Water leaks were occuring at a reservoir in Scotland. Geobear were contacted to help with water leaking from some of the joints between concrete at Cobbinshaw Reservoir, the water leaks could be stopped using Geobear’s geopolymer which acts as a water sealant.
Background
Cobbinshaw Reservoir is a site of special scientific interest (SSSI) located in West Lothian, Scotland. For several years, the reservoir had suffered water leaks from a discharge chamber following the installation of siphon pipes.
In 2013, three siphon pipes were installed together with three discharge control valves and a discharge chamber at the downstream end of the siphon pipes. As the reservoir was refilling leakage appeared from shutter holes in the back wall of the siphons discharge chamber and at several other locations. The estimated leakage was 500m3 /day.
Scottish Canals manage the reservoir, and they had a responsibility to investigate and control the leakage local to the siphon outlets. The investigation was undertaken by Scottish Canals technical manager who designed some remedial works to try to abate the flow. Initial works centred around the slab joints which they thought could be the problem. The joints were replaced; however, upon refilling the reservoir, the leakage flow continued.
They concluded that the leak could only be occurring at the joints of a supporting wall that lay beneath a 250mm concrete slab and adjoined the old weir to the new siphon wall. Rectifying the water leaks appeared to be a challenging project.
Customer alternatives
The option open to Scottish Canals was to reduce the water level lower than -0.7m and carry out traditional grouting. This scheme would require approval from the Scottish Environment Protection Agency due to the impact it could have on the SSSI site at the opposite end of the reservoir to the siphons.
Lowering the level could only be done at certain times of the year so as not to affect the wildlife breeding season. There was concern that a cementitious grout could contaminate the water plus they’d have to wait months for the reservoir to fill back up to see if the problem had been resolved. An alternative was sought.
Why Geobear
Scottish Canals approached Geobear’s to propose a solution. Using our geopolymer injection process meant that the water level only needed to be reduced to -0.3m to access the work area. The non-invasive method also meant only small drill holes through the slab were required and would not impact upon its integrity. We proposed treatment to 2 metres below the slab and back up to its underside, this was easily accessible using Geobear’s small diameter injection tubes.
On the day of the works, the exposed site was hit with unseasonable weather; however, with the requirement for minimal plant the Geobear technicians were able to improvise to maintain a clear working area. Injections were completed at 0.5m vertical increments adjacent to the ends of the supporting wall. The flow of the geopolymer through the silty clay fill below the slab, with its controlled expansion and rapid curing time, provided instant results that the client was hoping for. The continuous flow of water through the shutter holes into the siphon chamber gradually slowed and finally stopped a matter of minutes following the final injections taking place.
Scottish Canals have a legal requirement to inspect the reservoir weekly and, to date, no further reports of leakage recurring have been made.
