Sealing lateral connections on lined sewers to prevent infiltration
The point at which a lateral or service connection joins a main sewer pipe can be problematic. Open joints, caused by relative movement in the ground between lateral and main or poor installation procedures during construction of the original pipe network, can often lead to major groundwater infiltration or effluent exfiltration problems or simply a convenient point of access for roots or soils which in turn cause blockages...
SAUGUS, MA -- For very many years now, pipeline engineers have known that, particularly in aging pipes but also sometimes in relatively young pipes, the point at which a lateral or service connection joins a main sewer pipe can be problematical. Open joints, caused by relative movement in the ground between lateral and main or poor installation procedures during construction of the original pipe network can often lead to major groundwater infiltration or effluent exfiltration problems or simply a convenient point of access for roots or soils which in turn cause blockages.
One such situation occurred recently in the town of Saugus, Massachusetts, USA. Saugus is located some 11 miles north of the centre of Boston and the local municipality had recently undertaken a major sewer rehabilitation program. On reopening lateral connections on completion of the lining program, the pipes were found to still be experiencing significant infiltration of groundwater. Further inspection indicated that the vast majority of this was emanating from the lateral connections.
The main line sewers comprised either 200 or 300 mm diameter pipes, which had connecting 100 and 150 mm diameter laterals. Due to the amount of infiltration being experienced, it was decided that around 500 lateral connection points across the rehabilitated sewer network required sealing.
After careful consideration of the available options it was decided that the lateral connections would be sealed using 'Lateral Connection Repair' seals. In this instance, the lateral connection repair seals chosen to complete the work were manufactured by Trelleborg epros. Trelleborg AB, the parent company headquartered in Sweden recently acquired Germany-based epros GmbH of Duisburg, with a view to such an acquisition significantly enhancing the company's presence in the pipeline rehabilitation sector world-wide.
The lateral connection repair system, known as the Drain LCR Liner repair method, was developed in-house by epros engineers and can be used in main sewers of between DN 130 and DN 400. The Drain LCR Liner repair method uses special LCR packers for inverting the lateral connection repair profile lining into the lateral connection pipe.
The LCR liners or felt caps and the inflatable relining balloon are transported in the pipe to the point of repair using epros LCR packers. The packer has two telescope-style wheel sets and so can be pushed into the pipe with locked air push rods and turned around its horizontal axis at the point of repair. It carries a camera for ensuring that positioning of the liner is correct before final insertion. The packer also supports the inflatable balloon by pressing the rim of the felt cap of the liner firmly against the wall of the main pipe. The shaft of the felt lateral connection repair liner is then inverted into the lateral connection.
During preparation of the lateral seal, the lateral connection repair unit is initially impregnated with silicate-based resin which will cure under ambient conditions. The lateral connection repair profile is then place around the 'calibration' tube. This combination is then reversed into the body of the robotic carrier, which is then ready to launch into the main sewer.
Once in position in the base of the access manhole the robotic unit is winched into position adjacent to the lateral connection. The lining operator uses a CCTV monitoring camera to ensure the launch robot is both correctly aligned and orientated to the lateral joint. The launch packer is then inflated holding the lateral connection repair 'lip' in close fit to the inner sewer main wall. The calibration hose is then inflated and this inverts the body of the lateral seal into the lateral pipe and pushes it against the lateral pipe wall. After a predetermined cure time the calibration is evacuated to draw it back into the launch robot body, leaving the cured in place Lateral connection repair seal bonded to both the inner lateral pipe wall and around the joint position with the main sewer, making the seal complete.
Inverting the lateral connection repair seal into the lateral pipe also enabled the resin within the system to migrate into defects in the surrounding pipe and joint so ensuring a very effective seal. The lateral connection repair 'tail' also extended into the lateral connection by between 300 and 500 mm so enabling the seal to be effective not just at the joint position but also for some distance into the lateral.
The lateral connection repair itself is designed using a mixture of both fibreglass and needle felt materials, which once cured enables the effectiveness of the seal to be tested using an air pressure test system.
Trelleborg epros has also ensured that the lateral connection repair system has been product tested by WRc in the UK where it passed a 6 month hydrostatic test. The system has also achieved DIBT Certification in Germany.
With some 500 such installations to be completed on the Saugus project, National Water Main, part of the Carylon Corporation of Chicago and Newark New Jersey, was appointed to complete the work, in agreement with Insituform Technologies Inc (the US licensee for the Trelleborg epros Lateral Connection Repair System).
In all two installation crews were used, achieving average installation rates of between 5 and 6 lateral connection repair insertions per crew per day over an 8 hour working day.
One problem that had to be overcome by the installation crews was that the lateral connections across the project were at all different angles, which they were difficult to access and each had to set up individually with no distinct pattern for set ups being established.
However, after completing full onsite training and certification under the tuition of epros engineers, this situation was easily handled and, in the event, all seals were achieved with excellent bonding to both main sewer and lateral pipes with no direct surface access of the laterals being required, and with access only being needed at main/lateral joint, which was pin-pointed using the patented location system.
One interesting point about the lateral seals that were installed on the Saugus project was that some 15% of the installations were specified to be what is termed 'Full Wrap' seals. Whilst traditional lateral seals look rather like an inverted 'T', with the T crossbar acting as the seal face within the main sewer pipe, for Full Wrap installations the 'in main' section of the lateral seal actually forms a complete circular 'patch' around the inner circumference of the main pipe.
On completion of the installations and having studied the post project survey results, all the parties involved with the work were very pleased with results. With the opinion being that the system gives a straight forward sealing option system which results in a long term solution to the infiltration problems encountered.
Commenting on the lateral connection repair system Joe Peronne, project engineer for National Water Main said: "We have had a long and solid relationship with Trelleborg epros and we were please to be able bring this new sealing technology into the USA. During the course of the works we were very well supported by our suppliers and the system has achieved everything that we were told it would, if not more."
Ian Ramsay for Trelleborg epros commented: "Given our long term relationship with National Water Main, which has very competent crews and management, we knew immediately that the introduction of the new lateral sealing system could be achieved without any problem. After some initial training the National Water Main crews became very adept with the new system and were extremely pleased at how easy it was to operate and install. We were also very aware that the client would need to see good results, given the application was using a relatively new system, and ultimately they too were very pleased with the results."
Epros has, to date, sold over 60 of the very compact lateral connection repair systems world-wide to over 14 countries. The Trelleborg/epros operation now exports lining, patching and lateral lining and sealing systems and products to over 40 countries worldwide and with the recently established Trelleborg connection, the epros division will be well placed to encourage growth both in the overall renovation market and in its renovation product range to meet the increasing demands of the worldwide rehabilitation market.