Completion year 2018
Following a land slip, WGE were engaged to assess the slope and provide a design to stabilise the slope. Improved access in the form of a composite plastic and galvanised modular stairway was designed to upgrade the existing hillside path to the cable way pulley wheel, to allow operatives to safely access and maintain the cable way.
The world heritage listed site is Queensland’s second highest mountain, holding the record for Australia’s highest recorded annual rainfall of between 8-12m. The site is only accessible by a two-day hike through the rainforest, helicopter or on the privately owned and operated cable car. Therefore, simplicity and constructability were key to the design as construction plant cannot access the site.
Tropical soils in other areas of the site were suffering from extensive erosion and had started to undermine structures. WGE carried out hydraulic analysis and provided drainage design to effectively capture and manage the high rainfall and surface flows experienced at the site.
WGE were engaged to provide a safe and constructible design to stabilise the slope, using geomorphological and a geological mapping and pragmatic site investigation to note the difficult access to the site. Slope monitoring of the land slip and surrounding areas was also investigated to provide insight into the slope’s behaviour.
WGE’s ground engineering team used slide software to back analyse the stability of the slope, and design a safe and constructible retaining wall. The retaining wall selected was a gabion wall for its superior permeability and ease of construction in a difficult location.
WGE’s structural engineering team designed a shear key to stabilise an under mined foundation and designed a modular composite walkway structure and maintenance platform.
WGE’s civil team designed a regraded site drainage system to cope with the high surface water flows to minimise material and labour on site soil excavated from the land slide was placed in the eroded areas and then covered with the proprietary concrete composite material concrete canvas.
Due to the difficult accessibility of the site, concrete canvas was used in lieu of concrete lining which would be difficult to transport, mix and pour on site. The high rainfall required careful design and selection of the retaining wall system, while working in a world heritage site meant designs had to be sympathetic to the environment and minimise impacts to the surrounding rainforest.
To add to the difficulty, no as-built drawings of the cable car and top station existed. As such, WGE engaged and managed surveyors and, using a 3D laser survey, quickly and efficiently allowed designs to progress.