Spatial variability of pile founding layers: a case study

This paper explores the design and construction of a single span road bridge, highlighting the impact of geotechnical spatial variability on deep foundation projects. Due to various project constraints, the geotechnical boreholes used for initial design were located a considerable distance from the proposed bridge abutments. As the project progressed, and further geotechnical investigations were carried out, it was observed that the proposed pile founding layer showed signs of spatial variability in both thickness and strength. To address potential risks, the design was revised to extend the piles into a deeper layer of very dense sand, and proof bores were planned at the abutment locations to verify ground conditions before construction. This study incorporates 3D geological modelling, adopting the previous investigations and the latest proof bore data and provides a clearer representation of the variable properties of the pile founding layer, supporting the pre-construction design changes. The findings underscore the critical nature of geotechnical spatial variability and the need for strategic placement of investigative efforts. The paper also details observation and monitoring activities undertaken during construction to ensure that design intent and local government compliance criteria are met, and steps taken to manage potential risks during pile excavation in dense sands below the groundwater table, which are envisioned to be useful for deep foundation projects under similar conditions.