Preloading as a Sustainable Ground Improvement Solution for Road Infrastructure

Construction of infrastructure over soft soils presents significant challenges for sustainable foundation solutions due to low bearing capacity, high compressibility, ongoing long-term creep and onerous design performance criteria. The commonly adopted solution to these challenges is to construct a rigid structure which is often carbon intensive, costly and does not necessarily circumvent all differential settlement issues. This paper presents a case study of the preloading treatment design of a road embankment at a site in Wentworth Point, NSW, underlain by soft reclaimed and alluvial sediments between 12–20 m deep. Ground improvement through preloading and surcharging was proposed for the new road infrastructure servicing the development buildings, in lieu of piled foundations or rigid inclusions adopted for neighbouring developments. By using clusters of investigation (boreholes, CPT, sDMT) with laboratory testing, detailed ground profile interpretation was possible to develop Finite Element models to predict soft soil creep model under proposed treatments. During the ground treatment period, the contractor and design team adopted an observational method in determining the treatment period, following a set monitoring regime and a response plan. This case study includes a discussion on the considerations and lessons learned in pursuing a more sustainable foundation solution in soft soil including monitored impacts of Prefabricated Vertical Drain Installation and the value of plotting data differently to see what is happening through a different lens.