Brockenhurst and District Probus
The Brockenhurst and District Probus welcomed Dr Colin Jolly who described the preparatory work to blow down a tall industrial building in London. The Astral Site in Erith, South East London, has been used for cable manufacturing for over a century. During the last 20 years of its operational life, until closure by Pirelli in 2003, it was mainly used for the manufacture of high-tension sub-sea power transmission cables.
The site was earmarked for development and in 2005 clearance began. The main challenge was the demolition of the 84 metre high cable tower. The structure was constructed using steel columns and girders imported from the USA as Europe did not produce the heavy gauge steel required at the time.
The demolition site presented significant challenges due to the proximity of key buildings and infrastructure. Offices, factories, a War Memorial, gas processing plant and road network had to be protected and disruption minimised. The ground substrate alongside the river Thames is fluid and readily transmits shock waves. Vibrations from heavy lorries can result in local damage. Explosive shock waves from the demolition could cause significant damage to building foundations over a large area.
The topple zone was identified and berms of crushed concrete were build along the fall path to reduce the ground shock. The removal of some low rise buildings on the site was delayed until after the tower demolition in order to trap dust and flying debris.
The ground floor of the tower was stripped of its sheet cladding exposing the main steel columns. These were pre weakened by cutting the arc of a sphere through the steel and below this a diagonal cut. These reduced the amount of linear explosive cutting charges required. A combination of shaped cutting charge in the weakened areas and a dynamite sideways kicking charge were used on each column. A digital sequence of detonation resulted in an accurate collapse of the tower along the topple zone.
The successful demolition enabled the tower to be removed safely and economically. It took only 36 hours to completely clear the site.