The Use of Shape Accel Array for Monitoring Utilities during Urban Tunnel Drives

Summary

The protection of third party assets with reliable monitoring instruments is essential for the running of a successful urban tunnelling project. With a twin bore tunnel being excavated below the Ranelagh Sewer, in Paddington for the Western Tunnel drive of Crossrail, a reliable method was required to measure displacements (convergence) in near real time. The design of the system required careful planning and an installation method that would be safe and comply with the stringent requirements of the asset owner.

The introduction of Shape Accel Arrays (SAA) for the measurement of convergence within large sewers is a new concept in the UK construction industry. The instrument is successfully being used for the monitoring of slopes, embankments and diaphragm walls. SAA are very quick to install and base read, with the data output configurable for various types of monitoring software.
This paper documents the use of Shape Accel Arrays within the Ranelagh Sewer. It will describe the method of installation, the results obtained and lessons learnt during the first large tunnel drive directly below the shape accel arrays.