Satellite Insar Technique For Urban Tunnelling Monitoring: The Crossrail Project Case Study

One of the challenges in urban tunnelling projects is to guarantee that the infrastructure assets crossing or adjacent to the tunnel alignment and other new build elements are not affected by the construction activity.

Radar Satellite Interferometry (InSAR) is a non-invasive surveying technique, which uses a stack of synthetic aperture radar images (SAR) to measure millimetric deformations of terrain structures over wide areas. This technique allows a comprehensive and periodic vision, without any need to access site, with the same accuracy as manual levelling in cities for a fraction of the cost of traditional systems.

Sixense has been using its interferometric processing chain, ATLAS, with the aim of monitoring geotechnical and structural deformations linked to urban construction, specially aimed at tunnelling monitoring, using the experiences in geotechnical and automatic surveying.

ATLAS processing chain was successfully applied to Crossrail I, The Elisabeth Line, in London. In this context InSAR has proved to be a fundamental tool to: (i) present the historical ground/structure behaviour before the start of any construction was presented, (ii) monitor the movements during the construction works covering a huge extension for just a fraction of the cost and resources of what should be expended in order to be done by more traditional approaches, and (iii) keep a monitoring system in place for the long term movement performance of ground and structures, even years after the end of the construction phase.

In this paper, the technique will be briefly detailed and the application case of the monitoring of the different phases of the project will be shown.