Insituform Pacific was recently awarded a contract to rehabilitate a series of 450 mm clay stormwater pipes by an inner city council in Sydney. An 86 m length of pipe presented a number of risks and challenges rarely seen by the company before.
On first inspection, the pipe was found to have a 5 m length that was crushed and ovalised, resulting in a diameter loss of 35 per cent and close to collapse. Further downstream, a missing section of pipe was discovered resulting in a hole between “÷6 – 12 o’clock’. To make the project even more challenging, the majority of the pipe was cracked/broken and there was a sharp bend at the downstream end.
The pipe ran under a number of residential and commercial properties in a densely populated area and the two main pipe breaks were under buildings making dig up repairs almost impossible.
The extremely poor condition of the pipe – combined with the building loads acting on it – meant that any disturbance could collapse the pipe completely. Therefore, Insituform decided to invert its CIPP liner using water pressure to maintain constant head on the liner during curing, thereby supporting the ground around the host pipe.
A further challenge was the design of the liner to deal with the pipe section that had ovalised by 35 per cent, putting it outside the scope of conventional liner design. Insituform Pacific received advice from its designers in the USA, where advanced computer design theory has been used to design structural liners of various shapes including oviform and ovalised pipes. While it was hoped that the crushed section would be re-rounded to some extent during the lining process, there was no guarantee that this would happen. Therefore, an 18 mm thick liner was specified which is double the normal thickness used in standard applications.
During the pre-lining cleaning operation, a further complication was encountered. In the week prior to lining, a massive storm swept through Sydney causing significant flooding in the vicinity of the works. Unfortunately, a large amount of debris was washed into the pipe and lodged in the hole. Most concerning was a timber fence paling which speared itself into the hole blocking the entire pipe. Insituform”÷s crew worked for an entire day to carefully clear the debris using robotic and mechanical methods as normal high pressure water cleaning could collapse the pipe.
The following day, the lining crew immediately went about the installation of the liner before the pipe condition deteriorated further. The liner was installed slowly and with extreme care in order to minimise the stress on the pipe and the entire procedure was monitored using CCTV equipment.
Following the successful inversion and curing of the liner, the robotic cutting crew immediately went to work on the reinstatement of 24 lateral connections.
When the final CCTV inspection was carried out on the liner, both Insituform and the client were incredibly pleased with the results. The liner partially re-rounded the pipe in the crushed sections which meant that the hydraulic capacity was not only restored but increased due to the improved flow characteristics of the smooth joint-free liner. The liner also negotiated the large hole in the pipe as well as the bends without any issues.
One of the key advantages of the CIPP lining system is its ability to be installed into the deteriorated pipe in a soft or flexible state allowing the liner to negotiate significant bends, deflections and diameter reductions. Once the liner is inflated and cured in position, the result is a brand new structural pipe that is a tight fit and joint free.
This project was another example of what can be achieved when an open minded client and a determined contractor work in partnership to apply the correct technology to a difficult challenge.