Mobile mapping technology is invaluable, particularly in unstable or difficult-to-reach areas, to build a detailed picture of a site and detect hazardous land changes. RICHARD PIDCOCK explains how it greatly reduced the risks and improved results in Cumbria

The UK is home to the world’s oldest rail network, covering a diverse terrain that includes cities and remote coastal regions and mountains, as well as bridges, viaducts and tunnels.

Ongoing maintenance work is unavoidable, especially if passenger numbers and services continue to increase at the rates we have seen. Lines that cut through hillsides and coastal areas, for example, are particularly problematic since the terrain can be unstable and prone to erosion.

Central Alliance has successfully worked on some challenging projects in recent times, with our emergency response teams assisting on major landslide sites that have seriously affected rail routes including Harbury Cutting, Eden Brows and Farnley Haugh. With the challenges of acquiring data in these often difficult to access locations posing a severe safety risk, gathering information quickly and accurately becomes invaluable for this type of work. Where an accurate representation of the geomorphological features for assessing slope stability is key, mobile mapping using ROBIN technology can be of real benefit.

The challenge
In recent years, there’s been a raft of emergency works carried out across Europe, which have required the latest mobile mapping technology. One such project that has undoubtedly benefited has been a Central Alliance coastal rail project in the northwest of England.

With every scheme bringing its own challenges, it was the sheer complexity of the site, as well as extremely limited access, that presented the biggest obstacles for contractors working in Cumbria.

Central Alliance were tasked with acquiring detailed topographical data for civil engineering firm Story Contracting – however, access via the Network Rail managed infrastructure was only possible under a site warden safe system of work, along a single cess.

With an area measuring 225,000 square metres, it would have been time prohibitive to survey the rail corridor and adjacent land/coastal terrain using conventional tools like Global Navigation Satellite Systems (GNSS – similar to GPS), total stations and terrestrial laser scanners.

This type of mapping would have meant increased duration of survey and associated costs, particularly due to ground control establishment. Vast swathes of data would also have gone uncollected because it was not possible to safely access all areas of the site.

As well as gathering data on the rail corridor, Central Alliance had to conduct a detailed geomorphological survey of the terrain, including tidal flats, embankments and rock formations, without direct access to all areas and without putting staff at risk.

Robin to the rescue
In response to this challenging site, the Central Alliance team deployed its multi-platform mobile mapping system called ROBIN to access the site, which included large areas of uneven terrain due to the limited access. If conventional methods had been used, it would have taken up to four days to collect sufficient data. In the end, just three hours was needed on the site – which included only one hour of ROBIN data capture.

As well as drastically reducing the survey time, ROBIN also provided more accurate and comprehensive data that was used to create a highly complex model landscape. Whereas traditional techniques would have generated around 10,000 points of data, ROBIN produced 1.1 billion. This meant the team could draw up detailed three-dimensional images of the area’s geomorphological features, Additionally, full information was captured for the supporting infrastructure, including overhead line equipment and adjacent structures and buildings, which would not have been included using conventional surveying techniques.

Following this success, the captured data proved useful for other project requirements. This included design collaboration/update meetings, site inductions and assistance with enabling works phase planning, as well as increasing the efficiency and commercial viability of using mobile mapping technology.

Given the safety concerns of working in an environment like this, Central Alliance wanted to limit the amount of time people spent on the ground. In the end, just two surveyors were needed for a few hours – one on-site using ROBIN in backpack mode and another to establish sparse ground control for verification and adjustments of the final LiDAR data.

By the time the project had been completed, the survey team had spent 90 per cent less time on-site, reducing their exposure to high risk site areas.

Now, and perhaps more so in years to come, construction teams will rely on mobile mapping technology to gain a more in-depth understanding of the surface where rail works are being carried out. This will capture comprehensive point clouds to assist in a greater understanding of the terrain of problematic sites.