Case Study: Preserving Reliable Access to a World-Heritage National Park
Client: Department of Transport and Main Roads
Location: Springbrook Road, Gold Coast, Queensland, Australia
Executive Summary
Geobotica worked with Queensland’s Department of Transport and Main Roads (TMR) RoadTek Branch to monitor the stability of a colonial-era wall above a trafficked roadway following a series of significant rain events and a landslip.
The GeoLidar solution was quick to determine both the wall and road infrastructure were moving. With Geobotica’s continuous monitoring and early warning system in place, geotechnical engineers were able to devise solutions to secure both the wall and road. These repairs and protections allowed the infrastructure to remain safe while works were undertaken to prevent any collapse.
Background
Springbrook National Park is a World Heritage listed park located in the Gold Coast Hinterland in Queensland, Australia. It is known for its stunning natural beauty, including unique and diverse landscapes such as subtropical rainforests, waterfalls, and volcanic plateaus.
Springbrook National Park is a popular destination for nature lovers, hikers, and photographers, offering a range of scenic walks and activities. Its designation as a World Heritage Site reflects the area’s exceptional natural beauty and importance for conservation.
Gold Coast Springbrook Road was constructed in the time of horse-and-cart travel, with several horse watering troughs still preserved. In some places, the original track remains though has been expanded over the decades. Many of the original documents regarding the construction method, design and any geotechnical considerations either never existed or are unknown. As a result, when a slope instability or landslip occurs, a modern-day geotechnical engineer has little documentation to better understand if a slope can withstand the forces subjected to it.
The road was closed following several major landslips that occurred following severe rain events in February and March 2022.
Six months later, another rain event saw more than 200mm fall in 24 hours.
It caused a localised collapse on the downslope embankment of the road. The landslip led to an old dry-stacked stone wall being exposed, with concrete pipe from a culvert passing through it.
A small stream comes down the slope and passes under the road via this pipe.
Solution
Geobotica was engaged to monitor the area to determine if the old wall and the road above it were stable, or if a further landslip was imminent.
With GeoLidar installed, a further 100mm of rain fell over a two-week period, and the system detected a rapid change in the slope and the road surface meaning the ground was moving quickly.
A visual inspection determined that the culvert was blocked. A large amount of water continued to flow down the hill, but only a small amount trickled out the pipe. GeoLidar data showed the drystone wall was deforming quickly at a rate over 2mm per day, and the crest of the road was also moving, but at a slower rate, suggesting a classic rotational failure was developing. Movement was also detected along the road surface but only downhill of the line of the culvert, suggesting that the water flow was impacting the stability of the slope.
The small movements detected by GeoLidar ranged from as little as 2mm on areas of the road surface and up to 30mm on the vertical wall, providing a valuable early warning.
Fortunately, little rain fell over the subsequent four weeks, giving RoadTek a window to effectively apply remedial construction works to trouble-shoot the problem. Using the data from GeoLidar, design implementation included a vacuum truck removal of two large rocks and a lot of smaller material that had blocked the culvert.
A new pipelining was designed and installed, and interim slope remediation work began. Working swiftly with excavators, rock funnels, geofabrics and reno mattresses and teams working on ropes, the Geobotica data was used to quickly install the temporary support. The slope immediately responded: within 48 hours the road surface was stabilised and deformation of the road and cliff face reduced its velocity.
These remedial works, plus ongoing monitoring for assurance, secured a permanent geotechnical ground support plan to be designed and installed over the coming months.
The early warning given by GeoLidar data, combined with the intelligent, fast, and efficient works performed by RoadTek, meant the slope was stabilised and a potential collapse was averted. If the collapse were to occur, it would significantly reduce access for local communities and tourism for the internationally recognised natural area.
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