Geotechnical Investigations on Sensitive Sites
Bold Plans for Expansion
In 2010, Port Waratah Coal Services was given the opportunity to develop a new loading terminal in Port of Newcastle to meet the rising demand for Australian coal exports.
The proposed Terminal 4 would double the capacity of its Kooragang Coal Terminal, already the world’s largest coal export terminal with a licensed capacity of 120 million tonnes per annum (mtpa).
The 246 hectares allocated for the $5B expansion plan, posed geo-environmental challenges with most of the site made up of industrial landfill with contaminants, and the northern area adjoining conserved estuarine and freshwater wetland communities.
The sensitivity of the project required an extensive geotechnical investigation program to conduct the environmental assessment.
Proceed with Caution
The immediate challenge faced by geotechnics specialists Douglas Partners was how to access the sites for investigation with minimal site disturbance. Reaching many of the test sites required traveling through mangrove complexes, salt marshes, and natural alluvial clay grounds with potential Acid Sulfate Soils. Acid sulfate soils, common in New South Wales’ coastal estuaries, are safe if left undisturbed. However, once it is exposed to air from topsoil-breaking activities, its iron sulfides oxidises and releases sulfuric acid, which can turn the ground and waterways into toxic hazards.
Adding to the complexity was the proximity of neighbouring conservation lands, which are home to a number of threatened fauna (blue-billed duck, freckled duck, green and golden bell frog) and flora (Zannichellia palustris).
Traditional methods of temporary access using plywood and imported fill materials such as crushed rock needed additional measures to prevent cross-contamination. They could only be used once and needed to be taken off-site for treatment upon removal.
Pic: NSW Dept of Environment, Climate Change and Water.
A Simple and Clean Way Forward
The investigation team proceeded with Dura-Base Composite Mats as means of temporary site access and drill platforms.
The modular panels proved to be the simplest solution with the least risk to the environment. Once interlocked together, the composite mats form a continuous stable surface for vehicles and equipment to travel on. This stops heavy vehicle tracks and tires from rutting the ground, leaving the buried acid sulfate soils undisturbed and inactive.
While the Dura-Base has a proven record for supporting heavy machinery in soft ground conditions, the team took the innovative approach of reusing cleared mangroves as mulch to level the ground, and provide an additional layer of padding under the mats.
Lowering the Risk of Cross-Contamination
Dura-Base mats which are made from HDPE have the advantages of:
- made from HDPE, an inert material that is safe for use on sensitive soils.
- being non-porous, making it easy to clean with just water sprayed on its surface, and eliminates the risk of being a carrier of contaminated soils.
Compared with roads made from aggregates, removing composite mats on job completion is much quicker, less messy, and does not need expensive off-site decontamination.
And unlike timber or plywood, composite mats do not pose the risk of rotting, breaking, harbouring insects, or coated with strong pesticidal chemicals.
This allows the same mats to be reused over multiple investigation points which reduces the number of truck movements that would have been needed for the equivalent amount of fill material.
Protecting the Future
A single Dura-Base mat measures 4.27m x 2.44m with a 105mm thickness. Specially designed to have overlapping sections, the mats once interconnected creates a protective layer that helps with the load spreading of vehicle tires across the entire working surface to the ground below.
This ensures protection of ground against not just accidental rutting and the subsequent exposure of acid sulfate soils to the air, but also protecting the underlying root substructure of cleared mangroves. Along with the use of mulched mangroves, this gave areas cleared for access the best chance of recovery once the job was done.
Safe Completion
The field investigations were completed safely with the scope delivered on time. In addition, the team reported positive signs of regrowth in areas where mangroves were cleared, in just under 8 months.
JWA Oilfield Supplies provides to the Australia’s resource and construction sector with composite matting solutions for temporary roadways and ground stabilisation on sensitive soils. To find out more about Dura-Base Composite Mats, click here or call 1800 264 628.
Enquire now