Several lining methods have proven effective in structurally rehabilitating deteriorated sewers. Cured-in-place (CIP) liners, fold-and-form (FF) thermoplastic liners, and spirally wound liners are all well accepted throughout the world. All these systems, if properly installed, provide an ‘as new’ pipe from manhole to manhole. However, the problem of the water path between the liner and the host pipe still remains, creating points of potential infiltration and exfiltration where the liner must be cut to make a lateral connection.

The liner annulus exists for a number of reasons including:

• Shrinkage in liners using resin and/or thermal curing processes; • Tolerances in both liner and original host pipe manufacture; • Irregularities in the cross sectional shape of the deteriorated pipe; and, • Inherent design of the liner.

The existence of this issue is universally acknowledged.

The American Society for Testing and Materials (ASTM) has a comprehensive range of Specifications covering the design and installation of sewer liners. Specifications F 1606, F 1743, F 1867, F 1947, F 2019 are applicable to various types of CIP and FF liners. Each of these Specifications carries a note with a statement similar to:

“…this practice (installation of the liner) should not be construed to provide a watertight seal at service connections. If total elimination of infiltration and inflow is desired, other means which are beyond the scope of this practice may be necessary to seal service connections and to rehabilitate service lines and manholes.”

Better Solution Needed

Until 2001, the accepted material for sealing house connections into lined pipes was hydrophilic polyurethane grout injected under pressure using a packer. However, experience showed that while a water-tight seal could be provided, its effective life was not sufficiently long to make the practice economical. A paper presented by Sydney Water at the 2002 ASTT Conference in Sydney stated that the expected life of polyurethane grout is five years.

Once this deficiency was identified, Sydney Water led the way in upgrading its Specification to require a more permanent seal, in line with the expected service life of the liner.

Interflow, along with other pre-qualified contractors on the Sydney Water SewerFix Program, invested considerable time and money in developing a superior long-term solution to the junction sealing problem. The result was the LCR (Lateral Connection Repair) System which uses a felt/resin short-form liner combination cured under pressure within the connection.

These LCRs provide a full-circle short-form liner in the lined host pipe, integrally connected to a full bore liner extending up the house service line up to 100 mm beyond the first joint (Refer to Figure 2 and Photographs 1 & 2 right). The LCR is installed into junctions via the sewer main without the need for excavation.

LCRs are now being widely included in Specifications throughout Australia. Typically these call for the use of high strength/low shrinkage resins such as silicates and epoxies. Interflow has now installed well in excess of 3,000 LCRs for clients around Australia since 2002, ranging in main sizes between DN150-DN375.

LCRs provide clients with several inherent benefits including:

• The installation packer positively locates the short-form liner and applies a high, uniform pressure to ensure it makes firm contact with the main liner and the house service line at the junction. It is held at this pressure while the resin cures. • The pressure applied by the packer squeezes excess resin into cracks or gaps, including the gap between the liner and the host pipe. This means that the LCR liner is mechanically held in place, as well as being bonded to the main and lateral. • A physical barrier against roots and infiltration which can be easily assessed by means of a CCTV inspection. The condition of traditional polyurethane seals could only be assessed via a hydrostatic test of the connection. • A structural seal which can also repair a structurally deteriorated connection which might otherwise have to be excavated and replaced.

Australian contractors are now leading the world in the application of LCRs and there is keen interest being shown by European, American, and New Zealand contractors who would like to apply such technology.

The current goal for Interflow is to continue to develop the LCR process to make it as cost effective as traditional polyurethane sealing methods and make LCRs the specified industry standard.

Options for Large Diameter Sewers

While the use of LCRs is now accepted for the sealing of junctions into DN150-DN300 lined sewer mains, the same option has not been widely available for the sealing of junctions into larger diameter sewers. This has mainly been due to the size and mass of the installation equipment requiring significant resources for each installation, thereby making the cost of the process prohibitive for some clients.

However, effective long-term sealing of junctions into larger diameter sewers is often more critical since larger pipelines tend to be deeper and subjected to higher groundwater levels.

Interflow, in conjunction with its partner Epros GmbH of Germany, have taken steps to fill this gap in the large diameter junction sealing market by completing recent trials on the Epros DrainLCR system which is suitable for pipelines up to DN600.

The system is more compact and lightweight than existing systems, and utilises a lateral inversion system to install a “top-hat” junction seal (Refer to Photographs 3 - 5).

This type of seal derives its name from its obvious top-hat appearance and is different from the Interflow LCR system in that it does not fully envelop the main. (Refer to Photographs 6 & 7). However, the materials used for the seal are exactly the same as those utilised in the tried and proven Interflow LCR system.

Interflow is currently nearing successful completion of a Queensland sewer rehabilitation contract installing the Epros DrainLCR seals on all lined DN375 sewers and will continue to offer the system for future large diameter lining projects.

Conclusion

As at previous times in the history of the development of Trenchless Technology, the Australian industry in particular has responded to the challenge. Australian rehabilitation contractors currently lead the world with the sealing systems being offered.

This latest development means that trenchless systems are available to cost effectively seal junction connections with a permanent physical barrier against roots and water ingress for pipes up to 600 mm in diameter.