Bulli pass landslide hazard assessment and control measures

Dr Phil Flentje, The University of Wollongong


The Bulli Pass section of the Princes Highway is a century old two-lane road which is located approximately 11km North of Wollongong and traverses steep slopes of the Illawarra Escarpment. It is an important arterial road for the northern suburbs of Wollongong, connecting Mt Ousley Road (M1 Princes Motorway) at the crest of the escarpment to Thirroul at the foot of the escarpment. This artery provides a commuter conduit between southwestern Sydney and the northern Illawarra with about 15,000 AADT.

The pass has a long history of landslide and rockfall events, some of which were reported as early as 1890. One of the most significant of these events occurred on 17 August 1998 during a greater than 1 in 100-year 6-hour peak intensity rainfall event. The 1998 landslide event comprised of an estimated 30 debris flows and numerous large rockfalls which partially inundated several cars and trapped about 15 vehicles on the pass. More recently, in early 2015, a small rockfall penetrated the windscreen of a car travelling up the pass.

This talk will present an overview of the methods used to investigate the hazards and assess risk at the site over a five-year period. This has included research into the landslide history, geomorphological mapping, acquisition and review of airborne laser scanning (ALS) data, review of rainfall data, and the development of a landslide volume frequency model. The development of this model allowed hazards to be readily communicated and risks to be assessed. Following a cost-benefit design process, the RMS selected a GeoBrugg solution that comprised a series of Shallow Landslide and Debris Flow Barriers. These have been installed in a two-phase construction program in late 2016 and 2017 that involved two, 10 week road closures. During this time, the contractor- Specialised Geotechnical installed the GeoBrugg solution with support from Mr Adam Morrison and Martin Boerner. Specialised Geotechnical were managed by Public Works and RMS, and advised by Engineering Geologists Dr. Phil Flentje from the University of Wollongong, and Mr Andrew Hunter who was from Coffey at the time and GHD at present. This project recently won an Excellence in Road Engineering Award at the Institute of Public Works Engineering Australia Conference (November 2017).

About Dr Phil Flentje

Dr Phil Flentje is an Engineering Geologist and senior research fellow at the University of Wollongong whose principal area of interest lies in landslide risk management, landslide monitoring and GIS applications. His research is industry based where he collaborates with the Wollongong City Council, NSW Roads and Maritime Services, and the NSW Rail Corporation. He has worked as an engineering geology consultant in the Sydney Basin and as an exploration and petroleum geologist across Australia.

Venue location


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