On a $40 million liquefied petroleum gas jetty project, there is no place for down time or ineffective equipment. Such was the case offshore on the Burrup Peninsula in Australia. John Holland Construction & Engineering was required to drill 30-inch pile sockets 18.4 degrees off vertical through difficult formations of sand, clay, coral, extremely hard cobbles of rhyodacite and heavily fractured rhyodacite below. Normally, you have a drill that can do one of the formations but not the other. The company was looking for a method of drilling that could handle all of these formations while, at the same time, would meet its environmental requirements.
To undertake this task, the contractor utilized the Numa Champion RC300, one of the world’s largest reverse circulation DTH hammers, fitted with a 30-inch bit. This single hammer design allowed efficient penetration in rock formations containing strata of highly variable hardness and competence.
With the unstable, fractured ground conditions, any conventional hammer that displaces cuttings up the annulus was expected to cause hole collapse. The reverse circulation method allowed the cuttings to be ejected up the center of the hammer, eliminating the incidence of this problem. In addition, the small (1 in.) annulus between the hole wall and the hammer reduced the problem of unkeyed boulders from falling against the tool and becoming jammed.
In the Burrup Peninsula, environmental safety is a top concern. The reverse circulation hammer required no foam to clean the hole, used a completely biodegradable lubricant, and, most importantly, could bring all the cuttings back up the center of the hammer. To effectively drill these pile sockets to the depth required was a very difficult engineering feat, but John Holland Construction & Engineering successfully accomplished just that.