Axial and perpendicular behaviour of inclined piles retaining excavations in clay

A novel retaining system consisting of vertical and inclined piles (VIPs) is increasingly used in China to support large-area excavations in clay, simultaneously satisfying safety and serviceability requirements but consuming less time, cost and energy compared with normal supporting schemes using temporary props. Due to a lack of both understanding and calculation methods for the axial and perpendicular behaviour of inclined piles, the design of the VIP retaining system is currently totally dependent on complex finite-element models. A centrifuge study on axial and perpendicular behaviour of a single pile in clay was therefore conducted, considering variable pile inclination angles and embedment lengths, with accurate but simple methods for calculating the axial and perpendicular pile stiffness at small displacements being developed. The mobilisable strength design method was subsequently extended for the excavations retained by VIPs in clay, with a well-recorded field case and triaxial tests on the soil at the site being used for validation. This research provides an insight into pile stiffness at small displacements and builds a theoretical foundation for the application of the novel VIP retaining system.