Sewer rehabilitation in Nagold: quick work despite large volumes of water
Brandenburger Partner U&W, location Frankfurt am MainIn June and July 2009, the Brandenburger partner company Umwelttechnik & Wasserbau GmbH (U & W) rehabilitated an overall 1.4 kilometres of leaking DN 600 and DN 700 sewers for the Nagold wastewater cooperative. The goal of the project was to stop infiltration by extraneous water. The long storage life of Brandenburger GFRP liners allowed for a flexible work schedule and made waiting unnecessary despite the large volumes of water involved.
Extraneous water continuously infiltrated the sewer network through cracks and defective collars. Flow measurements recorded an increase of almost 40 litres per second. Such infiltrations, especially by ground water, put a high load on sewage treatment plants. "There is a large amount of extraneous water in the Nagold sewage treatment plant", says Gerhard Renz, the director of the Albstadt branch of the ISAS GmbH engineering firm. The negative effects of extraneous water in sewage treatment plants include problems with denitrification, i.e. treatment with bacteria. This is compounded by capacity issues, for instance in the rainwater overflow tank. The goal of the rehabilitation project was to rectify these issues.
The damaged sewer is situated between four and five metres below ground, and parts of it are underneath the bed of the Nagold river. The high groundwater pressure is especially conducive to infiltrations. The problem becomes more severe when the river floods. "We had a very strong flood in 1993. The sewers were inundated, and the main collection drains were filled accordingly", remembers Joachim Flik, the mayor of the municipality of Rohdorf, which is a member in the wastewater cooperative. The ever shortening flood cycles are one of the reasons why it is important that the sewers are in good condition, "so that the sewage disposal can be resumed as quickly as possible after a flood and everything goes back to normal."Rehabilitation with light curing does not require potable water
All in all, the project had a duration of three months, during which a total of four kilometres of sewers were rehabilitated. In a first stage, U & W were contracted to repair all visible damage in an overall 1.4 kilometres of sewers. This was followed by the rehabilitation of leaky branch sewers. Afterwards, an assessment will be made to determine possible further measures. "We settled for light curing because it is faster and simpler", says Flik. Previous experiences with hot-water curing involving the use of water from municipal utilities were a factor that figured into the decision. "The problem was that curing required relatively large amounts of potable water from the utility. For a project on a scale like the ongoing rehabilitation of the collection drains, this wouldn't have been feasible. We wouldn't have been able to tap our utilities for such volumes in the short term." The possible alternatives were to use river water – or straightforward light curing. Flexible schedules thanks to the long storage life of impregnated liner
The GFRP liners used were DN 600 and DN 700 with wall thicknesses ranging from 4.9 to 7.7 millimetres, as appropriate to the depth and groundwater load. For curing, U & W relied on the new BLUETEC® technology by Brandenburger using a light chain of nine UVA lamps at 1000 Watts each. According to U & W site manager Engelbert Schröder, the special challenge during the Nagold project were the large volumes of water that required extensive drainage measures. Pumping capacities of up to 100 litres per second were necessary. Still, the company was even able to work when it was raining. The long storage life of the liner material was a great benefit. The UV liners are manufactured and pre-impregnated at the factory. In a UV-proof packaging they can be stored for months, and they are resistant towards high temperatures. This allows a great degree of flexibility at the construction site. 
"We had a major part of the materials in storage at the construction site right from the start. This enabled us to work on critical sections, or sections with high drainage requirements, at times where there was very little water in the sewer", says Schröder. During those times when there was a lot of rainwater in the sewer, we were able to move to conduits with low drainage requirements. The installation itself of 1.4 kilometres of liner took only a little over three weeks. There was also preparatory work such as extensive shaft rehabilitation and partial rehabilitation work.Curing with BLUETEC®: reliable and fast
Brandenburger curing technology was one of the factors contributing to the quick and smooth proceedings. U & W has been one of the first companies to employ the BLUETEC® technology. This technology excels with a patented quality and curing control by measuring the temperature of the exothermic curing reaction. "One benefit is that the BLUETEC® method's comprehensive options for documentation enable us to fulfil our clients' quality requirements", Schröder explains. "Another is that we are able to ensure proper curing at a relatively high speed. This has been demonstrated by extensive quality control measures and material tests."
Contact and further Information
Umwelttechnik & Wasserbau GmbH
Niederlassung Frankfurt am Main
Ferdinand-Porsche-Straße 9 a
D-60386 Frankfurt am Main
Fon +49 69 42 01 18 11
Fax +49 69 42 01 18 19
www.umwelttechnik-wasserbau.de
frankfurt-m@umwelttechnik-wasserbau.de
Brandenburger Liner GmbH & Co. KG
Taubensuhlstraße 6
D-76829 Landau / Pfalz
Fon +49 6341 5104 0
Fax +49 6341 5104 155
info@brandenburger.de
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