Narrabri to North Star Phase 1 April possession update
In April, the final stage of the Narrabri to North Star Phase 1 section kicked off with the temporary closure and possession, of the operating rail line between Narrabri and South Moree, for major construction until 31 October 2022.
June 28, 2022
Where are we up to?
Motorists using the Newell Highway are seeing plenty of construction progress, with the installation of concrete structures to support the new Ten Mile and Bobbiwaa Creek bridges continuing over the next few months. Upgrade works have also progressed at multiple level crossings and areas that require concrete culverts at creek crossings.
However, most of the work along the 55km of rail corridor has involved bulk earthworks, which is stage 2 of our 7 stages of track construction graphic. Earthworks involve moving, stabilising and transforming 1000’s of cubic metres of earth to reconstruct the track foundation.
Before earthworks can start, we need to clear vegetation and strip the topsoil. We then excavate and remove the existing embankment, including any existing ballast and general fill.
Earthwork activities occur in a six-step process:
- Backfilling the formation – the materials that were initially removed from site are mixed and placed back on the formation using an excavator or dozer
- Trim, roll and compact – as the fill can only be loosely placed by an excavator or dozer, the material is uniformly spread and compacted with heavy rollers and then trimmed by a grader to ensure the right thickness and levels.
- Lime placement and slaking – specialist trucks spread lime uniformly over the placed layer. A water cart then sprays the lime with an even coverage to start a chemical reaction known as slaking
- Soil stabilising – once the lime has been slaked, a specialised machine cuts, pulverises and mixes the material together
- Layer finishing – immediately after the layer has been stabilised, heavy rollers compact the mixed layer and a grader trims the layer to the specified thickness and levels
- Repeat – repeat steps one to five three times to achieve the formation level.
But wait, there’s more! After the first part of the foundation is built up and stable, a final layer called capping goes down before stage 3 can commence. Capping is a high-quality material that has less clay and more crushed rock, has better drainage properties and can be compacted to a very uniform level. Now the foundation is ready for stage 3 – laying of the bottom ballast.
TOP IMAGE: Infographic showing the seven stages of track construction with stage two, earthworks, circled.
BOTTOM IMAGE: Photo of earthworks in progress along the Narrabri to Bellata section. Excavators, rollers and other earth moving equipment.
