Lateral thinking solves dilemma
A serious flooding issue in Leeds was tackled by a challenging sewer renovation project. On behalf of Insituform Technologies, Ian Clarke reports
Insituform Technologies (IT) recently completed a particularly challenging project for client BarhaleWSP, a Yorkshire Water (YW) framework partner. The project was part of YW’s AMP5 programme and was located in Burley, a district close to Leeds city centre, covering 2,400 homes and serving a population of about 10,000.
Burley was one of YW’s worst performing areas when it came to properties being flooded from the sewers for reasons other than those sewers being hydraulically overloaded. A strategy to reduce the number of ‘other causes’ blockages was devised, which required the renovation of all the lateral sewers to prevent future problems.
Initially the project was thought to comprise the survey, cleaning, lining and post survey of some 1,200 straight laterals each averaging about 7m in length in either 100mm or 150mm diameter pipe. Inversion lining using CIPP techniques and an ambient cured resin option was planned.
However, IT’s initial pre-renovation surveys, undertaken in January 2011, highlighted an unexpected difficulty; whilst some of the laterals being renovated did conform to the basic straight, single-diameter pipe expected, the greater majority did not.
The survey showed that many of the laterals actually comprised multi-bend pipes with a conical diameter transition from 100mm to 150mm over the average 7m length. One pipe even showed a multiple transitions from 100mm to 150mm and back to 100mm.
The survey also showed that many of these laterals had several connecting sub-laterals flowing into them that would require reopening after lining operations were complete. Suddenly the project had become extremely challenging.
The IT lining system that was initially to be employed for the work, whilst suitable for the laterals that conformed to the expected conditions at the start of the project, could not handle renovation of the lateral pipe layouts uncovered by the survey work. A new system had to be found that could be used to complete linings in small diameter pipe, using blind installation techniques, and not just in pipes with multiple bends, but in those which also had diameter transitions.
There was also a requirement to obtain a robotic reopening system that could operate in the laterals subsequent to lining in order to reopen the sub-laterals whilst being able to negotiate multiple bends and the diameter transitions without detriment to its cutting capacity. Investigations showed no systems existed in the UK market that could do this and allow a lateral reopening cutter to operate in a blind access situation. This raised questions as to how to move the project forward.
Over a period of 10 to 12 weeks IT investigated several potential lining systems globally. Eventually, after trying out seven or eight different systems, which ultimately did not meet all of the project’s requirements, an option from lining manufacturer Fluvius, known as TopFlex, showed real potential. The system offered a ‘stretch-to-fit’ capability that allowed the diameter transition to be negotiated without detriment to the ultimate lined lateral operation. The TopFlex System looked like it could be installed blind through bends.
Working closely with engineers from Fluvius, the liner began ‘in the lab’ tests to see if the system would work successfully with IT’s Air Tail installation system, which utilises a calibration hose as part of the installation process. These tests showed that the initial calibration hose used was too rigid for negotiation of the bends, which could in some cases be up to 90°.
Tests then took place using a more flexible calibration hose. However, it was found that this hose would not carry the liner around the bends correctly and bunching occurred.
This led to testing being undertaken using a Fluvius inversion drum, a double inversion system. First the liner was inserted from the drum. Once it had reached the insertion distance, it was allowed to deflate. The calibration hose was then passed through the liner to re-inflate it tightly against the pipe wall and then it was allowed to cure. Unfortunately, whilst the installation technique worked, some unforeseen issues arose which led to this method being unsuitable.
Engineers then agreed that using a combination of the techniques from the Air Tail system and the inversion drum may offer a solution. Using this combined method, first the calibration hose was placed inside the impregnated liner outside of the inversion drum. The combined liner/hose was then loaded into the drum and inverted into the pipe. This allowed the liner to be positioned without the PU coating delaminating from the liner material. With the more flexible calibration hose, installation was also successful in terms of lining around the bends without bunching or wrinkling. A new system with multi-bend, diameter transition and reopening capability had been developed. Once the lining system was available, work continued to complete the project, which had continued during the new liner development phase on the ‘standard’ pipes. In all, the 1,200 or so laterals to be renovated lay in an area covering about 5km2, with every property in that area having its lateral renovated.
Despite delays caused by having to research the new liner and installation technique the project was completed by the end of September 2011. Approximately 7,500m of liner was installed using three lining gangs installing four linings per day. This shows just how effectively the project was delivered whilst developing the new innovative technique that was then implemented to achieve completion.
Once it became possible to line the multi-bend, diameter transition pipes, the next obstacle was the problem of reopening the sub-connections. Most robotic cutters on the market capable of cutting in 100mm diameter pipe are inflexible and need to operate in the right pipe conditions. They also tend to use independent CCTV cameras to monitor the cutting operations that need a second access to utilise them effectively. Traditional cutters would not work in Burley for two reasons; first, lack of the ‘second’ access and second, and equally as important, traditional robots would not handle the multi-bend/transitional pipe configurations in which they were required to operate.
Research then found IMS, a German-based company which offered a range of cutters with built-in, on-board CCTV that could monitor its own cutting operations. The IMS Micro Comfort system was also designed to be flexible enough to handle pipe bends and could accommodate the transition of diameters without reducing the cutting capacity of the unit. Working with ANT Hire in the UK, two units were brought into the UK, both of which IT used on Burley, and which proved highly effective with each unit achieving up to 12 reopening operations per day in support of the three lining crews.
Rob McKay, IT project manager said of the project: “From when we found the first multi-bend, diameter transitional pipe, this became a very challenging project, possibly the most difficult I have worked on. Despite the long hours of research, conference calls, et cetera, over the 10 to 12 weeks it took to find this solution, the effort has been rewarding.”
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