The QL-B survey used a variety of electronic designating equipment to initially map out the underground utility network. Specifically, ground penetrating radar (GPR) and a range of high frequency and low frequency detection systems were used to map the existing buried utilities. A total base survey station was also located on-site to record all the field data through CAD. The results were then overlaid onto an existing topographic survey previously commissioned by the client.

The QL-A survey is used to verify the QL-B survey and accurately determine the precise depth and horizontal position of the utilities detected. This QL-A requires the use of the vacuum excavation technique which exposes utilities in a safe and non-destructive way.

Cardno TBE exposed a number of trenches with a width of 20 cm and lengths between 1.0 m to 2.5 m. The exact depth and horizontal positions were then added to the QL-B survey including accurate diameter information. A number of 20 cm2 excavations were also carried out to confirm details on individual utilities.

James Lewis, branch manager of Cardno TBE UK explained why EarthTech Morrison went on to commission further QL-A surveys across other areas of the site: “The vacuum excavation process, from start to finish, can take as little as 45 minutes (for a 20 cm2 square excavation) in the highway. It is a safe, minimum excavation method of exposing utilities to determine their exact depth, horizontal position and diameter. QL-A excavations are safer and commercially competitive when compared to excavating a trench with a hand digging team. Earth Tech Morrison clearly saw it’s potential and subsequently extended our original contract specification.”