The use of air decks in production blasting in an open pit coal mine

The influence of air deck blasting on blast performance and blast economics and its feasibility has been studied in the production blasting of soft and medium strength sandstone overburden rocks in an open pit coal mine in India. The air deck blasting technique was very effective in soft and medium strength rocks. Its main effects resulted in reducing fines, in producing more uniform fragmentation and in improving blast economics. The fines were reduced by 60-70% in homogeneous sandstones. Oversize boulders were reduced by 80% and shovel loading efficiency was improved by 20-40% in blocky sandstones. The explosive cost was reduced by 10-35% dependent on the type of rock mass. Throw, backbreak and ground vibration were reduced by 10-35%, 50-80% and 30-94% respectively. For a particular rock mass and blast design environment, air deck length (ADL) significantly influenced the fragmentation. ADL as represented by air deck factor (ADF) in the range of 0.10-0.35 times the original charge length (OCL) produced optimum results. ADF beyond 0.35 resulted in poor fragmentation and in inadequate burden movement.