WorldWide Drilling Resource

Urban Construction Blasting Adapted from Information by Orica Mining Services Southport Central is a large, three-tower residential and commercial precinct developed by the Raptis Group in Queensland, Australia. Tower 1 was completed without the need of blasting. While excavating the basements for Tower 2, the earthmoving contractor encountered rock which could not be excavated using a bulldozer or excavator, so the call for blasting was made. With the delay in exca- vation causing the project schedule to slide, there was intense pressure to get blasting started as fast as possible. Blasting in a busy urban environment requires special techniques to reduce adverse effects on the public and surrounding worksite. Conventional blasting methods would have required firing one small blast every afternoon. Using this method, over 120 blasts would have been required to complete the excavation, increasing the project duration by several months. Additionally, each blast would require road closures and portions of the worksite to be shutdown, causing considerable and costly daily disruption to workers and neighbors. To reduce delays and costs, Orica Mining Services developed unique methods to fire one large blast a week instead of a small blast every day, thereby reducing the overall number of blasts required to complete the project. The innovative method involved loading blastholes with up to five individual explosive decks. To control vibration levels, each charge fired separately. Electronic detonators were employed to allow large, complex blast geometries and guarantee the security of loaded blastholes. Martin Adam, Orica’s principal blasting engineer remarked, “The largest blasts were loaded over the course of five days, so we had to be sure nothing could happen to the explosives in the ground each night. Electronic detonators are virtually im- possible to activate unintentionally once in the ground, so they were the best choice in this case.” Blast vibration levels were managed to minimize the overall impact on the neighboring residents and businesses. This meant not arbitrarily targeting the lowest vibration levels, since it would have increased the number of blasts and duration of persistent drilling noise by several months. Instead, higher limits were used without impacting safety. Each blast clearance in- volved up to 20 blast sentries, clearing workers from the towers under construction, stopping traffic on two streets, and tem- porarily closing the busy Gold Coast City Council Library across the road. Adam said, “By talking to the neighbors, we found that as long as they knew exactly when the blast was going to occur, the blast effects were not upsetting. Therefore, we aimed to fire one big blast a week, making absolutely sure everyone knew exactly when it was going to occur, and then sticking to that time, even if the blast was ready a day early.” 20 APRIL 2018 WorldWide Drilling Resource ®