Tech to reduce surveying and setting out errors

Referring to GIRI’s research on the top ten causes of error, Skanska’s chief engineering surveyor Mark Lawton noted that ‘setting out’ scored highly as a cause both in the building and civil engineering sectors. This did not reflect his own experience, he told delegates at the recent GIRI members’ meeting, and he wondered whether such errors resulted from the use of more conventional tools such as tape measures and pencils, or ‘new’ technologies.   

Mark gave his audience a whistle-stop tour of the established and emerging technologies that support error reduction in surveying and setting out, with examples of how Skanska is applying them, and insights into how their adoption might be accelerated. 

Whatever technology you are using, accuracy and error-free working starts with the basics, he emphasised. “Coordinate systems are behind everything we do.” They ensure that data and items are mapped in the right location, and that setting out information for these items is correct, assuming maps, models and drawings are appropriate to the project. 

On large-scale, linear projects such as HS2, the distortion caused by flattening is a significant consideration – in this case resulting in a difference of nearly 60m between the HS2 survey grid and the Ordnance Survey grid over the length of the project. “Always ask for the survey report, and who has verified it,” he advised.

Firstly, he stressed that 3D machine control (3DMC) systems which guide operators or even drive autonomous machines should not be considered as ‘innovation’ but rather ‘business as usual’. And he challenged the view that uptake was slow because machine operators were technologically challenged. “They like these systems because it makes their work easier and safer. What’s more they are comfortable with digital technology through smartphones and so on.” 

His belief is that adoption is slow because designers are failing to create data in the right form; they still think of the engineer and not of the robotic device, whether that be an earthmover, total station, or a paver. “We congratulate ourselves for ‘flipping’ the data to make it suitable for these machines, when really we should be generating data in this form from the outset,” he said. 

He called on designers to supporter leaner ways of working, which would cut out the need to convert data. “Carry out a digital fire drill and push your design through the workflow to the end product in order to test the method,” he suggested.

Mark ran through a number of surveying and setting out technologies. These include machine control, which has been in use since 2006, eliminates the use of profile boards and stakes, and improves safety through reducing the interface between people and plant. He also discussed laser scanning, another long-established technology, which has benefits not just for recording topography, but also for checking dimensions of fabricated elements before they are delivered to site. 

Drones are in regular use to record progress and carry out topographical surveys with an accuracy of up to 30mm, and for photogrammetry of inaccessible elements such as roofs, to establish whether in-person inspections are necessary. Surveys of as-built elements can be used to analyse interfaces before the next stage is cast. For example, by scanning cast-in starter bars and overlaying the next lift of concrete from the digital model, the site team can discover in advance whether any remedial work is required. 

Augmented reality is another commonly used tool for collaborating in real-time across teams split between site and office, or in different countries, Mark added. Skanska is using Trimble’s Sitevision system at Euston Station, to visualise future design, verify as-built works and analyse the feasibility and buildability of designs on site.

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