This remote iron ore mine off the Kimberly Coast in WA required a staged construction of seawall extension and cut-off wall for an alignment seepage barrier. Work required expanding the rock-filled seawall around the open-cut mining operation to facilitate mining 50m below sea level.
Wagstaff Piling’s early involvement with the client and the consultants enabled innovative grouting techniques to be successfully developed and executed in difficult site conditions.
The project required a seepage control structure through 260 metres of permeable seawall to enable the safe excavation of high-grade iron ore up to 60 metres below sea level.
Wagstaff Piling developed the following innovative techniques to create the seepage control structure: low pressure permeation grouting, high pressure jet grouting, innovative hybrid grouting techniques involving intermediate pressure grouting and high-pressure jet grouting.
- The seepage barrier was 260m long and 17m deep through the rockfill and hematite sands. Wagstaff sealed into the coralline sediment aquiclude soft silty clays.
- Following Stage 1 chemical permeation grouting, holes were reopened, allowing jet grouting to hydraulically mix and grout the permeable seabed for the underlying sediments.
- Jet grouting extended upwards into seawall fill to overlap previous permeation grouting.
- A soil/cement mixed capping trench was installed using a slurry trenching technique, with soil/cement/bentonite mixed backfill completing the grout treatment.
- The approach taken allowed considerable onsite flexibility in technique.
