The Geospatial department of Glanville was recently involved in a complex sewer survey in partnership with Kier and Arcadis below The Barcode in Plymouth City Centre, Devon, UK.
The objective of this sewer survey was to identify defects that may have been caused as a result of construction in the area. The tunnel network below had remained largely uninspected since construction and was deemed too dangerous to access by humans. A drone inspection represented a significant opportunity to collect high-resolution survey data on otherwise inaccessible but critical assets, without the need to deploy a confined space team and therefore eliminating the human exposure to hazardous environments.
The intricate survey required the use of a drone to survey the tunnel due to access restrictions making it hazardous for human access and non-feasible for other forms of
survey. A significant concern revolved around working with the possible gases that can be experienced within some confined spaces. To assist in this robust ventilation and
monitoring protocols were created and established before the survey commenced. This was built upon past historic knowledge of the tunnel and its functionality.
The survey required three crews at different shaft entry points linked to the tunnel to lift the manhole covers to provide ventilation within the tunnel and to monitor the gas levels prior to drone entry. Gas monitoring was necessary to mitigate the risk of explosive gases present in the tunnel and once the gas levels had been monitored for over 2 hours and all crews were satisfied the gas levels were steady, the drone was loaded into the tunnel to carry out the survey. Glanville Geospatial carefully carried out this assessment with the drone surveying in two sections, one of which was over 200 m in length (400 m in total), this complex survey proved the superior capabilities the drone has with the battery and Wi-Fi range reaching a distance of over 200 m.
This sewer survey demonstrated that with careful planning and resourcing, combined with a robust dynamic approach to safety, that drone surveys potentially offer a solution to
difficult situations, providing 3D and measured deliverables that may not be possible with humans.