An automated electrolevel deformation monitoring system for tunnels

A newly developed deformation monitoring system comprising electrolevels mounted on a ring of interconnected beams has undergone field trials and further development in a London Underground Ltd running tunnel, prior to its installation in existing tunnels requiring deformation monitoring during construction of the Jubilee Line Extension Project. The system, its mechanics and the geometric principles upon which it functions are described. Details are given of the performance of the system and the measurements made. It is shown that the system is minimally intrusive, enabling continuous monitoring of operational tunnels, and is sufficiently sensitive to detect small cyclical displacements which may correlate to the tidal effects of the River Thames while remaining sufficiently robust to effects of temperature, vibration and dust.