David Lees and Associates was appointed by Baulderstone Hornibrook to determine suitable methodology for the removal of large basalt boulders adjacent to the existing Princes Highway near Balina as part of upgrading works.

The basalt boulders were part of a weathered sill forming the high ground adjacent to the Princes Highway. The sill was between 4 to 6 metres high and the boulders were about 2m3 with large clay voids between. The location of these voids was unknown.

A drill and blast system was designed to fulfill  production requirements whilst maintaining the safety of motorists on the busy highway, and controlling vibration limits for a nearby farm and petrol service station.