The principle is simple. Drive a hollow steel pile into the ground using a vibratory hammer. Fill the pile core with sand. Having reached the desired depth, air pressure forces the sand out of the pile, pushing the steel tube up by three metres. Then drive the pile down by two meters, creating a densely packed, one-metre-long pile. Repeat the process as many times as necessary.

“We used sand drains on the Busan-Geoje Fixed Link project as well,” says Peter de Haas on behalf of Tunnel Engineering Consultants, which has for the past four years been advising Korean contractor Daewoo. The specialist, hired out by Royal Haskoning gave his client the tip to contact Strukton for the immersion tunnel linking Busan and the Geoje peninsula. “At a depth of 75 metres, our sand drains are the deepest in the world. We have installed them as vertical drains to accelerate consolidation of the clay layers.”

Source: Cobouw, 13 November 2007
Photo and text: Theo Leoné