Following the intense rainfall caused by ex-Tropical Cyclone Debbie that hit coastal Queensland in late March 2017, over 80 landslip sites at the Lamington National Park Road were seriously damaged by scour and slope instability.
The road is located on the flanks of the Lamington Plateau, formed by the ancient Tweed Volcano, and provides access to the popular Lamington National Park. Repairing and re-opening the road as quickly as possible was a priority for the local community as well as for restoring public access to the park.
Remediating sites scattered along a 22 km section of winding, mountainous road was very challenging due to the steep terrain and access constraints. This section of road was often narrow (single lane) with steep cuts up to 30 m high and natural slopes up to 75 m high. On the lower side of the road, sidelong fills were located on natural slopes of up to 100 m high.
In response to the need for quick solutions, Golder’s geotechnical, hydrological and construction design/drafting teams collaborated across offices to deliver remedial designs for multiple sites in a compressed time frame.
Engineered design solutions were required at approximately 54 sites and included gabion walls, soldier pile walls, concrete beams with bored piles, debris flow fences, steel wire mesh with rock anchors and soil nail and shotcrete treatments. In addition to the geotechnical design solutions, a number of up slope sites required mechanical scaling and revegetation in accordance with TMR’s specifications. The remedial work also included repairs to existing damaged assets such as drainage culverts, outlet structures, drystone walls and pavements.
For some very steep sections of damaged slope and road, standard solutions used by our client in the past (i.e. gabion walls and soil nail walls) were not feasible. We overcame this challenge by developing a soldier pile wall solution that could be constructed from the existing road. This included preparation of new, site-specific design guidance and specification documents.
Our team also provided a highly tailored solution in another area where overhead powerlines posed access problems. For easier constructability at this site, we developed a site-specific solution to overcome a latent condition by incorporating micropiles into the original footing design that could be installed using small plant. This eliminated the need for large-diameter bored piles requiring larger plant and major earthworks to provide temporary access ramps and working platforms.
Golder also provided services during the construction phase, including design support and an on-site geotechnical engineer to facilitate the implementation of the remedial designs.
Golder’s experience, highly tailored designs and rapid delivery of practical solutions allowed this scenic road to be remediated and completed on schedule. Our quick response and quality solutions were highly valued by our client, allowing them to meet their commitments while achieving the design requirements in accordance with TMR’s Geotechnical Design Manual.