Lateral connections to lined sewers have always presented problems for water authorities.
While there are several technologies that can structurally line a deteriorated sewer main, none can reliably provide a seal when cut to make a lateral connection. This means roots and groundwater can infiltrate the sewer, while sewage can leak into the water table.
Attempts to provide seals by trenchless methods have been regularly thwarted because of the conditions of the junctions. Poorly made original connections, ground movement, junction cracking, and shrinkage of the liner all challenge any “÷no dig’ attempts to apply a long term seal.
The project in Geelong for Barwon Water aimed to install “÷short form liners’ at six lateral connections that had previously been abandoned as too difficult. Previously it was considered that the only sealing option was to excavate and install new junctions.
For Interflow, the success of the project was the culmination of an extensive research and development program.
The need for sealing lateral connections to lined sewers, whatever the type of liner, has been recognised worldwide for some years. Whether cured-in-place, fold and form or wound-in-place, no type of liner is water tight at lateral connections unless a seal is applied. European Standards, ASTMs and Australian Water Authority Specifications all specify separate seals at these locations.
Polyurethane grout installed either by flooding or by using a specially developed inflatable lateral sleeve grouting packer was common practice until a few years ago. The seal could easily be hydrostatically tested immediately after installation. While it became the industry standard, experience showed it could not maintain an effective seal for a sufficient length of time to justify its expense.
When water authorities demanded a better solution, the Trenchless Technology industry responded. Various types of cured-in-place “÷short form liners’ with a tee or “÷top hat’ configuration were developed that could be installed without digging. Made from materials known to be suitable for use in sewer conditions, they had the advantage of providing not just a seal, but a positive barrier against infiltration from water or roots.
Interflow’s junction seal, called the LCR (Lateral Connection Repair) was developed by the company’s Sydney-based Research and Development team.
The installation procedure involved impregnating silicate resin onto a polyurethane coated, polyester felt tee, mounting it on an inflatable tee-shaped packer and installing it from the manhole nearest to the lateral connection. The packer was pushed up the pipeline until CCTV monitoring showed it had reached the lateral connection The packer was then inflated to hold the resin impregnated tee tightly against the pipe (or liner) and the junction of the house service line up to past the first joint. The inflated packer would be left in position until the resin had cured then deflated and removed.
The result was a cured silicate resin fitting strongly bonded to both the liner in the sewer main and the house service line up to past the first joint.
The use of this and similar technology was limited by the high proportion of non-standard junctions. Many house service lines connected after construction of the main presented obstructions which prevented trenchless installation of a seal. Disruptive excavation to construct a new connection to the lined sewer main was still frequently required.
In mid-2006 Interflow received an AusIndustry Grant to further develop this technology. The aim was to develop an improved solution that offered better sealing properties and which could be installed in a wider range of “÷non-standard’ junctions.
The result has been a new product to be called Interfit. As demonstrated at Geelong, it is an important advance in lateral connection repair technology.
Interfit uses a proprietary silicate resin blended by Interflow to suit this application. When installed in sewer conditions, curing time at ambient temperatures is typically reduced from 2 hours to 45 minutes. This means the sewer is obstructed for less time, and more seals can be installed in a working day.
The tee, which is impregnated with the resin, is of PVC-coated glass fibre felt. Together with the resin, it offers increased strength, toughness and impermeability.
The two part resin is pre-packaged in the correct quantities for the size of Interfit to be installed and is mixed and applied with a specially developed “÷gun’. The gun ensures complete mixing, essential to the fitting developing the correct properties, and offers greater quality assurance.
The packer is smaller and lighter for easier handling. Its patented design offers the ability to install Interfit in a wider range of non-standard junctions. The packer has a hollow core and so allows flow to continue in the pipeline during installation.
The project at Geelong involved installing fittings at six “÷cut in’ junctions. These were junctions that had been installed by cutting into the existing pipelines some time after they were installed – using varying degrees of care. On most of the junctions the first joint was displaced, whether by original installation or subsequent ground movement. Four of the six junctions had 45 or 60 degree bends coming straight off the connection. The original pipelines and all of the house service lines were of vitrified clay.
Sealing of these junctions had been specified as part of a previous sewer lining contract, but was not possible with the available technology. As excavation to install new connections was considered too inconvenient, they were left unsealed.
Interflow’s crew was able to demonstrate that the Interfit could be successfully installed in all of these junctions. With the light weight and smaller size of the packer meaning less force needed to move it, greater care was possible to manoeuvre the lateral sealing bulb past the potential obstructions at the entrance to the house service line.
Further installations are planned on similar projects.
The development of the Interfit is another example of Australian ingenuity advancing the Trenchless Technology industry and has potential application worldwide.