Strengthen Rail Index Machine Slab

The causeway features three 12m long concrete reinforced culverts, each measuring 750mm in diameter, situated beneath the road and within an embankment.

The embankment consisted of compacted bedding material and backfill, with an ageing bluestone protection wall supporting the culvert pipes. The bluestone wall was significantly compromised in multiple places due to the force of the creek’s water flow, which became a raging torrent during rain events. Prior to the heavy rainfall, the reserve was exposed to bushfires which had destroyed vital areas of protective vegetation.

This allowed the creek’s fast flowing water to breach the bluestone wall in a number of places and washed away large amounts of soil fines from the embankment, creating several voids in the protective wall and erosion beneath the causeway.

Worried about the ongoing stability of the road and culverts, the ACT Parks and Conservation Service commissioned a ground penetrating radar (GPR) test to assess the damage and severity of the voiding beneath the roadway. While the road was determined to be structurally adequate for general vehicle use, the load limit had been compromised, preventing trucks and tourist buses from accessing the road.

To arrest the damage, ground improvement works were required to stabilise the embankment and re-support the ground beneath the road, while also protecting the long-term performance and durability of the culverts.

As the nature reserve was located in an environmentally sensitive area, replacing the existing culverts was quickly ruled out. Instead, Mainmark was commissioned to provide an environmentally safe, non-intrusive and cost-effective remediation solution.

The mine’s senior engineer accepted the methodology proposed, namely the Deep-Injection of proprietary engineered structural resins beneath the machine slabs to strengthen the sub-base soils and Uretek Slab-Lifting to re-level the slabs.

The work was successfully completed using the self contained Operations Rig and experienced personnel.

The index machine slab was given strengthened support and restored to level so that the iron ore trains could travel safely and efficiently on the rail.

We were required to ensure appropriate Occupational Health and Safety standards, and provide quality assurance method statements to the client.