Reticulation sewers are predominantly 150 mm to 300 mm in diameter and the rehabilitation of these systems has generally involved the installation of tight fitting structural linings. If a continuous lining system, such as Kembla Watertech’s EX method, is installed then all root penetration and water ingress through faults, such as cracks and defective joints, will be completely eliminated. If this lining operation is then followed by the installation of a junction T seal system then root penetration and water ingress are also eliminated up to the first joint; the limit of responsibility for most authorities.

The only remaining point of concern with respect to ongoing maintenance is the possibility of root penetration from further up the branch line. While this is the responsibility of the property owner, these roots may grow down the branch and into the mainline, causing blockages.

The length of linings now installed measures thousands of kilometres, while the number of T seals numbers in the tens of thousands. When Sydney Water sends out a crew to respond to a sewer blockage, there is an increasing likelihood that the sewer has been lined and may also have T seals installed. Sydney Water has therefore asked its two SRP2006-2009 term contractors, Kembla Watertech and Interflow, to undertake testing to determine safe cleaning pressures that will then be specified by Sydney Water when cleaning and/or whether root removal is required in any of their lined sewers.

Any recommendation needed to take into account that Sydney Water cleaning crews do not carry CCTV survey cameras. This means that when called out to a choke, they are operating ‘blind’. It was also requested that the companies include short form patch linings into these tests. The results of these tests are important to the industry as a whole, not just Sydney Water.

Components to be tested

For some time now the installation of T seals at junction cut outs in lined pipes has been a contractual requirement of most authorities. Kembla’s T seal system is called Tiger T.

The resin impregnated patch is placed over a purpose built packer, which is then transported into the sewer and positioned at the location of the connection using a small camera or other means. The packer is inflated, which pushes the T seal out and into the branch connection. It is held in this position until the resin has hardened, at which time the packer is deflated and retrieved.

In those instances when only a localised fault is found in an otherwise serviceable pipe, a short form structural patch can be effectively used instead of lining the entire pipe length. This type of patch is offered by many companies under a variety of names.

The fibre reinforced plastic (FRP) patch, after being impregnated with a suitable resin, is wound around a rubber sleeve and placed at the repair point using a CCTV Camera Unit. The sleeve is then inflated and held in position until the curing process is complete.

The material composition of the Kembla systems to be assessed was divided into three categories. The first material was the Ex method lining, consisting of a PVC of a similar grade to standard sewer grade pipe. The second material was the Tiger T junction seal, with fibrous open weave tubing impregnated with silicate resin. The final material assessed was the Tiger patch short form repair, with glass fibre reinforcement fabric impregnated with vinyl ester resin.

It was agreed between Sydney Water and Kembla that three separate tests would be undertaken. The first tested the Tiger T seal inside a pipe but above ground at Kembla’s Strathfield Depot. The second test was conducted onsite with a Tiger Patch installed by Kembla some six months ago into a sewer at Roseville. The final test was performed on a Tiger T installed twelve months ago into a lined sewer pipe at Punchbowl.

Jetting Nozzles

Kembla has been conducting R&D trials on a robotic branch cleaning device imported from Germany. To this end, a number of 150 x 150 Tiger T’s had been installed into a 150 mm VC pipe set up in the yard of the Strathfield Operations Depot. The VC pipe had been lined with Ex prior to installing the Tiger T’s to simulate an actual field installation. It was decided to utilise this existing set up for the first test, which was witnessed by a number of Sydney Water personnel.

Test Procedure and Results

In the first test the CCTV camera was run through the line to record the condition of the Ex lining and Tiger T before any cleaning. The ‘bomb’ nozzle was fitted and two passes, up-back, were made at a pressure of 7,000 kPa (1000 psi). Normal cleaning procedure is one pass but as the test was trying to find the safety limits, two passes were carried out. The pipe was resurveyed and it was agreed by those present that there was no change in the condition of the Ex lining or Tiger T. Another two passes were then made at 10,500 kPa (1500 psi). Again there was no change in condition. Another two passes were made at full pressure of just under 14,000 kPa (2000 psi). There was still no damage or change in condition that gave rise to any concern. The plastic coating on the Tiger T lining material showed minor separation at one location but there was no structural damage or any sign of lifting to the leading edge of the Tiger T itself. Sydney Water crews carry a ‘warthog’ nozzle, so the ‘bomb’ nozzle was replaced with the ‘warthog’ and two passes made at full pressure (just less than 14,000 kPa). The Ex lining showed no effect whatsoever.

It was observed that there was additional deterioration in the plastic coating, but no structural damage. The consensus was that while the warthog could be used under extreme conditions, it was probably prudent not to recommend it as a routine method. The final test was then made by carrying out two passes with a root cutter fitted. Under this extreme test condition there was no damage to the Ex lining but some minor damage to the Tiger T. The recommendation would be to use a root cutter only as a last resort and then have in place a procedure that required a CCTV survey to be carried out to check on the condition of the pipe at the location in question.

The photos on page 40 are from the CCTV after root cut i.e. after two passes with the ‘bomb’ plus two passes with the ‘warthog ’ plus two passes with the root cutter.

Test two was the onsite test of a Tiger Patch. The trial was carried out using exactly the same procedure as test one and was witnessed by the same personnel. The Tiger Patch was located approximately 1.5 metres from the access chamber. The patch suffered no adverse effects from any of the tests.

Test three, a repeat procedure of test one, was performed inside a sewer lined with Ex and with a Tiger T fitted. This final test was completed in the second week of October. Again, no damage was caused by the two passes, using the ‘bomb’ and the ‘warthog’ nozzles at the pressures of 7,000 kPa and 14,000 kPa.

Conclusions

A full report including CCTV video of the tests is being prepared for Sydney Water; however, the results are of importance to all authorities. Therefore, Kembla wanted to present this summary report as soon as possible. The various cleaning tests had no effect on the Ex lining whatsoever. This is not unexpected because the PVC material used in Ex pipe is essentially the same grade as standard sewer grade PVC pipe. PVC is now the material of choice for new reticulation sewer pipes, which means the Ex lining should perform the same as a new sewer pipe.

After numerous passes at a pressure of 14,000 kPa using a standard cleaning nozzle, the ‘bomb’, the Tiger T’s were unaffected. Some minor superficial damage was noted in the above ground trial after the ‘warthog’ nozzle was used and so the routine use of the ‘warthog’ will not be recommended by Kembla. However, it was of comfort to Kembla, as to well as the Sydney Water personnel present, to observe that if this method of cleaning is used accidentally, then the Ex lining and Tiger T should not be adversely affected.

No detrimental damage was caused to the Tiger patch by the ‘bomb’, the ‘warthog’ or the root cutter. This result confirmed the effectiveness of this type of repair.

Current Sydney Water policy is not to root cut a lined pipe. As already mentioned, an Ex lining is in reality a sewer grade PVC pipe without any joints for the entire manhole to manhole length. Therefore, and as observed in the tests, root cutting within an Ex lined pipe will not present a problem to the lining itself. Root cutting through a Tiger patch was observed to be acceptable. Root cutting through a Tiger T should only be used as a last resort.