COTTER DAM

Foundation grout curtain and drainage under Australia's largest roller compacted concrete dam

Project Overview

Completed in 2013, the Enlarged Cotter Dam (ECD) comprises an 87m high roller compacted concrete dam (RCC) wall built downstream from
the old 26m high dam wall, along with two auxiliary dam walls along low-lying adjoining valleys. As of 2019 the ECD remains the highest
RCC dam constructed in Australia with a water storage of 78 gigalitres with a 482-hectare catchment. Geovert constructed the 60m deep
grout curtain under the full length of the 330m long ECD.

Using a contactor as diverse as Geovert allowed the restricted access drilling inside the steep galleries, foundation grouting, drainage works, depressurization drilling, rock bolting and over 2 years of rock scaling works to be completed using just one competent contractor without having to manage the interface of multiple subcontractors.

Geovert Solution

Hydraulic winches were installed at the top of each gallery incline to allow a 5t tracked drill rig and a skid mounted diamond coring rig to be hauled up the 42° stairs, gaining 80m elevation over the length
of the incline. The foundation grouting was undertaken in this confined gallery to allow the RCC construction to continue above. A fully automated grout injection control system was installed in the
gallery, ensuring the GIN stop criteria were met, providing real time construction monitoring using the Jean-Lutz instrumentation.

Upon completion of the grout curtain foundation which required primary, secondary, tertiary and quaternary grouting, drainage holes were drilled beneath the dam monolith. Pressure relief drains were drilled from the crest of the dam, requiring extremely low deviation drilling to intersect the breakthrough target area, 1.5m wide, on the gallery roof, up to 65m below (2% deviation).