In order to successfully demolish two brick chimneys and two reinforced concrete chimneys located in the same plant area where is a complex environment by blasting. The overall blasting scheme of “single cut, directional collapse” is determined to demolish the four chimneys at one time, by analyzing the surrounding environmental conditions and the structural characteristics. According to the engineering experience, it is determined that the bottom edge of the chimney cut is at the elevation of+0.5 m, the cut angle is 215°, the cut height, cut length and relevant blasting parameters are calculated by theoretical formula. The cut form is trapezoid like, and the initiation network uses the digital electronic detonator initiation system with higher accuracy to initiate in the way of parallel firing. Considering the different structural composition of the four chimneys, corresponding pretreatment schemes are formulated respectively. Through the safety check of the collapse reliability, blasting vibration and collapse vibration of the chimneys and the effective control of the flying debris and flying stones after blasting, the four chimneys collapse in the design direction and prevent harm to the surrounding protection targets. By using the finite element software LS-DYNA to simulate the collapse process of four chimneys, the results show that the simulated collapse process is almost the same as the actual process, and the collapse completion time is around 14 s. Moreover, by analyzing the displacement and velocity law of the top node, it can be judged that the chimney collapse effect is sufficient and the expected goal is achieved, which further shows a guiding significance of the numerical simulation for engineering practice and can provide reference for similar projects.

In order to determine the degree of impact of blasting vibrations on main haulage roadways and surface buildings near an underground mine, and to control these effects, it is necessary to obtain field test data through industrial experimentation. The Blast-NET blasting monitoring instrument was first used to monitor the radial, tangential, and vertical vibration velocities and frequencies caused by the blasting. According to the Sadovsky formula, the K and α values related to geological conditions were calculated using single-factor regression analysis, and the actual blasting vibration velocity calculation formula was obtained. The reliability of the calculation formula was then verified through continuous vibration monitoring, and optimization experiments were conducted on three different blasting network configurations: row-by-row, segmented, and hole-by-hole. The research results showed that if the protection of surface buildings is considered, the minimum safe distance between the source of the explosion and the protected buildings is 250 meters, 200 meters, and 125 meters respectively for row-by-row, segmented, and hole-by-hole blasting. If the protection of underground haulage roadways is considered, the minimum safe distance between the source of the explosion and the protected roadways is 30 meters, 25 meters, and 25 meters respectively for row-by-row, segmented, and hole-by-hole blasting. Finally, it is concluded that when the predicted vibration velocity meets the requirements of row-by-row or segmented blasting, the mine can use nonel detonators for blasting. If the hole-by-hole blasting network is required, only digital electronic detonators or high-precision nonel detonators can be used.

When the local high voltage discharge occurs in the internal area of a converter transformer oil tank, the transformer oil in the discharge area will be vaporized instantly and explosion pressure wave will be generated. In order to study the propagation characteristics of the pressure wave in the transformer tank and elevated seat area in the above process, a three-dimensional geometric model was established and divided into polyhedral meshes according to the actual experimental situation. For numerical simulation, a fluent software was used. During the calculation, the actual discharge energy curve was loaded in the discharge area through the profile file, and the compressibility of gas and liquid was considered through the gas-liquid two-phase flow model. The results show that when the arc energy is 4.929 MJ and the duration is 58.6 ms, the peak pressures at the monitoring point on the top of the elevated seat, on the left and right top of the oil tank are 1.21 MPa, 4.62 MPa and 3.79 MPa, respectively. The pressure peak in the elevated seat area decreases with the increase of the distance from the fault point. The simulated pressure peak and pressure variation trends obtained by simulation at different monitoring points display a satisfied consistence with the experimental results, which verifies the effectiveness of the simulation calculation model. By establishing and solving the arc fault discharge simulation model in the oil tank through numerical simulation, the detailed pressure variation curve and the pressure wave propagation law in the three-dimensional space can be obtained. It can greatly reduce the loss of manpower and material resources caused by the discharge experiment, and provide an effective theoretical basis for the prevention of arc explosion accident in the transformer oil tank.

Using a closed explosion experimental system, the combustion performance of a new type of rock-splitting equipment's loading agent was studied, providing guidance for the drug components and proportions in subsequent products. Different gradient components with a ratio of 9∶1 to 4∶6 were designed to mix the loading agents for the closed explosion experimental, and the p-t curve and dp/dt-t curve of all agents were analyzed. The drug ratio used in the explosive strength experiment was determined to be 7∶3 and 5.5∶4.5. The mixed drugs were subjected to the explosive strength experiment using two types of loading densities, 0.12 g/cm³ and 0.2 g/cm³. The mixed drug was assumed as a single entity with a density of 1.5 g/cm³, referring to the method of treating the gunpowder burning speed. On this assumption basis, the Γ-ψ curve of the drug combustion and the corresponding parameters such as explosive strength and burning rate coefficient were obtained, among which the explosive power of the single + additive (7∶3) formula was the highest, reaching 564.87 kJ/kg. The explosive power of the dual + additive (7∶3) formula was slightly lower but still higher than that of the 5.5∶4.5 formula. The reason for the apparent incomplete combustion phenomenon observed in the experiment of the dual + additive (5.5∶4.5) formula was explained by analyzing the Γ-ψ curve of the drug. The analysis of the corresponding explosive strength and burning rate coefficient of the mixed drugs showed that the explosive force of the gunpowder on the overall drug is the dominant factor, and the increase in the ratio of the gunpowder will significantly improve the efficiency of the drug's combustion. However, the effect of the change in loading density on the burning of the two types of gunpowder is inconsistent. The increase in loading density will cause a decrease in the burning efficiency of the monobasic formula, while the dual-base formula will exhibit an increase in burning efficiency.

Quartz sandstone samples were tested under cyclic impact loadings by the drop weight impact test equipment to study its mechanical properties and failure process under medium strain rates. Three specimens were selected at each impact height of 0.3~0.6 m, and each specimen was subjected to 8 cycles of impact with medium strain rates of 26.33 s^-1, 29.7 s^-1, 32.03 s^-1 and 35.17 s^-1, respectively. Then, the influence of cyclic loading times on the dynamic compressive strength, elastic modulus and energy efficiency of quartz sandstone were discussed. The results show that under different medium strain rates, the dynamic compressive strength of the specimens under the impact loading of the 8th cycle is about 13 MPa, which is lower than that of the first cycle. During the process, the resistance to deformation is weakened, and the elastic modulus is significantly reduced. The dynamic compressive strength of the specimens has a positively correlation with the elastic modulus. From the perspective of energy, the dissipated energy, energy efficiency and unit volume dissipated energy of the specimen are improved after 8 cycles of impact loading. The effect is most obvious when the impact energy is 70.27 J, the dissipated energy of rock is increased by 6 J, the energy efficiency is increased by 8.8%, and the unit volume dissipated energy is increased by 50%. For fracture fractal, the fracture morphology of rock under medium strain rates includes splitting failure, edge collapse failure, block failure and crushing failure. When the strain rate increases from 26.33 s^-1 to 35.17 s^-1, the characteristic value of the average particle size of the sample fragments decreases from 24.49 mm to 21.15 mm. The fractal dimension increases from 1.07 to 1.75 linearly.

In the blasting demolition of large-volume reinforced concrete bridges in China, the traditional method of manual drilling of 40 mm small-diameter holes for blasting of bridge pier columns is time-consuming, labor-intensive, difficult to ensure drilling accuracy, and has high construction costs. Based on the experience of previous studies, a new method of large-diameter drilling for bridge demolition has been proposed, which includes technical measures for blast hole diameter, hole layout, powder factor, initiation network, and safety protection. To verify the effectiveness of this new method, the blasting demolition project of Ronghui 2 bridge of Chongqing Lijiatuo compound line bridge south diversion project was selected. According to the structural loading of the bridge and the environmental conditions, delayed initiation technology was used, and explosives were detonated at a certain height above the bridge pier, which led to the bridge sequentially collapsing in place from the center to both ends, achieving the goal of one-time completion of the demolition. In this method, water-mill drilling was used to dig holes into the bridge piers, with a hole diameter of 70 mm and crosswise drilling layout, and nonel millisecond delay detonators were used inside the holes, while electronic detonators were used outside for ignition. Multiple layers of protection were provided by bamboo boards, rubber mats and flexible wire mesh. After ignition, the blasting sound was muffled, and the bridge completely collapsed and disintegrated according to the design requirements, while the impact of flying rocks, blasting vibrations, collapse ground vibrations, and explosion shock waves were all controlled within the allowable range.

No matter violent & terrorist incidents or explosion accidents, parameters related to the explosion source, such as explosive equivalent, are always important for the post-explosion accident investigation. The characteristic trace of the medium under explosion load is an important basis for tracing the cause of an explosion accident and obtaining the corresponding explosion source parameters. After reviewing the typical research progress of explosive characteristic traces, including explosion crater, damage of surrounding buildings, and personnel damage degree, it is found that there are significant differences in the shape and size among the explosion craters created by near surface explosions, exposed surface explosions and explosions with certain depth. This research is based on an underground explosion accident in a gold mine in 2021, which was caused by that the dropped welding slag from the shaft ignited the underground combustible materials and explosive equipment. According to the sizes of three explosion craters formed at the accident site, the TNT equivalents are calculated as 654.17 kg, 232.49 kg and 193.83 kg, respectively. Then, the particle vibration velocity and the shock wave overpressure of the shaft wall are calculated as 40 cm/s and 2129 Pa, according to the TNT equivalents. The calculation results are consistent with the damage degree of the cage and shaft wall.

Ground surface settlement caused by explosion-induced liquefaction of saturated sand foundation is an important subject in the seismic safety evaluation and explosion compaction of dam foundation. In this paper, the characteristics of ground surface settlement caused by liquefaction under contained explosions are studied for layered saturated sand foundation with roller compaction. Based on the existing empirical prediction models of explosion-induced liquefaction and surface settlement, the calculation formula of liquefaction volume is derived, and the rapid prediction model of surface settlement area is established and verified for reliability. Based on the above model, the characteristics of the explosion-induced liquefaction zone of saturated sand foundation and the resulted surface settlement funnel are investigated by changing the control factors such as compactness, explosive amount and burial depth, and the influence of stratified ground compaction on the characteristics of the surface settlement funnel is also discussed. The results show that the explosion liquefaction zone of saturated sand foundation has three types from small to large, including ellipsoid type, funnel type and pot bottom type. From small to large, there are two types of surface settlement area: inverted cone type and butterfly type. The liquefaction and settlement zones increase with the increase of explosive amount and the decrease of burial depth and compactness. For the layered saturated sand foundation with rolling compaction, the explosion-induced liquefaction and the resulted surface settlement are not only affected by the amount of explosive, buried depth and density, but also determined by the relative size of delamination thickness compared with the initiation depth, which further affects the range of surface settlement area.

In order to study the influence of faults and internal karst on the propagation law of blasting seismic waves in open-pit mining, the change of seismic waves passing through faults and karst was analyzed. To collect the seismic data after blasting, monitoring points were arranged at the upper and lower walls of a large fault on the south slope and a karst cave at the+1014 m platform of the north slope of the Tangya limestone open pit mine. The Hilbert Huang transform method was used to process the original waveforms, and the changes of blasting seismic waves passing through the fault and the karst cave were analyzed by the time-spectrum energy spectrum, marginal spectrum, and instantaneous energy spectrum. The results showed that the energy attenuation of blasting seismic waves passing through the fault is very obvious. With the same vibration duration, the maximum instantaneous energy decreased from 1.7 10^-5 at the front of the fault to 6.0 10^-6 at the rear of the fault which was reduced to about 1/3 of the previous value. Among them, the energy at the rear of the fault in the frequency band of 60~80 Hz attenuated to 1/2 of that at front the fault. At the same time, the energy proportion of lower frequency band increased while the overall seismic wave energy decreased. The fault objectively hinders the propagation of blasting seismic waves. In addition, the energy change of blasting seismic wave was not obvious with the maximum instantaneous energy changed from 2.3 10^-4 to 1.9 10^-4 when it passed through the karst cave. However, the filtering effect of the high-frequency signal of seismic waves passing through the karst was obvious, and the energy distribution was more concentrated. The peak particle velocity on the rear part of the karst cave was slightly larger with an amplification coefficient of 1.10~2.53. The frequency band of energy generally developed to the low-frequency direction. Therefore, it is suggested to strengthen the support of rock mass above the karst.

Aiming at the problem that the blasting effect is not good due to poor or even no stemming of blast holes in underground coal mine, numerical simulation was used to analyze the mechanism of rock breaking and stemming mechanism. A 3 m×3 m two-dimensional concrete model with blast hole diameter of 0.04 m and hole depth of 1m was established using the finite element analysis software. In addition, the continuous emulsion explosive charge was set as 0.3 kg, and the stemming material was set as sand. For the explosive simulation, concrete and sand were modeled by Lagrange grid, and the air was modeled by Euler grid. ALE algorithm was used to simulate the explosion stress nephogram and damage cloud maps with a single hole stemming length of 0 mm, 200 mm and 400 mm respectively under the blast load. The results show that the maximum stress around the hole with stemming is significantly higher than that without stemming. Meanwhile, the damage degree around the hole with stemming is more severe with smaller fragments than that without stemming. On the basis of analyzing the advantages and disadvantages of clay and water stemming structures commonly used in underground mines, a stemming structure by expansion-pipe water injection was designed, which can replace the clay and water stemming structure in underground coal mine blasting as a good field application.