Using GISmapp to retrieve a CCTV camera and avoid a robin

Challenge

We were engaged by Manx Utilities to provide a one stop shop service on a project at Walpole Drive, Ramsey, on the Isle of Man (IOM). The project aim was to recover an expensive CCTV camera that had become firmly stuck in a deep combined sewer.

Debris in the sewer, and the CCTV camera, resulted in significant operational problems. Manx Utilities required an urgent resolution to the problem.

The sewer is located in a narrow lane to the rear of Victorian properties. Over the years encroaching development has made access to the sewer very constrained. To make matters worse the affected length of sewer did not have the benefit of having any nearby manholes.

In order to recover the camera a deep excavation was needed, however, “running sand” was a potential issue. The team was aware of bad ground in the area as evidenced by structural cracking in adjacent buildings and structures.

Whilst setting up site it came to light that a robin was sitting nesting on the adjacent Vicarage wall. For health and safety reasons it was proposed to take down this section of wall, however the robins nest meant alternative approaches had to be explored.

Additionally, the team were challenged with liaising closely with the affected stakeholders who regularly use the lane, as well as having to work around the busy IOM TT races schedule!

Solution

Our team therefore quickly mobilised to carry out a desk study with respect to site information, ground conditions and to gather details on the nearby structures, where available.

Prior to any site works, we carried out surveys of affected properties. We captured the data using an iPad and our software package GISmapp. This data was supplemented with a detailed video survey of the site and surrounding areas.

It was essential to establish ground condition. An experienced contractor was therefore deployed to dig a trial pit in the location of the proposed excavation.

Having carried out the investigations, the preferred solution was quickly progressed. Rather than digging directly down on to the CCTV camera (approx. 4.5 metres deep) as originally proposed, an alternative solution was developed. The preferred solution was to dig down onto a downstream bend (approx. 3.2 metres deep) and construct a new manhole from where the camera could be retrieved.

The robins nest had to be taken into consideration. After liaising with the expert from the IOM’s Department of Environment, Food and Agriculture (DEFA) a specialist contractor was brought in to provide temporary support to the wall during the construction operations.

The end solution was to dig down to the sewer, retrieve the camera and construct a new manhole using precast concrete rings. The ground conditions proved to be good and there were no issues with running sand.

Benefits

This small project has realised several benefits for Manx Utilities: the camera has been successfully retrieved and it is currently being used on further CCTV surveys. The blockage has also been removed and the sewerage system is now fully operational, much to the satisfaction of Manx Utilities. The new manhole is of strategic importance for Manx Utilities future operations and maintenance on this length of sewer.

Owing to the temporary working methods, the robins nest remained in situ much to the delight of interested parties.

Want to know more?

Contact Greg Parkinson, Chartered Senior Engineer, for more information on this project. You can also visit our engineering web pages to find out more about the varying projects we could assist you with.



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