Abstract:The crack propagation mechanism and influence of closed and open jointed medium were studied on crack propagation law of cutting seam cartridge fracture with controlled blasting. Dynamic caustics experiment of blasting loading was carried out in PMMA material by forming initial cracks through cutting seam cartridge directional fracture. The experimental results show that those two kinds of jointed medium have great influence on crack propagation;and the initial cracks do not traverse joints;and wing-cracks are generated at both ends of joints and basically go on extending along original explosion crack. In open joint experiment,a caustics speckle appears in two wing-cracks about 25 μs after cutting seam cartridge blasting;and the largest width of wing-crack is 2.5 cm. While in closed joint experiment,a caustic appears 1 μs after cutting seam cartridge blasting,which is 24 μs ahead of open joint and the largest width of wing-crack is 5.6 cm. The dynamic stress intensity factor(SIF) of wing-crack changes from small to large firstly,and then falls from large to small. During the initial stage,dynamic stress intensity factor is smaller than that of . The peak value of closed joint is larger than that of open joint;the former is 1.72 MN/m3/2,and the latter is 1.28 MN/m3/2. The research results can provide theoretical basis for directional fracture with controlled blasting of jointed rock mass.