Deformation Characteristics and Electrical Resistivity Response of Soft Coal Under Blast Loading

A series of experiments of soft coal under different explosive dosages were carried out in this paper. The crack morphology and deformation characteristics of coal were analysed and the regional response characteristics of the internal resistivity of coal obtained. The results indicated that under blast loading, the soft coal presented three types of blasting-induced cracks: radial main crack, circumferential main crack and radial microcrack. The movement deformation of coal led to the change in coal density in different regions. The coal density around the circumferential main crack and the radial microcrack generally decreased, while the coal density around the radial main crack generally increased. The electrical resistivity tomography analysis of soft coal after blasting showed that resistivity increasing and decreasing zones were evident. Coal resistivity under the squeezing of explosion gas decreased, whereas the coal resistivity affected only by explosion stress wave increased. With the increase in explosive dosage, the area of the blasting-induced crack and the volume of blasting cavity both increased first and then decreased. However, under the same explosive dosage, compared with the experiment with the sealing blast hole, the blasting-induced crack area of coal was reduced by 9.69% and the blasting cavity volume was reduced by 70% in the experiment without sealing blast hole, thereby indicating that explosion gas was essential in the movement and deformation of coal in the blasting process of the soft coal.