In order to explore the dynamic crack propagation law of beam members, bar defects with the heights of 22 mm, 28.5 mm and 35 mm were designed in a three-point bending beam, and then tested by the digital laser dynamic caustic line experiment system and the drop weight impact test system. The results show that the crack propagation rate and stress intensity factor are affected by the defect height in two stages in the drop weight impact experiment. In the first stage, the maximum growth rates of crack propagation have a trend of first rising and then stabilizing as 247.49 m/s, 292.49 m/s and 284.99 m/s with the increase of defect height, and the cracking stress intensity factor was respectively 1.480 MPa/m^3/2, 1.665 MPa/m^3/2 and 1.812 MPa/m^3/2, which increased with the increase of defect height. Meanwhile, the crack initiation and propagation rates respectively decreased by 634.42 m/s, 524.97 m/s and 377.67 m/s, the cracking stress intensity factors of K_Ⅰ type respectively decreased by 3.281 MPa/m^3/2, 3.192 MPa/m^3/2 and 2.876 MPa/m^3/2, and the cracking stress intensity factors of K_Ⅱ type respectively increased by 1.254 MPa/m^3/2, 1.319 MPa/m^3/2, and 1.398 MPa/m^3/2. Furthermore, the K_Ⅰ-K_Ⅱ composite stress intensity factor was transformed into a K_Ⅰ type stress intensity factor by deflection.

The slope stability is bound to be affected in the blasting process of open-pit mine, especially when the slope is in the karst area. In order to study the influence of karst on slope stability under blasting and based on Tangya limestone mine slope project, this paper takes the exposed karst at the 1014 m platform of the mine as the research object, and uses ANSYS/LS-DYNA finite element analysis software to conduct numerical simulation. Considering the effect of blasting vibration, the stress distribution of the surrounding rock is obtained, and the effects of blasting on slope stress, vibration velocity, rock damage and effective stress of slope with or without karst cave are compared. The results show that the force of the bench changes and stress concentration occurs for several times due to the existence of karst caves, but the stress value generated by the bench loads is only 7.6 MPa, which still cannot reach the degree of rock mass destruction. For monitoring points at different spatial locations, the difference of vibration velocity becomes larger due to the existence of karst caves, and the vibration velocity in the vertical direction changes more than that in the horizontal direction. In particular, the spatial locations of the monitoring points near the slope edge are more sensitive to this situation. The vibration velocity difference of the monitoring points on the slope edge is about 1 cm/s at most, which does not exceed the allowable vibration velocity. In the process of increasing blasting times, the damage inside the rock mass is also gradually increasing, and the damage is more obvious under the influence of karst caves. The larger the radius of karst area, the more blasting times, the more serious the damage. Compared with previous uniaxial compressive strength experiments, it is found that although the existence of karst caves will cause the change of stress value and stress concentration phenomenon, the peak effective stress generated is far lower than the uniaxial compressive strength of rock mass. In view of the influence of blasting process on slope stability, the support treatment measures of slope in karst area are put forward.

Aiming at the construction problems of a subway tunnel adjacent existing buildings in the section between Jialingjiang Road station and Xiangjiang Road station of Qingdao Metro Line 13, a new construction scheme of mechanical excavation combined with blasting is proposed. In the scheme, bench method is used with the upper bench in the weak stratum excavated by mechanical method, and the lower bench in the hard stratum excavated by blasting method. Furthermore, the vibration velocities of the adjacent buildings caused by the proposed scheme and the traditional full-section blasting scheme are analyzed and compared by using FLAC3D and blasting equivalent load method. The results show that, the peak vibration velocity of each monitoring point under the mechanical-blasting scheme decreases significantly compared with the full-section blasting with the maximum reduction rate of 61.1% which is within the allowable range and validates the new scheme. The construction parameters of the mechanical-blasting scheme are compared and selected based on the building settlement, plastic zone of surrounding rock mass, vibration velocity of the buildings, etc. Finally, the mechanical excavation advance of the upper bench is determined to as 0.5 m. Besides, the construction effect of the optimized parameters is monitored and evaluated. The mechanical-blasting construction scheme successfully solved the problems encountered in the project, and shortened the expected construction period by 3 months, which shows the rationality of the proposed construction scheme and parameters, as well as the validity of the calculation results.

In order to improve the analysis accuracy of loosening blasting vibration signals, a hybrid denoising method based on local mean decomposition (LMD), multiscale fuzzy entropy (MFE), and singular value filtering (SVD) was established. Firstly, the vibration signal was decomposed by LMD method to obtain a series of product components (PF). Then, the blasting vibration signal was preliminarily denoised by calculating MFE and correlation coefficients. Finally, the real signal components were denoised and extracted by SVD filtering on the residual noise of the main PF components. The results show that the proposed LMD-MFE-SVD denoising method can effectively deal with the noisy PF components. For the simulated signal with multiple components with noise, the LMD algorithm is more efficient than the EMD algorithm. Furthermore, the signal-to-noise ratio (SNR), root mean square error (RMSE) and percentage of distortion (PRD) of the proposed LMD-MFE-SVD method are significantly improved by 11.73%, 22.07% and 9.25%, respectively, compared with the LMD algorithm, which indicates that the noise reduction efficiency is considerable. According to the waveform and spectrum comparison of the measured loosening blasting vibration signal after denoising by the proposed LMD-MFE-SVD method, the denoised signal waveform is more concentrated with most of the signal information retained. The frequency spectrum is clearer, and the signal frequency peaks are effectively displayed.

In order to study the protective performance of minesweeper protective equipment on the chest and abdomen under the action of explosion shock wave, it is necessary to explore efficient test methods to improve the experimental research index system and overall performance of individual soldier protective equipment. In this paper, two sets of minesweeper protective equipment were taken as experimental research objects, and the real explosion test of minesweeper EOD operators for typical kneeling posture was designed based on Hybird III dummy model under different sealing conditions. The shock wave was generated by the explosion of 50 g TNT charge column. Two wall overpressure sensors were installed in the chest and abdomen of the dummy model to measure the shock wave overpressure generated by four real explosion tests, and a free field pressure sensor was set at the same distance relative to the explosion source to compare the test data. Using the dummy data acquisition system, the whole process data of overpressure on the chest and abdomen after the shock wave penetration of the minesweeper protective equipment were obtained. Through data processing, the pressure-time curve of chest and abdomen subjected to explosion impact and the peak attenuation rate of overpressure were obtained and compared. The test results preliminarily verify that the better the sealing performance of the joint, the higher the protection performance, which indicates that the protective equipment with high sealing performance has a certain blocking attenuation effect on the diffraction of explosion shock wave, and can reduce the damage caused by superimposed overpressure to the chest and abdomen to a certain extent. The experimental design and data analysis in this paper can be used for further equipment performance improvement.

Reinforced concrete (RC) short beam is the key load-bearing component of buildings. In order to study its dynamic response and failure mechanism under impact load, drop hammer impact tests with different impact mass, impact velocity and impact energy were carried out by combining strain gauge sensor, high-speed photography and digital image technology (DIC). The results show that, the failure forms of the short RC beams under impact loads are arch collapse cracks and overall bending deformation, which are obviously different from those of shallow beams. The axial strain in the mid span of a short RC beam changes from tensile strain to compressive strain. With the increase of impact energy (18 061 J≤E≤49 831 J), the axial peak tensile strain and residual compressive strain in the mid span increase first and then decrease. The short RC beam is in the stage of elastic flexural deformation, elastic-plastic flexural deformation and punching shear failure mode in turn. The crack initiation and propagation process of the short RC beam under impact load is not unidirectional. And the fracture zone is formed by the multidirectional fracture propagation with multiple times, and then the plastic hinge is formed, resulting in the overall short beam failure. The deformation degree of the beam mainly depends on the impact speed rather than the impact energy. Specifically, the peak deflection and residual deflection in the middle span of the beam (26.81 mm≤w_p≤29.85 mm; 17.12 mm≤w_r≤21.66 mm) increase with the increase of the impact speed (5.53 m/s≤v≤7.13 m/s) under the same impact energy (30 000 J).

To explore the destructive forms of bridge damage caused by explosions of hazardous materials in vehicles and the distribution of explosion load pressures on the bridge deck, a refined numerical model was established using AUTODYN software. The study analyzed the regional distribution characteristics of the bridge load pressure field under various explosion conditions with different shapes and sizes of steel plates, and determined the critical dimensions at which the steel plates play a blocking role against shock waves. In response to the challenges of conducting bridge explosion experiments, which involve high risks and large expenses, the research referred to a detailed inspection report of a real bridge after an explosion accident and inferred its explosion damage process. Based on the least squares method, a polynomial curve fitting was applied to numerous of numerical calculation results, and the traditional calculation formula for explosion shock wave pressure in the free air domain was modified. A prediction formula for the peak overpressure on the bridge deck under the explosive effects from the vehicle-borne cargo, taking into account the blocking of carriage steel plates, was proposed. The load pressure distribution calculated by this formula corresponded well to the damaged areas on the bridge deck as reported in the real bridge inspection report.

In order to improve the quality of tunnel blasting and reduce the disturbance to surrounding rock during blasting construction, it is necessary to carry out optimization research on the original blasting scheme. Taking the parallel guide tunnel of a railway project as the engineering background, more reasonable blasting parameters are determined by using the empirical formula to calculate the powder factor, the number of holes and the parameters of each hole, aiming at the problems such as serious over-under excavation, poor working environment and slow construction progress. The number of medium and large diameter empty holes in the original blasting scheme is changed from 8 to 2, and the layout of cut holes is adjusted to provide better free surface for subsequent holes. At the same time, the orifice of the charging structure is blocked by water bags, which reduces the concentration of dust and harmful gases in the tunnel after explosion. The results show that the average linear over excavation can be reduced from 0.2~0.4 m to 0.15 m with smooth working face and bottom by using the optimized blasting scheme. At the same time, compared with the original scheme, the number of holes and the amount of explosives used in each cycle can be reduced by 37 and 49.2 kg, respectively. In addition, the construction time can be saved by 1.1 h and the cost is about 800 yuan, which has a relatively significant technical effect and economic value, and also verifies the feasibility of the optimized blasting scheme.

Using traditional continuous charge blasting method in Zijin Mine is easy to produce powder near the crushing circle of the hole, resulting in substandard ore gradation and waste of resources. Therefore, in order to improve the ore gradation and increase the aggregate products, a blasting test was carried out under the conditions of 0 m, 1 m, 1.2 m, and 1.5 m in the middle of the air-decked charge blasting technology. Firstly, a limestone model using HJC constitutive relation was established to simulate the actual geological by ANSYS/LS-DYNA finite element software. And then, the damage distribution characteristics of rock mass under different spacing distance conditions were analyzed, and the relatively optimal air spacing charge length was obtained. Finally, the 1.2 m and 1.5 m middle air decking are selected to control the blasting powder rate. The field blasting tests and the comparison of rock gradations under different conditions show that it is effective to reduce the powder rate by adopting the intermediate air decked charge. When the air decking length is 1.5 m, the non-uniformity coefficient Cu and the blasting powder rate can be reduced. Before the technical transformation, the average powder ore rate is about 15.94%, and after the technical transformation, the powder ore rate below 4.75 mm can be reduced to about 9.37%, making the grading to a good level.

In order to explore the interaction mechanism between the structure of different sizes and the bubbles, an underwater explosion experiment of 2.5 g TNT was carried out at the bottom 15cm of the fixed square plates with side lengths of 20 cm, 40 cm and 70 cm. Through the observation of the experimental high-speed video and the pressure data measured by the sensor, it is found that when the size of the plate is too small, the bubble will contact with the air during the expansion process, and the bubble pulsation process will be terminated. In order to further explore the matching relationship between the explosion bubble and the target size, CEL algorithm in Abaqus software was used to establish the fixed square plate with Lagrange grid and the remaining part with Euler grid. The dynamic behavior and pressure data of the near-field underwater explosion bubble were numerically simulated. The feasibility of the simulation method is verified by comparing the simulation results with the bubble phenomenon captured in the experiment and the measured pressure time history curve. Taking the explosion depth divided by the maximum bubble radius as the specific depth and the side length of the board divided by the maximum bubble radius as the side length, a series of simulations were carried out with the side length of the board being 0.455 to 3.182 times the maximum theoretical bubble radius and the explosion distance being 0.455 to 1.136 times the maximum theoretical bubble radius. The simulation results show that with the decrease of plate size, the bubbles are more likely to collapse in advance. With dimensionless plate size and dimensionless explosion depth as variables, a boundary function is given to complete the bubble pulsation. The closer the distance between explosion distance and plate size, the earlier the end time of bubble pulsation.