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Client: SEAGAS
Location: Mutton Cove, Osborne
Contract Value: $80k
Description:
Spry Civil Construction were engaged to undertake a deep excavation of the Port Campbell to Adelaide SEA Gas pipeline at Mutton Cove Conservation Park (Osborne, SA). The purpose of the excavation was to perform a pipeline defect assessment and rectification works where necessary.
Prior to works commencing, a permit was obtained from the Environment Protection Authority to discharge treated excavation water back into the Port River. A licence was also obtained from the Department of Environment and Water (DEW) to enter and work on the land parcel, which is a conservation area.
An excavation dewatering system was installed, and additional pumps were brought in to ensure the excavation was dry enough for personnel entry. An engineered shoring system was then installed to hold back the pressure of water and surrounding soils from entering the excavation.
The excavation was considered to be a confined space with a potential contaminated atmosphere, so each person entering was connected via a harness to a fall arrest inertial reel, and then once inside, to a winch extraction system. When the presence of hydrogen sulphide gas was detected above the minimum safe threshold, the workers also had to wear an approved respirator. The pipeline was fully exposed back to the bare metal for close inspection and engineering assessment by SEA Gas. Coating defects and metal loss rectification works were then managed by SEA Gas in accordance with industry protocols..
The entire 4m length of exposed pipeline was then re-coated using an approved two tape system, tested for discontinuities, sand shaded and backfilled. In re-coating the pipeline, several challenges were overcome by the project team, including keeping the pipeline dry during recoating (as water continued to ingress down the side of the shoring onto the pipeline) and surface preparation of the existing coating, which was either disbonding or holding moisture, at the pipeline /shoring interface.
Works Undertaken:
The excavation was very challenging due to the depth, which was 5.5m to bottom of excavation, the close proximity to the tidal influences of the Port River and the fact that the pipeline was fully pressurised (>100 Bar).
The high-risk work included:
Bulk Earthworks, Stormwater Installation, Sewer Installation, Portable Water Installation, Gas Main Installation, Electrical Installation, Installation of Lighting, Common Service Tenching, Kerbing, Footpath, Pavement Works, Asphalt Supply
