After a three-year moratorium, first successful pipe liner rehabilitation carried out in Göttingen
By means of the professional execution of the first rehabilitation project using pipe liners after the lifting of a general installation ban for liners in Göttingen, Brandenburger was able to prove the advantages of GFRP liners at the end of 2007.For three years, the Göttingen water works did not invite tenders for pipe lining projects. The reason for this has been bad experience in regards to the supplied quality. “The Göttingen water works had in 1993 already seen pipe lining as an important component in the field of rehabilitation measures and has installed over 40 km of liner, primarily needled felt, into the network till today,” explained civil engineer Manfred Fiedler of the Göttingen water works. However, as of the year 2000 the liners often did not meet the requirements of the certifications, which accompanied the continual drop in prices. In several cases, the required wall thicknesses, Young modulus, annular rigidity and in particular the necessary seal of the liners were not reached. As of the spring of 2004, a general installation prohibition for liners was announced in Göttingen.
Market research turned the balance for GFRP pipe lining
A market research should first of all determine the further application of liners. The first liner report of the IKT confirmed the faults objected to in Göttingen with liner inspections carried out across the nation as well as the noticeable trend also in Göttingen towards light-curing glass fibre liners documented in the liner reports. “We made the decision therefore in 2006 to call for tenders again for pipe lining based on glass fibre liners,” said Fiedler.
The contract for the first measure to be carried out again was awarded to Brandenburger for a sewer rehabilitation that covered several streets in a residential area. It was awarded because of the proven, very good construction site test results, as confirmed also in the IKT Liner Report 2006, and the technical and practical qualification of the light curing Brandenburger pipe lining procedure in regards to the technical requirements legally mandated in this case. “In past years, GFRP liners were employed only in a few rehabilitations in Göttingen,” explained Marc Mielke, project manager with Brandenburger. “But there with good results though.” What tipped the balance for a trenchless process for the now tendered project were the damage images: Infiltrations, pipe connector offsets, leaks and cracks to a degree that a different method would have involved too great of an expense. The project covered the Breslauerstraße, the Ewaldstraße, the Hauptstraße, the street Posthof as well as the Flüthenweg.
Difficult traffic conditions made a short construction time necessary
The tendered project - 115.3 metres DN 150, 203.6 metres DN 200, 174.1 metres DN 250, 151.5 metres DN 300 and 36.5 metres DN 800 extraneous water sewer - had been delayed twice after the 2006 tender. The reason for this was that the streets over the sewers were used for a longer time for detours and that you could not operate here at the same time. The release for starting the rehabilitation was not given until the street constructions were completed at the end of 2006. The project was carried out finally between the 26th of November and the 4th of December 2007. The preparatory work included the cleaning of the sewers, a TV pre-calibration, the tested stress analysis as well as milling work and the levelling of the liner. All tasks needed to be carried out in close cooperation with the water works, the construction company and the Göttingen transportation authorities. The conditions were not particularly easy: The Posthof street is a four-lane highway access of which the left outwards-bound lane needed to be blocked by warning indicators and lighted directional boards for the duration of the installation. Within four hours, about 70 metres of pipe liner with DN 200 and a wall thickness of 3.5 millimetres was installed and samples taken.
The largest liner with a diameter of DN 800 and 10.5 millimetre wall thickness was installed at a length of 36.5 metres in the Hauptstraße. Due to the difficult traffic conditions there, strict time periods and very short construction times were necessary because of the detours to bus lines. “We set up the construction site starting at 9 o'clock,” reported Mielke. “The liner was rapidly installed, cured and cut. By 16:35, the samples had been taken and the four side inlets opened. After the work needed to be interrupted for the traffic as planned till 18:00, the connection of the inliner to the shafts was done along with the clearing of the construction site.” All liners are cured as quickly as possible using UVA light. The pure curing speed was 0.3 m/min at DN 800, 1.4 m/min at DN 300, 1.5 m/min at DN 250 and 1.6 m/min at DN 200 and DN 150. Upon completion, a TV approval inspection was conducted.
The installation was followed through despite winter conditions
There was a time frame of two weeks for the whole project ; the actual installation was to be accomplished in six days. Just in that time, there was a cold snap with rather bitter temperatures of down to minus 10 °C. The shafts were partially frozen shut. Thanks to good technical equipment and well-planned logistics, the rehabilitation could be completed uninterrupted as scheduled: Work was done with heated winders; the liners that were pre-saturated with UP resin were temporarily stored in temperate halls of the Göttingen municipal facilities. The delivery to the construction site was done just-in-time then. This ensured a good processability of the material and the schedule was adhered to.
Excellent test results - all nominal values exceeded
On the basis of the known history in Göttingen, the water works gave special order to the IKT to evaluate this rehabilitation project with heightened scrutiny. The result: All nominal values concerning the wall thickness, the Young modulus, the bending stress as well as the sealing were outperformed. Furthermore, all existing sewers were calibrated once more based on the construction site samples and the precise diameter checked. This also made it possible to prove that all the liners were form-fitted to the pipe lines to be rehabilitated.
Fiedler: Signal, that Göttingen permits glass fibre liners again
“The expertise of the rehabilitation team and the results of the liner tests make the process fit for the future,” concludes Fiedler. Since the project had been postponed twice, its execution seemed to have been ill-fated. Experience has shown: “Once a project has got bugs in it, then the trouble is carried through the entire construction project.” The Brandenburger company has fortunately broken this law of series by the execution. “Thanks to the successful completion of the project, the signal is upheld on the market that Göttingen permits liner once more, limited to glass fibre,” Fiedler explained. Further tenders are being prepared, the results of which will be reported on during the Göttingen sewage days and at the seminar series “Auf den Punkt gebracht” ('Brought to a Point').
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