Small but perfectly formed
Repairing downpipes, house sewers and lateral connection pipes can be a real problem. But a successfully trialled scaled down method for sewer rehabilitation could prove the answer.Trenchless repairs of lateral connections are tricky jobs to do. Many of the commonly available packer systems cannot cope with pipe diameters that are rarely larger than DN100, and sometimes even with additional pipe bends. Until recently, no repair system for the DN100 to DN150 pipe range had been available for sealing the service laterals of downpipes, house sewers and lateral connection pipes, i.e. pipe sizes from DN50 to DN150.
Therefore the general trend in cured-in-place (CIPP) lining operations has been to leave out the lateral connections, except in drinking water protection zones or in cases of infiltration risk.
To most people this is not a problem as liners are sufficiently close to the lateral opening so as to need no further action. That, however, is not the whole truth, especially for longer pipe runs where it is rarely possible to make accurate liner calculations due to intrinsic dilatation.
The result is that liners tend to protrude into the communicating pipe and need to be cut, at high cost, in a separate operation, or they end far from the main/lateral interface and do not cover the exposed connection of the lateral joint.
Trelleborg epros has scaled down to lateral and house sewer sizes the method used for main sewer rehabilitation where a packer is used to invert a fibreglass lateral connection repair (LCR) unit into the main/lateral interface.
Its new eprosLCR-B system is designed for applications in DN100 to DN150 main pipes, with DN 50 to DN 150 laterals at connecting angles of 45_ to 90_ with LCR lengths of 150-280mm. Also, the packer negotiates bends of up to 90_.
A field trial was set up in cooperation with the State Building Administration of W,rzburg, Germany, to subject the eprosLCR-B to a performance test. The test results convinced both the customers and the relining experts of its applicability in the field.
Robert Thoma, from the Building Administration in W,rzburg, offered to use and test the new method in the rehabilitation of a large barracks site. The sewers across the site and the house sewer pipelines under the buildings had already been relined using different methods.
However, the 100-150mm diameter lateral connections in the relined house sewer pipes had been omitted, because no appropriate method had been available at the time.
The first test phase was to install four LCRs and see if these were satisfactory, the repair of the remaining 15 service laterals would follow. The DN100 laterals formed 45_ connections with the underground house sewer, which had a diameter of either DN125 or DN150.
Both the fibreglass LCR and the packer needed to be consistent with the angle of the lateral connection otherwise the connection seal would wrinkle and potentially cause an obstacle to service flows.
The preparations in the sewer line are identical to those for CIPP or packer-based methods. After thorough jetting, a camera is put down the pipeline to inspect the pipe for cracks, collapses or bottlenecks that might prevent the introduction and positioning of the packer. The test project installation in W,rzburg was undertaken by contractor Kanal-T,rpe Gochsheim.
The fibreglass LCR was first impregnated with epros patch liner resin and then inverted over the packer finger, which had been lubricated with a release agent, with the rim of the LCR being in firm contact with the packer body. In contrast with other known packers, the eprosLCR-B packer includes a lateral finger that is extended into the lateral.
The packer finger must of course be retracted during packer introduction into the main pipe. A specifically designed reversion technique retracts the finger while inverting the LCR down to its rim. A thin binding wire holds the reversed finger during transport.
The wire comes off as soon as pressure is applied to the packer during the installation process.
A camera is put into the pipeline from the building side through the pipe to the connection point. This is used to monitor the exact positioning of the packer. The packer itself is introduced from a manhole or cleanout of the house sewer and pushed with air rods to the lateral opening.
During this operation, it is important to prevent the air push rods from twisting, because their correct alignment along the longitudinal axis is important for the accurate positioning of the packer finger at the opening of the lateral.
The commands from the camera operator are transmitted by voice radio.
"We always recommend a trial run before installing the LCR, to include simulated positioning of the packer and installation of the LCR," says M,hlin. In this way it is possible to mark the push rods to identify the distance to be travelled by the packer and to make a final check to ensure the diameter and angle of the packer are consistent with the geometry of the host pipe.
The remaining work is easy with just a little exercise being required. The camera operator gives directions for the accurate positioning of the packer. At his command, the packer will then be slowly inflated. Due to the binding wire, the rim of the LCR is first pressed against the main pipe wall around the lateral opening.
Then, as the binder comes off, the LCR on the finger is inverted into the lateral, job done. The cure time is about 90 minutes. After this time the packer is removed from the line and the result can be inspected with the camera.
"The results of the test repairs have convinced me," said Thoma. "Simple handling and short installation time are two key benefits for any method, because they are crucial to the price-performance ratio.
But the final result is what matters. We were very positively surprised by the smooth operation and the result."