CTS Raft Build and Surveys (Nos Sewers, 12 Kilometres)

CTS Raft Build and Surveys

CTS were awarded by their client J Murphy and Sons a project to inspect and record the internal surface of the NOS Sewer system in East London, The Nos sewers consist of mainly of 4 barrels which are 2.6m diameter, in places they pass under roads and bridges.

The sewers span from wick lane to Beckton treatment works over 7 Kilometres, where the sewers pass under the bridges and roads, they spilt into 5 and 8 barrels, the flow is constant and generally the barrel is 50% full of effluent water.

Access into the sewer’s barrels are from Different kinds of manholes, some square, some round, and others as a rectangle construction where dams boards can be inserted.

With all this in mind the first stage of the surveys where to carry out Recces on the manholes to understand the launch positions, access sizes and general conditions of the entry and the surrounding area.

Whilst the recce information started to be collected, information was sent to the CTS workshop where the raft was in the process of being set up and later modified to allow for deployment.

The focus of the Raft build was stability & strength, the raft was built from a metal construction with two pontoons, and metal plate was used to straddle the pontoons to allow for the camera equipment to be mounted, wire rope was used for the attachment from the pulling rope to the raft.

CTS where also investigating the camera set up for the surveys, after testing 4 HD wide lens cameras where used, the cameras where mounted to the raft, forward, to both sides and one mounted looking upwards to capture the crown, a custom box was made to house all the electronics.

The raft cabling for live vision was established early on in this task, CTS modified a cable drum and housed 550 meters of fibre optic cable which was passed though a fibre optic slip ring, another custom box was made to house all the electronics for receiving the video footage from all of the cameras, using software the system was able to see all four cameras at once and switch to full screen and view individually, the receiver unit was installed in the CCTV van along with a HD monitor.

Pulling the raft through the barrels also posed a challenge, a Custom Porto reel on tracks was used for this part of the task, an encoder was built into the Porto reel to allow for the meterage count as the raft travelled through the tunnel. The focus for the potro reel was keeping hands of ropes and allowing the Potro reel to take the strain out of the movement of the raft.

The surveys commenced, after the first 5 or 6 deployments adjustments were made to the operation to achieve a smooth-running process, the raft travelled though the barrels with the aid of the flow of the water, early distances were achieved to 460 meters with stable connections and vision from all the cameras, after this stage CTS used a live streaming system, all four camera feeds were streamed directly to the internet, a link was sent to enable others to view the cameras with a 5-10 second delay, The footage was viewable in 1080p HD and was saved directly to the cloud for instance sharing.

As the days and weeks passed the surveys and recces continued, it was discovered that some of the survey lengths where further than initially anticipated due to the access into the barrels,

CTS, Murphy, and Thames water had discussions to establish a way forward, further investigations were carried out to establish extending the cable length, eventually a 1200m cable was used to overcome the distance, signals from the cameras were not affected by this and the live streams continued to work with the same lag.

In conclusion the overall project and surveys where complex, considering the conditions the system worked, the result was 1080P HD wide lens video of the internal barrels and structures which allowed for close examination and analysis, overall, 12 kilometres of the Nos Sewers system was surveyed.