Case Studies

Colus Undertake CCTV Survey at York Minster

Innovative sewer rehabilitation provider Colus Ltd have recently carried out a series of services to repair a brick culvert that runs within the grounds of York Minster, the largest gothic cathedral in northern Europe.

Working in conjunction with leading UK design and construction company Mott MacDonald Bentley (MMB)- on behalf of Yorkshire Water- Colus were called to investigate the problem of kerb stones on the footpath outside the Minster showing signs of sinking.

Colus utilised their extensive knowledge and skills to successfully undertake a culvert CCTV inspection and subsequent repair.

In November 2012, managing the work from their Northern depot in Rotherham (South Yorkshire), Colus began by carrying out a CCTV inspection of the culvert and this identified that the bricks that formed the invert of the culvert where starting to sink due to mortar between them being washed away over a period of time.

In addition the CCTV inspection also found that a 525mm diameter circular concrete pipe that had been joined to the 990mm x 750mm brick culvert was not connected properly. The issue was due to the crown of the pipe being manufactured from ply wood and there was a 600mm plus deep void in the invert at that particular point. This void was subsequently leading to the sewer flow finding its way under the brick work that formed the invert and ultimately washing the ground.

Colus and MMB decided that a ‘no dig’ repair was the most suitable method of repairing the pipe as the line of the sewer was less than 4 metres from the wall of the Minster.

In late November, the process began with Colus initially carrying out a man entry repair to grout up the void and stop the flow progressing and causing any further damage.

York Minster is naturally a popular visitor destination in December and, because of the annual Christmas Market due to take place where the lining work was to be carried out, the project was put on hold until January 2013.

Once the festive period was over, Colus designed and manufactured a Cured In Place Pipe (CIPP) liner that would suit the structural criteria of the project and provide increased strength and flow to the culvert. The liner was made to fit the shape of the brick culvert (arched bottom and arched top with straight brick sides that are 990mm high x 750mm wide) and the culvert was made to change shape at the point where the 525mm started.

The next stage was to clean the culvert and install the liner and a suitable date and time needed to be agreed with the roads department and the Minster in order to decide on when the works will take place and minimise any possible disruption.

A water jetting unit was used to clean the culvert of any debris. The use of a recycler jetting unit is an environmentally friendly method of clearing the pipe as it uses the water from the sewer and not the mains. Any debris and water is sucked up through the pipe before the water is then filtered to clean the sewer.

Once cleared, a pre CCTV survey was carried out to ensure the culvert was in a suitable state prior to the lining being inserted. A scaffold tower was then built above the downstream manhole in preparation to install the liner.

Using a crane, the liner was then lifted up the tower and attached to the inversion ring. The liner (990mm x 750mm x22mm thick tapered to fit 525mm x 16mm thick) was then filled with water from the water jetting unit and the liner then started to pass through the sewer until it reached the end manhole. Once the liner had reached the end manhole, the water was then heated to cure the liner and efficiently repair the culvert.

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