Before building a new sign gantry for the M4 smart motorway the location of a rising main that passed very close to the intended location needed to be found. The rising main is 24” in diameter and if damaged it could cause a pollution incident and result in emergency tankers being required at a cost of around £100k per week until it could be repaired.
Trial holes dug at the recorded location of the rising main had failed to find it and the need to find the location was becoming increasingly critical as installation of the gantry was being delayed. WRc were asked to survey the rising main and identify its location using the Sahara Pipeline Inspection System.
The survey was carried out while the rising main remained in service and involved sending a sensor on an umbilical along the rising main for 730m. Using the Sahara system, the location and depth of rising main was established at several critical locations across the motorway within a few hours of the start of the survey. The final location of the gantry can now be planned avoiding this delaying the upgrade of the motorway.
The survey planning was carried out with close cooperation between WRc, Thames Water and Balfour Beatty on behalf of Highways England.
The location of the rising main is marked outside the area of the 20m long trail hole dug to try and find it.
The location of the rising main is pin-pointed on the hard shoulder of the M4