At 260 metres long and at a depth of 26 metres, the platform tunnels for Crossrail’s Bond Street Station sit below some of the most expensive real estate in the world. Excavated in Londa Clay, the platform tunnels were formed first by segmental lining from the passing of two Earth Pressure Balance (EPB) Tunnel Boring Machines (TBM) and then enlarged using Sprayed Concrete Lining (SCL). As a mitigation for the predicted settlement from tunnelling, compensation grouting was employed in the geology above the tunnels.
The variations in settlements observed by others on-site during construction, the mechanics and in-tunnel movements (1) (Sismondi et al., 2015) and consequently, the qualities of grout applied for mitigation (2) (Haris et al., 2015) have been described previously. However, this paper aims to explore the potential causes for the variations in grout quantities applied.
An analysis is undertaken of the geological data ascertained during the projects ground investigation stages that could have been an impact on compensation grouting. It also looks again at evidence of other geological features noted in the Bond Street area and similar scenario on previous projects at other locations locally.
This paper examines the model illustrated prior to construction and provides a more accurate geological interpretation around the Westbound Platform Tunnels and cross passages where uncreased grouting was applied.