In order to comprehensively evaluate the effect of deep hole bench blasting in Weijiamao Coal Mine, considering the three objectives of blasting quality, safety and economy, eight parameters such as block rate, root rate, back crack distance, loose coefficient, unit consumption, long-meter blasting amount, vibration speed and flying distance were selected as evaluation indexes. Through UAV, high-speed photography, vibration monitoring and other technical means, the field monitoring of four production blasting flat plates in Weijiamao Coal Mine was carried out. In the meantime, the data analysis was carried out by Split-desktop, Motion studio and other software, and the quantitative indexes of the above parameters were obtained. The subjective and objective weights of evaluation indexes are obtained by using analytic hierarchy process and CRITIC method respectively, and then the combined weights of each index are determined based on the principle of maximum sum of squares of deviations. The grey clustering method is optimized by using the center point triangle whitening weight function, and the grey clustering evaluation model of blasting effect is established. The deep hole bench blasting effect of Weijiamao Coal Mine is comprehensively evaluated, and the order of blasting effect of four flat plates is obtained according to the comprehensive clustering coefficient. Finally, the main problems of the flat plate with the worst blasting effect are analyzed by comparing the index data. The results show that the combined weight of explosive unit consumption, bulk rate and base rate is greater than 0.15, which has a great influence on the blasting effect. The order of blasting effect of four flat plates is that 1080 flat plate > 1064 flat plate > 1096 flat plate > 1112 flat plate. The 1112 flat plate needs to be combined with geological conditions to optimize the bench blasting parameters for the problems of large back crack distance, high unit consumption, small blasting amount per meter and large flying distance.

Explosive welding is an efficient, economical and practical technique that uses explosives as energy to achieve solid-state connection of the same or dissimilar materials. Because it can achieve large-area welding and combination of dissimilar materials, it is widely used in the preparation of layered metal composites. In order to explain the research development of explosive welding of dissimilar metal materials, the related concepts and basic principles of explosive welding are reviewed. Through the introduction of welding window theory, it is pointed out that choosing explosion welding parameters in the welding window surrounded by four boundaries can obtain relatively high-quality corrugation. Based on the research status at home and abroad, explosive welding interface is discussed in detail from three aspects: the structure and mechanical properties of the explosive welding interface, the influence of heat treatment on the interface structure, and the influencing factors of the bonding interface. Studies have found that defects such as cracks, adiabatic shear bands, and intermetallic compounds often appear at the interface junctions, which can be improved by heat treatment, use of intermediate layers, and gas shielded explosive welding. However, the formation mechanism and control methods still need further in-depth research. In addition, the current numerical simulation is mainly based on the SPH method. After comparative analysis, this method can effectively simulate the bonding interface and jet flow, but it also has the disadvantage of a single simulation process, and the formation mechanism of the interface wave is still unclear. Therefore, it is necessary to establish a scientific and perfect interface wave formation mechanism and a systematic and comprehensive numerical simulation process. With the continuous emergence of new materials, explosive welding technique will continue to play an important role in more fields.

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.

The conclusions including: the Kuznetsov and kansake models are still applicable to the prediction of unit explosive consumption in bench blasting tunnel engineering, and the Kuznetsov model considers the influence of rock mass characteristics, which is more practical than the kansake model. In addition, the Kuznetsov model can predict the average blasting fragment as the basis of the distribution model of blasting fragment. Compared with the lower bench, the upper bench has higher single blasting consumption, higher content of fine particles and smaller fragments. The Kuz-Ram model has a good prediction effect for the small blasting fragments that below the average value. For the large blasting fragments that above the average value, the KCO model has a better prediction effect, and it has more accurate for the prediction of the largest blasting fragment. This paper analyzes the applicable conditions and scope of the prediction model for rock fragment, which provides a basis for the unit explosive consumption and fragment distribution of tunnel blasting. The methods for predicting the specific consumption of explosives and the fragmentation of rock mass during blasting originated from open-pit blasting. However, the stress state of the rock mass in stepped tunnels is different from that in open-pit mines, so it is unknown whether the above prediction methods are applicable to stepped tunnel blasting. Based on statistical data from the bench blasting in the Tianjiangli tunnel, several commonly used calculation methods in open-pit mines were used to predict the specific consumption of explosives and the distribution of fragments, and the predicted results were compared with the actual measurements. The results show that the Kuznetsov model and the Kansake model are still applicable to predicting the specific consumption of explosives in stepped tunnel blasting, and the Kuznetsov model takes into account the influence of rock mass characteristics, making it more practical than the Kansake model. In addition, the Kuznetsov model can predict the average value of the blasting fragmentation and serve as a basis for the fragmentation distribution model. The specific consumption of explosives is higher on the upper bench, resulting in a higher content of fine particles and smaller overall rock mass after blasting, while the specific consumption is lower on the lower step, resulting in a lower content of fine particles and a larger overall rock mass after blasting. The Kuz-Ram model is better in predicting the blasting fragmentation of small rock masses with a block size below the average value, while the KCO model is better for predicting the blasting fragmentation of large rock masses with a block size above the average value, and the KCO model can accurately predict the maximum blasting block. This article analyzes the applicable conditions and scope of the prediction models and provides a basis for the specific consumption and fragmentation distribution in tunnel blasting.

Shallow hole blasting is com in roadway or tunnel excavation, which has the disadvantages of more work cycles, less footage per cycle and low excavation speed. Meanwhile, deep-hole blasting which is widely used in mining engineering usually adopts continuous charge structure. This brings problems such as high charge quantity per delay, significant blast-induced harmful effect and high boulder yield. To overcome these problems, it is effective to adopt the in-hole sectional blasting technique. Firstly, key factors such as charging structure, charging materials, decking length, sectional delay and charging method are emphatically introduced based on the patents of in-hole sectional blasting in recent years. Then, taking the open-pit bench blasting of a mine adjacent to a railway as an example, the new two-deck charge blasting technology with rock powder barrier as the decking material was presented and compared with the traditional continuous charge blasting technology. After application of the new technique, the boulder yield was reduced by 54%, preventing secondary blasting. At the same time, the explosive usage was saved by 20%. The blasting vibration at the nearest monitoring point to the railway was reduced by 7.62%, and the flying rocks were all within the allowable range. The new technical scheme can also make the bench surface smoother after loading and transporting, which is more conducive to the subsequent stage of blasting operations.

In order to improve the efficiency of the directional cracking of hard rocks, starting from the mechanism of cracking from hard rocks to breaking rocks, based on the empty hole effect theory, the stress variation law of the empty hole wall under the 200 mm、250 mm、300 mm、400 mm hole spacing and the 20 mm、40 mm、90 mm、120 mm hole radius is studied, and the theoretical calculation and numerical simulation are compared and analyzed to verify. The results show that the existence of empty hole makes the stress concentration near the expansion hole, with the increase of empty hole spacing and the decrease of empty hole radius, the stress concentration of empty hole effect becomes weaker. The maximum tensile stress appears on the connection line of the empty hole and the expansion hole. The maximum pressure stress appears near the empty hole circle 70°. The stress intensity factor of type I rock on the inter-hole connection line corresponds to the law of stress variation. When the hole spacing reaches 400 mm, the stress intensity factor K_I is smaller than the fracture toughness K_IC of rock and the condition for formation of through cracks cannot be reached. According to the research results, set the parameters of the empty hole and in Shenzhen Tiegang-Shiyan reservoir Shiyan North clear water diversion tunnel to carry out the rock breaking test. The test results show that empty holes play a guiding role in the direction of crack propagation, which can cause the main crack to form on the connecting line between the empty hole and the expansion hole and is beneficial to improving the efficiency of the breaking rocks in hard rocks, which can provide reference for similar projects.

It is an important content in the course of "Blasting Engineering" to master the dynamic mechanical response of rock (body) under the action of blasting dynamic load. Since students majoring in civil or mining engineering lack basic theories such as wave mechanics and rock dynamics, the teaching effect is poor when the knowledge of dynamic mechanical properties of rock is explained in class, which will affect the subsequent learning of rock breakage mechanism. Therefore, the Split Hopkinson Pressure Bar (SHPB) experiment of rock materials is applied to the practical teaching of “Blasting Engineering”. By measuring the dynamic compression strength of rock samples and observing the failure forms of specimens, students are guided to understand the dynamic mechanical response of rock materials under different strain rates. The finite element software LS-DYNA is also used to simulate the SHPB experiment, and the process of stress wave propagation and rock failure is reproduced to achieve the demonstration function of dynamic impact. Practice shows that this teaching method enables students to intuitively perceive the stress wave propagation, clearly understand the dynamic failure mechanism of rock, master the relationship between dynamic mechanical properties of rock materials and strain rate, and lay a foundation for further study of blasting engineering theory.

In the process of blasting excavation of rear tunnel with mall clear distance and large section, it is very important to ensure the safety of front tunnel exposed to blasting vibrations. Based on the six-lane Xiaoyu Tunnel of Beijing-Qinhuangdao Expressway, a blasting vibration velocity distribution law of the longitudinal and transverse sections of the front tunnel was monitored and analyzed during the excavation of the rear tunnel. The blasting parameters of the rear tunnel were dynamically adjusted and optimized, and the safety control measures of blasting vibration were put forward according the monitoring results. The results showed that the vibration velocity on the radial direction of the side wall of the front tunnel was the largest when the rear tunnel was excavated, and it is mainly caused by cut hole blasting. The vertical vibration velocity is slightly lower than the transverse vibration velocity. However, there is little difference between them, and the blasting vibration energy is mainly concentrated in the frequency band of 30~100 Hz. For the vibration distribution on the longitudinal section of the front tunnel, the peak vibration velocity decays with distance, but the vibration velocity on the unexcavated direction is relatively higher, which is 1.2~1.6 times of the vibration velocity on the same excavated distance. For the vibration velocity distribution on the cross-section of the front tunnel, the vibration velocity on the front side is 5~10 times higher than that on the back side. Multi-stage cutting was adopted to optimize the distribution of the holes.12 different delays were adopted to reduce the charge per delay, and the delay interval was increased to 60 ms to control the blasting vibration. The field practice shows that the optimized blasting design can reduce the vibration velocity of the side wall of the front tunnel by about 50%.

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 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.