GERMAN PILING METHOD EXPLODES MORE HASTE LESS SPEED MYTH

The Rosenstock shock blasting process of bursting rock into small pieces to allow sheet piles through was demonstrated on the found60 M Rochester way relief road construction site in South-East London. Small amounts of explosive are used to provide shock waves just strong enough to burst the rock in a small area to accommodate the piles. Site conditions consisted of 5 M of fill and a 10 M layer of sand, gravel and cemented shells overlaying clays. The piles had to be driven through to found 3 M into the clay - a total of 18 M below surface level. Holes of 125 mm diameter were drilled into the clay at the founding level and strings of explosive set at pre-determined levels were lowered into the plastic-lined holes. Following blasting, the piles are driven before the rock and clay can re-consolidate. The first eight pairs of piles were driven into place within about 75 minutes. However, after a delay of three days, refusal took place at a depth of 16 M when driving a pair of Larsen piles. Consequently it is essential that piling must take place soon after blasting. (TRRL)