As part of a new flood alleviation programme the Government of Gibraltar needed to find a way to release the water which was trapped on the higher inland side of the Battlement Wall. This effectively required the wall to be breached, something it had been designed to resist over a century ago!
Rock Foundations (Gibraltar) was asked to consider a method which would not only result in the 4m thick solid rock wall being penetrated but would also facilitate the insertion of two large diameter plastic ducts.
The method chosen by the engineers at Rock Foundations was to stitch-drill the wall with a 240mm diameter DTH hammer supported by a 17,000 litre compressor.
Drilling had to proceed with caution as it was important not to deviate from the starting position but also to prevent a build up of excess arisings behind the drill head which would prevent extraction. In addition to the physical challenges of drilling the rock the rig would be positioned below the water level at periods of high tide. The client operated a water extraction system for the period of drilling but the rig needed to be removed from the subterranean platform each evening.
After a week of drilling the holes were complete and the client was able to successfully position the two new ducts and backfill to allow the remainder of the works to progress on time.