One of our multinational clients asked us to provide a GPR survey at Dauntsey Lock after a syphon pipe was struck during pile installation. The purpose of the survey was to determine the line and depth of the existing syphon pipe and if possible, to note the profile of underground construction and depth of direction change.
In summary we included for the following scope of works:
- Provide a Full Non-Intrusive Utility and Topographic Survey
- Provide a basic topographic survey co-ordinated to OSGB national grid.
- Topographic survey to include, 10m spot levels, fixed furniture, Rail, walls, inspection covers and any other standard detail.
- Utility survey to include the line and level (every 10m or significant direction change) of syphon pipe including significant depth change to understand where the horizontal/vertical fitting was located.
- Deliverables to be issued in AutoCAD 2D/3D with sectional drawing.
Due to the location of the worksite, works were carried out on dayshift as this section is on the main line between Royal Wooten Basset and Chippenham. Works were undertaken by a team of 2 comprising of Snr Utility surveyor and Land surveyor. Client supplied supervision/COSS
GPR was the method that the client’s Project Managers had suggested, and the survey area had undergone a de-veg but due to the undulating ground and remaining vegetation ground penetrating radar would have been ineffective.
As the pipe was constructed of cast iron, Geo-Info decided that radio detection was an ideal method to detect the pipe and give more accurate depth readings. The direct connection method was used by attaching leads to the drainage pipe and using a frequency of 8.19Khz via the transmitter.
Site works were completed within 4 hours and syphon pipe was fully traced with depths recorded. From this information we were able to see that there was a significant depth change over a small area thus noting the underground profile/direction change.
Deliverables were compiled in 1 dayshift and issued to client. I managed to catch up with the supervisor who attended the worksite on the day of survey a few weeks later and he informed me that he was also present at the remedial works to repair the damaged syphon pipe and that the survey information was “bang on”, the pipe was only damaged on the horizontal section as noted.
Client had expressed concern that the area of pipe that had been struck was a fitting or connection of pipe and, therefore, would require full excavation of the pipe to replace.
With the results of the survey, the client’s engineers could tell that this was not the case and remedial works would only require the application of a slip collar on the pipe to seal the pipe and therefore further excavation and full replacement of pipe sections would not be required.
Total Cost – £1,230.00
Cost Saving – No need to excavate further than required to expose pipe reducing remedial works. Possibly saved an additional shift for RRV/plant/labour etc. Circa – £5,000.00