Tunnelling Below, Safety Above: Monitoring One of the Busiest UK Highways During Rail Construction

Case study

Monitoring One of the Busiest UK Highways During Rail Construction - Leica Geosystems

Author: Megan Hansen, Simon Hall, Craig-Lee Holt

As critical transportation projects take place across the UK, monitoring existing nearby infrastructure for deformations is essential to ensure safety and continued operation. During the tunnelling of the HS2 high-speed railway under the M25 highway near London, SOCOTEC UK successfully monitored the difficult to access and busy motorway with a Leica Geosystems solution featuring automated laser scanning and a range of other monitoring techniques. 

A high-speed train, a critical highway and a monitoring challenge

Britain’s first passenger railway opened in 1830, initiating a transit revolution. Nearly two centuries later, UK commuters still ride railways laid in the Victorian era while demand for more lines and faster cross-country connections has outpaced rail infrastructure development. The UK’s High Speed 2 (HS2), a dedicated high-speed railway currently under construction, will help alleviate these problems by linking major cities and airports to further connect Britain’s largest economic regions.

However, building this extensive railway between major cities, including London, Birmingham and Manchester, requires tunnel construction that potentially could disrupt existing transit and create structural deformations to the roadways above. This was the case for tunnelling under the M25, a critical national highway carrying over 250,000 vehicles each day along 117 miles of tarmac. 

Particularly, the construction of two separate tunnels underneath this asset led National Highways, a government-owned company in charge of maintaining the M25 to require a monitoring solution that would ensure the safety of travellers and evaluate the structural integrity of the roadway throughout the project’s progression. 

Monitoring such a busy highway, however, posed problems: the roadway, with consistently high traffic volumes, had only limited access to monitoring areas and it was not feasible to close the highway for the initial or regular data collection during construction periods. At the same time, it was impractical to install prisms on the road surface where they would be destroyed by heavy vehicles or traffic would have to be redirected to avoid them.

Monitoring One of the Busiest UK Highways During Rail Construction

Industry leader SOCOTEC UK takes on the challenge

To meet this challenge, Align – the joint venture company completing 21.6 kilometres of the rail infrastructure, including the 16.04 km twin-bored tunnels under the M25 - contracted monitoring experts from SOCOTEC UK, a leading UK provider of testing, inspection and compliance services across industries. With specialisations in geotechnical and structural monitoring and over 30 years of experience on large-scale civil engineering projects like the Victoria Station Upgrade in London, they were the perfect project partner.

SOCOTEC UK not only considered the practicality of the setup in terms of access and instrument installation, but they also wanted to minimise disruptions and, most importantly, secure the safety of M25 travellers and their own staff while working along the highway. Therefore, they required a solution with minimal installation to the road surface, reduced installations to earthworks and the ability for the monitoring system to be fully remote and run autonomously 24/7 over several years. 

Dedicated to digital innovation, SOCOTEC UK saw this as an opportunity to incorporate laser scanning and automation available through the Leica Geosystems monitoring solution.

Patch scanning: A non-intrusive monitoring solution from Leica Geosystems

The custom monitoring scheme was designed in consultation with SCCS, part of Hexagon and the UKs leading Leica Geosystems distributor, and implemented a range of automated features, including patch scanning, imaging, instrument levelling and reporting. 

“We chose SCCS to provide us with the hardware, software and the customer support we needed to install a system capable of surveying accurate patch scans, prisms and reflectorless points,” explains Jeff Foggo, Senior Project Manager at SOCOTEC UK. 

The solution comprised of:

To solve the access and disruption issues, SOCOTEC UK chose a unique, non-intrusive monitoring solution called patch scanning that utilises laser scanning and automated monitoring software to generate data and analyses. The combination of the MS60’s high-accuracy laser scanner, capturing thousands of points per second, with GeoMoS software minimised the need to install reflective targets or prisms and enabled monitoring to proceed in even the most restrictive areas. This decreased disruptions to live traffic during installation and operation, removed SOCOTEC UK staff from potentially hazardous areas and ensured safety for road users.

SOCOTEC UK captured reference measurement data for 12 months ahead of the excavations to determine the normal movements of the road surface. During the monitoring period, the MS60, installed high up on adjacent plinths to optimise visibility, scanned small areas or “patches” of surfaces at determined intervals with arrays of 20, 40 and 60 metres. Other measurement arrays included prisms set up on the top of the embankments and multiple reflectorless points on structures. Additional prisms were installed as survey control in stable areas. 

Utilising hybrid techniques with MultiStations helped SOCOTEC UK optimise their monitoring installation and ensured impeccable measurement reliability.  GeoMoS compared the measurements to baseline reference values, enabling deformation detection and notifications to key stakeholders if tolerance thresholds for movements were exceeded. 

Patch scanning - A non-intrusive monitoring solution from Leica Geosystems

Additional automation for 24/7 monitoring

Complementing the patch scans, SCCS also recommended further automation of the project using imagery to minimise visits to the site. Remote access to live video and still images via integrated cameras in the MS60 made it possible to easily resolve and verify any data measurement questions without delay. 

The intelligent measurement sensors, including the MS60s and TM50, were centrally controlled through GeoMoS and used custom power sources with backups to ensure continuous monitoring. Additionally, since the instruments were installed in remote locations where environmental factors could impact stability, SOCOTEC UK needed a way to ensure the total stations remained level. Connected through the ComGate20, GeoMoS remotely and automatically activated the AD12 self-levelling tribrach for each TPS before each measurement cycle, ensuring result quality and reducing maintenance visits.

However, SCCS provided more than the instruments and software – they also supported SOCOTEC UK with remote and onsite training during the operation and delivery of the monitoring scheme and overall solution. 

“SCCS delivered excellent support and assistance and, when combined with SOCOTEC UK Monitoring UK’s wealth of knowledge and experience installing, commissioning, managing and maintaining monitoring systems, the results were of a very high quality,” says Foggo.

Continuous monitoring benefits from constant protection

Given the remote nature of the site, power outages and environmental factors weren’t the only issues SOCOTEC UK had to consider when determining how to ensure 24/7 monitoring. To protect the valuable equipment in the field, they mounted the instruments within secure cages and installed the Leica LOC8 theft deterrence and location solution

LOC8 enables geofencing, custom alerts via messaging and instrument tracking and locking.  While useful for fleet management daily, this solution was especially crucial to the project when three instruments were stolen from the site. With LOC8, SOCOTEC UK was able to provide tracking information to local police, who recovered £120,000 worth of stolen equipment. Once returned, the instruments were inspected, serviced and quality checked by SCCS before returning to the site so monitoring could resume as quickly as possible.

Results of the innovative monitoring system

Ultimately, SOCOTEC UK’s use of the Leica Geosystems monitoring solution allowed the M25 to operate as usual during the tunnelling period, ensuring that one project to improve transportation didn’t interfere with critical existing transit. 

“Through our collective effort with SCCS, we confidently monitored the M25 and surrounding assets on an hourly basis during the passing of two tunnel boring machines under the M25 along the HS2 in quick succession,” reflects Foggo. 

“Having the opportunity to provide an innovative monitoring system for one of the busiest parts of the highway infrastructure in the UK has been, and continues to be, a rewarding experience. The data certainly spoke for itself in terms of the monitoring system being a success: the record of minimal asset movement was clear during the tunnelling phase and all stakeholders, such as National Highways, received the reassurance they required”

A non-intrusive monitoring solution from Leica Geosystems


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The ultimate all-rounder, combining total station functionality with 3D laser scanning, GNSS connectivity and digital imaging.

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LOC8 – Theft Deterrence & Location Solution

With LOC8 you can track and locate your total station remotely by simply using your mobile phone or computer
With LOC8 you can track and locate your total station remotely by simply using your mobile phone or computer