Rockburst Prevention Research Articles

Intelligent prevention and control method of deep rock burst and its development path

Intelligent prevention and control method of deep rock burst and its development path

Experimental study on material performance of separation grouting for prevention of rock burst

The purpose of this study is to obtain the optimal proportion of the full tailings cement filling, reduce the filling cost of the mine and ensure the stability of the empty area. Taking the whole tailings cemented backing block as the research object, the uniaxial compressive strength of the test block as the index, the filling body is investigated comprehensively. The influencing factors of strength were studied by orthogonal experiment, and the sensitivity and significance of the influence factors of the filling body strength were analyzed by using the range and variance analysis methods. The results show that, when cement content is increased, paste setting time is shorten and paste strength is enhanced; proper quantity of fly ash can improve the liquidity of paste, while degree of segregation and bleeding rate of paste are increased with the increase of fly ash; When cement ratio is 20% and the rate of fly ash: coal gangue is 1: 4 and the concentration of the paste is 75%, the pumpability and strength of paste is the best.

Destabilization and energy characteristics of coal pillar in roadway driving along gob based on rockburst risk assessment.

Roadway driving along adjacent goafs is an effective method to develop the recovery rate of coal resources. However, rock burst triggered by dynamic destabilization of coal pillars poses a serious threat to safe and efficient mining, thereby significantly restricting the sustainable development of coal mines. In this study, from the perspectives of energy accumulation and dissipation, a mathematical model of coal pillars is established and the energy equilibrium relationship of the mechanical system is analysed. The rock burst mechanism of coal pillars in gob-side entry is obtained based on a fold catastrophe mathematical model. Results indicate that the rock burst triggered by the instability is a destabilization phenomenon. If the stiffness factor of the mechanical system is less than 1 and the external force is enough to lead coal pillars to the peak stress point, then rock burst disaster occurs. The engineering analysis and numerical simulation are conducted to study the rock burst in the gob-side entry that occurred in Xin'an coal mine. Stress release caused by mining can reduce the risk of rock burst to a certain extent. The amount of elastic energy released is 6.4512 × 107 J, which is close to the observation data and verifies the correctness and rationality of the research method. The research result provides a theoretical basis and technical guidance for rock burst prevention and control in roadway driving along adjacent goafs.

Volumetric changes in the focal areas of seismic events corresponding to destress blasting

The typical development of total volumetric change in the focal areas of seismic events, corresponding to destress blasting, is characterized as an explosive phase followed by an implosive phase and with alternating additional phases following on from that. In a few cases, a non-typical development of volumetric change was identified, where the first phase was implosive and the second phase, explosive. This development is mainly typical for induced seismic events recorded during mining, not for destress blasting. Seismic events were recorded during longwall mining in the Czech part of the Upper Silesian Coal Basin, where the destress blasting technique is used as a rockburst prevention active measure. Kinematic source processes in the focal areas of selected seismic events were analyzed by the seismic moment tensor inversion method, as well as by studying geomechanical rock mass conditions at the localities of the seismic events. The main goal of the analysis was to attempt to identify the reasons for non-typical development of volumetric changes in these cases. Volumetric changes were analyzed for seismic events with energy greater than 104 J, recorded in the period of time from 1993 to 2009 (1109 events). 80% (891) of the recorded seismic events were induced seismic events that were registered during longwall mining and 20% (218) corresponded to destress blasting events. Research shows that the main reason for the non-typical development of volumetric changes in the focal areas of seismic events is an association with destress blasting in the rock mass, which is very close to rock mass overstressing. The detonation of explosives in boreholes, which would dominate the first phase of volumetric changes, probably obscured stress release in the rock mass, as manifested in the first implosion phase of the volumetric changes in this case.

Experimental simulation analysis of the process and failure characteristics of spalling in D-shaped tunnels under true-triaxial loading conditions

Spalling is a typical failure mode encountered on the sidewalls after the tunnel face excavation of deep D-shaped tunnels or caverns. It significantly affects the safe and efficient construction and long-term stability of tunnels. To study the process and failure characteristics of sidewall spalling in D-shaped tunnels, four different three-dimensional initial stress states were established to perform a series of true-triaxial tests on cube specimens with a D-shaped hole. During the tests, a wireless micro camera was used to monitor and record the failure process of the sidewall in real time. Based on the test results, the process and failure characteristics of sidewall spalling were summarised, and the influence of cross-section shape on tunnel failure characteristics and tunnel stability were discussed. The results indicate that both sidewalls perpendicular to the maximum principal stress are cut into approximately parallel rock slabs, demonstrating typical spalling features. Failure zones on both sidewalls are located primarily between the corner and spandrel, and their outlines are “V” shaped (i.e., V-shaped notch). Spalling slabs are thin in both wings, and thick in the middle; they are cut into multilayer thin slices that are not completely detached from one another. With the increase in failure depth, the shape of the cracks first evolved from a straight shape into an arced shape, and subsequently evolved into a “V” shape. When the maximum principal stress is perpendicular to the tunnel axis, tunnel excavation along the minimum principal stress is conducive to the prevention of spalling. Compared with the circular tunnels, the D-shaped tunnels can effectively reduce the severity of rock failure and transform the rockburst into a static spalling. In a relatively low stress environment, the D-shaped cross section can improve the stability of the tunnel, while it is not conducive to the stability of the tunnel in a high stress environment. The result of this study benefits the design and prevention of spalling and rockburst of hard rock tunnels.

Static and Dynamic Mechanical Properties of Granite from Various Burial Depths

The exploitation of mineral resources is gradually shifting from shallow to deep targets. However, the corresponding basic theoretical research has not determined the differences in rock-mining engineering at different depths. In this paper, longitudinal wave velocity measurements, uniaxial compression tests, and dynamic impact tests were conducted on granite from various burial depths to reveal the static and dynamic mechanical properties of the rocks. The initial damage variables of the rock specimens decrease after a rapid increase with increasing burial depth. The stress–strain curves of the deep rocks for various strain rates can be divided into two modes. The relationships between the secant modulus, peak stress, elastic modulus, and burial depth basically follow a quadratic function. The rock failure patterns observed in the uniaxial compression tests are basically tensile. In the dynamic loading experiments at various strain rates, the failure pattern of the rock changes with burial depth, when the strain rate is small, from local instability to overall instability and back to local instability; while the strain rate increases, the failure pattern transforms into overall instability. In the dynamic impact experiments with different confining pressures, the rock only undergoes shear failure due to the restriction of the lateral deformation from the confining pressure. These research achievements could provide significant theoretical support for rockburst prevention at greater mining depths.

Discussion on the Mechanism of Coal and Gas Outburst Prevention and Control by the Coal Seam Water Injection

Coal seam waterflooding hydraulic wetting has been widely used in coal mines, and plays an increasingly important role in coal and gas outburst prevention, dust prevention, and rock burst prevention. In order to explore the mechanism of coal and gas outburst prevention and control by hydraulic wetting, this paper analyses the three stages of hydraulic wetting through Gibbs function: wetting, soaking and spreading; explains the solution of the three stages through Young’s equation, and finally discusses the release and stress of coal gas potential caused by water movement in coal. The centralized influence provides a theoretical basis for the application of coal and gas outburst prevention and control technology in mines.

Rockburst in Sandstone Containing Elliptic Holes with Varying Axial Ratios

Rockburst disaster is one of the prominent problems faced by deep underground engineering. In this study, rockburst in four elliptical holes with different axial ratios in sandstone under biaxial loading is studied as an analogue for underground roadways. Video and acoustic emission (AE) equipment is used to monitor the biaxial loading tests. Experimental results indicate that each of the elliptical holes goes through four stages: quiet period, small particle ejection, spalling, and rockburst. The duration of quiet and spalling periods increased with increasing axial ratio of ellipse. The duration of the ejection and rockburst periods remains unchanged. All the four elliptical holes have V-shaped pits after rockburst occurs. The fragments produced during rockburst are divided into coarse, medium, fine, and micro grains. The quantity of coarse and medium grains increases with increasing axial ratio. The mass ratio of coarse and medium grains increases and that of fine and micro grains decreases. The depth, angle, and area of the V-shaped pits decrease with increasing axis ratio. Tensile cracks play an important role in rockburst failure. Tensile cracks are the dominant crack types formed during rockburst and account for over 70% of all cracks in the samples. The number of tensile cracks increased and the number of shear cracks decreased. This paper has some reference value for practical engineering design and prevention of rockburst.

Study on Properties of Grouting Materials and Reinforcement Effect in Coal Roadways Influenced by Dynamic Pressure

In order to study the occurrence mechanism of rock burst in coal roadways under the influence of mining activities, the study took five main coal roadways in Yuwu Colliery as an engineering background. The occurrence mechanism of rock burst was analyzed by theory of dynamic and static combined load. Furthermore, based on the prevention mechanism of weak-strong structure, this paper puts forward to use a hierarchical coupled grouting method to reinforce the cataclastic surrounding rock of main coal roadways, and the laboratory test results show that slurry properties of superfine cement is better than that of regular cement. The numerical simulation law of slurry diffusion shows that the water-cement ratio and fracture aperture have obvious influence on the final diffusion distance, but the grouting pressure almost has no effect on it. A bolt-mesh-cable and grouting combined reinforcement method was applied in the five main coal roadways, and the borehole observation and deformation monitoring results show that the control effect of surrounding rock is satisfactory and the rock burst accidents caused by mining disturbance are effectively prevented. The study conclusions provide theoretical foundation and a new guidance for preventing rock burst in coal roadways.

Профилактика горных ударов в низких рудных целиках посредством образования разгрузочных щелей (для условий Ловозерского редкометалльного месторождения)

Профилактика горных ударов в низких рудных целиках посредством образования разгрузочных щелей (для условий Ловозерского редкометалльного месторождения)

TBM in Azad Kashmir region of Pakistan: in situ stress measurements for rockburst prevision

Using the authors’ experience, this paper details the in situ stress measurements in twin tunnel boring machine (TBM) tunnels of the Neelum Jhelum hydropower project, located in the Azad Kashmir region of north-east Pakistan in foothills of the Himalayas, with overburdens up to 2000 m and high tectonic stresses in very complex geology. The ability to predict the likelihood, location, severity and number of rockbursts directly impacts on the tunnel safety and daily production rates. This, combined with the lack of previous project experience in similar conditions, has required the use of all the available advanced geological prediction methods: forward probing, tunnel seismic tomography, continuous microseismic monitoring and in situ stress measurements were used. These methods, except in situ stress measurements, only gave an indication of likelihood and severity of rockbursts. The in situ tests provided the actual ground stresses and their orientations. The in situ stress results contradicted the forecasts based on the classical empirical rules combining stress analysis and rock strength. This paper is focused on the in situ stress measurements carried out behind the two TBMs and details the information obtained and how data were interpreted and integrated to support excavation, prevention and control of rockbursts, which improved tunnel safety and productivity.

Rockburst mechanism and control in coal seam with both syncline and hard strata

The rockburst, that is one of the leading disasters in mining and rock engineering causing serious casualties and property losses, frequently occurs with various features and complex evolution mechanisms. Thus, it is difficult to prevent such disasters. In this paper, evolution mechanisms of two rockburst cases of different types were outlined through microseismicity, energy density clouds and seismic velocity tomography. Measures of caving mining, deep-hole blasting and large-diameter hole were then proposed for risk control of future rockburst disasters during subsequent mining activities. Long-term tremor activities were analyzed to verify the effectiveness of these controlling measures. The results indicate that static and dynamic stresses had played different roles in the two rockbursts. Compared to the first “6.26” rockburst, an obvious characteristic of progressive development of tremors occurred before the “10.15” rockburst. In subsequent mining, controlling measures were proved effective by energy density clouds and seismic velocity tomography. No rockburst happened due to the hard roof and syncline structure again. Only an energy density cloud with small intensity appeared, augmented and then disappeared at the same location where the “10.15” rockburst occurred. The conclusions could expand the understanding of rockburst mechanisms and provide significant theoretical reference for rockburst prevention.

Influence of Different Advancing Directions on Mining Effect Caused by a Fault

To study the correlation among advancing direction, strata behaviors, and rock burst induction, two physical models utilizing similar materials are established. Subsequently, the influence of advancing direction on the mining effect, caused by a fault, is studied. Moreover, the rock bursts affected by faults with different mining directions are compared and analyzed. The results show that the overlying structure varies notably, affected by fault cutting and fault dip, and the fault‐affected zone and the cause of induced rock burst differ with different mining directions. However, regardless of mining directions, the overlying structure of the hanging wall is stable and fault activation is not obvious, while that of the footwall is relatively active and fault activation is violent; the risk of rock burst on the footwall is larger than that of mining on the hanging wall. Finally, an engineering case regarding two rock bursts in panel 6303 is used to verify some physical simulation results to a certain extent. Study results can serve as a reference for face layout and prevention of rock bursts under similar conditions.

Experimental Study on Dynamic Tensile Failure of Sandstone Specimens with Different Water Contents

Understanding the effect of water saturation on dynamic failure of rocks is of great importance to tunnel excavation at water‐rich coal mines and prevention of rock bursts by water injection. Dynamic Brazilian disc tests are performed to study mechanical behaviour of sandstones in this paper. The results indicate that water saturation significantly weakens the dynamic tensile strength of sandstones and increases the specimen strain at which the specimen fails. The damage degree of sandstones reduces gradually with increasing water contents. Failure of the sandstone specimen includes the crack initiation at the center of the specimen, macroscopic crack propagation, and stretch of the macroscopic crack through the specimen. In addition, parallel macroscopic crack propagation is found in the specimen with a low water content. From the observation of fracture sections, microstructures are compact in the specimen with high water contents. This is due to the swell of the kaolinite in the specimen after water saturation. The failure mechanism of microstructures is typical brittle failure in the specimen with a high water content, whereas ductile fracture is found in the specimen with a low water content. Different failure processes of microstructures lead to the differences between mechanical properties and macroscopic failure characteristics of the specimens with various water contents.

Assessment of Seismic Hazard in Relation to Rock-Burst Prevention Modifications in KGHM Polish Copper JSC Polkowice - Sieroszowice Mine, Poland

The Polkowice-Sieroszowice mine is one of three underground copper ore mines in Poland. These three mines belong to KGHM Polish Copper JSC, excavating one of the largest copper ore deposits in the world. The deposit is situated in the south-western part of Poland in the Lower Silesia province. Due to the specific and difficult geological-and-mining conditions in the three mines, seismic events occur which often result in an excavation serious damage defined as the rock-burst or elastic recovery. Such dynamic phenomena have been occurring since 1972 and have posed the most dangerous natural threats in underground workings. Therefore, the mining technology has to take the account of seismic hazard prevention. Numerous preventive measures adjusted to the conditions prevailing in the given operating field have to be applied so that the hazards can be mitigated, fought or limited. The appropriate choice of prevention activities must be preceded by measurements and observations, which constitute different methods for identifying, predicting and assessing the condition of the rock mass as well as for evaluating the protection effectiveness. In the Polkowice-Sieroszowice mine the rock-burst prevention involves: assessment of rock mass state and active, technological, and organizational-technical methods for combating the hazard. The active prevention consists in blasting works which provoke the rock mass to distress itself and thus to reduce its capability to accumulate elastic energy. The technological prevention embraces yielding the edges of the walls and pillars in the place of development, the extraction of the deposit with a wide opening of the front and the adjustment of the size of the technological pillar to the local geological and mining conditions. The organizational-technical measures introduce after-blasting waiting time and high hazard zones where the number of employees should be reduced. The influence of changes and improvements in the prevention activities on the seismic hazard was analysed and determined. The effectiveness of prevention methods was assessed in connection with their modifications, which concerned certain elements of active methods, the pillar size changes and alterations in the frequency of rock mass observations. Most of these modifications resulted from the operational progress and had a little impact on the seismic activity. Nevertheless, the effectiveness of such alterations was calculated. The research was carried out for one mining division in the Polkowice-Sieroszowice mine over the period of 2013-2015 years. The increase in the effectiveness of seismic/rock-burst prevention in most cases resulted in reduction of seismic activity.

A Control Method of Rock Burst for Dynamic Roadway Floor in Deep Mining Mine

Roadway floor rock burst is an important manifestation of rock bursts in deeply buried mines. With the increase of mining depth and mining intensity, rock burst disasters in the roadway floor such as floor heaves are becoming more serious. The article investigated the roadway floor severe heave caused by floor rock burst during excavation of the No. 3401 working face, which was controlled by an anticlinal structure and deep mining in Shandong Mine, China. Firstly, by analyzing geological conditions of the working face, roadway support parameters, and characteristics of coal and rock, it was revealed that high tectonic stress and high crustal stress were main causes of the floor rock burst. Secondly, based on the Theory of Mechanics and Theory of Energy, the energy conversion process in the roadway floor was discussed, and the rock burst condition caused by elastic energy in the roadway floor was analyzed. The failure characteristics of roadway‐surrounding rock were also inspected, using a borehole recorder. The roof and sidewalls of roadway mainly contained fissures and cracks, whereas cracks and broken areas are distributed in the roadway floor. Finally, based on the deformation and failure characteristics of roadway‐surrounding rock, a method termed “overbreaking‐bolting and grouting‐backfill” was proposed to control roadway floor rock burst. The method was tested in the field, and the results showed that it could effectively control the deformation of roadway floor and rock burst, guaranteeing the stability of roadway floor. This impact control method for the roadway floor can provide a reference for the prevention and control of roadway rock burst in mines with similar geological conditions.

Blasting Delay Pattern Development in the Light of Rockburst Prevention – Case Study from Polish Copper Mine

In order to reduce the risk of induced seismicity related to underground mining, a number of preventive actions are applied in the form of passive and active prevention methods. The former are mainly of an organisational nature and their effectiveness is usually considered in the long term, while the active methods are mostly based on the detonation of explosives and are aimed to release the seismic energy accumulated in the rock mass. In this paper, modifications of the firing pattern aimed to concentrate the paraseismic vibrations while maintaining the appropriate excavation of the mining face has been verified on the basis of underground tests. The evaluation was based on fragmentation analysis. The obtained results confirmed, that the blasting pattern modifications related to the reducing of the face firing time do not cause significant differences in terms of the appropriate excavation of the mining face.

Case of Rock Burst Danger and Its Prediction and Prevention in Tunneling and Mining Period at an Irregular Coal Face

Irregular coal faces, ineluctable in coal mines within the eastern mining area in China owing to its complex geological condition, face higher rock burst danger because of their high-stress concentration and complicated spatial structure. Considering geological characteristics, rock burst liability and in situ stress in the 3303 irregular coal face at the Yangcheng coal mine, rock burst danger during tunneling and mining was analyzed to select targeted mitigation measures. The results indicate that the dynamic pressure adjustment movement (DPAM) of the roof plays an important role in the occurrence of rock bursts. Rock burst danger in tunneling of the tailgate is caused by the combination of dynamic and static stress, where the static stress is from the large depth and nearby faults, and the dynamic stress is from the DPAM of the roof above the near the 3301 mined-out area. The tunneling construction was halted for 3 months to reduce the high dynamic stress σd, and destressing large-diameter holes were drilled to reduce the static stress σ0. The rest of the tunneling construction was deemed safe. Furthermore, the rock burst danger in mining was divided into two types: I (high static stress type) and II (high dynamic stress type). The former is located at the triangular coal pillar and within a 20–150 m range ahead of the coal face. The latter acts on the tailgate caused by the intense mine seismic activity arising from the secondary DPAM. More destress holes are drilled within the danger zones of the former to release the stress fully. A combination of rigid support and flexible support (i.e., single props, double T-steel shed, bolt, anchor rope and anchor net) and monitoring is an efficient method to address the latter. The results show safe mining during the rest of the mining period. This paper provides a reference for prevention and control of rock burst for similar coal faces.

The Spatiotemporal Distribution Law of Microseismic Events and Rockburst Characteristics of the Deeply Buried Tunnel Group

Rockburst disaster is one of the prominent problems faced by deep underground engineering. Microseismic (MS) monitoring techniques can be used to warn of rockburst in tunnels to provide scientific basis for rock burst prevention and control measures. Described in this paper, is an MS monitoring system based on MS source location with hierarchical strategy implemented in the tunnel group of the Jinping II hydropower station in Sichuan Province, China. The spatiotemporal distribution of MS events was analyzed in the construction process and the size effect of rockburst risk discussed by statistical analysis and numerical calculation of rockburst in seven tunnels. The results show that the active period of microseisms and the high-incidence period of rockburst are within 1.5 h after the rock disturbance. The MS events within 1D from the tunnel wall are the most intensive and are mainly concentrated near the heading face, the side wall, and the left spandrel. At the construction site, the accuracy rate of rockburst prediction is 61.8%, of which the accuracy rate of the medium and strong rockburst is 80.3%. Based on field statistics of rockburst, the increase of the tunnel excavation section size can reduce the rockburst strength to a certain extent, which is consistent with the numerical simulation results.

Risk assessment of rockburst via an extended MABAC method under fuzzy environment

The rockburst is a severe underground geological disaster, which has great damage to the workers, equipments and engineering structures. This paper aims to find a suitable way to assess the risk of rockburst within complicated decision making circumstances. First, plenty of literature related to the risk assessment indexes and methods of rockburst is reviewed. On account of the specific characteristics of rockburst, both quantitative and qualitative evaluation indexes are recognized in this paper. Owing to the fuzziness of human thinking and the complexity of risk assessment problems, triangular fuzzy numbers (TFNs) are advised to describe these indexes values. Meanwhile, the superiority linguistic ratings of decision makers (DMs) are used to determine the weights of indexes. After that, an extended multi-attributive border approximation area comparison (MABAC) method corresponding to TFNs is put forward to obtain the ranking results and specific risk levels of rockburst under fuzzy environment. Finally, an example of assessing the risk of rockburst in Kaiyang phosphate mine is illustrated. The rockburst proneness of four crucial areas is evaluated with the proposed method, and the ranking result is consistent with the field status. Besides, the effectiveness of this method is demonstrated with parameter and comparison analyses. The results show that the extended MABAC method is reliable and effective for evaluating the risk of rockburst, and provides references for the prevention and management of rockburst.