Civil Engineering


M11 Birchanger Roundabout Lighting

Using HDAGPR Surveys to improve safety and efficiency

Carnell used High Density Array Ground Probing Radar (HDAGPR) surveys during preliminary works on the M11 Birchanger Roundabout Lighting Scheme. As well as providing a safer environment for road workers, the innovation has delivered cost-savings and customer benefits.

As principal contractor on the National Highways scheme, Carnell carried out the renewal of lighting columns, cabling ducting and feeder pillars at the busy M11 Junction 8 Interchange outside Stansted Airport.

As no survey works had been undertaken in advance of the scheme, Carnell used the HDAGPR technique which they pioneered on the SRN. This technology gives more accurate data compared to any other survey method, and located uncharted buried services throughout the roundabout, which was found to be heavily congested with power, traffic signal and communications and cables.

Innovating for safety

The detailed picture of the sub-surface environment, including the identification of cables at just 150mm deep (later found to be buried in concrete), helped build the case for the use of vacuum excavation, aligning to National Highways Raising the Bar 9: Utility Avoidance. This further reduced the risk of cable strikes as the use of excavators was minimised.

Although the design allowed for full construction of 16 road crossings, HDAGPR combined with physical investigations located and proved existing crossings with spare capacity. Liaison with Atkins, the design services contractor, led to significant design changes, reducing the number of new road crossings down to just 3.

Carnell’s electrical team successfully delivered the scheme to programme and under budget.