Safeguarding New London Station with Leica GeoMoS

Crossrail, London’s GBP15 billion railway line, is Europe’s largest infrastructure project. A new station, under construction at Paddington, will be a key hub in the east-west route linking Heathrow in the west to Central London. As work progresses within a densely built area of the capital, the largest automated monitoring network in the world is continuously measuring the impact on the buildings in the vicinity. A 24-hour monitoring system, using up to 52 Leica Geosystems robotic total stations and precise levelling, measures changes in ground movement caused by deep excavation works alongside an historic London site.

Construction on the underground station continues alongside the existing Grade 1 listed terminus, whilst 18 metres below the site two tunnel boring machines (TBMs) are also in operation. Base readings taken prior to construction allow the surveying team from Costain Skanska to define the level of ground deformation caused by natural daily and seasonal changes and to define the tolerance level for ground movement caused by the excavation process.

3D monitoring measurements

Meticulous planning by the engineering surveyors, with support from Leica Geosystems, included innovative installation techniques positioning the network of automatic total stations to provide 24-hour, uninterrupted 3D measurements to the buildings of interest. Simultaneous, precise levelling traverses added another layer of information to provide a definitive picture of ground movement over time. The integrity of the data is under constant scrutiny as it is received and processed through the Leica GeoMoS monitoring software. Out of tolerance measurements trigger alerts so that engineers can take fast, corrective action.

Accuracy and precision

Steve Thurgood, engineering surveying manager for Costain Skanska JV, said, Leica GeoMoS is robust and provides the versatility and reliability needed to deal with the particular complexity and ever changing demands of this – the largest monitoring project within Skanksa worldwide. Both the automatic monitoring system and manual levelling log a phenomenal amount of data which correlates with an astonishing degree of accuracy and precision. Monitoring the Paddington station site is a case study in best practice survey methodology, combining the highest accuracy survey equipment with experienced practitioners.