Blasting Energy Transmission and Oversize Boulders Formation Mechanism in Soft Rock Blasting with High Porosity

The blasting fragmentation mechanisms of high-porosity soft rock under blast loading is significantly different from that of ordinary rock.Based on the theory of impact dynamics and explosion mechanics,a blasting energy transfer efficiency model considering rock porosity was established.Theoretical analysis shows that the pore structure of the rock mass affects the explosion energy transmission between the explosive-rock interface,and the attenuation of stress waves increases with the increase of porosity.The quantitative relationship between blasting fragmentation distribution and porosity was investigated by numerical simulation.And the formation mechanism of oversize boulders in soft rock blasting with high porosity was revealed.The results show that the porosity has two different effects of “promoting” and “inhibiting” on the propagation of blasting cracks at the same time.When the porosity is low (ϕ<10%),the “promoting” effect on the crack is dominant,and the explosion energy is mainly consumed in the formation of new fracture surface.When the porosity is high (ϕ>15%),the “inhibition” effect on the crack is dominant,the explosion energy is mainly consumed in pore deformation and crushing.And the expansion of micro cracks is restrained,resulting in the formation of oversize boulders in high porosity soft rock.This study is helpful to optimize the blasting design in high porosity soft rock and improve the utilization rate of blasting energy.