Fibre Optic Monitoring of Existing Under Ream Piles for Tunneling Interception

The opportunity to re-use existing piled foundations on a project brings a set of challenges to address the unique circumstances of the situation and proposed development. The use of fibre optics to measure strain in new piled foundations is now a well-established technique and this technique, transferred to existing piles, was an important aspect in the verification of the design of the pile interceptions. This paper will provide details of a tunnelling project in London that installed and monitored fibre optics in 50 year old unreinforced under ream piles in order to monitor the behaviour of piles during the interception and removal of four under ream bells supporting an occupied building.

It is believed to be only the second project in the UK to use optical fibre instrumentation to observe the behaviour of existing piles for reuse and the first project for piling interception for a tunnelling project. As urban environments become more congested below ground, the technique and approach discussed in this paper will become increasingly valuable. The monitoring data is presented and discussed in detail and the role of using these sets of data in assessing the reuse strategy were also highlighted in this paper.