The BRAWOLINER® 3D lining system was recently utilised on a very challenging sewer re
habilitation project which was part of the on-going £1 million Torbay Sewer Rehabilitation Program being undertaken by South West Water (SWW) in association with its consulting engineer AECOM. The main contractor for the works was Balfour Beatty Utility Solutions Ltd (BBUSL).
In an ‘old town’ area of Torquay on the English Riviera, a section of clayware sewer pipeline running beneath steep steps (with 85 steps) connecting Melville Street and Rock Road was found to be in need of renovation after CCTV inspection and analysis. These steps are believed to be the steepest in the town.
Originally, the proposed solution was to replace the sewer using the traditional ‘open cut’ technique. The steps are a maximum of 2 m in width and run adjacent to dwellings on the one side and a substantial retaining wall on the other. The sewer is at a depth of between 2 m and 2.5 m. An inspection of the site showed that to open cut the section would require structural surveys to be undertaken on the properties and wall adjacent to these steps together with specialist designed excavation and shoring techniques to safeguard the structures stability during the excavation operation. Therefore, the client sought a trenchless rehabilitation solution that would eliminate the need to open cut the pipeline.
Whilst this might sound an easy option given the number of renovation systems currently available, practically this was far from the truth.
Over its 42 m length, the fall from one end of the sewer to the other was 13 m. This gave an average gradient of 1 in 3.23 making this an extremely steep lining. If this was not enough to make the project challenging, within the run length there were two diameter changes in the pipeline, one from 225 mm to 150 mm and then a second from the 150 mm back to 225 mm. To further add to the complications of the project, the sewer also had over its length several relatively sharp bends at various locations and 6 lateral connections, two of which lay within the narrow diameter section of the pipe.
BBUSL called upon Exjet Services, a regular sewer renovation services provider to SWW, to develop a no-dig option.
Having inspected the site and noted the access difficulties at either end of the pipeline, it was decided to utilise the Brawoliner® 3D lining system to complete the work. Exjet has used Brawoliner® systems for many years and was confident that the 3D lining system could be utilised to handle the diameter changes as well as providing a high standard of liner for the future life of the pipeline.
As well as having to surmount the difficulties within the pipeline itself, Exjet also had to accommodate the fact that, whilst manhole access was available at both ends of the pipeline, the local highway authority would not allow closure of both Melville Street and Rock Road at the same time. This was because the works were being undertaken at the height of the tourist season in Torbay. Not being able to close both roads added to the complications of the liner installation operation.
Initially Exjet completed a pre-installation survey of the pipeline to ensure that it was suitable for lining. This survey showed some significant root ingress that had to be cleaned out using a rotary head high-pressure jetting system before lining could commence.
The BRAWOLINER® 3D liner system was developed especially to meet the demands of pipelines with varying dimension changes or situations where several diameter jumps occur over one pipe length.
Over dimensions from DN 100 to DN 225, the seamless textile liner adjusts itself to every pipe diameter during the installation process without operator intervention. This ensures a crease free finish to the cured liner.
The technology behind the liner’s ability to achieve such an installation is unique to BRAWOLINER®. The liner material comprises of an extremely flexible polyester-loop construction which allows a huge lateral stretch without compromising the final liner structure. In addition to the multi-diameter capability, just like the proven BRAWOLINER®, the outstanding winner of the IKT product test, the new 3D-Liner is still capable of lining bends of up to 90 degrees without folds or wrinkles. This means that BRAWOLINER® 3D is an ideal renovation solution for difficult sewer systems and is available in lengths of 25 m, 50 m, or 100 m.
Given the complications of this lining and the road closure restriction at the site, Exjet planned the lining operation including the reopening of the laterals to be completed within a two-day time frame with a road closure being implemented at the reception (Rock Road) end of the site only.
On the first day, after finalising the cleaning process, the liner installation including the liner impregnation was completed in just 8 hours. This may sound a somewhat simple task but according to Darryl Pass, Site Foreman for Exjet: “This was probably the most challenging liner installation I have ever undertaken. Furthermore, it is probably just as true to say that this job probably took the Brawoliner® 3D to the edge of its capabilities and yet was still completed successfully.”
The careful installation started by inverting the liner material with minimal water usage and pressure. Just enough water was utilised to get the liner to invert into the host pipe using an inversion unit. Once inversion was completed, this water was released from the downstream end of the run and the liner was allowed to deflate.
The liner was then re-inflated with a calibration hose using compressed air pressurised to just the point where the liner contact pressure was achieved so as to hold the liner against the inner wall of the host pipe. This meant there was not a high pressure from the head of water in the liner that would normally have existed using ‘full bore’ water inversion. A valve was installed at the downstream end of the liner to allow the lining crew to monitor and adjust the internal pressure at all times.
To cure the liner, instead of heating a full pipe bore of water to the cure temperature and holding this temperature for approximately two hours, hot water was introduced at the upstream end of the liner via the inversion drum. Only a small amount was introduced so as not to over pressurise the liner at the lateral connections, which may have caused excessive stretching or even a burst.
The hot water was ‘trickled’ through the liner calibration hose combination. This was to ensure that the internal air temperature reached the cure temp required by the impregnated liner. To ensure a full liner cure, the air temperature was then held at the cure temperature for a period longer than that normally recommended by Brawoliner® for its liners, but it does mean that a full cure is achieved even in the most difficult and challenging circumstances.
Once the liner had cured, the supply of hot water was closed and the calibration hose was removed.
According to Robin Dowell Senior Manager at Exjet: “The liner is very flexible and easy to install but it usually has a relatively low burst strength. When we install it, the liner has to be handled with care so as not to exceed the manufacturers recommended 0.3 bar installation pressure which is why we developed the above technique.”
It was not possible in the time frame of the project for Exjet to look at reopening the laterals from the customer side as this would have meant extensive CCTV work within the residential properties to track the lateral pipes and SWW did not wish to inconvenience its customers with such works unless absolutely necessary.
Therefore, on day two of the project Exjet used its IMS cutter to reopen the four lateral connections that lay outside of the 150 mm diameter restricted area of the pipe. For the remaining two lateral connections within the 150 mm diameter section and knowing their location within the system, Exjet sourced a Springbok cutter system which was successfully applied for the final re-opening cuts.
Robin said of the project: “Given the complications we encountered and the difficulties that this gave us on this project, we have been surprised at just how well the work went and how well the Brawoliner® 3D has performed in the circumstances. It must be said in recognition of the crews’ efforts that it is only their experience after having spent many years working with Brawoliner® that enabled them to generate such a successful outcome for our clients in such demanding circumstances.”
For the main contractor Balfour Beatty Utility Solutions Limited, Geoff Willcocks, Infrastructure Project Manager said: “The Brawoliner is a versatile solution successfully employed to mitigate the difficulty of having an inaccessible pipeline of varied diameter where open cut was not a safe or economic option. The completion of this scheme was an excellent example of innovative thinking and skilled delivery to provide the required scheme output”.
For CJ Kelly Associates, John Kelly, senior partner said: “BRAWOLINER® 3D has once again stepped up to meet the demands of a complex and difficult lining operation. It is with innovations like the BRAWOLINER® 3D and the experience of contractors like Exjet that increasingly difficult rehabilitation projects can now be undertaken instead of highly disruptive and costly excavations.”