In view of the problem that mining and crushing of magnetite ore require huge energy consumption, the split Hopkinson pressure bar (SHPB) is used to test and analyze the dynamic mechanical properties and energy dissipation characteristics of magnetite ore during crushing process under different strain rates. Meanwhile, the complete dynamic failure process of the sample is simulated by ANSYS/LS-DYNA software. The results show that the dynamic compressive strength of the magnetite ore samples has a significant strain rate correlation, and increases from 126.77 MPa to 220.62 MPa when the strain rate ranges from 43.94 s^-1 to 147.75 s^-1. Besides, The analysis of energy transfer law shows that the increase trend of reflected energy become more obvious with the increase of incident energy, and the maximum proportion accounts for about 22% of the total incident energy. However, The increase trend of transmission energy become weaker, and the proportion of transmission energy decreases from 78% at low incident energy to 38% at high incident energy. At the same time, the dissipated energy used for specimen crushing increases gradually, which has a linear relationship with the incident energy. The failure mode changes from the splitting failure at low and medium strain rates to crushing failure at a high strain rate. In terms of the crushing scale, most of the fragments at low and medium strain rates are large, while the fragments at high strain rates are small and mostly fine-grained and needle shaped. Numerical simulation results indicate that the initial failure is caused by the "cross" shaped reflected tensile waves on the incident end of the specimen. The results of this study can provide a reference for judging the difficulty of dynamic crushing of magnetite ore and improving the efficiency of rock breaking by impact.

The safety control standard of buildings subjected to blast vibrations should not ignore the influence of the cyclic blasts. It is suggested that the critical peak vibration velocity which makes each part in elastic deformation stage is taken as the safety control standard and damage law of brick-concrete buildings or structures under frequent blast vibrations based on the cumulative damage theory and numerical simulations. According to the specific material parameters and model conditions, the critical peak vibration velocity of an intact brick-concrete structure is 0.67 cm/s, and tensile damage occurs in the stress concentration parts. It is therefore recommended that for buildings with weak anti-vibration ability, such as brick-concrete structures, the range of the safety control standard under frequent blast vibrations can be determined by multiplying the lower limit value set by the most unfavorable frequency in the current blasting safety regulations for general civil buildings by a reduction factor, which can be 0.45~0.55. When determining the safety control standard of damaged structures under frequent blast vibrations, the actual damage situation of the buildings should be comprehensively considered. The vibration safety control standard is taken as the smaller value between the critical peak vibration velocity which does not lead to crack propagation and the critical peak vibration velocity which ensures that all parts of the structure are in elastic deformation stage.

To reveal the propagation characteristics of blasting vibrations induced by blasting demolition of a reinforced concrete support beam in a deep foundation support system, the vibration velocities and frequencies in the horizontal and vertical directions of the support system and the response spectrum characteristic of the enclosure structure of the foundation pit are analyzed based on the monitored vibration data. The vibration test lines were laid in the same and the upper layer to the support beam. The results show that the vibration velocity decays rapidly with the increase of distance. The peak vibration velocity at the blasting layer is 5~7 times than that of the upper layer within 50 m of the blasting area. However, the peak vibration velocity of the blasting layer gradually attenuates to 1~2 times than that of the upper layer outside 50 m of blasting area. Besides, there are obvious differences among the components of vibration velocities in three directions in the blasting layer. The radial component has the largest peak value, which is 2~5 times of the vertical component. On the contrary, the three components of vibration velocities in the non-blasting layer are close to each other. Meanwhile, it is high frequency vibration in the support beam, and the vibration frequency of the blasting layer is slightly smaller than that of the non-blasting layer, and both of them have a steep increase phenomenon in the supporting structure of the foundation pit. When the support beam is demolished by blasting, the short-period response spectrum of the enclosure structure of the foundation pit is obviously beyond the designed spectrum, and the blasting vibrations will have a certain influence on the enclosure structure. The related results can provide references for the design of blasting demolition of support beams, vibration control, and the dynamic response analysis of enclosure structure of a deep foundation pit.