The Design, Construction and Performance of Buttress Piles for Efficient Deep Basement Construction

The temporary support of deep basements presents a range of technical and commercial challenges, with conventional temporary propping systems often proving to be impractical and uneconomical due to site constraints. This paper describes the design, construction and performance of a novel temporary support system, utilising buttress piles, to facilitate a deep basement excavation in Battersea, London. The development on a former gas works had considerable constraints, both on and surrounding the site. This case study will detail the construction of a double storey basement within a secant pile wall, supporting an 11m excavation adjacent to structures, rail and gas infrastructure. Internal constraints and construction sequencing made the use of conventional propping solutions impractical and uneconomical. The buttress pile solution was designed utilising sophisticated 3D numerical soil-structure interaction analysis software to capture design efficiencies that would be difficult to duplicate using conventional 2D software. Given the constraints onsite and to manage risk, a robust monitoring strategy operating in accordance with the Observational Method, with trigger limits and contingency measures, was developed and implemented for the key construction stages. The results were compared against predicted performance allowing for back analysis to develop further improvements and efficiencies and gain additional knowledge of the system performance for future schemes. The system was cost effective, generated programme savings and a safe working solution, as well as improving overall buildability and site logistics compared to conventional methods. The importance of project team and stakeholder collaboration for the successful implication and execution of this non-conventional solution proved a vital element in its overall success. This paper will briefly outline variations of the buttress scheme using different construction methods and arrangements that have been successfully implemented on other schemes, as well as where buttress piles can prove beneficial when utilised in the permanent condition.