Study on the Bending Effect and Rock Burst Mechanism of Middle Rock Pillars in Extremely Thick Subvertical Coal Seams

Rock bursts occur in nearly vertical coal seam mines at shallow to moderate burial depths, which endangers safe mining. To study the rock burst mechanisms of nearly vertical and extremely thick coal seams, the characteristics of rock bursts were studied via on-site investigation, and a field test of in situ stress was carried out. The mechanical behavior of rock pillars in the middle of the B1+2 and B3+6 coal seams was analyzed using theoretical and numerical simulation methods. The results show that the horizontal maximum principal stress orientation and the nearly vertical coal seam strike were both 82°. The bending of the rock pillars occurred due to the horizontal unbalanced force, and a large amount of bending energy was accumulated within 50 m above the mining level. Rock pillars were bent toward the B1+2 mining goaf and exerted a reverse bending and squeezing effect on the B3+6 coal seam below the mining levels. In addition to the inclination and compression of the B3+6 coal seam roof, stress concentration zones formed in the B3+6 coal seam, where a large amount of elastic energy had accumulated in the coal-rock mass. Consequently, both the rock pillars and the B3+6 coal body at the mining level are in an unstable state undue to mining disturbance. Rock burst energy theory and numerical calculation results showed that in the stress concentration zones of the B3+6 coal seam, the energy density of the coal mass reached or exceeded its critical value before rock burst occurred, and rock bursts were prone to occur under mining disturbances. The in situ microseismic results showed that high-energy microseismic events were mainly concentrated in middle rock pillars around the mining levels and the coal mass in high-stress concentration zones.

Investigation of Rock Burst Mechanism under Thermomechanical Coupling Conditions Based on Rock Mechanical Tests

Abstract The thermomechanical (TM) coupling effects of rock bursts have attracted considerable attention from researchers owing to the high geothermal and geostresses in deep tunnels in regions such as Western China. To study the brittleness and rock burst mechanism under TM conditions, various tests, such as splitting, uniaxial compression, rock burst tendency, and rock burst physical model tests, were conducted at temperatures ranging from 20°C to 80°C. The results revealed that, when granite samples were heated, their tensile strengths decreased in the splitting tests. Their peak stresses and the corresponding strains increased; their macroscopic tensile fracture surfaces became more evident; and the microcosmic tensile properties of intergranular fractures became prominent under uniaxial compression. Rock burst physical model tests and acoustic emission monitoring results revealed that, at higher temperatures, the fracture degree and failure range were larger, the energy was higher and more concentrated during failure, and failure occurred earlier. The brittleness index B, rock burst tendency Wet, and σθ/σc all exhibited a clear increasing tendency with an increase in temperature. The rock burst mechanism, considering the temperature effect, can be summarized as follows: the increase in brittle tensile fracture components and geostress caused by temperature increasing is conducive to the rapid release of energy, which will promote the occurrence of rock burst. The researching result is of great academic value and practical significance for the prevention, design, and safe construction of rock burst in deep high geothermal tunnels.

The mechanics of plastic volumetric deformation of rock and the rockburst mechanism

Relevance and problematics. The problem of rock pressure dynamic manifestations, primarily rockbursts and tectonic shocks, is particularly acute for both coal fields and ore deposits. Dynamic manifestations of rock pressure lead to injury and death, to kilometers of destroyed mine workings, loss of minerals, business interruption and additional costs for forecast and prevention. However, these geomechanical phenomena seem to be the most unexplored. They have been studied purely at the empirical level. This is due to poor understanding of the elastic energy accumulation and release mechanism in dynamic phenomena. Methods of research. The proposed model of plastic deformation of rock and the resulting mechanism of rockbursts and tectonic shocks, impacts and earthquakes are based on analytical criteria for rock plasticity and strength, confirmed by a large amount of experimental data. Results, their analysis and recommendations for use. Based on the previous studies performed by the author, a new model of plastic deformation of rocks at the stage of deformation strengthening is proposed. Based on this model, the mechanism of rock plastic deformation, the mechanism of fractured block media destruction and accumulation of deformation energy by rocks are substantiated. It is shown that blocks of various ranks turning leads to deformation energy accumulation in the rock mass. The energy is accumulated both in the blocks and in the surrounding. Conclusions. The proposed model of rockburst and other dynamic phenomena, as well as block mass strength criterion, made it possible to obtain a burst hazard criterion in an analytical form for the first time. The fracturing (blocking) role and contribution to the rockburst mechanism has been shown for the first time. Comparison of the proposed burst hazard criterion with an empirical analogue shows good convergence.

Research on the Nucleation Mechanism and Early Warning Method of Strain Rockburst in Deep-Buried Tunnel Based on Microseismic Monitoring

Abstract In order to discuss the nucleation mechanism of strain rockburst, this paper takes the rockburst section of deep diversion tunnel of Jinping Hydropower Project of Yalong River as the research object. Through the study of microseismic monitoring technology and the regularity of microseismic parameters, as well as combining the qualitative and quantitative analysis, the nucleation process and instability failure mechanism of strain rockburst were revealed, and the internal relationship between microseismic evolution law and rockburst process was explored. The monitoring results and analysis showed that the development process of strain rockburst under engineering disturbance can be divided into three stages: tensile crack initiation and development stage, macroscopic shear crack formation stage, and overall instability stage, respectively. The failure process was mainly that two macroscopic shear cracks caused by tensile failure were connected and developed to the tunnel wall and then formed a closed triangle region. The rock mass in this area appeared plate-like splitting, spalling, and wedge-shaped rock mass ejection at a certain initial velocity, which eventually lead to intense rockburst and overall instability failure. The results also showed that the rockburst failure process under engineering excavation was in good agreement with the traditional syllogism of rockburst. Meanwhile, based on the evolution characteristics of source parameters and statistical parameters, including microseismic energy, moment magnitude, cumulative apparent volume, energy index, and b value, the quantitative interpretation of the source parameter provided significant evidence and insight into characterization of strainbursts. In addition, these parameter fluctuation characteristics can be effectively used as the precursor information and early warning index of strain rockburst failure. The results of this study can provide reference for monitoring and early warning of rockburst in deep tunnel and taking effective prevention and support measures in time.

Numerical and Field Investigations of Rockburst Mechanisms Triggered by Thick-Hard Roof Fracturing

Numerical and Field Investigations of Rockburst Mechanisms Triggered by Thick-Hard Roof Fracturing

Game Theory and an Improved Maximum Entropy-Attribute Measure Interval Model for Predicting Rockburst Intensity

To improve the accuracy of predicting rockburst intensity, game theory and an improved maximum entropy-attribute measure interval model were established. First, by studying the mechanism of rockburst and typical cases, rock uniaxial compressive strength σc, rock compression-tension ratio σc/σt, rock shear compression ratio σθ/σc, rock elastic deformation coefficient Wet, and rock integrity coefficient Kv were selected as indexes for predicting rockburst intensity. Second, by combining the maximum entropy principle with the attribute measure interval and using the minimum distance Di−k between sample and class as the guide, the entropy solution of the attribute measure was obtained, which eliminates the greyness and ambiguity of the rockburst indexes to the maximum extent. Third, using the compromise coefficient to integrate the comprehensive attribute measure, which avoids the ambiguity about the number of attribute measure intervals. Fourth, from the essence of measurement theory, the Euclidean distance formula was used to improve the attribute identification mode, which overcomes the effect of the confidence coefficient taking on the results. Moreover, in order to balance the shortcomings of the subjective weights of the Analytic Hierarchy Process and the objective weights of the CRITIC method, game theory was used for the combined weights, which balances experts’ experience and the amount of data information. Finally, 20 sets of typical cases for rockburst in the world were selected as samples. On the one hand, the reasonableness of the combined weights of indexes was analyzed; on the other hand, the results of this paper’s model were compared with the three analytical models for predicting rockburst, and this paper’s model had the lowest number of misjudged samples and an accuracy rate of 80%, which was better than other models, verifying the accuracy and applicability.

Research on Temporal and Spatial Distribution Characteristics of Microseismic Events of Slip-Type Rockburst

Based on the microseismic monitoring data of underground cavern of Shuangjiangkou Hydropower Station, the internal relationship between rockburst and microseismic events is analyzed and the occurrence mechanism of slip-type rockburst in underground cavern of Shuangjiangkou Hydropower Station is analyzed through the change of microseismic monitoring b value to warn the risk level of rockburst. The results show that microseismic events are closely related to excavation activities, and the change of b value reflects the rockburst risk level. The smaller the b value of microseismic events is, the more large magnitude events is and the greater the possibility of rockburst is. The slip-type rockburst was mainly affected by structural plane; it is due to the accumulation of elastic strain energy at the structural plane and the sudden release under the action of unloading or disturbance, driving the block on the structure surface fast slide, mainly manifested as the sliding of large blocks of surrounding rock, and forming a “V” shape pit blasting or cuneate blasting crater, as well as destruction with crackle. Compared with the strained rockburst, the damage is more serious. The research results can provide reference for rockburst prediction and prevention in similar deep rock engineering.

Rock burst mechanism induced by stress anomaly in roof thickness variation zone: a case study

The variation of hard roof thickness is an essential contributor in triggering rock bursts during longwall mining. Case analysis and numerical modeling were used to study the stress and energy characteristics of the coal and rock mass and its fracture behaviour in the roof thickness variation zone (RTVZ). The results show that the coal seam has higher initial stress if overlain by a thicker hard roof, whose stress monitoring value is 1.8–2.6 times that of the thin zone. The increasing variation in the roof thickness or the roof properties causes a greater initial stress change in the coal seam. In the thick roof zones, the superposition of the advanced abutment pressure and the increased initial stress will result in a high-stress concentration area, where the stress mutation coefficient value can be up to 1.08–1.15. A higher rock burst risk might thus present in the roadway near the longwall in the thick roof zone, where more intensive elastic energy was released in the coal/rock mass. Also, it is more likely to have a significant dynamic load in the thin roof zone due to the higher possibility of roof breakage, and the total microseismic energy can reach 1.8–3.2E + 08J. Highlights Case analysis and numerical modelling were used to study the formation mechanism of stress anomaly in coal seams, energy evolution characteristics of the coal/rock mass and its fracture behaviour in the RTVZ. The mechanism of rock bursts induced by coal mining in the RTVZ is determined. The thick roof zone has high-stress concentration, where more intensive elastic energy is released in the coal/rock mass. Due to easier roof breakage, it is more likely to have a significant dynamic load in the thin roof zone. The prevention and control method of rock bursts in the RTVZ is put forward. The rock bursts can be relieved by reducing the initial stress increased in the thick roof zone. Strengthening roadway support can reduce the influence of dynamic load on the roadway.

Development and Occurrence Mechanisms of Fault-Slip Rockburst in a Deep Tunnel Excavated by Drilling and Blasting: A Case Study

Development and Occurrence Mechanisms of Fault-Slip Rockburst in a Deep Tunnel Excavated by Drilling and Blasting: A Case Study

Static creep rockburst mechanism and CT inversion verification of deep thick coal seam roadways

AbstractCompared with the traditional “dynamic‐static” load rockburst induced by working face mining, a new typical disaster with concealment characteristics has appeared in deep thick coal seam roadways, namely, static creep rockburst, the occurrence mechanism of which remains unclear. Through the method of combining theory with practice, this paper elucidated the mechanical mechanism of static creep rockburst of deep thick coal seam roadways, along with the CT inversion of its rockburst risk. Next, by establishing the creep model and three‐dimensional creep formula under static conditions, it was observed that the main conditions for the unstable creep of deep thick coal seam roadway were high stress and thick coal seam. In addition, by analyzing the unstable creep failure process of surrounding rock in static roadways, it was found that the weakening of surrounding rock strength and stress relief were the reasons for starting rockburst and reducing impedance. The mechanical conditions of creep rockburst caused by stress superposition in weak areas of the roadway under static conditions were proposed, and the criterion of rockburst possibility was given. Finally, according to the characteristics of spontaneity and time delay of such a rockburst disaster, the static creep rockburst evaluation of thick coal seam roadway before mining was achieved by CT inversion, and the research conclusions were thoroughly verified.

Focal Mechanism and Source Parameters Analysis of Mining-Induced Earthquakes Based on Relative Moment Tensor Inversion.

Mining-induced earthquakes (MIEs) in underground coal mines have been a common phenomenon that easily triggers rock bursts, but the mechanism is not understood clearly. This research investigates the laws of focal mechanism and source parameters based on focal mechanism and source parameters analysis of MIEs in three frequent rock burst areas. The relative moment tensor inversion (MTI) method was introduced, and the way to construct the inversion matrix was modified. The minimum ray and source number conditions were calculated, and an optimized identification criterion for source rupture type was proposed. Results show that the geological structure, stress environment, and source horizon influence the focal mechanism. The tensile type sources can distribute in the roof and coal seam, while the shear types are primarily located in the coal seam. In the typical fold structure area, the difference in source rupture strength and stress adjustment between tensile and shear types is negligible, while the disturbance scale of tensile types is distinct. The shear types have higher apparent volume and seismic moment in the deep buried fault area but lower source energy. The apparent stress of the tensile types is higher than that of the shear types, representing that the stress concentration still exists in the roof after the MIEs, but the stress near the faults could be effectively released. In the high-stress roadway pillar area, the primary fracture of the coal pillar easily produces a continuous shear rupture along the dominant stress direction under the extrusion of the roof and floor. The source parameters (except apparent stress) of shear types are higher than tensile types and have higher dynamic risk. The results contribute to expanding the understanding of rock burst mechanisms and guide MIEs’ prevention.

Rockburst mechanism of rock mass with structural planes in underground chamber excavation

Natural rock mass generally contains discontinuous structural planes, such as joints, fractures and faults, which have great influence on the occurrence of rockburst. The rockburst mechanism of rock mass with structural planes in underground chamber excavation is studied by means of model test and numerical simulation in this paper. Firstly, quartz sand, barite powder, gypsum powder, cement and water are selected as raw materials to configure the similar materials suitable for the rockburst model test. Secondly, four working conditions of none structural plane, single structural plane, multiple structural planes and through structural plane are designed, and the corresponding rockburst model tests are carried out. The stress and displacement laws of surrounding rock during excavation are analyzed. Finally, the numerical calculation of chamber excavation is conducted under the above four working conditions and the model test is verified. The failure modes and laws of surrounding rock mass with different structural planes during chamber excavation are obtained. The results show that: (i) After the tunnel excavation in rock mass with single structural plane, the tension of structural plane and the expansion of fractures occur, accompanied by small-scale rockburst. (ii) After the tunnel excavation in rock mass with multiple structural planes, the stress level of surrounding rock mass decreases significantly and no rockburst occurs, but the surrounding rock is prone to large-scale collapse or spalling. (iii) After the tunnel excavation in rock mass with through structural plane, the fractures appear in the vault and arch bottom and expand rapidly, accompanied by rockburst phenomena such as granules ejection. The research results of this paper are of great significance for understanding the deformation and failure mechanism of rock mass with structural planes in the underground chamber excavation.

Study on Mechanism of Rock Burst in Horizontal Section Mining of a Steeply Inclined Extra-Thick Coal Seam

Abstract With the increase of mining depth, rock burst disasters frequently occur in steeply inclined coal seams. Firstly, this paper analyzes the rock burst of 5521-20 working face in Yaojie No. 3 coal mine and summarizes the characteristics of rock burst in horizontal section mining of steeply inclined extra-thick coal seam (SIETCS). Then, the static load distribution characteristics and the influence of dynamic load in the horizontal section mining of SIETCS are systematically studied by combining theoretical analysis with numerical simulation. On this basis, the mechanism of rock burst in horizontal section mining of SIETCS is put forward, verified by actual measurement. The results show that the SIETCS is “clamped” under the combined action of the same change trend of roof and floor. The maximum principal stress peak values on the roof and floor sides reach 22.0 MPa and 20.5 MPa. The maximum shear stress earned 8.7 MPa and 8.4 MPa, which makes the shear stress concentration in the coal body high and tends to “shear dislocation.” Under this “shear-clamping” action, an approximate “trapezoidal” plastic zone and a “rectangular” stress concentration zone are formed under the section. With the increase of mining depth, the “shear-clamping” action of SIETCS becomes more and more intense. When the roof cantilever reaches the ultimate span and breaks, the intense dynamic load increases the shear stress and failure of coal, which is easy to induce rock burst. The superimposed load greatly affects the area from the roof side to the middle of the working face, and the rock burst is intense. The rock burst is weak on the floor side due to the pressure relief of the surrounding plastic zone. The monitoring results show that the supports pressure and MS events activity on the roof side and near the middle part of the working face is considerable, while the floor side is opposite, which verifies the research results.

Applied Research of Water Jet Technology in Preventing Rock Burst Occurred in Roadways

Taking mining area 2502 in the Huayan mine field which was affected by strong geological tectonic stress as an engineering background, the water jet technology is studied through in-site survey, laboratory test, theoretical analysis, numerical simulation, and field industrial test. The research results are as follows: the burst tendency of No. 5 coal seam can be reduced to a certain extent after softening with water, and then the water jet technology is used to prevent rock burst of roadways; the typical characteristics of rock-burst accidents mainly cause heaving floor and serious deformation of two sides. The occurrence mechanism of rock burst in roadway ribs has two different forms, and they are static load dominant type and dynamic load dominant type. The abutment stress concentration value is higher than a certain concentration static load, it will affect the coal and rock medium in the floor, and the coal and rock medium in the floor will be transformed into a plastic state and then occur rock burst; the water jet technology for roadway ribs can effectively prevent rock burst of roadway ribs and floor based on the dynamic and static loads superposition theory and Terzaghi theory. Based on the results of numerical simulation, the specific parameters of water jet technology for roadway ribs in 250204 tailgate are as follows: the diameter and length of initial borehole are 110 mm and 20.0 m, the diameter and length of water jet section are 500 mm and 15.0 m, and the spacing between adjacent water jet boreholes is 3.0 m; the monitoring result of signal intensity by EMR indicates that the decreasing amplitude of signal intensity of EMR is about 60.2% on the side of coal-pillar rib, and the decreasing amplitude of signal intensity of EMR is about 68.6% on the side of solid-coal rib; the convergences monitoring result indicates that the convergence ratio of roadway height is about 3.2%, and the convergence ratio of roadway width is about 2.3% in the pressure relief roadway part; the water jet technology is not only helpful to the prevention of rock burst for the roadway ribs but also can play a good prevention of rock burst for roadway floor. The research results provide a theoretical foundation and a new guidance for preventing rock burst in roadway ribs and floor with similar engineering geological conditions.

Impact of Brittle Creep Failure on Time-Delayed Characteristics of Rockburst.

In this research, the combination of theoretical approach and numerical simulation was employed to comprehensively understand the initiation mechanism of time-delayed rockburst and analyze the time-delayed failure laws for surrounding rock after excavation unloading without prompt support. The investigations are principally at the angle of time and space, which refers to the creep property and damaged scope for surrounding rock. For the theoretical method, the analytical elastic and elastoplastic models for deep tunnel cross section and the creep model for brittle rock material from a microscopic view were combined. It was found that the time-delayed failure for surrounding rock resulted from the damage accumulation with crack development during the creep process. The surrounding rock with the elastic state was more stable than that in the plastic zone and the creep duration increased with growing distance from the center of tunnel section. Based on the theoretical creep model, the numerical simulation ulteriorly analyzed the brittle creep duration on the key positions. The surrounding rock tended to fail more in the strong excavation damage zone (SEDZ) than that in the weakly damaged zone (WEDZ), and brittle creep failure mainly occurred on the excavation border (EB) in a short space of time. In addition, the increase in the radius for tunnel cross section and the higher in situ stress distribution around the opening led to the acceleration of the creep process for surrounding rock, and the irregular cross-section shape of the tunnel caused the local damaged range extension and decreased the duration for time-delayed failure.

Mechanism and Prevention of Rockburst in Deep Multipillar Gob-Side Entry

Abstract Rockburst frequently occurs in deep multipillar gob-side entry in Inner Mongolia and Shaanxi, China. A case study of the Hongqinghe coal mine was analyzed to reveal the occurrence mechanism of rockburst in deep multipillar gob-side entry through theoretical and applied research. And new control methods were put forward. The results show that there is an essential difference between the surrounding rock load characteristics of multipillar gob-side entry and single-pillar gob-side entry. Within the influence area of the lateral goaf, more coal pillars will promote stress concentration, and the high stress concentration area will migrate to the coal pillar of mining roadway. The hanging roof of the working face can cause the stress concentration in the area of leading coal pillar to reach 5 times. The multipillar gob-side entry is less affected by the dynamic load of the roof of the lateral goaf. The ‘F-shaped and L-shaped’ stress source structure model of the deep gob-side multipillar entry was established, and the occurrence mechanism of rockburst is revealed. On the one hand, the static load of rockburst start foundation is formed under the superposition of lateral goaf, rear goaf, and multicoal pillar. On the other hand, the superposition of the foundation static load and the opportune static load induces the start of rockburst. Aiming at the two types of load sources, the fracturing method of kilometer bedding drilling in the roof of coal pillar area is proposed to reduce the foundation static load. The treatment method of periodic tendency blasting fracture of leading roadway roof in a working face reduces opportune static load. The field test has been carried out, and the effect was good.

Mechanism and Control of Rockburst Induced by Draining Spatial Islands and Squaring

A small-pillar gob-side roadway showed rockburst appearance during the mining of a gob-side working face located in the Shaanxi-Inner Mongolia mining area. This study examines the 2202 gob-side working face of a coal mine in Inner Mongolia as a case study. A stress evolution model was built for the static-stress spatial islands formed by drainage regions and goafs based on the spatial relationships between drainage regions and goafs. The average microseismic frequency and energy of the high-stress zone of spatial islands were at least 1.37 times of those of other zones, validating the presence of spatial islands. The dynamic and static load effects of working face squaring were obtained based on the evolution of the stope roof as well as changes in microseismic data. Microseismically active zones were advanced to 200 m–300 m on working faces. The rockbursts induced by high static loads and dynamic and static loads formed by spatial islands and squaring were calculated. According to calculation results, the critical stress concentration value under high static loads was 3.27; the critical static stress concentration value under dynamic and static loads was 1.81. The superposition of drainage boundary stress, goaf lateral stress, and lead stress might reach the critical stress concentration under dynamic load disturbances, causing rockbursts. A stress adjustment scheme was established, including overall hydraulic fracturing of the external roof of the drainage region, reduction of stoping speed, and pressure relief of large-diameter boreholes. The stress adjustment scheme was implemented on-site and supplemented by monitoring and early warning methods to safely advance by the first squaring region.

Stress distribution and rockburst characteristics of roadway group under the influence of fault and fold structures: a case study

Dynamic disasters such as rockbursts have different characteristics with different geological structures. The rockburst mechanism and the influencing factors of a typical composite fault-fold structure were explored by theoretical analysis and numerical simulation. The results showed that: (1) the influence of the composite fault-fold structure on the roadway group rockburst was mainly caused by tectonic stress disturbance; (2) the stress peak value and the influence range of the hanging wall of the fault were larger than those in the footwall, and the stress of the syncline axis was larger than that of the anticline axis; (3) the tectonic stress of the composite fault-fold structure was the highest, the stress value reached to the peak when the fault dip angle was 65°, and the tectonic stress was directly proportional to the elastic modulus of coal and first increased and then decreased with the increase in coal seam thickness; and (4) before rockburst, seismic activities concentrated within 200 m from the footwall and 0–250 m in the hanging wall of the fault, mainly concentrated in 0–20 and 0–40 m, respectively. The spatial distribution coincided with the high static stress area. Highlights The asymmetry of stress and microseismic events of composite fault-fold structure reveals the asymmetry of rockburst potential. The rockburst potential of the hanging wall of the fault is greater than that of the footwall, and the rockburst potential of the syncline is greater than that of the anticline Based on the analysis of stress characteristics and fault activation, it is revealed that the rockburst of roadway group is mainly affected by the static tectonic stress of composite fault-fold structure. Four influencing factors: structure type, fault dip angle, coal seam thickness, and coal elastic modulus are analysed, and the causes of stress concentration of composite fault-fold structure are revealed.

An Investigation Into the Mechanism of Rock Bursts in Mines for Tunnel-Cut Isolated Areas with Multiple Stress Fields

Tunnels in several mines in Shaanxi Province, China, which are subject to multiple stress fields, are used as case studies to clarify the structural problems associated with rock bursts that occur in high-stress mines. Field studies featuring field measurements and theoretical analysis are used to investigate the modes and mechanisms of failure. The following are the main findings: (1) a model for distributing the dominant pressure features around the goaf was established by analyzing the stress distribution induced by the goafs on both sides of the excavated zone in a coal seam. The model reveals the pressure distribution in the tunnel-cut area, which is the mechanical factor responsible for rockburst. (2) Because of the goafs acting on both sides of the tunnel, an area of concentrated stress was formed, and stress was transferred to the coal seam. The intense tunnel-cutting action can reduce the stability of the coal. The plastic area caused by tunnel mining and a reduction in the elastic area of the tunnel-cut coal pillars in each segment, increase the possibility for rockburst under the application of dynamic-static stress; this process is known as a stabilizing factor. (3) Due to the combined effect of the tunnel-cut and goafs on both sides, most of the microseismic incidents happened in the core area of coal pillar and in the side of tunnels. When the stress applied on coal pillar is more than critical strength, burst and mine earthquake can be induced. Our study focused mainly on rockburst incidents that occurred in coal mines in Shaanxi Province, which were caused by tunnel-cut coal seams that were subject to multiple stress fields. The study has direct implications for developing new and improved guidelines for preventing rockburst in mines.