The survey was required by Transport for London to enable detailed design proposals to be developed for the construction of the Silvertown Tunnel, linking the Greenwich Peninsula and Silvertown. This high profile and much anticipated scheme that has been proposed to reduce congestion at the Blackwall Tunnel and improve the reliability and resilience of the road network in the wider East London area.
To enable the initial scheme designs to be prepared, Transport for London required a PAS128 M4Pb (High Density Array) underground utility mapping survey to be carried out to assist with the design and construction management. 40Sevens’ brief was to locate all underground services and features, including voids and any areas of subsurface concrete in the roads and footpaths within the survey area.
While the resolution of the utility survey was critical to an efficient and effective design and build of the scheme, the timescales were tight and gaining as much information within the available time would be key.
Due to the scale of the survey and the amount of ground penetrating radar data that needed to be collected 40Seven utilised our mobile mapping MIRA system to collect the GPR data in the carriageways.
The MIRA GPR mobile mapping system employees high frequency pulsed radio waves, between 25MHz – 2.3GHz, to map metallic and non-metallic structures and features buried in the ground, including man-made structures. The MIRA utilizes a 400MHz pulse and captures large volumes of data allowing the required anomalies to be extracted from the data during post processing. The MIRA GPR was employed using a vehicle mounted operating system for the majority of the survey areas to minimise the impact on the road network by removing the requirement for Traffic Management. It was then manually operated in all remaining areas where the vehicle mounted method is not possible. All utility features and targets were positioned and mapped using Trimble Total Stations and then overlaid on to the existing topographical survey provided by Transport for London. Any street furniture or utility service related information not shown on the existing topographical survey was added to the drawing by our survey teams.