Wedge Block Tunnels (40 Kilometres)

The wedge block tunnels are large diameter sewer & Storm Tunnels that are in regular demand and use. As they came up for routine inspection, Thames water awarded the task of surveying them for inspection to Barhale and CTS.

The aim of our inspection surveys, are to identify the condition of the wedge block tunnels, assessing for any general condition & damage. With the size and the sheer distance these tunnels cover, CTS made the decision to invest in new equipment and also added additional hardware to enhance the lighting and Video imagery.

We invested in a crawler system, one that could tackle long distances, and overcome obstacles like silt and water flow. CTS also invested in the new cable drum, which allowed for surveys up to 500m in length.

Some of tunnels brought the challenge of flow levels, too high for the crawler to drive through. This was something we had prepared for.

In our workshop we had designed and built two float systems. Both vessels were equipped with enough buoyancy and protection to withstand the harsh environment. We kept the raft attached to the rope which came from the Porto reel and using a drogue system, we launched from one shaft and surveyed the tunnels whilst the raft floated down to the next shaft. 

CTS teamed up with Barhale on site, and worked together to safely enter the deep, large diameter shafts. Safety was the number 1 priority, for our teams but also the public. For each entry, we set up a site around the manhole, barriering us off to prevent any hazards. Working directly from the back of the CTS survey van allowed us to complete our surveys effectively.

Where conditions were appropriate, we decided to put our innovative prototypes into practise. After extensive research and development, we had customised an RC Crawler system, that would prove to be faster and managed to reach 800m from our RF control unit. We improved this once more, by converting from radio frequencies to fibre optic cable allowing for survey lengths of 1200 meters.

Across 5 months of work on site, we surveyed a total 40 kilometres of wedge block tunnel, diameters ranging from 1.8 meters to 3 meters. Back in the office, CTS brought the footage and information into a suitable format to be viewed and analysed by our clients.