Distributed fibre-optic monitoring of tension piles under a basement excavation at the V&A Museum in London

A part of the Victoria & Albert Museum in London is currently being redeveloped and as part of this redevelopment an underground space of 2 levels was planned to be created for exhibitions and general storage. The deep excavation is supported by a base slab and a number of foundation "tension piles" which aim to carry the upward heave. Innovative distributed fibre optic (FO) sensors were installed within two tension piles prior to the excavation and regular readings were undertaken before and during basement excavation. This allowed the assessment of the induced stresses and strains within the instrumented piles due to the deep excavation. The monitoring data showed that the FO cables were able to pick up some tensile axial strains and forces due to concrete curing and basement excavation. During concrete curing the temperature within the pile drops whereas the axial strains increase, becoming more tensile. Finally, after the excavation the observed axial strain is tensile at the pile mid-depth and compressive at the pile top which is connected to the base slab.