Blast-Induced Ground Vibration Damage Assessment for Foundation Work at a Thermal Power Project in India

This paper presents the extensive trial blasts conducted for damage assessment due to blast-induced ground vibrations for removal of hard rocks as well as establishment of safe blasting zones during excavation work at a proposed thermal power project in India. During the excavation work it was feared that the impact of blasting may cause damage to the rocks or extension of cracks to the nearby foundations/foundation bases for various types of sensitive structures. A number of trial blasts with varying designs and charging patterns were carried out at the site. The impact of ground vibration waves were assessed on nearby structures/foundations. Ground vibrations were monitored at varying distances in a straight line, to find out the characteristics of wave propagation in the particular medium. Based on the analyses of recorded vibration data, it was suggested that no blasting should be carried out within 5 m when the foundation work is in progress. Within 5–15 m, controlled blasting should be carried out with 32 mm diameter Jack Hammer Drilling Machine while beyond 15 m and up to 25 m, 100 mm diameter drill machine can be used with hole depths up to 3.0 m. Within the zone of 25 m to 35 m from the foundation, the depth of blastholes may be more than 3.0 m but it should not be greater than 4.5 m. Beyond 35 m zone, the depth of blast holes should be between 4.5–6.0 m. It was also suggested that a clearance of at least 0.5 m from both the edges of the blasting face should be used between the boundary of excavation line and the last row of holes to minimize over break beyond the excavation line. Lighter explosive charges with longer delay periods should be used for the blastholes adjacent to the excavation boundary.