• The energy-focusing blast achieves directional fracturing through a two-stage mechanism: suppression of explosion energy in non-focusing directions and redirection of energy to produce tensile stress in the focusing direction.
• The filling medium critically influences energy regulation; water, with higher wave impedance and lower compressibility, yields the highest shaped-energy coefficient (6.12) and most uniform stress distribution, enhancing directional crack growth.
• Sand as a filling medium increases crack irregularity (fractal dimension 1.112) due to its granularity and heterogeneity, while air and water produce more uniform stress fields and smoother cracks.
• Water strikes an optimal balance between energy transition and distribution, maintaining the least flatness of directional cracks, making it the most effective filling medium for energy-focusing blasts.