This paper will share the controlled rock blasting experiences in two underground MRT projects in Singapore. Dedicated rock blasting design elements including decoupled charging, suitable spacing/burden, time delay and loading density to promote forward movement of the rock with balanced blasting efficiency and impact to surrounding amenities and buildings are presented. The empirical formulae which was used to predict the blasting induced ground vibration was calibrated against the instrumentation data. Parameters such as the site specific constant and the attenuation coefficients in typical Bukit Timah granite are validated and recommended. Various measures which were implemented to minimize the vibration at nearby structures and mitigate fly rocks within blasting site will be shared and discussed. This includes the traffic management efforts at the heavily plied vehicular and pedestrian movements above the blasting area. Effectiveness of line drilling of relief holes to prevent the blasting induced damage to king post and ERSS are discussed. The appropriate blasting limit in the aspect of peak particle velocity (PPV) for ERSS, king post, decking and surrounding utilities and buildings are suggested. Since no blasting codes and guidelines are currently available in Singapore, the shared data could serve as reference for future projects.
Thomson-East Coast Line (TEL) (Fig. 1), as 6th MRT line in Singapore, is currently under construction. TEL is 43km long, fully underground and adds 31 underground stations to the existing rail network, including 7 interchange stations, which will link to the existing East-West Line, North-South Line, North-East Line, Circle Line and the Downtown Line. It will run through a combined north-south and east-west corridor, starting from Woodland North to Gardens by the Bay, followed by east coast stretch that will connect commuters in the eastern part of Singapore. The TEL will strengthen the connectivity and resilience of the current rail network by providing alternative travel route for many more commuters on the existing lines. The line will open in five stages from 2019 onwards. When fully open, it is expected to serve about 500,000 commuters daily in initial years, rising to one million commuters daily in long term.
Slated to open in 2021, TEL stage 3 (from Mt Pleasant to Gardens by the Bay) expects high rock crop above station formation level in 2 stations located at Bukit Timah formation, i.e. T217 Napier Station and T221 Havelock Station. The estimated rock volumes are 40,000m3 and 57,000m3, respectively. With consideration of the difficulty in breaking and removing the bedrock by any other feasible method, drilling & blasting using high explosives along with the latest electronics blasting system would be the most practical and feasible way to remove the bedrock in the shortest time frame.