Cavern Excavation & Ground Support

RIX excels at civil projects in areas of limited access or confined space, such as the North Head STP Mini Hydro Electric Project. Works were undertaken in a cavern 60m underground and below the access shaft, with materials, plant and equipment being dismantled and craned down a shaft to be re-built within the cavern.

There were four phases to the project:

Phase 1 – Staged excavation

Staged excavation of the roof and walls, including support consisting of rock bolts, meshing and shotcreting of the new turbine room.

Phase 2 – Gantry beam

Gantry beam construction and installation, where form and pour in-situ concrete reinforced gantry crane rail beams.

Phase 3 – Pipe and flange installation

Unable to turn the wastewater off completely, professional scuba divers cut out sections of the mainline pipe and weld from the inside.

Phase 4 – Concrete encasement

The valve and DOOS were concrete incased, and due to long pumping distances underground, the concrete was put to ‘sleep’ at the concrete plant and ‘re-actived’ when it reached its final position.

The project was successfully completed to program, safely and to the highest quality.

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