A trenchless solution was found for a main ascending canal in Norfolk that had suffered from repeated outbreaks
The Loddon Anglish Water Remediation Program was designed to allow the repair of a rising main pipe 300mm in diameter that had suffered multiple breakouts. The customer commissioned the on-site water and wastewater specialist to quickly assess the location and provide a suitable solution.
A major complication to completing the proposed redevelopment was that part of the ascending Main’s route passed through an Area of Special Scientific Interest (SSSI). This meant that an open solution couldn’t even be considered. In addition, access to the pipeline was difficult. A site meeting was arranged with client Anglian Water, Onsite and Claret Civil Engineering (the contractor) to discuss the options available and address the problematic areas of the route.
During the discussions, it was suggested that because the existing host pipe had failed multiple times, any solution was needed to achieve a stand-alone result that did not require the host pipe to be part of the final structure. In addition, the lining had to be designed for an internal operating pressure of no more than 5 bar.
The actual length of the sewer to be rehabilitated was ultimately identified as running between a pumping station and a collection point or about 713 m of pipe with a 300 mm diameter. It would be useful to have a redundant ascending main line in addition to the existing ascending main line which was installed as a backup pipeline. It was decided that this could be used to manage the main increasing currents for the duration of the lining activity, as the currents could be switched fairly easily at the pumping station.
It was of course crucial that the right liner material was used for such a sensitive project. That is why OnSite decided to introduce the NORDIPIPE system from Austria-based NordiTube Technologies SE in Great Britain for the first time. This is a strong and flexible liner that can withstand not only internal pressure but also external pressure from hydrostatic, ground and payload situations.
The liner for Loddon consisted of a combination of a coated felt, two layers of glass fiber and an additional layer of felt. The fiberglass layers in the liner have excellent properties under tension, with their own inherent strength and rigidity. The host pipe is not required for structural support, but it must be in close contact with the host pipe to maximize the cross-section of the final lined pipe and to properly seal the ends.
Before the liner is impregnated, the correct liner length must be determined. The pipe length must be measured and transmitted from the job site to the impregnation plant, including any kickbacks required to get to the face of the host pipe.
In the impregnation plant, the liner must be sealed at both ends. This allows a vacuum to be drawn at the end where the resin is to be poured into the liner. The resin and hardener are then mixed and poured into the liner.
The resin plug can then run in the liner. The liner is then clamped between the roll bars of the impregnation bed and the liner is slowly pulled through the rollers to ensure complete saturation of the layers of liner material. When the liner comes off the bed, it is immersed in an ice bath to slow the hardening of the resin. The liner is then pulled into the refrigerated vehicle, with ice being introduced between each stacked layer. The refrigerated vehicle is then driven to the construction site.
To install the 300mm diameter, 6mm wall thickness liner in Loddon, Onsite opted for air inversion using a steam cure method as it was a much easier and less expensive method of installing the liner.
The doors of the refrigerated truck are opened and the liner is then wrapped in an inversion drum. The end of the liner is closed and attached to a restraint rope / strap that is wound on the spindle of the turning unit in the inversion drum. The spindle is wound so that the liner is picked up on the drum. When the liner is completely wound onto the spindle, the front part of the liner (to which the vacuum system was previously attached) is connected to the inversion cone. If the liner has a tension strap, this must be removed and passed through the opening of the cone. When the entire liner is wrapped in the inversion drum, the cone is attached to the drum. The drum is then pressurized so that the liner can be pushed out under control through a protective support which then leads to the host pipe. The drum maintains the air pressure constant, allowing the liner to rotate through the host pipe until it reaches the end point.
After the liner is inverted through the host pipe to the endpoint, vent pipes are attached to the exposed end of the liner to allow hot air / steam to be released from the liner. The vent pipes are typically equipped with a valve and hose coupling, and a hose runs from the vent pipe to the ground or street level to act as a muffler. The valves either on the ventilation pipes or on the silencer regulate the air volume and / or the air-steam flow and thus the pressure in the lining. A small steam condensate drain hole is pierced through the liner at a low point (bottom) of the exposed liner to drive out any accumulated condensate that accumulates at the end of the liner.
Steam is then introduced at the steam generating station, which is connected to a suitable air flow through the inversion drum. This is released at the exhaust station in order to achieve an even distribution of heat over the length of the lining in the pipe. The correct boiler size and air compressor size are determined from the diameter, length and thickness of the liner and, to some extent, the temperature of the soil around the host pipe.
When the steam is applied, the resin in the liner begins the curing process with steam at temperatures up to 100 ° C (212 ° F). This is generally held for about four hours, after which the liner is allowed to cool until both ends are below 40 ° C.
The steam pipes are removed and the pipe cut back to the nominal area of the host pipe. The end sealing mechanisms are then installed.
The end seals prevent water from migrating along an annular gap that may exist between the liner and the host pipe. This can be especially important if a hydrostatic pressure test is to be performed on the installed liner. In the case of non-potable applications, such as B. power lines, applications with a certain particle content, a final treatment prevents long-term damage from abrasion or wear at the liner end and ensures a smooth transmission between the host pipe and the liner.
For the Loddon project, OnSite used Weko gaskets to provide a tight seal against the host pipe of the lined length, which was then coupled to the rest of the pipeline with Viking Johnson fittings.
The Loddon project was managed, resourced and delivered by Scott Weston, Senior Engineer at Onsite. Working with Claret Civil Engineering and the lining team, he programmed the work required, waterproofing the lining, delivering and installing five individual lining lines, which were completed in three weeks. Tests were carried out for the project and the pipeline was put back into operation a few weeks later.
-This article appears in the March 2018 issue of WET News.