A pre-fabricated Combined Sewer Overflow (CSO) chamber from leading precast drainage manufacturer Kijlstra has helped contractor Clancy Docwra cut installation times and minimise disruption during a flood alleviation project for Scottish Water Solutions.
The scheme involved upsizing the surface water drainage system and installing a CSO to protect homes in Kingsknowe Road North, located in the residential area of Saughton, Edinburgh.
The 36-tonne CSO base unit, measuring 4.1m x 2.5m x 2.0m, was lifted into place in one piece. Once all connections had been made, the concrete cover, weighing another 10 tonnes, was then grouted on top. The excavation was then back-filled and the road surface reinstated.
The new CSO allows for the foul sewer to flow into the surface water sewer through a screen, thereby avoiding any surcharge of effluent. In the past, heavy rain has caused the foul sewer to overflow and flood a number of houses in the street.
Installing the CSO and enlarged sewer meant significant excavation in the highway and potentially massive disruption to traffic and residents. Although not a major thoroughfare, the road is relatively narrow and is on a busy bus route.
The use of a traditional in-situ concrete CSO would have required a large excavation which would have had to remain open while the formwork was assembled and the concrete poured. This excavation would have had to remain open until the concrete had cured and the formwork removed – a period of up to two weeks.
“Speed of installation was a major factor in choosing the Kijlstra CSO,” explains Scott Heath, senior project manager with Clancy Docwra.
Installing the Kijlstra CSO only required the excavation to remain open long enough for the unit to be craned in, the cover installed and the necessary connections to be made.
Instead of the two weeks required for the conventional method, Kijlstra’s CSO was delivered and installed in a single day. But speed of installation was not the only advantage, says Mr Heath:
“Because the CSO was pre-cast we could reduce the size of the excavation which was a key factor given the amount of services located within the area,” he says.
“I’d never used Kijlstra’s pre-cast units before,” concludes Mr Heath, “but after this job I’d definitely consider using them for future projects.”