Fig 1.
Layout and Roof Conditions of the 13303 Working Face in a Certain Mine.
Table 1.
Measured stress results of primary rock.
Fig 2.
Charge Configuration Diagram (a) Schematic diagram of hole parameters and cartridge form (b) Initial blast hole observation.
Fig 3.
Numerical Model of Shaped Charge Blasting in Rock Masses (a) Schematic Diagram of Shaped Charge Blasting (b) Mesh Division for Hole and Air.
Table 2.
Explosive materials and parameters of the equation of state.
Table 3.
Air material properties and equation of state parameters.
Table 4.
HJC rock material parameters.
Table 5.
Shaped charge liner material properties.
Table 6.
Stress application scheme.
Fig 4.
Stress Application Diagram (a) Static load effect (b) Dynamic load effect (c) Superposition effect.
Fig 5.
Diagram of Single-Hole Shaped Charge Blasting and Slot Formation Process (a) 8μs (b) 30μs (c) 60μs (d) 120μs (e)300μs (f) Physical Test Results [25].
Fig 6.
Circumferential Stress Distribution Around the Blasthole (a) σx = σy = 18MPa (b) σx = 9Mpa; σy = 18MPa (c) σx = 36MPa; σy = 18MPa.
Fig 7.
Circumferential Stress Distribution on the Blasthole Wall under Different Lateral Pressure Coefficients (a) Numerical model circumferential stress (b) Horizontal Hole Stress (Formula (4)) (c) Vertical circumferential stress (Formula (4)).
Fig 8.
Effect of primary rock stress on crack growth in shaped charge blasting (a) Model crack propagation length (b) Crack propagation ultimate length line graphTo accurately assess crack propagation dynamics, the main crack length in case 5 (27−18 MPa) was measured every 20 μs.
As shown in Fig 9(a) and based on rock blasting theory [26], the period from 0 to 60 μs represents the initial crack development phase. During this phase, the shaped charge jet exhibits high energy density and penetration capability, forming preliminary guided cracks near the blast hole wall. This jet directs subsequent crack propagation. From 60 to 130 μs, cracks aggregate and propagate, with the propagation rate increasing due to stress waves. After 130 μs, the crack enters a stabilization phase where quasi-static stress further drives propagation. By 160 μs, the crack reaches a relatively stable propagation stage, with a slowed yet ongoing propagation. Residual strain energy in the rock continues to promote crack extension and interconnection, although stress wave energy and velocity diminish. At this stage, cracks form but fail to meet the technical specifications for roof cutting and retention, which require “the opening position to be a line, the longitudinal angle a plane, and the horizontal base a line”.
Fig 9.
Shaped charge blasting into cracks and crack length extension (a) Shaped charge blasting process (27−18MPa) (b) Crack propagation length.
Fig 10.
The fractal dimension fitting line of blasting crack under different side pressure coefficients (a) Unconfined pressure (b) Hydrostatic confinement pressure (c) Various lateral pressure coefficients (d) Fracture damage zone.
Fig 11.
Proportion of Elastic Vibration Energy under Different In-situ Stress Conditions.
Fig 12.
Shear stress time history curve.
Fig 13.
Borehole inspection map of blasting effect (a) fracture zone sandstone (b) Initial blasting crack generation (c) Formation of blasting cracks (d) Crack condition of hole bottom blasting.
Fig 14.
Deformation curves of roadway (a) Roof-to-floor convergence (b) Rib-to-rib convergence (c) Load Change in Anchorage Systems.