Rockburst Occurrence Research Articles

Факторы изменения сейсмического режима и локализации опасных зон при крупномасштабном техногенном воздействии

Large-scale mining operations over 90 years at the Khibiny apatite-nepheline deposits that are characterized with the conspicuous gravity-tectonic type of the stress-strain state have transformed the initial stress field of the rock massif, which has led to the recurrent occurrence of rockbursts. This problem retains its relevance due to constant increasing intensity of mining operations at the apatite mines during the last two decades and complicated mining, geological and geomechanical conditions. Accordingly, the dynamic rock pressure is increasing. We have retrospectively analyzed data on the manifestations of geodynamic events in the Khibiny rockburst-hazardous deposits and determined a set of factors that influence the changes in seismic behavior and localization of hazardous zones in complicated mining and engineering systems. We have systematized the data of long-term observations on dynamic rock pressure manifestations at the Khibiny apatite mines, taking into account the seismicity parameters, the scale of mine damage, the mining-induced stress fields, and geological and geomechanical features of the rock massif at specific time points. A structural scheme has been developed and ranking of factors has been carried out, considering the time of impact on the rock massif.

Ensemble Tree Model for Long-Term Rockburst Prediction in Incomplete Datasets

The occurrence of rockburst can seriously impact the construction and production of deep underground engineering. To prevent rockburst, machine learning (ML) models have been widely employed to predict rockburst based on some related variables. However, due to the costs and complicated geological conditions, complete datasets to evaluate rockburst cannot always be obtained in rock engineering. To fill this limitation, this study proposed an ensemble tree model suitable for incomplete datasets, i.e., the histogram gradient boosting tree (HGBT), to build intelligent models for rockburst prediction. Three hundred fourteen rockburst cases were employed to develop the HGBT model. The hunger game search (HGS) algorithm was implemented to optimize the HGBT model. The established HGBT model had an excellent testing performance (accuracy of 88.9%). An incomplete database with missing values was applied to compare the performances of HGBT and other ML models (random forest, artificial neural network, and so on). HGBT received an accuracy of 78.8% in the incomplete database, and its capacity was better than that of other ML models. Additionally, the importance of input variables in the HGBT model was analyzed. Finally, the feasibility of the HGBT model was validated by rockburst cases from Sanshandao Gold Mine, China.

Rock dynamic fracture by destress blasting and application in controlling rockbursts in deep underground

Destress blasting is regarded as an active mitigation measure for preventing rockbursts in deep underground works, whose mechanism and effectiveness, however, have still been in debate. A self-developed combined finite-discrete element method software is implemented in this study to first model the rock fracture process induced by a single-hole destress blasting based on a practical blast in a deep gold mine with high in-situ stresses. The effects of accelerometer holes and bedding planes are discussed. Then, a two-round tunnel face excavation in deep underground with high in-situ stresses is modelled, which reproduces the occurrence of the excavation-induced rockbursts. Finally, destress blast-holes are introduced into the same model prior to the two-round tunnel face excavation to investigate the effect of the destress blasting on the excavation-induced rockbursts. It is found that the fractures induced by the destress blasting shift the high abutment pressure induced by the excavation away from the tunnel face and then protect the tunnel wall from fracturing. The numerical modellings reveal that the success of the destress blasting in controlling excavation-induced rockbursts depends on not only the site condition but also the design of the destress blasting such as the arrangement of the blast-holes and the explosive charges.

WALL STABILIZATION IN MINES BY SPRAY-ON LINERS

AbstractThin spray-on liners (TSLs) have been found to be effective for structurally supporting the walls of mining tunnels and thus reducing the occurrence of rock bursts, an effect primarily due to the penetration of cracks by the liner. Surface tension effects are thus important. However, TSLs are also used to simply stabilize rock surfaces, for example, to prevent rock fall, and in this context crack penetration is desirable but not necessary, and the tensile and shearing strength and adhesive properties of the liner determine its effectiveness. We examine the effectiveness of nonpenetrating TSLs in a global lined tunnel and in a local rock support context. In the tunnel context, we examine the effect of the liner on the stress distribution in a tunnel subjected to a geological or mining event. We show that the liner has little effect on stresses in the surrounding rock and that tensile stresses in the rock surface are transmitted across the liner, so that failure is likely to be due to liner rupture or detachment from the surface. In the local rock support context, loose rock movements are shown to be better achieved using a liner with small Young’s modulus, but high rupture strength.

Experimental investigation on the influence of a single structural plane on rockburst

The structural planes adjacent to the tunnel have a significant effect on rockburst, which has become an important engineering issue. To investigate the influence of such a rigid structural plane on rockburst, four different types of block specimens containing a through circular hole are designed with a prefabricated unfilled crack. A series of biaxial compression tests are then performed to simulate the rockburst process, followed by a detailed analysis of the strength characteristics, the strain field, the rockburst evolution process, and the microscopic characteristics of fracture surfaces. A prefabricated unfilled crack causes a decrease of the initial damage stress and the overall strength of block specimen, the earlier occurrence of rockburst but a decrease of initial rockburst intensity. Compared with the exposed crack, the non-exposed crack facilitates the occurrence of the rockburst more. Three mechanisms are proposed to explain these effects, including (i) the local stress concentration that alters the location of initial damage and the following crack propagation pattern, further affecting the location and scope of rockburst; (ii) the weakening effect that promotes rockburst evolution and inhibits rockburst intensity; and (iii) the sliding-induced secondary rockburst that contributes with significant energy release once the pre-existing crack is compacted. In light of the experimental observations, four different rockburst evolution modes are summarized to help to understand the rockburst in practical tunnels, and some engineering measures are recommended for the controlling and prevention of rockburst.

Rockburst and microseismic activity in a lagging tunnel as the spacing between twin TBM excavated tunnels changes: A case from the Neelum-Jhelum hydropower project

A reasonable spacing between tunnels is very important in deeply buried tunnels, as it may mitigate the risk of rockburst occurrence. This spacing is particularly important for tunnels excavated using a tunnel boring machine (TBM), as the methods available for controlling rockburst occurrence are inflexible and limited using these machines (compared to tunnels excavated using the drilling and blasting (D&B) method). In this paper, a rare example was studied in situ in which the spacing between twin tunnels was changed to mitigate the rockburst risk during TBM excavation. First, the characteristics of the rockburst and microseismic activity were investigated in three sections of the lagging tunnel before, during, and after the spacing between the tunnels was changed (we concentrated on the lagging TBM696 tunnel, which is part of the Neelum-Jhelum hydropower project). We observed a significant occurrence of rockburst and microseismic activity in the lagging tunnel at the original spacing of the twin tunnels in both the sandstone and siltstone lithologies, and thus a consideration of enlarging the spacing between the twin tunnels is reasonable. A more detailed investigation was then conducted to explore the effects of tunnel spacing on rockburst occurrence and microseismicity. The rockburst frequency and microseismic radiated energy due to excavation unloading generally decrease as the spacing between the twin tunnels increases (substantially at first and then more slowly as separation increases). In particular, the microseismic radiated energy exhibits a power-decreasing type in both the sandstone and siltstone. Increasing the spacing beyond a certain point, therefore, exerts a very limited effect on the microseismic radiated energy and occurrence of rockbursts (increments of 16–21 m and 15–20 m in sandstone and siltstone, respectively). Consequently, in practice, a very reasonable approach would be to enlarge the spacing of twin tunnels by 22.48 m. Thus, microseismic monitoring is a useful technique for assessing the rockburst risk and deriving a reasonable value for tunnel spacing. This study can be used as a guideline to derive reasonable tunnel spacings when using not only TBMs but also D&B.

Damage evolution, fractal dimension and a new crushing energy formula for coal with bursting liability

The failure and instability process of surrounding rock in deep engineering is accompanied by energy accumulation and dissipation and results in damage and failure, which play an important role in the inoculation and occurrence of rockbursts. The bursting liability, energy transformation, and total damage evolution during the coal failure process were investigated using uniaxial compression tests. A damage evolution model and constitutive relation were developed in which the initial damage is considered, and the primary fissures of the specimens were also observed from their computed tomography images. Sieve analysis was used to determine the size distribution of the fragments, a crushing energy formula model was developed that is associated with the fractal dimension, which corrects the energy dissipation of coal in the total process of deformation and failure. The relationships among the crushing, surplus energy density, and fractal dimension of coal with different bursting liabilities were explored in detail.

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.

Numerical modelling of destress blasting – A state-of-the-art review

As a proactive mine safety measure against the occurrence of rockburst, destress blasting has been applied to numerous mining conditions to precondition highly stressed rock mass to mitigate the risk of rockburst occurrence in deep mines as well as in deep underground constructions. However, the application of destress blasting mostly depends on engineering experience, while its mechanism and efficiency have not been well understood. Rapid advances in computer technology have made numerical simulation an economical and effective method to study the rock blasting effect. Enormous research efforts have been made to numerically investigate the blasting fracture mechanism, optimize blasting design, and assess the efficiency of destress blasting. This review focuses on the state-of-the-art progress in numerical modelling associated with destress blasting over the last two decades. Some commonly used modelling approaches for destressing blasting are compared and reviewed. Currently, two different ways of modelling based on static and dynamic modes are typically used to study the effect of blasting. In the static method, destress blasting is simulated by modifying the rock mass’s stiffness and strength properties to obtain the post-blast stress state in the destressed zone. The dynamic modelling technique focuses on the dynamic fracture process of coals and rock masses, during which the predetermination of the damage induced by blasting is not necessary. Moreover, the extent of damage zones around the blast hole can be precisely estimated in the dynamic modelling method by considering time-varying blast pressure and strain rate dependency on the strength of rock mass but at the cost of increased computation and complexity. Besides, different destress blasting modelling methods, generally classified into continuum-based, discrete-based, and coupled methods, are compared and reviewed. The fracture mechanism of blasting in the rock mass is revealed, and the destressing efficiency of the existing destress blasting design is assessed and compared with classical results. The factors that may affect the efficiency of destress blasting are summarized. Finally, the difficulties and challenges associated with the numerical modelling of destress blasting are highlighted briefly.

A multi-index evaluation method for rockburst proneness of deep underground rock openings with attribute recognition model and its application

As the tunnel excavation and resource exploitation go deeper into the Earth, increasing number of rockburst occur all over the world. However, the understanding of rockburst prediction and rockburst proneness evaluation is still at its infancy. In this paper, to accurately and efficiently predict rockburst proneness, a multi-index evaluation method for rockburst proneness of deep underground rock openings is established, verified and applied. The multi-index evaluation method is put forward based on attribute recognition model and combined weighting method. Eight discriminate indexes are taken into account, i.e., in-situ stress, rock brittleness, elastic deformation energy, maximum storage elastic strain energy, rock integrity, groundwater condition, section design size and site construction status. Through analyzing a variety of practical engineering cases, the weight values of each index are evaluated by combined method of analytic hierarchy process and random forest algorithm. It is found that the groundwater condition, in-situ stress, rock integrity and elastic deformation energy are the most important evaluation indexes. The attribute recognition model of rockburst proneness is established with weight evaluation and the attribute measure function of each index, where the attribute measure function is developed by analyzing the rockburst proneness of each index and setting up the standards for risk classes. The accuracy and applicability of the proposed multi-index evaluation method are verified through analyzing rockburst cases of twenty engineering projects. It is then applied to the rockburst hazard evaluation of the Caoguoshan Tunnel. Results showed that the predictions for rockburst proneness are consistent with the actual rockburst occurrence. The findings in this paper could facilitate evaluating of rockburst proneness for deep underground rock opening and be of great significance for rockburst risk prediction.

Application of KNN-based isometric mapping and fuzzy c-means algorithm to predict short-term rockburst risk in deep underground projects.

The rockburst phenomenon is the major source of the high number of casualties and fatalities during the construction of deep underground projects. Rockburst poses a severe hazard to the safety of employees and equipment in subsurface mining operations. It is a hot topic in recent years to examine and overcome rockburst risks for the safe installation of deep urban engineering designs. Therefore, for a cost-effective and safe underground environment, it is crucial to determine and predict rockburst intensity prior to its occurrence. A novel model is presented in this study that combines unsupervised and supervised machine learning approaches in order to predict rockburst risk. The database for this study was built using authentic microseismic monitoring occurrences from the Jinping-II hydropower project in China, which consists of 93 short-term rockburst occurrences with six influential features. The prediction process was succeeded in three steps. Firstly, the original rockburst database's magnification was reduced using a state-of-the-art method called isometric mapping (ISOMAP) algorithm. Secondly, the dataset acquired from ISOMAP was categorized using the fuzzy c-means algorithm (FCM) to reduce the minor spectral heterogeneity impact in homogenous areas. Thirdly, K-Nearest neighbor (KNN) was employed to anticipate different levels of short-term rockburst datasets. The KNN's classification performance was examined using several performance metrics. The proposed model correctly classified about 96% of the rockbursts events in the testing datasets. Hence, the suggested model is a realistic and effective tool for evaluating rockburst intensity. Therefore, the proposed model can be employed to forecast the rockburst risk in the early stages of underground projects that will help to minimize casualties from rockburst.

Rockburst and Gas Outburst Forecasting using a Probabilistic Risk Assessment Framework in Longwall Top Coal Caving Faces

A probabilistic risk assessment framework was developed to mathematically represent the complex engineering phenomena of rock bursts and gas outbursts for a heterogeneous coal seam. An innovative object-based non-conditional simulation approach was used to distribute lithological heterogeneity present in the coal seam to respect their geological origin. The changing mining conditions during longwall top coal caving mining (LTCC) were extracted from a coupled numerical model to provide statistically sufficient data for probabilistic analysis. The complex interdependencies among abutment stress, pore pressure, the volume of total gas emission and incremental energy release rate, their stochastic variations and uncertainty were realistically implemented in the GoldSim software, and 100,000 equally likely scenarios were simulated using the Monte Carlo method to determine the probability of rock bursts and gas outbursts. The results obtained from the analysis incorporate the variability in mechanical, elastic and reservoir properties of coal due to lithological heterogeneity and result in the probability of the occurrence of rock bursts, coal and gas outbursts, and safe mining conditions. The framework realistically represents the complex mining environment, is resilient and results are reliable. The framework is generic and can be suitably modified to be used in different underground mining scenarios, overcoming the limitations of earlier empirical indices used.

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.

Study on Overburden Structure Characteristics and Induced Scour Mechanisms of Horizontal Sublevel Mining in Steep and Extra-Thick Coal Seams

In order to study the space–time evolution law and the induced impact mechanism of overburden breaking in the tangential horizontal sublevel during the fully mechanized mining of extra-thick and steep coal seams, we took the Yaojie No. 3 mine as an example. Through the establishment of an overburden breaking mechanical model, the structural characteristics of hinged rock beams after overburden breaking and the space–time evolution law of overburden structure instability were analyzed, the static and dynamic load conditions that induce rockbursts were analyzed, and the induced impact mechanism of dynamic and static load superposition was revealed. Our research showed that, due to the asymmetry of the roof and floor, the coal body in the working face is in the strong shear stress zone at the end of the air inlet roadway, which easily produces shear failure. The lateral support pressure and the shear stress of the coal body in the goaf are the static load sources of the rockburst in the steep coal seam; after the roof overburden is broken, a hinge-bearing structure is formed under the support of the sliding force of the fault block and the floating gangue in the goaf. When the coal is mined in the lower section, the strong dynamic load formed by the impact of the fault block on the topmost coal is the main dynamic load source of the impact on the working face. Under the superpositions of the dynamic load and static load, the coal and rock lose stability and release energy in a large range, generating dynamic and static superimposed rockbursts. Furthermore, the internal mechanism of the occurrence of rockbursts during the mining of steep and extra-thick coal seams in the Yaojie No. 3 coal mine was revealed. The static load of the coal body comes from the clamping actions of the roof and floor, and the dynamic impact load comes from the clamping structure’s instability. The reason for the occurrence of rockbursts in the mining of steep and extra-thick coal seams in the Yaojie No. 3 coal mine was reasonably explained.

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.

Continuous three-dimensional stress monitoring in roof of coal mines for investigating the rockburst control effect with hydraulic fracturing

The occurrence of rockburst in coal mines is closely related to the stress in coal and rock mass. Through hydraulic fracturing measurements in roof, the three-dimensional stress in roof before and after hydraulic fracturing as well as during working face advancing was monitored, and the effect of hydraulic fracturing in roof on controlling rockburst was studied. The test results show that (1) after hydraulic fracturing, the three principal stresses in roof decreased remarkably, whose maximum reduction was about 20%, while the elastic strain energy in roof decreased by about 31% as well; (2) as the working face advanced, the three principal stresses in roof in front of the working face would increase continuously until reaching peaks and induce the strata fracture, and the variation of the elastic strain energy in roof was basically consistent with that of the magnitude of the stress; (3) with hydraulic fracturing, the position of the peak stress moved from 11 to 21 m in front of the working face, the peaks of the three principal stresses decreased, whose maximum reduction was about 32%, and the peak of the elastic strain energy in roof also significantly decreased by about 51%. The field investigation shows that hydraulic fracturing in roof can release the stress and elastic strain energy in coal and rock mass instantaneously, and will reduce the risk of rockburst; hydraulic fracturing in roof can be an effective pre-destressing method to reduce the stress and energy concentration in coal and rock mass during mining, and will prevent the risk of rockburst.

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.

Head-On Dynamic Manifestations in the Roadway Driving with Small Coal Pillar under the Influence of Roof Drainage: A Case Study from Uxin Banner

In the Uxin Banner area of the Inner Mongolia Autonomous Region, mines that have experienced rock bursts have all been affected by the presence of confined water in the roof strata. Strong mine pressure appears in the working face with about 30 m wide coal pillar in this area, and the research and practice of prevention and control of rock burst by small coal pillar are carried out. Mining-related events linked to the preservation of small coal pillars in the 2-2 coal seam of this region, and studies of the phenomenon, have shown that head-on rock bursts occur during gob-side roadway driving at the edge of the drained area, making it necessary to identify the sources of pressure triggering the events, to determine the related threshold criteria, and to identify methods to reduce the occurrence and magnitude of the rock burst events. This study used the gob-side entry driving in the drained area of the 2202 auxiliary haulage roadway of a mine as a case study. The paper built a structural and computational model for overburdens (including the drained stratum) before mining disturbance, based on the theory for a continuously distributed Winkler elastic foundation. The models used and developed in our study were used to identify, quantify, and describe the changes to stress and the transfer of stress during the drainage process. On the basis of the effects of drainage stress induced by the gob-side entry driving, we outlined a method for ranking the level of rock burst hazard associated with the areas in and adjacent to the drained area. The level of rock burst hazard associated with the entry driving could be arranged in descending order as follows: parallel boundary > vertical boundary > undrained area > drained area. Stress threshold criteria for head-on ejection were also proposed in the paper, namely, (1) the occurrence (or not) of coal ejection during loading and (2) the critical stress for the occurrence of ejection. Field monitoring indicated that microseismic events and energy are mainly concentrated in the driving region parallel to the boundary of the drained area. We concluded that head-on large-diameter borehole destressing would effectively reduce the likelihood of a rock burst occurrence.

Research on Rock Burst Control Mechanism of Deep Buried Tunnel Using Surrounding Rock Modification Theory

In order to solve the rock burst disaster during the excavation of deep buried high stress hard rock tunnel, the method of changing the properties of surrounding rock by blasting is proposed in this paper. This method can effectively change the physical and mechanical properties of surrounding rock, reduce the storage capacity of surrounding rock corresponding to variable energy, and transfer the stress concentration position to the deep layer, which is an effective means to control rock burst. Taking the tunnel with rockburst tendency as an example, the stress distribution characteristics and displacement changes of surrounding rock under different modification depths are studied by using the numerical calculation method and elastic-plastic mechanics theory, and the effect is tested combined with microseismic data. The results show that the thickness of tunnel blasting loosening is closely related to the stress concentration of surrounding rock, and blasting loosening can effectively inhibit the occurrence and prevention of rock burst. With the increase of blasting depth, the maximum stress concentration decreases. The relevant research results can be used to reasonably design the blasting and loose surrounding rock reconstruction of high stress rock burst tunnel and improve the theoretical and practical basis.

Numerical Study on the Pressure Relief Characteristics of a Large-Diameter Borehole

Large-diameter drilling is an effective method for preventing rock burst disasters in coal mines. In this paper, the roadway stability of the W1123 fully mechanized caving work face of the Kuangou coal mine, located in northwest China, is investigated. A set of numerical modelling techniques were carried out to study the characteristics of stress, displacement, strain energy and the plastic zone of the roadway side rock with different parameters, including the large-diameter drilling hole diameter, depth and spacing. The results showed that: (1) after drilling, the peak values of the stress and strain energy are reduced and transferred to a deeper location, and the control effect presents a positive correlation with the diameter of the drilling hole; (2) when Lh < LP, there are no pressure relief and energy release effects, which may induce impact, whereas when LP < Lh ≤ 2.5LP, with the increase of the hole depth, the effects of pressure relief and energy release are enhanced, and further extension is not conducive to the long-term stability of the roadway; and (3) when the hole spacing decreases, the plastic zone and the broken zone between the holes are gradually penetrated, and the stress pattern transforms from a double peak to a saddle shape and then to single peak. Reducing the hole diameter reduces the efficiency of the plastic zone, failure zone and the stress form transformation between the boreholes, and weakens the pressure relief effect. Therefore, the main factor affecting the pressure relief effect is the hole diameter, and the secondary factor is the hole spacing. The engineering practice employed here showcases how a larger-diameter hole is an effective way of enhancing the effect of pressure relief and controlling the occurrence of rock burst. These research results are of great significance for guiding engineering practice.