ABSTRACT
Considering the bridge structure, abutments of arches were observed to be vulnerable locations for destabilization. Similarly, for the pillars, base of the pillars were analyzed to be the locations for destabilization. Characteristics of bridge (overhead bridge) facilitated to use top surface of the bridge for drilling in arch portions. Road constructing materials viz., rubble and bituminous, were removed from top surface to expose brick work along the length of the bridge and near abutments. For independent behavior of each arch and execute proper drilling operation along width of the bridge, especially near the arch abutments, side walls near the junction of arches and at ends, each 1.5 m length, were manually dismantled (Fig. 5). This was carried out during no-train movement. The remaining side walls were left intact to add weight and momentum for easy demolition with blasting. To reduce the impact of central arch on the tracks, two horizontal rows were planned to be drilled and blasted during vertical fall. For destabilization of pillars, planning was made to drill from track level during no-train movement for a minimum period of three hours. Apprehending jamming of drill rods due to moist nature of bricks, four jack hammers and one BOSCH electrical drill machine (32/38 mm drill diameter) were executed twenty four hours before the actual block period. Actual block period was planned for only charging of blast holes, taking protective measures to contain blast-induced hazards viz., flyrock and air
2 ABOUT THE SITE
The overhead bridge, bridge no. 66, near Dubrajpur rail station is 221.39 km from Howrah and lies between Pandabeswar and Sainthia rail stations in Asansol Division of Eastern railways. The arch shaped bridge, about 8 m height above track level, had three arches, each of 6 m span. The abutments for central arch were on two pillars running close to the tracks. Base of the remaining two side arches were abutted on pillar and on rock foundation (Fig. 4). Top surface of the bridge, total length 20 m, was filled with rubble and bituminous for movement of vehicles. For safety of road traffic and trains, bridge was provided with sidewalls, 1.2 m height, along the lengths of the bridge.
