Damage threat to sensitive structures of a thermal power plant from hard rock blasting operations in track hopper area: A case study

The article deals with the development of controlled blast design patterns and methodologies for excavation of hard rock for foundation work of a track hopper in a running thermal power plant in close proximity of many sensitive structures. Test blasts were conducted with different blast geometries and charge loading patterns at selected locations. The results of the test blasts were analysed to evolve safe controlled blast design patterns and methodologies for completing the total excavation work. The threshold value of vibration for the safety of various structures/foundations present has been taken as 25 mm/s based on the dominant frequency content as well as guidelines from the regulatory authority. The dominant frequency content of the ground vibration waves was in the range of 10–40 Hz. Controlled blast design parameters, namely maximum explosive per delay, size of the blasts and blast geometry were formulated based on established ground vibration predictor equation and nearness of structures concerned from the blasting point. Two blasting zones were classified for safe excavation work. For the first zone within 20 m from the structures, controlled blasting using 32-mm diameter blast holes with small blast geometry was suggested, whereas for the second zone beyond 20 m, controlled blasting with 100-mm diameter holes with lesser hole depth and limited number of holes was suggested. The whole excavation work in the track hopper area was completed safely without causing any damage to the nearby sensitive structures of the running thermal power plant.