State of practice on soft ground instrumentation and monitoring on W2B project

The $5b Woolgoolga to Ballina (W2B) Pacific Highway upgrade, Australia’s largest regional infrastructure project, was successfully completed in 2020. It involved the upgrading of 155 kilometres of the Pacific Highway. One of the biggest challenges was to construct approximately 27 kilometres of road infrastructure on soft compressible ground in a tight construction program. Depending on the embankment height, soft ground depth/thickness, long term settlement criteria and construction program, ground treatment types varying from preload only to surcharging with wick drains and rigid inclusion (CMC or CIC) were adopted at different sections. A total of approximately 3000 instruments (7 types) were installed and monitored to assess the performance of the embankments during construction, to estimate post construction settlement in the long term, and to manage the risks of slope instability of high embankments on deep soft ground. This paper will discuss a typical procedure for instrumentation and monitoring, project specific instrumentation requirements, procurement process, instrument calibration and installation, monitoring and data processing, performance of various instruments, management of instrumentation contractors, decommissioning of installed instruments and handing over to the client. The lessons learned on what went well, what not and the root causes will be summarised; the best engineering practice for instrumentation will also be recommended for future projects.