Numerical Simulation And Experimental Study Of Air-Deck Charge Blasting In Fractured Rock Masses

In bench blasting, air-decking charge is a kind of charge structure. The position and the ratio of air-decking is the most important parameters of air-decking charge blasting, and suitable position and ratio of air-decking could not only reduce the cost of blasting effectively, but also improve the fragmentation effect, decrease toe rock and the blasting vibration.The researches of air-decking charge blasting theory are mainly based on the assuming conditions of homogeneous and intact rock, and it is extremely rare on the research of air-decking charge blasting in jointed and fractured rock mass. Numerical simulation and field test are used to study the air-decking charge blasting in jointed and fractured rock mass, and the best parameters of air-decking charge blasting are explored. The main work and the results obtained are listed as follows.(1) The finite element analysis software, ANSYS/LS-DYNA, is used to simulate the blasting process of air-decking charge blasting with different air-decking positions and ratios, different types of joints and fractures and different fracture spacing. The damage range and stress distribution of rock mass at different conditions of air-decking charge blasting are analyzed comparatively. The simulation results show that the blasting with air-decking in the middle of the hole has the greatest damage to the around rock compared with the air-decking at the top or at the bottom of the charge segment; the action time of stress wave of air-decking blasting is longer than continuous coupling charge blasting; comparing with the continuous coupling charge blasting, the rock around the air-decking has a stronger effect of tension stresses; the joints and fractures of rock mass have a noteworthy influence on the propagation of explosion stress wave, and the more concentrated joints and fractures are, the faster the explosion stress wave decreases.(2) Air-decking charge blasting experiments with different air-decking ratios and five air-decking positions (top of hole, bottom of hole, middle part of hole, middle-upper part of hole, and middle-down part of hole) were carried out at two sites in the typical Karst landforms area in Guizhou province, China, and the rock with developed joints, fractures and relatively intact rock. And the block size is analyzed with the Split-Desktop3.0software. The experiments results show that the average block size and boulder yield of air-decking charge blasting with suitable air-decking ratio in jointed rock mass are close to those of continuous coupling charge blasting, the fine ore ratio decreases effectively, and the block uniformity improves; the best position of air-decking is at the top and at the middle of the charge segment, and the reasonable air-decking ratio is10%～20%; and air-decking charge blasting technology is not suitable to be used in developed jointed and fractured rock mass.