Development of VSP Probe for Inspection of Blast Damaged Zone

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A series of experimental and theoretical investigation for the evaluation ofblast damaged zone has been carried out. Results obtained are as follows.(1) A compact VSP system to evaluate the loosened zone caused by excavation blasting has been developed. A super-elastic alloy plate has been adopted as material for the spring which presses a vibration sensor to the borehole wall with constant force. It is confirmed that the blast-damaged zone around a tunnel can be measured easily and quickly by using the developed system.(2) The fragmentation process of rock in the smooth blasting was analyzed by FEM with taking into account the crack propagation and the effect of delay time accuracy on surface smoothness and remaining rock damage has been clarified. Especially, it is pointed out that the interference of dynamic and/or quasi-static stress fields induced by blasts of adjacent holes plays an important role to control the crack propagation in SB.(3) Induced stress in damaged zone around a tunnel excavated by smooth blasting has been measured by the stress relieving technique. It is confirmed that the smooth blasting using electronic detonators decreases the damaged area in remaining rock.