Extraction of Dimensional Stone with Controlled Fracture Growth Blasting Technique

摘要

Explosive energy transmitted to the rock during blasting, besides doing useful work of fragmentation and displacement, may also cause damage to the rock in the form of unwanted macro to micro level cracks. Macro crack development in desired direction is required in extraction of dimensional stone and at the same time there is need to reduce micro crack development in the block and remaining rock. To achieve this objective, experimental work in the quarries was carried out for separating dimensional stone block by using detonating cord of 10 to 50 g/m by varying hole spacing, hole diameter, air cushioning, water and sand filled blast holes. Blast hole notching was also carried out. Further, tests were carried out by using various liners inside the blast hole. P-wave velocity was conducted for quantification of damages. The P-wave velocity close to hole always reduces after blast. By using notched hole with paper tube, decrease in P-wave is minimum indicating least damage. Economics of different methods is also compared. In comparison to conventional use when holes are lined with inexpensive cardboard or plastic liners with a slit, the cost and damage is the least and development of crack is in the desired direction.