In order to study the crushing energy dissipation characteristics of graphite ore rock under impact loads, ϕ 50 mm diameter split Hopkinson pressure bar(SHPB) test device is used to conduct impact compression tests. The crushing energy dissipation law of the graphite ore rock samples is analyzed under different loading rates with five different impact pressures from 0.2 MPa to 0.6 MPa with a 0.1 MPa interval. The test results show that the dynamic compressive strength of the samples have a strong third-order polynomial relationship with the average strain rate under impact loads. The graphite ore rock has dynamic hardening under impact loads, and its dynamic compressive strength increases nonlinearly with the increase of strain rate, which shows an obvious strain rate effect. In addition, there is an obvious logarithmic relationship between the crushing dissipation energy and the incident energy. With the increase of incident energy, the crushing dissipation energy also increases. However, the proportion of the crushing energy gradually decreases from 0.38 to 0.11. The crushing energy dissipation density of the samples has an obvious strain rate effect, and its value increases with the increase of strain rate. Besides, the average particle size of the broken samples is strongly correlated with the energy dissipation density of the samples. As the energy dissipation density increases, the crushing degree of the sample becomes more severe. Therefore, the average particle size of the crushing fragments can be used to quantitatively describe the crushing degree of the samples.

This study presents a comprehensive approach to solve the problem of low ore recovery caused by the difficulty in separating small-particle size ore from soil after blasting in a limestone building stone mine. Firstly, a correlation model between blasting fragmentation and dynamic damage of rock mass was established based on field measurement data and numerical simulation results, which can determine dynamic damage thresholds corresponding to various rock particle sizes. Secondly, the numerical simulation test of bench blasting in a three-dimensional fractured rock mass was carried out by using different air-decked charging stages and borehole distribution parameters, which can improve the particle size yield of 0.3~0.9 m and control the bulk ratio to obtain the best blasting parameters. Finally, the field blasting tests were conducted to optimize the charge structure and borehole distribution parameters based on numerical simulation results. The results show a negative exponential function relationship between the blasting block size and the dynamic damage value of the limestone. Specifically, the dynamic damage thresholds corresponding to the blasting size of 0.3 m and 0.9 m are 0.793 and 0.286, respectively. Using only an air-decked charging structure alone can increase the particle size ratio of 0.3~0.9 m and significantly raise the bulk rate. Conversely, combining an air-decked charging structure with a reduced hole spacing markedly enhances the particle size ratio of 0.3~0.9 m while maintaining a stable bulk rate. Optimal blasting results are achieved using a two-stage air interval charging structure and a strategic reduction in hole distribution parameters. The field application results show a 20.09 percentage point increase in the 0.3~0.9 m particle size ratio, with the bulk rate remaining virtually unchanged. Additionally, the unit consumption of explosives decreased by 10.29%.

The distribution of blasting fragmentation in open pit mines has a direct impact on subsequent excavation, transportation, and crushing operations. To effectively control the fragmentation distribution of blasted rocks in different regions of graphite mines, a new model for evaluating rock blastability was developed using the K-means unsupervised cluster learning method and entropy weight TOPSIS evaluation method. Evaluation indexes including rock density, dynamic energy dissipation rate, dynamic compressive strength, average strain rate, and brittleness index were selected. Through entropy weight calculation, it was determined that the degree of rock breakage is most influenced by the brittleness index and least influenced by the average strain rate. The model was then applied to an actual graphite mine to assess its effectiveness. The rock blastability was divided into 10 grades based on this evaluation model. The average particle size of rocks under different grades was calculated and it was observed that as blastability grade increased, so did the average particle size. This finding demonstrates clear classification characteristics and validates the efficacy of our model. From the perspective of rock mass type of graphite ore, the rock explosibility is ranked from easy to difficult: schist, gneiss, granodiorite, mixed rock. Combined with the analysis of microscopic observation results of graphite ore, it can be seen that the lithology changes from schist to mixed rock, and the graphite crystalline content in the rock decreases, and the graphite ore explosibility grade is also higher and higher. Additionally, there exists a linear positive relationship between density/energy dissipation rate/dynamic compressive strength with rock blastability while negative correlation is observed with respect to average strain rate/brittleness index.

The authenticity of fracture distribution model is one of the key factors during numerical simulation of blasting in jointed rock mass, which would obviously affect the numerical simulation results. It is hard to represent the complex three-dimensional joint distribution in the existing joint construction method. To explore a simple and feasible operation method for constructing the complex 3D joint model in LS-DYNA software, a K file of blasting numerical model was analyzed and reorganized by MATLAB software. Furthermore, a 3D refined numerical model for jointed rock mass was constructed by the 3D joint distribution law and the constitutive joint model parameters. Finally, a statistical analysis of the three-dimensional joint distribution law was carried out in an open-pit limestone mine, and the joints were reconstructed in the numerical model of a bench blasting. Consequently, a comparative study of the numerical simulation and the field blasting test for open-pit bench blasting was carried out. The results show that the error between the joints built in the numerical model and the actual joints is less than 13%. The joint surface changes the damage distribution of the rock mass. Compared with the intact rock mass, the damage rock mass range increases by 12.04%, and the proportion of fragments with the size of 0~100 mm decreases by 8.11%. The damage results obtained by blasting simulation are close to the field rock breaking effect, and the percentage error of fragments with the size of 0~100 mm is 4.16%. The analytical reconstruction method is feasible and easy to represent the complex three-dimensional joint distribution, and the numerical results are close to experimental results.