Engineered Tunnels for Alcoa’s Willowdale Bauxite Mine

Project Details
Location: 100km SSE of Perth, Western Australia
Owner: Alcoa
Consultant: Onyx Projects Pty Ltd
Contractor: Charles Hull Contracting
Construction Date: March 2020

The Project

West Australian mining giant Alcoa has recently relocated its Willowdale bauxite mine site from the 20 year old Orion location to a new location known as Larego. This challenging move included the safe relocation of an 850 metric tonne crusher to the new area, set to be the centre of the mine’s operations for the coming decades.

The Willowdale mine supplies all of the bauxite for Alcoa’s Wagerup alumina refinery with these two locations injecting $480 million annually into the local economy. During the crusher move, it was critical that day-to-day operations continue without incident in order to keep the Wagerup refinery productive.

The Challenges

The client had a heavy vehicle haul road crossing a light vehicle road and Conyour. The client required tunnels to make overpasses, however the client was also after a fast economical solution with low cover to reduce the overall backfill footprint while still catering for significant live loads. The live loads being two fully loaded Komatsu 830E Dump Trucks crossing simultaneously and Komatsu PC3000 Excavator on Bossitch 275T Float crossing on it own.

ACP’s Solution

Our team worked with the consultant and contractor as part of a carefully engineered process, designing and constructing two 33 metre long road arches and headwalls for the Zig Zag and Conveyor underpasses.

ACP supplied two Bolt-A-Plate heavy haul road arches and MSE wire face headwalls for Alcoa’s Larego Mine Site. The value-engineered project saw our team provide cost efficiencies for the client, as we worked with Onyx Projects to provide a shorter structure that offered comparable benefits.

This improved design offered considerable time and cost savings, reducing the structure footprint by 50% for Zig Zag and 31% for Conveyor 374 underpass. This, in turn, led to significant savings in footings and backfill, as well as shortening the time to complete earthworks and plate construction.

The Zig Zag tunnel featured a 5.9m rise and 6.2m span, and the Conveyor Tunnel 374 (HV Tunnel) featured a 3.1m rise and 6.6m span. Both 33m long structures provided strong, reliable and safe transport corridors to ensure heavy vehicles could pass over and mine operations could continue as per normal.

ACP Products Supplied:

Application – Haul Road Underpass:

  • Haul Road CH435 overpass Conveyor 374 CH450
  • Haul Road CH1355 overpass Zig Zag Road

Live Load:

  • Komatsu 830E Dump Trucks (Gross weight 386t)
  • Komatsu PC300 Excavator on Bossitch 275T Float (Gross weight 449t)

Construction Time:

  • Zig Zag Road: Plate assembly – 10 days / Backfill and headwalls – 40 days
  • Conveyor 374: Plate assembly – 5 days / Backfill and headwalls – 17 days