Explosive Blasting Research Articles

Study on ground vibration characteristics induced by liquid CO2 blasting technique in bench excavation

The liquid CO2 phase change fracturing technique has been widely applied in rock engineering for a long time. However, the ground vibration characteristics in bench excavation have not been well demonstrated. In this study, the particle velocities, main frequencies, and displacements of rock induced by liquid CO2 blasting are investigated based on field tests and numerical simulations. Firstly, three field tests of bench excavation using DM83-1.4 type liquid CO2 storage tube were implemented in a specific highway slope project, in which the TC-4850 N vibration monitors were installed at horizontal distances of 4.2 m, 10.6 m, 20.3 m and 32.2 m from the detonation source to detect the rock vibration velocity and frequency. Subsequently, by employing the dynamic finite element program LS-DYNA, a three-dimensional numerical model was established, and then the particle velocities and displacements were analyzed and discussed. The research results indicate that the peak particle velocity (PPV) decays with distance in an exponential pattern, that is, the PPV decays rapidly in the near zone of the blasting source, and it decays more slowly in the far zone. At the position of 20.3 m in the horizontal distance and 15.8 m in elevation, an elevation amplification effect appears with an amplification factor of 1.12. Moreover, the vibration frequency generated by the liquid CO2 phase change fracturing technique is in the range of 0-80 Hz, which is much smaller than that induced by explosive blasting. The main frequency in the near-field of the blasting source is dominated by the radial frequency (Fr), while the vertical frequency (Fv) is dominant in the far-field. The attenuation law of displacement is generally consistent with the vibration velocity, and the difference between radial and tangential displacement increases gradually with distance.

An Innovative Directional Blasting Technique for Coal Mine Exploration and Engineering Testing

Blasting is a key method of controlling large-area hanging roofs and strong mine pressure in coal mine. The crack propagation direction after blasting has a decisive influence on control effect, and the existing blasting techniques have poor directionality, making it difficult to form a continuous, precise crack. A compound blasting technique (CBT) was proposed; this could achieve a precision, directional crack by using the combination of perforating bullet and explosives, with perforating bullet detonation first and then explosive blasting. The principle of directional crack formation by CBT was studied and a complete set of equipment was introduced, and the effect of continuous directional crack forming was studied experimentally. A CBT test was conducted in Tashan coal mine (Datong mining area): the results showed that a single crack surface was formed in the borehole after the compound blasting, which indicated the desired blasting effect. The CBT improves the accuracy and controllability of fractures and realizes precise directional control of rock strata.

Investigation on the key techniques and application of the new-generation automatically formed roadway without coal pillars by roof cutting

The first-generation automatically formed roadway without coal pillars by roof cutting (AFRCPRC) technology has achieved significant technical and economic benefits in the period 2009–2019. However, it adopts shaped charge blasting for roof cutting, which is not only unsafe but also troublesome with respect to explosive approval. Besides, the installation procedure of macro-negative Poisson's ratio (NPR) anchor cable is rather complicated. To overcome these drawbacks, the second-generation AFRCPRC technology was developed in 2020. It employs a non-explosive blasting method, i.e., instantaneous expander, forming a single fracture (IESF), and thus its safety is greatly improved. In addition, micro-NPR anchor cables, which are easy to operate and have the characteristics of large elongation, high strength, strong impact resistance and no obvious necking phenomenon, are used for roadway support. In this paper, the basic principles, key techniques and main processes of the second-generation AFRCPRC technology are introduced, and experiments that were conducted in a coal mine are described. The experimental results show that IESF has excellent directional roof-cutting ability which can replace the explosive energy-focusing blasting, and the micro-NPR anchor cable boasts superior supporting performance which can effectively control roof deformation. The automatically formed roadway deforms insignificantly and satisfies the requirement of the next working face, illustrating the success of the second-generation AFRCPRC technology. Compared with the first-generation AFRCPRC technology, the remarkably improved second-generation one will have greater application potential in the mining field.

Study on the Stress Field and Crack Propagation of Coal Mass Induced by High-Pressure Air Blasting

High-pressure air blasting (HPAB) is one type of physical blasting technique that enhances the extraction rate of coalbed methane by impacting the coal mass with high-pressure gas to create cracks within it. First, based on the physical and mechanical parameters of the simulated coal rock mass, the RHT constitutive model of the coal rock mass was established, and its parameters were determined. Then, the laws of crack propagation and stress wave decay in coal induced by high-pressure air blasting were revealed by comparing the effect with that of equivalent explosive blasting. Next, the HPAB experiment was simulated to explore the coal crack propagation law under in-situ stress conditions. Finally, the HPAB experiment was carried out and the results of this experiment were compared with the numerical simulation results. The results indicate that the crack propagation induced by high-pressure air blasting is considered as two major stages, i.e., the crack initiation and crack propagation stage induced by the stress wave and the crack stable propagation stage induced by the duration high-pressure gas. In the case of equal energy, the peak stress wave of high-pressure gas is smaller, decays more slowly and has a longer action time, compared to explosive blasting. Therefore, the number of initial random cracks in coal mass induced by high-pressure air blasting is less, and the range of crack propagation induced by high-pressure air blasting is larger. When λ = 0 (λ is the ratio of the horizontal in-situ stress to the vertical in-situ stress), the in-situ stress in the coal seam can promote the propagation of vertical cracks but inhibit the propagation of horizontal cracks. When λ = 0.5 and 1, the in-situ stress inhibits the propagation of both horizontal and vertical cracks.

Liquid CO2 Phase-Transition Rock Fracturing: A Novel Technology for Safe Rock Excavation

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.

An improved outer pipe method for expansive pressure measurement of static cracking agents

Static cracking agent (SCA) is actively investigated as an alternative to explosive blasting for rock breakage due to its immense expansion property. SCA can eliminate the negative effects of shock, noise and harmful gases encountered in explosive blasting processes. Accurate measurement and deep understanding of the expansive properties of SCAs are important in their industrial application. An improved outer pipe method (OPM), termed the upper end surface method (UESM), is proposed in this paper to overcome the shortcomings of the OPM in the expansive pressure measurement of SCAs. Numerical simulation is used to proof the concept and a mathematical model established to relate the internal pressure and the radial strains at different positions in the upper end surface method test equipment. The new equipment is calibrated using oil pressure and strain measurements. The calibrated equipment is then used to measure the expansion pressure of SCA at three different water contents to proof its potential. The differences in the measurements with OPM and UESM at three different moisture contents are less than 4%. The experimental results confirm the accuracy and applicability of the more user friendly and less expensive UESM in the measurement of the expansive pressures of SCAs.

Numerical simulation of rock fractures induced by CO2 blasting

As a safe and environment-friendly rock breaking technique, CO2 blasting has been paid more and more attention. Most of previous researches estimate the radius of rock damage induced by CO2 blasting according to explosive equivalent method, with less attention to the mechanism. In fact, compared with explosive blasting, the peak pressure and loading rate of CO2 blasting are several orders of magnitude smaller. In order to further understand the mechanism, the commercial software LS-DYNA and Riedel-Hiermaier-Thoma material model have been used to simulate the rock fractures induced by CO2 blasting. First of all, according to the previous researches, the ranges of the rise time and corresponding peak pressure of CO2 blasting are estimated. Then, influences of the key parameters in blasting, viz., loading rate, in-situ stress and free face, on fracture patterns are explored. In the present study, the fracture patterns of CO2 blasting are successfully simulated, and some of the well-known phenomena observed by other researchers can be reproduced. The numerical simulation in the present study has the potential to be applied in practical CO2 blasting.

Study on Changes in Wave Velocity in Surrounding Tunnel Rock under Different High In-situ Stresses

Studies have indicated that in the tunnel’s surrounding rock, high in-situ stress influences the wave velocity changes. Under different ground stresses, an underground model system is used to study the propagation characteristics of the blasting seismic wave velocity. The electric spark was used to recreate explosive blasting by employing a model loading system to simulate gradient loading under high in-situ stress in the tunnel. The DH5983 dynamic signal analytical system was used to collect the vibration acceleration and calculate the average velocity. The average radial and axial wave velocities gradually increased with increasing in-situ stress, and the increase in the average radial wave velocity was greater than the axial wave velocity, according to the test results. The growth rate of the average wave velocity gradually slowed down under various high in-situ stressors, with that in the low in-situ stress stage being greater than in the high in-situ stress stage. A logarithmic growth trend is seen when the wave velocity gradually becomes constant. The average decay growth rate of the radial wave velocity was larger than the rate of axial velocity, which was approximately 1.5 times.

Investigating the mechanism of rock fracturing induced by high-pressure gas blasting with a hybrid continuum-discontinuum method

To study the rock-breaking mechanism resulting from high-pressure gas blasting, a hybrid continuum-discontinuum method considering the actual breakage of rocks was presented in this study. The mechanical parameters were calibrated against the uniaxial compression test and Brazilian disc test, and the capabilities of simulating blast-induced fractures were verified by laboratory tests. After that, the differences in rock-breaking mechanism between explosive blasting and high-pressure gas blasting were compared from the perspectives of peak pressure and loading rate. The results indicated that the crack patterns, fracture mode and vibration attenuation induced by high-pressure gas blasting were significantly different from that of explosive blasting: (a) no crushing zone and fewer radial cracks were formed in high-pressure gas blasting and the spalling cracks were absent near the free face in high-pressure gas blasting; (b) the difference of rock fracture mode in high-pressure gas blasting and explosive blasting indicated that the tensile fracturing was the dominant fracture mode in high pressure gas blasting which is different from the catastrophic fragments due to compressive-sheared fracturing surrounding the borehole in explosive blasting; (c) the intensity and attenuation factors of peak particle velocity both increased with the increase of peak pressure or loading rate, which indicated that the peak particle velocity induced by explosive blasting results in more intense and faster attenuated vibration disasters than that of high-pressure gas blasting.

Numerical Simulation Study on the Influence of Mine Earthquake on the Bolt Stress

Mine earthquake, as an underground disaster that occurs frequently, has a great impact on coal mine roadway and support. The stability analysis of the bolt support in roadway under different mine earthquake magnitudes is a key issue to be solved urgently in mining fields. This paper attempted to simulate the occurrence state of mine earthquake with explosive blasting process and verified it with actual coal mine microseismic monitoring data. ANSYS/LSDYNA software was used to analyze the impact of magnitude and location of mine earthquake hypocenter on the stability of bolt support and the dynamic stress characteristics of bolt. The results showed that with the increase in source energy of mine earthquake, the damage location of bolt mainly appears in the front of bolt and the loading position has no obvious change, but there is stress wave superposition effect, which deepens the damage of bolt. The bolts in the middle of the lane and the middle of the roof are greatly affected, so the support strength should be strengthened in these places. In addition, this paper compared the safety factor of bolt and the supporting effect of different schemes from three aspects such as roof subsidence, axial stress of bolt, and safety factor of bolt and then put forward a more economical and effective supporting scheme.

Liquid CO2 Phase Change Fracturing and Vibration Monitoring in Roadbed Slope Excavation

In order to analyze the vibration impact of carbon dioxide fracturing tube blasting red sandstone, combined with the engineering conditions and surrounding environment of Anqing High-tech Zone, the rock-breaking blasting plan is carefully designed. The fracturing tube is arranged in two rows, the first row has 23 holes with a spacing of 1.5m, and the second batch of holes has 22 holes, which are arranged in a quincunx pattern with a distance of ‘1.3m between the front and rear rows. And design the corresponding vibration signal monitoring test to study the crack propagation caused by blasting, the attenuation law of vibration and its frequency spectrum distribution. The results show that after blasting, there is a relatively smooth crack in the plane area of the fracture zone 7m away from the critical surface. The width of the crack is between 20-40cm. The vibration velocity of the measuring point decays rapidly with the increase of the vibration source distance, and the vibration velocity decay curves in the X and Y directions are basically the same. Spectrum analysis shows that the main frequency band of each sub-velocity is generally below 100Hz, and the main vibration frequencies in the X and Y directions are concentrated in 30∼60Hz. The main vibration frequency band of the rock-breaking blasting vibration signal has little correlation with the direction and propagation distance of the vibration signal. And compared with the analysis of emulsion explosives, it is found that the particle vibration speed caused by the emulsion explosive rock-breaking blasting is much greater than that of the liquid CO2 fracturing tube rock-breaking blasting, indicating that the use of liquid carbon dioxide to break the rock can effectively reduce the vibration generated by blasting.

Research on Crushing Concrete Members by High-Voltage Pulse Discharge Technology

High-voltage pulse discharge (HVPD) is an energy-saving, efficient, and green technique, which has broad prospects in concrete crushing. The finite element models of the concrete beam, slab, and column segments were established with ANSYS/LS-DYNA finite element software. Based on the principle of equal impact pressure, the shock wave generated by the fuse explosion caused by HVPD of 50 kJ is equivalent to the impact load of explosive blasting, and the stress of concrete beam segment was analyzed. The finite element models of the concrete beam sections were established to investigate the influence of diameter and spacing of the holes on the crushing effect of concrete beam segments. The width × height of each beam segment is 400 mm × 800 mm, and there are six types of beam segment length: 600 mm, 700 mm, 800 mm, 900 mm, 1000 mm, and 1100 mm. Two holes are drilled vertically on the surface of the width × length of each beam segment. The spacing of holes corresponding to beam segments of each length type is 200 mm, 300 mm, 400 mm, 500 mm, 600 mm, and 700 mm, respectively. The hole depth of each beam segment is 650 mm, and there are three types of aperture: 30 mm, 50 mm, and 70 mm. The analysis results show that the crushing effect of concrete beam segments increases with the increase of aperture and the decrease of hole spacing. According to the crushing effect of the beam segments, the aperture of 50 mm, the spacing of 400 mm, and the hole end (edge) spacing of 250 mm were determined as the optimal hole layout scheme. The finite element models of concrete slabs and columns were established. The square concrete slab thickness is 140 mm and side length is 700 mm, 800 mm, and 900 mm, respectively. Double-row holes were arranged in the slabs and the aperture is 50 mm and the hole spacing is 200 mm, 300 mm, and 400 mm, respectively. The section sizes of concrete columns are 500 mm × 500 mm, 600 mm × 600 mm, and 700 mm × 700 mm, respectively, and the aperture is 50 mm and the hole distance is 400 mm. According to the results of analysis, the optimal hole distribution scheme of concrete slab and column is chosen as the aperture of 50 mm and hole distance of 400 mm. The principle of the layout of multirow holes is that the spacing of row is not more than 400 mm, and the margin is not more than 250 mm.

Experimental Study on Blasting Energy Distribution and Utilization Efficiency Using Water Jet Test

The blasting stress wave and blasting gas generated by explosive blasting are the two main motive powers of rock fragmentation. An experimental method based on water jet test is used to study the energy distribution ratio of blasting stress wave and blasting gas; the utilization efficiency of blasting energy under different borehole constraint conditions is also analyzed. It proves that the blasting stress wave does not cause the water jet, and the blasting gas is the only power of the water column jet. The results show that the energy of the blasting gas and blasting stress wave respectively account for about 64% and 36% of the total energy generated by the explosion of lead azide. The utilization efficiency of the blasting gas energy under strong, medium, and weak constraint conditions is 100%, 80%, and 52%, respectively. The borehole constraint condition is crucial for the effective utilization of blasting energy.

Mechanical behaviour of rock subjected to uniaxial compression at intermediate strain rate

ABSTRACT This paper presents a study of the mechanical behaviour of rock under dynamic compression loading at intermediate strain rate (ISR). A series of laboratory tests were carried out to obtain dynamic uniaxial compressive strength by using a non-explosive powder reaction loading apparatus that was able to generate loading in the ISR range. It was found that the strength of granite and sandstone specimens increases at the ISR range. The results were discussed with a comparison with other findings from multiple references. In general, strength increases linearly at the lower rates and rises significantly at higher rates. Within the ISR range, the tendency is not consistent. Further understanding of rock behaviour within the ISR range needs to be extensively explored. This paper might be useful to understand phenomena involving a dynamic process such as mechanical excavation in which rock experiences a loading lower than high strain rate, i.e., explosive blasting, and higher than static loading.

An experimental study of a novel liquid carbon dioxide rock-breaking technology

Safely and high-efficiently breaking rock is of practical significance. In some engineering, explosive blasting may be restricted for its side effects. Traditional non-explosive methods like demolition agent and rock breaking machine are generally time-consuming. Therefore, this study proposes a novel liquid carbon dioxide rock-breaking technology and designs the relative device. The effectiveness, safety and high-efficiency of the proposed technology are investigated by shock pressure test, vibration site test and field rock breaking experiment. The experimental results show that the duration of the monitoring shock pressure is around 1500 μs. The shock pressure signal of liquid carbon dioxide tube breaking in free condition contains four stages, namely, increasing exponentially, decreasing oscillatory, stabilization, and negative pressure stage. As pressure sensor is set at 850 mm from the test tube radially, the shock pressure monitored increases to the maximum value of 115.7 kPa within 6 μs. During the liquid carbon dioxide rock breaking, the vertical component of the peak particle velocity of vibration is 173 mm/s, 85 mm/s and 35 mm/s along distance at 1.5 m, 2.5 m and 3.5 m from the tube, respectively. The Fourier power spectra results show that about 85% energy distributes at 6–60 Hz. The vibration caused by the novel technology can meet the requirement of mainstream blasting safety criteria better than that of explosive blasting. Finally, the technology is successfully applied in rock excavation at a metro station construction site. The proposed liquid carbon dioxide rock-breaking technology is preliminarily demonstrated to be safer than explosive blasting and more efficient than traditional non-explosive techniques.

Positive Phase Pressure Function and Pressure Attenuation Characteristic of a Liquid Carbon Dioxide Blasting System

As environmental requirements become more stringent, the liquid carbon dioxide blasting system is one of the non-explosive blasting technologies that, with low tensile stress energy, will replace the chemical explosive blasting technology, and the impact pressure characteristic of high-pressure fluid is a crucial factor in the process of rock breaking. To further investigate the impact and pressure attenuation characteristics of high-pressure fluid during the phase transition of liquid carbon dioxide blasting system, the pressure curves of high-pressure fluid in liquid carbon dioxide blasting systems at different distances were measured in the laboratory. Based on the mechanism analysis of phase transition kinetics, the initial jet velocity of the four experiments was calculated, and the rationality of results was verified by the Bernoulli equation. The general expression of the positive phase pressure–time function was proposed, and the idealized impact pressure curve can be divided into five stages. The impact pressure field of the liquid carbon dioxide blasting system can be divided into three areas at different distances: the explosive jet impact zone, the jet edge zone and the shock wave action zone, and the pressure–contrast distance fitting equation of the liquid carbon dioxide blasting system were obtained.

Технологические способы ведения взрывных работ, позволяющие безопасно управлять действием взрыва в массиве горных пород

Purpose. The work is devoted to improving the efficiency and safety of the escarpous blasting of rocks by borehole charges of explosives of a new design at iron ore quarries. In the thesis, the features of the process of explosive destruction of rocks by well charges of various designs are investigated. The dependences of their dynamics of explosive destruction on the physicomechanical properties of rocks are established, and the relationship between the distribution of energy of destruction in the medium and the magnitude of the specific impulse of the explosion is determined. Metodology. The obtained regularities of the impulse effect of an explosion associated with the overall energy balance imparted to a destructible medium can serve as a scale for evaluating the effectiveness of the action of well charges exploded simultaneously or through the definition of deceleration. Based on the obtained theoretical and laboratory results, a new design of a downhole charge of explosives with an air cavity in the bottom of the well has been developed. Findings. A feature of this design of the borehole charge is the concentration of the explosion energy in the bottom of the well. The optimal parameters of the air cavity and the location of the initiator relative to it in the technology of blasting have been established. Originality of the work lies in the fact that the conducted industrial tests of a new design of a borehole charge with an air cavity in the bottom part of the well showed its high efficiency. Practical value lies in achieving a reduced specific consumption of explosives. This technological process ensures uniform crushing of the blasted rock mass over the entire height of the ledge and high-quality development of the bottom of the ledge, which opens up real opportunities for the elimination of the re-drilling of the well at the inferior explosive blasting of rocks.

Research on the Energy Characteristics of Battlefield Blasting Noise Based on Wavelet Packet

When the acoustic fuse of smart landmines tries to detect and recognize a ground vehicle target, it is usually affected by gun shooting, explosive blasting or other similar noises on the actual battlefield. To improve the target recognition of smart landmines, it would be necessary to study the characteristics of these acoustic signals. Using sample data of the shooting noise of a certain type of rifle, the blasting noise of TNT, and the acoustic signals of a certain type of WAV, the energy characteristics of these noise signals are compared and analyzed. The result shows that the wavelet-packet energy method is effective in describing the characteristics of these acoustic signals with distinct intertype variations, and the frequency at the peak energy value can serve as a signature parameter for recognizing battlefield blasting noise signals from vehicle target signals.

Improved analysis of ground vibrations produced by man-made sources

Man-made sources of ground vibration must be carefully monitored in urban areas in order to ensure that structural damage and discomfort to residents is prevented or minimised. The research presented in this paper provides a comparative evaluation of various methods used to analyse a series of tri-axial ground vibration measurements generated by rail, road, and explosive blasting. The first part of the study is focused on comparing various techniques to estimate the dominant frequency, including time-frequency analysis. The comparative evaluation of the various methods to estimate the dominant frequency revealed that, depending on the method used, there can be significant variation in the estimates obtained. A new and improved analysis approach using the continuous wavelet transform was also presented, using the time-frequency distribution to estimate the localised dominant frequency and peak particle velocity. The technique can be used to accurately identify the level and frequency content of a ground vibration signal as it varies with time, and identify the number of times the threshold limits of damage are exceeded.

Rock-breaking mechanism and experimental analysis of confined blasting of borehole surrounding rock

The rock-breaking mechanism and effect of confined blasting were analysed by blasting and impact dynamic mechanics, fluid dynamic mechanics, fracture mechanics as well as blasting experiment. The results showed that the fracturing of surrounding rock in confined blasting condition is the result of coaction of rock pre-cracking by shock wave and stress wave and the continuing expanding crack-enhancement of confined medium, and the model of crack development of borehole surrounding rock in confined blasting condition was established. This study acquired the damage range of surrounding rock under the action of shock wave and stress wave, as well as the crack development characteristics of surrounding rock after the wedge-in confined medium into the crack space. Deep-hole confined blasting experiment on large rock showed that the high-efficient utilisation of in-hole explosive was achieved and the safety of rock blasting operation was ensured. Safe static rock-breaking under the action of high-efficient explosive blasting was achieved as well as the unification of super dynamic load of explosive blasting and static rock-breaking of water medium.