Search Results (17)

Due to the difficulty of creating directional fractures efficiently and accurately with existing non-explosive rock-breaking methods, a directional fracturing technique utilizing a coal-based solid waste expansive agent, termed the instantaneous expansion with a single fracture (IESF), has been developed. IESF can generate high-pressure gases within 0.05–0.5 s and utilize gas pressure to achieve directional rock fragmentation. The rock-breaking mechanisms under double-borehole conditions of conventional blasting (CB), shaped charge blasting (SCB), and IESF were studied by theoretical analysis, numerical simulation, and in situ test. The gas pressure distribution within directional fractures of IESF was determined, and the crack propagation criterion between double-borehole was established. Numerical simulation results indicated that the stress distribution in CB was random. SCB exhibited tensile stress of −10.89 MPa in the inter-borehole region and −8.33 MPa on the outer-borehole region, while IESF generated −14.47 MPa and −12.62 MPa in the corresponding regions, demonstrating that stresses generated between adjacent boreholes can be superimposed in the inter-hole region. In CB, strain was concentrated along main fractures. SCB exhibited strains of 7 mm and 8 mm in the shaped charge direction, while non-shaped charge directions showed a strain of 1.5 mm. For IESF, strain in the shaped charge direction measured 6 mm, compared to 1 mm in non-shaped charge directions, resulting in superior directional fracture control. In situ test results from Donglin Coal Mine demonstrated that IESF can form superior directional rock-breaking efficacy compared to both CB and SCB, with the average crack rates of 95.5% by IESF higher than 85.0% by SCB. This technique provides a non-explosive method that realizes precise control of the direction of cracks while avoiding the high-risk and high-disturbance problems of explosives blasting. Full article

When the coal mining face enters the final stage of mining, the roadway faces the superimposed influence of surrounding rock stress redistribution and roof rotary moment. As affected by the strong disturbance in the coal mining process, the roof plate of the roadway has undergone serious deformation, which seriously affects the stability of the roadway. Taking the 108 working face of the Jinjitan coal mine as the engineering background, a comprehensive study was conducted on the control of the perimeter rock in the retracement of a tunnel in a heavy coal seam with a large mining height. By analyzing the physical properties of the enclosing rock of the retreated roadway, and using theoretical analysis, numerical simulation, on-site monitoring, and other methods, the characteristics of the peripheral rock’s movement relationship and mineral pressure manifestation in the final mining stage of the large-height working face have been studied. The structural mechanics model was established, and in the case where the support cannot be solved just by strengthening the support, the design scheme of “blasting roof break + constant resistance anchor cable support” was innovatively tried. FLAC3D simulation results show that the stress release of the surrounding rock is more adequate when the height of roof cutting is 20 m. The stress of the surrounding rock near the roadway is reduced by 30~40%, and the stress state is reasonable. The constant resistance and large deformation anchors can absorb the deformation energy of the rock body, maintain constant working resistance and stable deformation, and have good rock stability control, which is conducive to the stability of the roadway. Full article

Blasting excavation of rock masses under high in-situ stress often encounters difficulties in rock fragmentation and a high boulder rate. To gain a deeper understanding of this issue, the stress distribution of rock masses under dynamic and static loads was first studied through theoretical analysis. Then, the ANSYS/LS-DYNA software was employed to simulate the blasting crack propagation in rock masses under various in-situ stress conditions. The fractal dimension was introduced to quantitatively analyze the influence of in-situ stress on the distribution of blasting cracks. The results indicate that in-situ stress primarily affects crack propagation in the later stages of the explosion, while crack initiation and propagation in the early stages are mainly driven by the explosion load. In-situ stress significantly influences the damage area and fractal dimension of cut blasting. Under hydrostatic in-situ stress, as the in-situ stress increases, the damage area and fractal dimension of blasting cracks gradually decrease. Under non-hydrostatic in-situ stress, when the principal stress difference is small, in-situ stress promotes the damage area and fractal dimension of the surrounding rock, enhancing rock fragmentation. However, when the principal stress difference is large, in-situ stress inhibits the damage area and fractal dimension of the surrounding rock, hindering effective rock breaking. Full article

Current tunnel blasting hole layouts are mostly designed based on a two-dimensional plane at the workface, without considering the distribution of the minimum burden at the bottom of the blast holes. This results in a significant number of residual holes at the bottom, reducing excavation efficiency. To address this issue, this study proposes an easer hole design method based on the principle of minimum burden at the hole bottom. The method involved the arithmetic distribution for the minimum burden at the bottom of easer holes, using the difficulty of rock breaking as the design principle for hole positioning. Through theoretical analysis, numerical simulation, and field tests, it is proposed that the minimum burden at the bottom of the holes should increase progressively with the initiation sequence, and the relationship between burden distribution and blasting effect was investigated. This study indicates that using the new design principle achieves better blasting results than the model with an evenly distributed burden. When the control ratio of the minimum burden at the bottom of each row of easer holes is 1.3, an average residual hole depth of 36.7 cm and a maximum damage volume of 4.638 m³ can be achieved, yielding the best overall blasting effect. The application of this blasting scheme in the field significantly improved the residual hole problem, reducing the average residual hole depth to 39.5 cm, which is a 43.4% reduction compared to the previous scheme. Additionally, the utilization rate of blast holes in the new scheme increased to 91.3%, an improvement of 11.0% over the previous scheme. This study provides new insights and methods for tunnel blasting hole layout design, offering significant engineering application value. Full article

Stemming has a major impact on energy containment inside a blasting hole and is essential for increasing the efficacy of explosive charges in rock blasting. This method is essential in many fields, including road project development, mining, tunneling, and underground construction. By fortifying the confinement of the energy generated by a loaded explosive charge in a blasting hole, stemming increases the fragmentation of rock. Improper or missing stemming leads to the gas escaping in advance from blast holes, resulting not only in the wastage of explosive energy and poor fragmentation but also in environmental problems such as ground vibration, noise, flying rocks, back breaks, and air blasts. When the process to keep gases inside blast holes is not performed correctly or is skipped, it can waste explosive energy and produce poorly fragmented rocks. This also causes problems like high ground vibrations, loud noise, flying rocks, cracks behind the blast area, and strong air shocks. In this study, a shock chamber blasting experiment and numerical analysis were conducted to evaluate the pressure confinement effect of stemming material and plug devices in a blast hole. The resulting stemming effect was compared with that of a shear-thickening fluid (STF)-based stemming material currently under development and sand, which is a commonly used blast stemming material. To evaluate the enhancement of the confinement effect inside the pressurized blast hole, three types of stemming plugs were adopted. The blasting experiment and numerical simulation results revealed that the STF-based stemming materials were superior to conventional stemming materials. In addition, the STF-based stemming and plug system can prevent detonation gas from prematurely overflowing the borehole and effectively prolong the action time and scope of the detonation gas in the borehole. Full article

Blasting is a cost-efficient and effective technique that utilizes explosive chemical energy to generate the necessary pressure for rock fragmentation in surface mines. However, a significant portion of this energy is dissipated in undesirable outcomes such as flyrock, ground vibration, back-break, etc. Among these, flyrock poses the gravest threat to structures, humans, and equipment. Consequently, the precise estimation of flyrock has garnered substantial attention as a prominent research domain. This research introduces an innovative approach for demarcating the hazardous zone for bench blasting through simulation of flyrock trajectories with probable launch conditions. To accomplish this, production blasts at five distinct surface mines in India were monitored using a high-speed video camera and data related to blast design and flyrock launch circumstances including the launch velocity (v_f) were gathered by conducting motion analysis. The dataset was then used to develop ten Bayesian optimized machine learning regression models for predicting v_f. Among all the models, the Extremely Randomized Trees Regression model (ERTR-BO) demonstrated the best predictive accuracy. Moreover, Shapely Additive Explanation (SHAP) analysis of the ERTR-BO model unveiled bulk density as the most influential input feature in predicting v_f, followed by other features. To apply the model in a real-world setting, a user interface was developed to aid in flyrock trajectory simulation during bench blast designing. Full article

Previously conducted studies have established that the rationality of the parameters of medium-deep hole blasting is one of the main factors affecting the blasting effect. To solve the problem of the parameter design and optimization design of medium-deep hole blasting in underground mines, a method of parameter design and the optimization of medium-deep hole blasting based on the blasting crater tests and numerical simulation analyses has been proposed in this study. Based on the background of deep underground mining in Gaofeng Mine, a two-hole blasting model has been established, and the blasting parameters are simulated and analyzed by the damage stress variation of the two-hole model. During the study, the initial values of blasting parameters were first obtained from the field blasting crater test, then the blasting parameters were optimized and analyzed by LS-DYNA software, and finally, the optimization scheme was demonstrated by the corresponding blasting test. The results of the field test showed that the design method of integrated blast crater test and numerical simulation analysis can effectively optimize the design of medium-deep hole blasting parameters and improve the blasting effect to a large extent. This study also provides an effective design system for the design of deep hole blasting parameters in similar mines. Full article

Blasting is essential for breaking hard rock in opencast mines and tunneling projects. It creates an adverse impact on flyrock. Thus, it is essential to forecast flyrock to minimize the environmental effects. The objective of this study is to forecast/estimate the amount of flyrock produced during blasting by applying three creative composite intelligent models: equilibrium optimizer-coupled extreme learning machine (EO-ELM), particle swarm optimization-based extreme learning machine (PSO-ELM), and particle swarm optimization-artificial neural network (PSO-ANN). To obtain a successful conclusion, we considered 114 blasting data parameters consisting of eight inputs (hole diameter, burden, stemming length, rock density, charge-per-meter, powder factor (PF), blastability index (BI), and weathering index), and one output parameter (flyrock distance). We then compared the results of different models using seven different performance indices. Every predictive model accomplished the results comparable with the measured values of flyrock. To show the effectiveness of the developed EO-ELM, the result from each model run 10-times is compared. The average result shows that the EO-ELM model in testing (R2 = 0.97, RMSE = 32.14, MAE = 19.78, MAPE = 20.37, NSE = 0.93, VAF = 93.97, A20 = 0.57) achieved a better performance as compared to the PSO-ANN model (R2 = 0.87, RMSE = 64.44, MAE = 36.02, MAPE = 29.96, NSE = 0.72, VAF = 74.72, A20 = 0.33) and PSO-ELM model (R2 = 0.88, RMSE = 48.55, MAE = 26.97, MAPE = 26.71, NSE = 0.84, VAF = 84.84, A20 = 0.51). Further, a non-parametric test is performed to assess the performance of these three models developed. It shows that the EO-ELM performed better in the prediction of flyrock compared to PSO-ELM and PSO-ANN. We did sensitivity analysis by introducing a new parameter, WI. Input parameters, PF and BI, showed the highest sensitivity with 0.98 each. Full article

The long and large-diameter uncharged hole-boring (LLB) method is a cut-blasting method used to reduce vibration induced by blasting. This method typically involves creating an uncharged hole with a 382 mm diameter and drilling 50 m in the tunnel excavation direction at a time. This method is reported to provide relatively good vibration reduction and with high blasting efficiency through short hole blasting compared to traditional cut methods. In this study, an advanced LLB method incorporating deck charge blasting was investigated to improve the blasting efficiency during long hole blasting. Numerical analysis was performed via ANSYS LS-DYNA to investigate the effectiveness of the deck charge technique. In the original LLB method, explosives were used to break the rocks more finely, and the fragmented rocks were concen trated at the end of the blast holes. On the contrary, the modified LLB, in which two-part explosives were loaded into the blast holes, is expected to push the fragmented rocks to the tunnel face more effectively than the original LLB method. Therefore, it is expected that the proposed LLB method combined with a deck charge technique can achieve superior blasting efficiency. Full article

Standard hydraulic breaking hammers are widely used for crushing oversized blasted materials and concrete structures demolition in industry. These hammers, installed in on-surface working excavators or stationary manipulators at the dumping points of underground conveyors, provide the required limited sizes of bulk materials and enable the safe operation of other equipment (screens, crushers). In parallel, hydraulic hammers have an alternative—fully electric hammers. This paper aims to review existing linear electric motor (LEM) hammers as an energy-saving and eco-friendly solution in industry. Global market analysis is presented with potential branches of LEM hammers. Several aspects for implementation—design optimization, dynamics simulation, machine control, and performance estimation—are considered. Different case studies for LEM-hammer application are given. The preliminary measurements are demonstrated on the electric hammer of Lekatech Company, which is intended for the mining industry and construction demolition. Experiments showed that depending on the impact frequency, type of rock, and shape of the crushing tool, the time to fracture varies significantly. Optimal parameters exist for every case, for which adjusting requires online hammer control. Full article

The deformation control of roadways surrounded by rock in the fully mechanized amplification sections of extra-thick coal seams is problematic. To analyze the failure and failure characteristics of a support frame, as well as the deformation and failure processes of the surrounding rock, through theoretical analysis and industrial tests, the deformation and support conditions of a return airway of a fully mechanized caving face in an extra-thick coal seam in the Yangchangwan Coal Mine, in the Ningdong mining, area were examined. Combined with limit equilibrium theory and roadway section size, the width of the coal pillar of the return air roadway at the 130,205 working face was calculated to be 6 m. The layout scheme and implementation parameters of roof blasting pressure relief, coal pillar grouting modification, and bolt (cable) support were designed. Based on the analysis, a “Coal pillar optimization–roof cutting destressing–routing modification–rock bolting” system for surrounding rock control in synergy with the fully enlarged section mining roadway in the extra-thick coal seam was proposed, and the deformation of the surrounding rock was monitored, along with the stress of the support body and the grouting effect on the site. Field experiments show that after the implementation of the surrounding rock control in synergy with the roadway, the maximum subsidence of the top plate was 55 mm, the maximum bottom heave of the bottom plate was 55 mm, the maximum values of the upper and lower side drums were 30 mm and 70 mm, respectively, and the breaking rate of the bolt (cable) and the deformation of the surrounding rock of the roadway was reduced by more than 90% and 70%, respectively. The effective performance of the coal pillar grouting was observed as well. Field practice of the roadway surrounding rock control in the synergy method indicated that rock deformation was effectively controlled, and the successful application of this technology was able to provide reliable technical and theoretical support for the Ningdong mining area and mines with similar conditions. Full article

Carbon dioxide phase transition blasting (CO₂-PB) technology is an effective and economical technology used for breaking rocks. The use of CO₂-PB can significantly reduce the vibration damage to surrounding rocks. There is little research on the shockwave generated by the CO₂-PB, and simulation can better show the flow field characteristics. In order to clarify the mechanism of its blasting load process, a theoretical analysis and a numerical model were developed to study the flow-field characteristics and the impact pressure of CO₂-PB. Our results show that the CO₂ absorbs heat from the surrounding environment, producing a significant low-temperature area. The overpressure is significantly lower than the driving gas pressure to the ambient pressure, limiting the maximum over-pressure that can be obtained. When the pressure in CO₂-PB reaches 100 MPa, the shockwave is about 4.25 MPa. As the distance increases, the peak value of the shockwave decays rapidly. As the dimensionless distance increases from 1 to 5, the dimensionless overpressure decreases from 1 to 0.23. Under the same blasting pressure, increasing the filling pressure and increasing the filling volume slightly reduce the initial pressure of the shockwave. In the shock stage, strong compression is formed on the surface of the shockwave, resulting in a higher peak pressure value. Meanwhile, the stable pressure is influenced by the target distance, blasting pressure, and CO₂-PB length. Full article

Explosives are commonly used in the mining industry to extract minerals from hard rock deposits. Therefore, an efficient explosive should ensure that the appropriate blast outcome is achieved, taking into account the desired rock-breaking parameters and the costs of drilling and blasting works. Depending on the type of deposit and follow-up processes, a proper blast result may be characterized by fragmentation, muckpile shape, overbreaks, etc. Industry has struggled to respond to the demand for bulk emulsion explosives with improved energetic parameters, having so far been unable to do so safely, effectively, and cost-efficiently. Methods of improving blasting parameters mainly rely on introducing a variety of additives to the emulsion explosive formulation during production, which creates additional hazards at that stage. Alternative, safe methods of achieving an improved energetic performance of emulsion explosives are, therefore, highly desirable. This paper is focused on one such proposed method as a continuation of previous research works and the performance of a novel bulk emulsion formulation under real mining conditions during the firing of mine faces is described. The tests included density measurements over time, measurements of impact and friction sensitivity, measurements of the detonation velocity in blastholes, determination of brisance via Hess test, and analysis of rock fragmentation. Results were compared with those obtained with a commercially available bulk emulsion explosive, highlighting that the performance improvement achieved by the proposed emulsion modification method is not limited to artificial test conditions, but translates well into actual application conditions. Full article

Precise control of casting velocity and effective throwing kinetic energy conversion efficiency in blasting engineering are challenges. To provide a theoretical basis and reference for the implementation plan and fine construction of the cast blasting project, we study the problems of casting velocity and energy consumption ratio of broken rock under the impact load of explosions in this manuscript. The calculation methods of casting velocity and throwing energy of broken rock under two blasting modes of spherical charge and cylindrical charge are established by using the theory of dimensional analysis and rock breaking by blasting. A large number of model tests are carried out by using high-speed photography. The results indicate that the casting velocity of broken rock after explosive initiation has two evident stages: instantaneous acceleration to a certain value and subsequent fluctuation; the velocity presents an ordinary distribution law with the step height, and the fitting correlation of high-speed photography results is more than 91%. With the minimum burden increasing from 0.12 m to 0.2 m, the energy consumption decreases from 1306.88 J to 747.49 J and the proportion of energy consumption decreases from 14.77% to 8.45%. Full article

In order to determine the applicability of liquid CO₂ phase-transition fracturing technology in rock mass excavations, the principles of CO₂ phase-transition fracturing were analyzed, and field tests of liquid CO₂ phase-transition fracturing were performed. An “Unmanned Aerial Vehicle (UAV) camera shooting + Microstructure Image Processing System (MIPS) analyzing” method was used to acquire the rock mass characteristics. Further, the Hilbert–Huang Transform (HHT) energy analysis principle was adopted to analyze the characteristics of fracturing vibration waves. The experimental results showed that during the process of fracturing, there were both dynamic actions of rock breakage due to excitation stress wave impacts, and quasi-static actions of rock breakage caused by gasification expansion wedges. In semi-infinite spaces, rock-breakage zones can mainly be divided into crushing zones, fracture zones, and vibration zones. At the same time, under ideal fracturing effects and large volumes, the fracturing granularity will be in accordance with the fractal laws. For example, the larger the fractal dimensions, the higher the proportion of small fragments, and vice versa. Moreover, the vibration waves of the liquid CO₂ phase-transition fracturing have short durations, fast attenuation, and fewer high-frequency components. The dominant frequency band of energy will range between 0 and 20 Hz. The liquid CO₂ phase-transition fracturing technology has been observed to overcome the shortcomings of traditional explosive blasting methods and can be applied to a variety of rock types. It is a safe and efficient method for rock-breaking excavations; therefore, the above technology effectively provides a new method for the follow-up of similar engineering practices. Full article