Burst Prevention Research Articles

Numerical simulation study on hard-thick roof inducing rock burst in coal mine

In order to reveal the dynamic process of hard-thick roof inducing rock burst, one of the most common and strongest dynamic disasters in coal mine, the numerical simulation is conducted to study the dynamic loading effect of roof vibration on roadway surrounding rocks as well as the impact on stability. The results show that, on one hand, hard-thick roof will result in high stress concentration on mining surrounding rocks; on the other hand, the breaking of hard-thick roof will lead to mining seismicity, causing dynamic loading effect on coal and rock mass. High stress concentration and dynamic loading combination reaches to the mechanical conditions for the occurrence of rock burst, which will induce rock burst. The mining induced seismic events occurring in the roof breaking act on the mining surrounding rocks in the form of stress wave. The stress wave then has a reflection on the free surface of roadway and the tensile stress will be generated around the free surface. Horizontal vibration of roadway surrounding particles will cause instant changes of horizontal stress of roadway surrounding rocks; the horizontal displacement is directly related to the horizontal stress but is not significantly correlated with the vertical stress; the increase of horizontal stress of roadway near surface surrounding rocks and the release of elastic deformation energy of deep surrounding coal and rock mass are immanent causes that lead to the impact instability of roadway surrounding rocks. The most significant measures for rock burst prevention are controlling of horizontal stress and vibration strength.

Microseismic Precursory Characteristics of Rock Burst Hazard in Mining Areas Near a Large Residual Coal Pillar: A Case Study from Xuzhuang Coal Mine, Xuzhou, China

Identification of precursory characteristics is a key issue for rock burst prevention. The aim of this research is to provide a reference for assessing rock burst risk and determining potential rock burst risk areas in coal mining. In this work, the microseismic multidimensional information for the identification of rock bursts and spatial–temporal pre-warning was investigated in a specific coalface which suffered high rock burst risk in a mining area near a large residual coal pillar. Firstly, microseismicity evolution prior to a disastrous rock burst was qualitatively analysed, and the abnormal clustering of seismic sources, abnormal variations in daily total energy release, and event counts can be regarded as precursors to rock burst. Secondly, passive tomographic imaging has been used to locate high seismic activity zones and assess rock burst hazard when the coalface passes through residual pillar areas. The results show that high-velocity or velocity anomaly regions correlated well with strong seismic activities in future mining periods and that passive tomography has the potential to describe, both quantitatively and periodically, hazardous regions and assess rock burst risk. Finally, the bursting strain energy index was further used for short-term spatial–temporal pre-warning of rock bursts. The temporal sequence curve and spatial contour nephograms indicate that the status of the danger and the specific hazardous zones, and levels of rock burst risk can be quantitatively and rapidly analysed in short time and in space. The multidimensional precursory characteristic identification of rock bursts, including qualitative analysis, intermediate and short-time quantitative predictions, can guide the choice of measures implemented to control rock bursts in the field, and provides a new approach to monitor and forecast rock bursts in space and time.

New Criteria to Assess Seismic and Rock Burst Hazard in Coal Mines / Nowe Kryteria Dla Oceny Zagrożenia Sejsmicznego I Tąpaniami W Kopalniach Węgla Kamiennego

Abstract The paper presents new criteria of seismic and rock burst hazard assessment in Polish hard coal mines where longwall mining system is common practice. The presented criteria are based on the results of continuous recording of seismic events and analysis of selected seismological parameters: spatial location of seismic event in relation to mining workings, seismic energy, seismic energy release per unit coal face advance, b-value of Gutenberg-Richter law, seismic energy index EI, seismic moment M0, weighted value of peak particle velocity PPVW. These parameters are determined in a moving daily time windows or time windows with fixed number of seismic tremors. Time changes of these parameters are then compared with mean value estimated in the analyzed area. This is the basis to indicate the zones of high seismic and rock burst hazard in specific moment in time during mining process. Additionally, the zones of high seismic and rock burst hazard are determined by utilization of passive seismic tomography method. All the calculated seismic parameters in moving time windows are used to quantify seismic and rock burst hazard by four level scales. In practice, assessment of seismic and rock burst hazard is used to make daily decision about using rock burst prevention activities and correction of further exploitation of monitored coal panel.

Mitigation of rock burst events by blasting techniques during deep-tunnel excavation

The buried depths of the auxiliary tunnels of the Jin-ping II Hydropower Station in China are between 1500m and 2300m, and some violent rock bursts were encountered during the excavation process. The measures of rock burst prevention adopted at this station are summarized in this paper, and the mechanisms of these measures are studied and discussed. Combined with the monitoring of the in-situ stress state and the burst proneness of surrounding rocks, the spatial distribution of the rock bursts along the deep tunnel axes and the statistics of rock bursts around the blasting working face are studied. It lays the foundation for generating the strategies for rock burst prevention. The results indicate that the development of rock bursts depends primarily on the level of in-situ stress and on the brittleness of rocks. Disturbances from excavation particularly under blasting excavation conditions have an important influence on the intensity and the scale of rock bursts. Therefore, two primary guidelines for controlled blasting are followed to control rock bursts. One is to decrease stress of the surrounding rocks; the other is to control the disturbance from the excavation. First, the stress-relief blasting method is adopted to reduce the stiffness of the surrounding rocks and reduce the concentration of stress in the blast area. Two different stress-relief blasting design schemes are applied and the extent of the damage and stress relieving effects are compared. Second, the effects of the blasting excavation disturbance in high-stressed rocks are examined. The results indicate that reducing the excavation footage can be used to control the blasting excavation disturbance in deep tunnels. The energy release rate (ERR) for different excavation footages is simulated to verify this conclusion. After the proper excavation footage and perimeter blasting parameters are adopted, the method is applicable to the control of blasting excavation and the reduction of rock burst intensity in engineering practices.

Research of explosives in an environment of high pressure and temperature using a new test stand

Abstract In this article the test stand for determining the blast abilities of explosives in high pressure and temperature conditions as well as the initial results of the research are presented. Explosives are used in rock burst and methane prevention to destroy precisely defined fragments of the rock mass where energy and methane are accumulated. Using this preventive method for fracturing the structure of the rocks which accumulate the energy or coal of the methane seam very often does not bring the anticipated results. It is because of the short range of destructive action of the post-blast gases around the blast hole. Evaluation of the blast dynamics of explosives in a test chamber, i.e. in the pressure and temperature conditions comparable to those found “in situ”, will enable evaluation of their real usefulness in commonly used mining hazard preventive methods. At the same time, it will enable the development of new designs of the explosive charges used for precisely determined mining hazards. In order to test the explosives for their use in difficult environmental conditions and to determine the characteristics of their explosion, a test chamber has been built. It is equipped with a system of sensors and a high-frequency recording system of pressure and temperature during a controlled explosion of an explosive charge. The results of the research will enable the development of new technologies for rock burst and methane prevention which will significantly increase workplace health and safety level. This paper presented results constitute the initial phase of research started in the middle of 2014.

Theoretical Calculation and Analysis on the Composite Rock-Bolt Bearing Structure in Burst-Prone Ground

Given the increase in mining depth and intensity, tunnel failure as a result of rock burst has become an important issue in the field of mining engineering in China. Based on the Composite Rock-Bolt Bearing Structure, which is formed due to the interaction of the bolts driven into the surrounding rock, this paper analyzes a rock burst prevention mechanism, establishes a mechanical model in burst-prone ground, deduces the strength calculation formula of the Composite Rock-Bolt Bearing Structure in burst-prone ground, and confirms the rock burst prevention criterion of the Composite Rock-Bolt Bearing Structure. According to the rock burst prevention criterion, the amount of the influence on rock burst prevention ability from the surrounding rock parameters and bolt support parameters is discussed.

Control Mechanism of Rock Burst in the Floor of Roadway Driven along Next Goaf in Thick Coal Seam with Large Obliquity Angle in Deep Well

This paper deals with the theoretical aspects combined with stress analysis over the floor strata of coal seam and the calculation model for the stress on the coal floor. Basically, this research presents the relevant results obtained for the rock burst prevention in the floor of roadway driven along next goaf in the exploitation of thick coal seam with large obliquity in deep well and rock burst tendency. The control mechanism of rock burst in the roadway driven along next goaf is revealed in the present work. That is, the danger of rock burst can be removed by changing the stress environment for the energy accumulation of the floor and by reducing the impact on the roadway floor from the strong dynamic pressure. This result can be profitable being used at the design stage of appropriate position of roadway undergoing rock burst tendency in similar conditions. Based on the analysis regarding the control mechanism, this paper presents a novel approach to the prevention of rock burst in roadway floor under the above conditions. That is, the return airway is placed within the goaf of the upper working face that can prevent the rock burst effectively. And in this way, mining without coal pillar in the thick coal seam with large obliquity and large burial depth (over a thousand meters) is realized. Practice also proves that the rock burst in the floor of roadway driven along next goaf is controlled and solved.

Numerical Analysis of Roof Pre-Splitting Roadway Effect in Incline Coal Seam

Roof pre-splitting roadway is a new technology in roof induced rock burst prevention and control of incline coal seam. With the purpose of increasing rock burst prevention and control effective, FLAC3D numerical simulation software was used to analyze stress distribution characteristics and roof pre-splitting effect and the layout of the roof pre-splitting roadway parameters. The results showed that the roof pre-splitting roadway changed roof and floor stress distribution, the stress concentration degree is high in the zone of roof and floor around pre-splitting roadway and the two ribs of pre-splitting roadway, which made the roof strength weakened and easy to break, avoiding a large overhang in the process of mining and rock-burst; The roof pre-splitting roadway led to stress concentration in the range of 5 ~ 10 m, roof effective weakening range 12 m, so the distance of two roof pre-splitting roadway should be more than 20m. The research provided the reference basis for rock burst prevention by roof pre-splitting roadway in the incline coal seam group mining.

Numerical simulation of rock-burst relief and prevention by water-jet cutting

The applications in coal mine rock burst prevention using water jet cutting technology (WJCT) have progressed slowly. In this paper we analyzed the possibility and reasonableness of WJCT application to rock burst relief and prevention, used the ABAQUS software to simulate the distributive characteristics of stress and energy fields suffered by hard coal roadway wallrock and the internal relationships of the fields to the instability due to WJC on roadway wallrock, and conducted field WJCT tests using electromagnetic radiation (EMR) measurement technology. The results showed that WJCT can unload rock burst effectively by inducing stress release and energy dissipation in coal mass near its cut slots; its annular slots also can decrease rock burst risks through blocking or weakening stress and energy transfer in coal mass. The horizontal radial slots and annular vertical slots may cause “the beam structure” and “the small pillar skeleton”, and “the layered energy reservoir structure”, respectively, which lead to an increase in stress concentration and energy accumulation in coal element mass near the slots. The reasonable design and optimization of slots׳ positions and their combination not only can significantly reduce the scope of stress concentration and energy accumulation, but also can destroy coal mass structure on a larger scale to force stress to transfer deeper coal mass, eventually avoiding high intensity and large-scale rock bursts. The field tests of WJC for pressure relief using EMR verified the above conclusions.

Analysis of Inducing Factor of Thin Seam Rock Burst in Xinxing Mine

For occurring frequent thin seam rock burst disasters in deep mining stage in Xinxing Mine, through summarizing the mineral basic geological and mining conditions, on this basis, analysing the occurrence characteristics of rock burst with statistical method in Xinxing Mine, analyzing the inducing factors of thin seam rock burst, and through FLAC3D roadways along on 41,051 workface exploitation right beside left stacks of rock burst was simulated, and made a rock burst prevention focus for the impact of land pressure control system provides an effective basis. On thin hard coal burst prevention of important guiding significance.

Theory and application of rock burst prevention using deep hole high pressure hydraulic fracturing

In order to analyze the mechanism of deep hole high pressure hydraulic fracturing, nonlinear dynamic theory, damage mechanics, elastic-plastic mechanics are used, and the law of crack propagation and stress transfer under two deep hole hydraulic fracturing in tectonic stress areas is studied using seepage-stress coupling models with RFPA simulation software. In addition, the effects of rock burst control are tested using multiple methods, either in the stress field or in the energy field. The research findings show that with two deep holes hydraulic fracturing in tectonic stress areas, the direction of the main crack propagation under shear-tensile stress is parallel to the greatest principal stress direction. High-pressure hydraulic fracturing water seepage can result in the destruction of the coal structure, while also weakening the physical and mechanical properties of coal and rock. Therefore the impact of high stress concentration in hazardous areas will level off, which has an effect on rock burst prevention and control in the region.

Rock burst induced by roof breakage and its prevention

Based on the research on rock burst phenomenon induced by the breakage of thick and hard roof around roadways and working faces in coal mines, a criterion of rock burst induced by roof breakage (RBRB) was proposed and the model was built. Through the model. a method calculating the varied stresses induced by roof breakage in support objects and coal body was proposed and a unified formula was derived for the calculation of stress increment on support objects and coal body under different breaking forms of roof. Whilst the formula for calculating dynamic load was derived by introducing dynamic index Kd. The formula was verified in Huating Mine by stress measurement. According to the formula for stress increment calculating, the sensitivities of dynamic load parameters were further studied. The results show that the thickness and breaking depth of roof, width of support object are the sensitive factors. Based on the discussion of the model, six associated effective methods for rock burst prevention are obtained.

Rock burst prevention based on dissipative structure theory

Dynamic collapses of deeply mined coal rocks are severe. In order to explore new ideas for rock burst prevention, the relationship between entropy equations and dissipative structure was studied, and a concept-rock burst activity system (RAS) was proposed and its entropy was analyzed. The energy features of RAS were analyzed, and the relationship between electromagnetic radiation (EMR) intensity E and dissipated energy Ud was initially established. We suggest that rock burst normally happens only when diS≪−deS in RAS; RAS is the dissipative structure before collapse, and after which it become a new orderly structure, i.e., a “dead”, a statically orderly structure. We advanced that the effective way to prevent rock burst is to introduce entropy to the system for it keeps the system away from the dissipative structure. E and Ud of RAS are positively related, which is used as a bridge between dissipative structure theory and rock burst prevention engineering applications. Based on this, and using the data of rock burst prevention for working face No. 250205up of Yanbei coal mine, an engineering verification for the dissipative structure of RAS was carried out, which showed good results.

Directional hydraulic fracturing to control hard-roof rockburst in coal mines

Hard roof is the main factor that induces rock-burst. In view of the present obvious weakness of control measures for hard roof rockburst in domestic collieries, the mechanism and field application of directional hydraulic fracturing technology for rock-burst prevention have been investigated in this paper using theoretical analysis and numerical simulation. The results show that the weighting span of the main roof and the released kinetic energy as well as the total elastic energy decreased greatly after the directional fracturing of hard roof with the mining progression, thereby reducing the rockburst hazard degree to coal body. The directional hydraulic fracturing technology was carried out in 6305 working face of Jisan Coal Mine to prevent rockburst. Field practices have proved that this technology is much simpler and safer to operate with better prevention effect compared with blasting. By optimizing the operation procedures and developing a new technology of automated high-pressure delivery pipe, the maximum fracturing radius now reaches more than 9 m and the borehole depth exceeds 20m. Additionally, drilling cutting method was applied to monitor the stress of the coal mass before and after the fracturing, and the drill cuttings dropped significantly which indicates that the burst prevention effect of directional hydraulic fracturing technology is very remarkable. The research results of this paper have laid a theoretical and practical foundation for the widespread application of the directional hydraulic fracturing technology in China.

Research and practice on fluctuation water injection technology at low permeability coal seam

In order to solve the problem of poor affusion effect on low permeability coal seam, the paper analyzes the micro process of the coal seam water infusion in wetting coal and determines the main factors affecting coal seam water infusion. The permeability of the NO.3 coal seam in east working face of Xingcun coal mine by MTS815.03 servo-controlled rock mechanical test system has been tested. Results show that when the peak stress in coal sample specimens reaches 48.53MPa, permeability ranges from 0.5158 to 2.9576×10−8Darcy, and it means that the coal seam is low in permeability and difficult in water injection. Based on the characteristics of low permeability and geostress situation, efficient fluctuation water injection technology with permeable agent and relevant process parameters have been designed. The surface tension of the permeable agent developed here is 31.18mN/m when mass concentration reaches 0.05%. The permeable agent can permeate into 2cm thick coal layer completely in 10s, thus improving the wettability of water effectively and the water injection pressure fluctuates between 7MPa and 25MPa. The application of the technique in the 3rd coal seam in east working face of Xingcun coal mine shows not only single-arch injection experienced a significant increase on average, from no more than 10m3 to 63.3886m3, but also the effect of dust fall, cooling and rock burst prevention is remarkable.

Key technologies for construction of Jinping traffic tunnel with an extremely deep overburden and a high water pressure

Jinping traffic tunnel is one of the deepest traffic tunnels in the world with a maximum overburden of 2 375 m and the overburden over 73% of its total length is larger than 1 500 m. The tunnel is 17.5 km long and designed to provide a shortcut road between two hydropower stations: Jinping I and Jinping II of the Jinping Hydropower Project, located on Yalong River, Liangshan State, Sichuan Province, China. The tunnel is so deep that building any shafts is impossible. The construction starts from both ends (east and west ends), and the construction length from the west end is 10 km with a blind heading. This paper deals with an overview of this project and analysis of the engineering features, as well as key technologies developed and applied during the construction, including geological prediction, rock burst prevention under a super high in-situ stress, sealing of groundwater with a high pressure and big flow rate, ventilation for a blind heading of 10 km, wet spraying of shotcrete at zones of rock burst and rich water, etc. The application of the new technologies to the construction achieved a high quality tunnel within the contract period.

Analysis and Optimizations on Retreating Mining Measures of Rock Burst Prevention on Steeply Dipping Thick Coal Seam in Deep Exploitation

Abstract With the reduction of mine reserves in shallow coal-bearing series, the mining proportion of steeply dipping thick coal seam in deep strata is increasingly high. Deep exploitation not only increases the chance rock burst happening in mine, but also there are some difficulties for the stability of corollary equipments in working face in the process of full-seam mining of steeply dipping thick coal seam. 4# coal seam of Huafeng colliery is under the geological condition of steeply dipping thick coal seam in deep mining. In the process of retreating mining, rock burst and stability of equipments always restrict the mine's production. Through comprehensive analysis of 4# coal seam, including the places of rock burst happened, comprehensive management actions of rock burst and the relevant mining method and so on, found that adopted the exterior entry layout of dislocated strata gateway in the colliery is still inadequate to improve the problem of stability of equipments along coal seam floor. Besides, continuous mining to the east is too long, reduce the mining speed and mining of protective seam are not effective measures, even the occurrence reasons of rock burst. In response to these issues, further proposed the internal entry layout of dislocated strata gateway, through theoretical and experimental analysis, getting that the reform of tunnels arrangement not only improve the stability of mining equipment, but also change the present situation of rock burst of 4# coal seam fundamentally in Huafeng colliery.

New development in test drilling for detection of hazards in rock burst prevention (In German) : Gluckauf V127, N23/24, Dec 1991, P1047–1051

New development in test drilling for detection of hazards in rock burst prevention (In German) : Gluckauf V127, N23/24, Dec 1991, P1047–1051

Rock burst prevention in the polish hard coal industry (in German) : Szecowka, Z Gluckauf-forschungshV45, N4, Aug 1984, P189–194

Rock burst prevention in the polish hard coal industry (in German) : Szecowka, Z Gluckauf-forschungshV45, N4, Aug 1984, P189–194

Control of measures for rock burst prevention (in Russian) : Voloshin, N E Bezopasnost Tr Prom-st, N2, Feb 1982, P38–41

Control of measures for rock burst prevention (in Russian) : Voloshin, N E Bezopasnost Tr Prom-st, N2, Feb 1982, P38–41