Remediation of cut and fill slope along linear transport infrastructure post-Cyclone Jasper, QLD

In response to the significant infrastructural damage inflicted during Tropical Cyclone Jasper (TC Jasper) between 13 and 18 December 2023, this paper presents the adopted approach to the restoration of linear transport infrastructure, particularly focusing on slope remediation at one of the most severely affected site. In collaboration with the Client, WSP carried out a detailed design to address slope instability at this location. An initial aerial inspection identified a compromised fill embankment and an exposed old retaining wall. An ensuing site inspection and slope risk assessment revealed stability risks at the downslope embankment, resulting in the temporary cessation of operations. In consultation with the stakeholders, WSP conducted an options analysis to explore temporary and permanent treatment measures to restore the asset promptly. After options analysis, WSP undertook a detailed design of two preferred treatment measures related to (i) remediation of a 30 m section of the downslope embankment and (ii) construction of temporary deviated alignment by excavating into the upslope batter and widening formation. The excavation of the cutting, measuring 145 m in length and up to 15 m in vertical height, was undertaken in the presence of WSP geotechnical engineers. A combination of passive dowels, reinforced shotcrete, pinned rockfall mesh and subsurface drainage enhancements were proposed for permanent treatment. The design considered local and global slope instability mechanisms, site constraints, and sensitive environmental and cultural heritage settings. Durability requirements were set for a 100-year lifespan for permanent in-ground elements, considering the site’s tropical environment and high annual rainfall.