All under control

Abstract

The presence of shear zones and distress problems in the cavern at the Sardar Sarovar Project complicated the excavation of the ramp. The following conclusions were drawn: • The ramp on the downstream wall of the cavern was removed completely and successfully by controlled blasting and by providing immediate support and reinforcement to the exposed wall. Suitable blasting patterns and sequences were arrived for the overall stability of the cavern. • The division of ramp into 'main' and 'bark' was a conservative approach compared to blasting in a single stage with smooth blasting. This method proved to be very safe and did not impede the progress of the excavation. Delay, if any, in excavating the ramp was due to operational difficulties in providing the reinforcement without which further blasting was suspended. • Some slides in the ramp that occurred during the excavation were expected due to intersection of the joints. Those slides were l ocalised and had nothing to do with overall safe blasting practices. A few blasts were taken to induce slides to prevent sudden collapse of the rock that could endanger the safety of men and equipment. • The lower specific charge for ramp blasting compared to bench blasting was attributed to the presence of an additional free face and better utilisation of explosive energy. • The ground vibration generated by blasting during ramp excavation was lower than that of earlier blasting for excavation of the cavern on account of an additional free face and increased blasting efficiency.