Auckland Hill, Gladstone Regional Council

Gladstone Regional Council opted to proceed with GSS’s design incorporating soil nails and shotcrete for the upper slope and soil nails and double-twist woven wire mesh (Mac Mat R) for the lower slope.

The scarp associated with the existing instability is a steep cliff face (approximately 70°) that is 45m wide and has a maximum height of 20m in the northern section, tapering to 2 m height in the southern section.

The exposed rock is highly weathered mudstone/arenite with moderately spaced sub-vertical defects. These are cross-cut by low-angle joints, forming blocks that have become loose and fallen from the slope.

The joints are generally tight to slightly open, rough, and weathered to form a distinct orange iron oxide or silt infill. Some scrub vegetation has become established on the older debris material and around the cliff exposure. The slope angle on the lower slope below the steep cliff face is approximately 25 -40°.

GSS used DTH drilling systems to install soil nails to a depth of 8m with a corrugated sheath to ensure a 100-year design life. The client was pleased with the delivery of this project on time and within budget, along with all the stakeholders.