SPI Piling Ltd was appointed by Sienna Construction Ltd to deliver a piled foundation solution for a new 11kV and 33kV switch house at Wycombe Marsh Substation in High Wycombe. The works took place within a live operational SSEN substation, requiring strict control of vibration, sequencing and access to ensure uninterrupted power and asset protection.

SPI Piling Ltd’s, scope involved the design, supply and installation of 20no. 324mm diameter CHS steel tubular bearing piles, each approximately 15m long. These piles were designed to resist vertical dead and imposed loads as well as horizontal wind loads. Activities included mobilisation within the substation, pitching and driving piles, impact driving to achieve set, CAPWAP dynamic load testing, welding extensions where required, and cutting piles to final level. All works were completed within a two‑week programme.

Piling was undertaken using a 35T excavator with side‑grip vibratory hammer for initial driving, followed by a DX25 impact hammer for final set and load‑testing requirements. Works were carefully sequenced across two electrical bays, ensuring one bay remained live at all times. A formal permit‑to‑work system controlled each zone change, and dynamic testing verified pile performance against the 180kN design load, with re‑driving and welded extensions implemented when required.

Safety and quality management were critical due to the live electrical environment. SPI operated under strict daily permit‑to‑work procedures, with physical segregation between live and isolated bays. Controls included certified piling platforms, vibration monitoring, exclusion zones, lift plans, hot‑works permits, and detailed RAMS. All personnel received briefings on live asset boundaries and emergency protocols.

The main challenge was sequencing piling activities while keeping one electrical bay operational. Close collaboration with Sienna Construction Ltd and SSEN ensured safe isolation, asset protection and adherence to tight working limits. SPI responded flexibly to dynamic testing outcomes without affecting the overall programme.
SPI delivered all 20 bearing piles to specification, verified through dynamic testing, within the agreed programme and budget. The works provided a robust foundation for the new switch house while maintaining uninterrupted substation operation. The project demonstrated SPI’s capability in live substation environments, controlled vibration piling and permit‑led delivery.