Search Results (45)

Vibrations generated by blasting operations in open-pit mines can have adverse effects on nearby buildings. To mitigate these vibrations by selecting an appropriate delay time, blasting vibration monitoring experiments were conducted in an open-pit mine. The characteristics of peak particle velocity (PPV) and principal frequencies of seismic waves from single-hole and group-hole blasting were analyzed, and an equation for the decay of PPV during the propagation of blasting seismic waves was established. To address the uncertainty in the principal frequency of seismic waves from single-hole blasting, the dominant principal frequency of single-hole blasting seismic waves was defined. A method for determining the optimal vibration-reduction delay time based on the dominant principal frequency of single-hole blasting seismic waves was proposed. Using the bootstrap method, the dominant principal frequency of single-hole blasting seismic waves was estimated to be 20 Hz. Combining this with the principle of staggered-phase superposition, the optimal vibration-reduction delay time between boreholes was determined to be 25 ms. The vibration-reduction effectiveness of the optimal delay time was verified through field experiments. The results show that, compared with the original inter-hole delay time of 42 ms, a delay time of 25 ms achieves good vibration reduction, with average reduction rates of 28.3%, 19.4%, and 20.6% in the horizontal radial, horizontal tangential, and vertical directions, respectively. These research findings can serve as a reference for optimizing delay times and controlling blasting vibrations in deep-hole open-pit blasting. Full article

The drilling and blasting method is the mainstream approach for excavating deep-buried tunnels. Nevertheless, a complex static–dynamic coupling environment is formed by the directional high in situ stress and the widely distributed weakly intercalated layers in rock masses, which frequently result in uncontrolled propagation of blasting-induced cracks. In this paper, deep-buried tunnels with weakly intercalated layers are selected as the research subject, and a numerical model for simulating blasting-induced crack evolution is developed using the material point method. After the model’s reliability is verified through single-hole blasting tests, the effects of in situ stress and weakly intercalated layers on the evolution of blasting-induced cracks are investigated using a typical case. The results demonstrate that geostress direction significantly guides and restrains crack propagation, with cracks extending preferentially along the maximum principal stress but being limited in the perpendicular direction. Compared with the zero-confining-pressure condition, the maximum crack length is reduced by more than 80% when an equal biaxial confining pressure of 20 MPa is applied. Weak interlayers attenuate the transmission of blasting energy, and crack propagation at their ends is significantly amplified when the principal in situ stress aligns with the interlayer orientation, leading to over-excavation. In addition, a targeted optimization strategy for blasting parameters was proposed that reduced the particle vibration velocity at the arch shoulder by 49%. Full article

The coal resource-rich areas in Guizhou Province are located at the overlapping junction of the southern part of the third fold and subsidence zones of the Neocathaysian structural system and the Nanling latitudinal structural belt. These areas are characterized by well-developed folds and faults, complex coal seam structures, high in situ stress, and poor air permeability, which lead to low-efficiency conventional gas drainage and failure to achieve the expected results. In terms of enhancing coal seam permeability and improving gas drainage and utilization, research is urgently needed on the permeability enhancement mechanism of deep-hole blasting in outburst-prone coal seams under combined multi-stress action. By analyzing the influence law of coal mass fracture evolution before and after blasting, developing an experimental device for blasting permeability enhancement under combined multi-stress action, and conducting research on the pore variation law of coal mass before and after blasting, it is found that in situ stress is negatively correlated with coal mass pores, while blasting and gas stresses are positively correlated with pores. This study provides a theoretical basis and experimental evidence for permeability enhancement via deep-hole blasting in outburst-prone coal seams and further supports the selection of reasonable parameters for field tests to improve the gas drainage efficiency of outburst-prone coal seams. Full article

Frequent rockbursts in staggered roadways beneath residual coal pillars pose a critical challenge for the slice mining of ultra-thick coal seams. Taking the LW250101-2 of Huating Coal Mine as a case study, this paper systematically reveals the stress evolution laws and rockburst mechanism induced by irregular residual pillars by integrating microseismic (MS) monitoring, moment tensor inversion, and numerical simulation. First, source mechanism inversion analysis elucidated that compressive-shear failure of coal pillars was the dominant rupture mode in five of the eight recorded rockburst events. Second, numerical simulations demonstrate that the width of the left wing and the thickness of the right wing of the “L-shaped” coal pillar structure are the key geometric factors controlling rockburst risk; larger dimensions correlate with more intense stress concentration and higher-energy MS events. Moreover, the stress deflection effect of “L-shaped” coal pillars causes the haulage gateway of the LW250101-2 to remain in a state of stress accumulation, increasing its susceptibility to rockburst. Finally, a synergistic prevention system consisting of deep-hole roof blasting, large-charge coal blasting, and ultra-deep large-diameter boreholes was implemented. Field monitoring confirms that these measures dissipated high-stress concentrations, reduced rockburst frequency to zero and ensured safe mining. Full article

Deep multi-coal seam mining is plagued by intense mining pressure, significant impacts of multi-working face mining on system roadways, and difficult surrounding rock deformation control—these issues severely threaten the safe and normal operation of roadways, creating an urgent need for effective dynamic disaster control technologies. Taking the 131,105 working face of Liuzhuang Mine (burial depth up to 740 m) as an example, this study addresses a critical research gap; existing roof cutting pressure relief technologies mostly focus on shallow/thin-coal-seam mining and fail to tackle secondary dynamic pressure induced by repeated mining in deep multi-coal seams—where the superposition of mining stress, ground stress, and goaf stress severely threatens system roadways. To fill this gap, three novel contributions are made. (1) A hierarchical “upper break and middle cut” deep-hole blasting design is proposed, distinct from single-mode roof cutting in existing studies. It achieves directional roof failure by “upper break” (damaging overlying hard rock) and “middle cut” (creating fissures between goaf and protective coal pillars), blocking stress transmission to roadways. (2) Numerical simulations specifically for deep strata (740 m) optimize key parameters: 25 m as the optimal cutting height and 35° as the optimal cutting angle, quantifying their effects on pressure relief (a gap in existing parameter optimization for deep mining). (3) A rapid sealing scheme combining AB material grouting with high-strength detonator pins is developed, solving the problem of slow hardening and poor sealing in traditional deep-hole processes (e.g., cement-only sealing), enabling blasting within 10 min after sealing. This cut off the integrity of the roof, blocked the pressure transmission of the roof stress to the existing system roadway, and achieved a 43.7% reduction in roadway surrounding rock stress (from 32 MPa to 18 MPa) and a 46.7% reduction in maximum roadway deformation (from the pre-blasting 15 cm to 8 cm). This study provides a reference for similar deep multi-coal seam projects. Field monitoring and numerical simulation results show the following. (1) The maximum deformation of the protected East Third Concentrated main roadway is only 8 cm, fully meeting normal operation requirements. (2) The “upper break and middle cut” technology effectively reduces the mining influence range (from 156 m without roof cutting to 125 m with 25 m roof cutting) and weakens roof stress transfer to roadways. This study verifies the feasibility and effectiveness of deep hole blasting for roof cutting, pressure relief, and roadway protection in deep multi-coal seam mining. It provides direct technical references and engineering application templates for similar projects facing roadway protection and dynamic disaster control challenges, contributing to the safe and efficient mining of deep coal resources. Full article

In order to enable safe pillarless mining in a deep, thick coal seam with a hard roof, an integrated approach combining presplitting roof blasting and a flexible formwork concrete support system was implemented and evaluated via theoretical analysis, numerical simulation, and field trials. The limit-equilibrium analysis indicated a minimum gob-side coal pillar width of approximately 6 m. A pumpable C40 flexible-formwork concrete was developed, achieving its design compressive strength within 28 days, to serve as a roadside support. Field implementation of the presplitting and composite support effectively controlled roadway deformation: total roof–floor convergence was limited to 340 mm (floor heave accounted for 65%), and support loads remained within safe ranges, with no structural failures observed. These results demonstrate that the proposed gob-side entry retaining technique maintains roadway stability without a coal pillar, offering a practical and economic solution for deep coal mines with hard roofs. Full article

Ensuring the dynamic safety of buildings near open-pit mines during blasting is a critical concern for the normal conduct of mining operations. This study investigates the effects of blasting vibrations on brick–concrete structures by using deep-hole blasting tests conducted at the mine site, employing blasting vibration monitoring and numerical simulation techniques. The peak particle velocity and energy distribution characteristics of blasting waves in structural columns and brick walls were analyzed. Furthermore, a three-dimensional numerical model was developed to analyze the response characteristics of buildings to blasting vibrations. Considering the impact of a building’s natural frequency on blasting vibrations, harmonic response was utilized to identify the natural frequencies of different components. The relationship between these frequencies and a building’s natural frequency is discussed. Dangerous frequencies and components were identified. The findings of this study can serve as a theoretical foundation for understanding the damage mechanisms of buildings under blasting waves and for controlling the impact of blasting vibration effects. Full article

To study the optimization of construction parameters and schemes for complex connecting tunnels in extra-long highway tunnels in granite strata, the research team, relying on the construction project of the complex connecting tunnel between the Xiaolongmen Extra-long Highway Tunnel and the ultra-deep shaft, established an on-site monitoring scheme and a refined numerical simulation model. It systematically analyzed the impact of various construction parameters on the construction process of connecting tunnels and the main tunnel, and on this basis, optimized the construction scheme, improving construction efficiency. The research results show that (1) after the excavation of the connecting tunnel, the confining pressure at the top of the working face decreases rapidly, while the confining pressure on both sides increases rapidly; the extreme point of the confining pressure decrease is located at the central point at the top of the excavated working face. (2) For Class III surrounding rock excavated using the full-face blasting method, the maximum influence range of working face excavation on the stratum along the tunneling direction is approximately 4D (where D represents the excavation step). (3) The larger the excavation step of the connecting tunnel, the more obvious the stress concentration phenomenon at the central point of the working face arch crown, and the excavation step should be optimally controlled within the range of 2–3 m. (4) When explosives in the blast hole adopt decoupled charging, the ratio of borehole diameter to charge diameter can be increased to utilize the air gap to buffer the energy generated by the explosion. Full article

In practice, the bending and fracturing of heavy layers is often considered the primary cause of surface damage, leading to significant environmental impacts, whereas heavy layer-type mining-induced earthquakes are frequently overlooked. This study combines theoretical analysis, UDEC numerical simulations, and industrial experiments to investigate the dynamic behavior of heavy layers and the mechanisms through which mining-induced earthquakes trigger surface damage. It aims to demonstrate that heavy layer movement and mining-induced earthquakes cause surface damage and to develop a replicable engineering solution for seismic prevention and subsidence control in heavy layer mining areas. The results reveal that surface damage stems from the synergistic effects of heavy layer fracturing and associated mining-induced earthquakes, where bending subsidence from heavy layer fracturing is the primary driver, and mining-induced earthquakes act as a secondary factor by compressing fragmented rock pores to amplify overlying layer subsidence. Industrial tests at the 7202 working face using deep-hole roof pre-splitting blasting successfully fractured the heavy conglomerate layer, enhanced goaf bulking, and reduced the intensity of layer movement. This intervention significantly decreased the frequency and energy of mining-induced earthquakes, mitigating surface damage. These findings provide a practical framework for the integrated control of mining-induced earthquakes and subsidence in heavy layer environments. Full article

The dynamic response law of the vibration cavity effect in the adjacent large-section rectangular coal roadways induced by deep-hole bench blasting vibrations was deeply revealed, and the prediction accuracy of the PPV in the coal roadway was improved. The vibration equations of the coal roadway were derived based on the stress wave propagation theory and the wave-front momentum conservation theorem. Based on coal roadway vibration monitoring data and numerical simulations, the cavity effect and vibration response characteristics of the coal roadway induced by deep-hole bench blasting under varying blast source distances and relative angle conditions were analyzed. A predictive model for PPV of rectangular coal roadway surrounding rock, incorporating the relative angle as one of the key influencing factors, was developed. The results showed that the presence of cavities and changes in the relative angle enhance the asymmetry of the dynamic response of blasting stress waves near the free surfaces of the surrounding rock on each side of the coal roadway, resulting in significant differences. Moreover, as the blasting distance decreases, the cavity effect tends to promote greater PPV differences on each side of the coal roadway. The prediction model exhibited improved accuracy by about 15.6% compared to the traditional Sadovski equation for the face-blasting side of the coal roadway. It demonstrates better adaptability and predictive capability. This research provides a theoretical basis for the dynamic response of adjacent large-section rectangular coal roadways and for preventing dynamic instability failures in open-pit mining. Full article

A combination of theoretical analysis, numerical simulation and physical model experiments is used to explore the mechanism of pressure relief and roof blasting effects along the gob-side roadway. The stress and displacement along the gob-side roadway before and after blasting were investigated using discrete unit code (UDEC) software. The results demonstrated that blasting can effectively decrease the peak stress of the coal seam along the gob-side roadway and transfer it to the depth. The maximum displacement of the roof of the gob-side roadway, the coal pillar and the solid coal was reduced from 9.5, 10.8 and 4 cm to 6.5, 2 and 3 cm, respectively, after roof blasting. The experimental results showed that the movement of the overburden strata showed obvious regional characteristics after blasting which included the height of the caving zone on the broken side being 3.3 times higher than that observed on the unbroken side, while the height of the fractured zone was 0.52 times higher. The field application of roof blasting was controlled by a drilling method, micro-seismic monitoring and stress monitoring. The results showed good application effects. This research provides valuable insights for managing the stability of gob-side entries. Full article

Ensuring the accurate prediction, prevention, and control of coal bursts in isolated working faces is crucial for ensuring safe mining operations. Coal bursts are typically caused by the accumulation of stress and energy released in coal seams and the overlying strata. This study focuses on the 76 isolated working faces at Shanxi Wuyang Mine, employing a combination of theoretical analysis, numerical simulation, and field monitoring. Through theoretical analysis, the study examines the influence of the spatial structure of the overlying strata on support stress and develops corresponding estimation functions. Additionally, bearing strength calculation formulas under varying confining pressures are derived. Numerical simulations are used to validate the effectiveness of borehole stress relief, while field monitoring further confirms the accuracy of the proposed model, leading to the development of the “overall–local” coal burst prediction method. The results demonstrate that the proposed method effectively assesses coal burst risks and, based on different coal burst types, recommends borehole stress relief and roof deep-hole blasting as primary mitigation strategies. These methods were successfully applied to the 76 isolated working faces at Wuyang Mine, yielding conclusions of overall stability with localized instability. This study provides new insights into coal burst prediction theory and offers practical guidance for preventive engineering in isolated working faces, demonstrating substantial engineering applicability. Full article

In view of the high-level, thick, and hard roof in a mine in Shaanxi, it is difficult for existing technology to solve the problem of frequent rock bursts, which are caused by the direct weakening of the whole underground layer. In this paper, a technology for preventing rock bursts using the long-distance drilling and blasting of a thick and hard roof in a high drilling field is proposed. The authors used theoretical analyses, numerical simulations, and other research methods to analyze the mechanisms of pressure relief and load reduction achieved by this technology, determined its layout parameters and layers, and carried out engineering practices in 2412 working faces in a mine in Shaanxi. The results show that the long-distance drilling and blasting technology can achieve the aim of unloading the pressure drop load by arranging a high-level drilling field to achieve the whole-layer presplitting of the thick and hard roof above the working face. According to the orthogonal test method, when using long-distance drilling and blasting under the condition of a high-level roof, the choice of the blasting layer is the biggest factor affecting the change in overburden subsidence. Using the identification basis of the main control disaster causing the layer of overburden, it was determined that 52~67 m above the coal seam of the 2412 working faces was the blasting layer. According to the periodic weighting interval of the working face and the development radius of the fractures in the blasting surrounding rock, the blast hole spacing was determined to be 30 m. After long-distance drilling and blasting, the frequency and energy of micro seismic events were reduced, the entry deformation was reduced compared with the common roof deep-hole blasting technology, and the pressure relief effect of the long-distance drilling and blasting technology was better. These research conclusions can provide theoretical support for the prevention and control of rock bursts during mining production under similar conditions by reducing the load and the unloading pressure on thick and hard roof layers that are difficult to unload from the source. Full article

The phenomenon of crushing the support of the hard roof of a coal seam occurs occasionally during the coal mining process. However, making the hard roof fall is difficult due to its good integrity and high strength. A vast area of unsupported, suspended roof can easily form in the goaf, inducing the hidden dangers of rock burst and coal and gas outbursts. A deep-hole pre-splitting blasting technique is used to fracture the roof and relieve the pressure exerted by the rigid roof in order to improve the caving of the hard roof and protect the stability of the roadway, ensuring safe and effective operational production of the 1127 (1) working face in Guqiao Coal Mine. By collecting field samples, the mechanical properties of relevant rock formations are ascertained. Combining numerical simulation with theoretical computation, a roof cutting pressure-relief scheme with a roof cutting height of 13.5 m and a roof cutting angle of 20° is selected. This scheme can decrease the peak vertical stress on the roadway roof from 22.01 MPa to 13.63 MPa compared to when roof cutting is not performed. By ensuring the effectiveness of roof cutting for pressure relief, this scheme can optimize the actual construction workload to a minimum. The study’s conclusions provide insightful information and can be used as a guide for future research on related technical topics. Full article

In order to address the issue of limited excavation footage in the drilling and blasting of a water diversion tunnel with a cross-section of approximately 10 m², which is unable to meet the demands of rapid construction, a blasting method combining long and short straight-hole cutting was proposed based on the theories of elastic mechanics, blasting craters, explosive gas and stress waves. A mechanical model was established to elucidate the parameter design method and cavity formation principle of the combined cutting. Numerical simulation and field tests were employed to analyze the rock-breaking process of combined cutting, with a view to comparing the blasting effect differences between the traditional inclined cutting method and the combined cutting method. The research results indicate that during the blasting process with combined long and short straight-hole cutting, the uncharged portion of the deep hole can serve as an empty hole during the subsequent blasting of the shallow hole. The concentration of stress at the wall of the empty hole and the superposition of reflected and incident waves serve to enhance the rock-breaking effect of the shallow hole, with the enhancement being influenced by the diameter of the hole and the distance between it and the empty hole. The preferential detonation of the shallow hole can provide a smaller resistance line and free surface distance for deep hole detonation, creating favorable conditions for rock fragmentation in deep hole blasting, making it easier for the rock in the cutting area to be thrown out and increasing the utilization rate of the blast holes. The shape of the formed cavity is a long strip-shaped cube, with its volume being influenced by the spacing between each group of deep and shallow holes. The rock mass damage is most severe in the vertical direction, while the rock mass damage at the center of the upper and lower edges is relatively weaker. In order to optimize the utilization of blasting energy, it is essential to select an appropriate spacing between each group of blast holes. In comparison to the utilization of traditional inclined cuts, the implementation of combined long and short holes has been observed to result in a greater extent of blasting footage and relatively lower explosive consumption. These research findings provide a reference point for the rapid and efficient construction of small-section tunnel engineering, as well as the design of straight-hole cut blasting with reduced consumption. Full article