Slope Remediation Responses by TfNSW Following the 2022 Natural Disaster Events

In March 2022, multiple natural disaster storm events caused flooding and slope failures across southern New South Wales (NSW), Australia, with over 750 mm of rainfall recorded across the Illawarra. Prolonged rainfall throughout the year led to over 100 recorded slope incidents with multiple closures across the Transport for NSW (TfNSW) network in the South Region. Two landslide case studies affecting TfNSW assets during the aforementioned storm events are presented herein. The paper will highlight the collaborative design and construction methodologies that allowed for expedited repair of the assets. Site 8 was a large fill embankment slip along a mountain pass that under-mined the westbound travel lane, creating stability concerns for the road. Due to the slope failures, the local communities were isolated and reinstating access was designated high priority. Remedial options considered included lightweight fill, soil nails and embankment reconstruction with earthfill. The preferred remedial option incorporated soil nails and embankment reconstruction using rockfill. Delivered in collaboration with Private Industry, and awarded as a design and construct contract, the works were completed within 3 months. Site 81 was an approximately 150 mm long tension crack at the crest of a fill embankment along the Illawarra Highway affecting both travel lanes. Due to continued and significant movement, the Highway was closed. This resulted in up to 2-h detours for the community. Remedial options considered included soil nails, a piled wall and lightweight fill. The preferred remedial option was a reconstruction using rockfill in combination with synthetic geogrids. TfNSW delivered the design and construction in 1 month.