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Pipe renewal ND 1,000 with GRUNDOBURST 1900G
17.08.20 - To the south-west of the Lower Saxony capital Hannover, at the centre of the city triangle Hannover – Hameln – Hildesheim, you can find a town called Springe, with 30,000 inhabitants and 12 urban districts.
The ravages of time
Springe is a modern and lively little town with a well-developed infrastructure, even underground. The town’s public sewer network currently has a total length of about 550 km, of which approximately 310 km are allotted to the main canals and approx. 240 km to house connection service lines. The SES (Urban drainage utilities Springe), is an economically and organisationally independent municipal company that takes care of the operating, maintenance and servicing of this sewer network. This also means that SES bears great responsibility, since the oldest drainage systems in operation date back to the 19th century and their condition requires constant monitoring and attention.
A particular challenge in this respect was the sewage pipe in the inner-city street Harmsmühlenstraße. In the section between Schulstraße and Schopenhauerstraße the condition of the reinforced ND 1,000 concrete pipes in the apex area over a length of 160 m was so poor, that a renewal was urgently required. Tears and most of all, corrosion had caused leakages over several decades, which endangered the ground water and the ground itself.
Decisive general conditions
After public tendering, SES assigned Oppermann GmbH Consulting Engineers from Velmmar with the planning for the pipe renewal in the Harmsmühlenstraße. The company really knows a thing or two about designing and planning new pipe installations and pipe renewals and is very familiar with the advantages and disadvantages of the various methods.
Therefore, it was soon clear that, due to the local conditions and the location at a depth of 2 m in sandy, gravelly and even clay soil underground, only the underground construction method could be considered for the renewal of the damaged ND 1,000 concrete pipeline. All general conditions indicated that static burstlining with all its advantages would provide the best possible solution in every respect – space saving, environmentally friendly, fast and economical. Because:
- Roads, pavements and trees are protected, no need to dig up any trenches
- Traffic is hardly influenced and residents are not disturbed
- Emissions and the consumption of natural capital are greatly reduced
- High cost saving as opposed to the open-trench method
- The working phases are fast and performances high (Short construction times)
- The already existing bore path is used to good effect
- The result is equal to a complete new installation
Expertise of the professionals
Company Kögel Bau GmbH & Co. KG from nearby Bad Oeynhausen was appointed by the Urban Drainage Council Springe as general contractor for various pipeline constructions (e. g. applying pipe pushing for the construction of rainwater pipes). For the trenchless renewal of the 160 m long section in the Harmsmühlenstraße, Kögel Bau assigned Rettberg GmbH & Co KG as a sub-contractor, who have gained many years of experience with the pipe bursting method and have had especially great success working with the relevant GRUNDOBURST machines from TRACTO-TECHNIK.
GRUNDOBURST rigs are perfectly suitable for pipe renewals with the static pipe bursting method, where the old pipe is cracked and displaced into the surrounding soil. At the same time a new pipe with either the same, a smaller or even larger diameter can be pulled in. With this sustainable method, damaged pipes up to ND 1,200 can be replaced trenchlessly with new pipes in the same bore path. The well-coordinated and experienced “Rettberg Team” has already mastered many a tricky task of this kind. Exactly what was needed in Springe.
Suitability of the machine
For the bursting of the old reinforced concrete pipe ND 1000 with the corresponding general conditions, the GRUNDOBURST 1900G fulfilled all requirements with all these performance capacities:
- Max. thrust force: 716 kN
- Max. pulling force: 1,900 kN
- Starting pit size: 8 x 2 m
- Drive capacity: 55.1 kW at 2,300 rpm
- Bursting rod diameter: 120 mm
- Bursting rod weight: 165 kg
- Bursting rod effective length: 2,250 mm
- Bore rig dimensions: 2,850 x 1,150 x 1,000 mm
in order to successfully complete the task. Quick thrusting of the bursting rods into the old pipe and during the new installation, a solid and job-site suitable construction for the highest strains, as well as a high working safety and reliability, are almost self-explanatory.
A reinforced concrete abutment, together with timber pilings (approx. 3 m deep), were installed inside the machine starting pit and then the GRUNDOBURST 1900G was brought into position and tensioned appropriately. The Quicklock bursting rods applied were quickly pushed into the old pipeline, mainly thanks to their quick click-shut couplings. Inside the pipe installation pit the new pipe PE 100 RC with an outer diameter of 990 mm and a wall thickness of 58.2 mm (Manufacturer: SIMONA AG, Kim) was connected with a PE-pulling head and an expander with 1,060 mm outer diameter (with blade strips) and then connected to the QuickLock-bursting rod. When pulling back, the old concrete pipes were cracked open and displaced into the surrounding soil. In the same working process, the bore hole was expanded and the new pipe pulled inside it. Due to the relatively low cover, only a small expanding dimension of 70 mm was chosen, in order not to damage or lift the surface.
The pulling-in process required a lot of experience and know-how, as well as the right feeling for the situation. At the start of this process, the pulling force was 910 kN and this climbed steadily during the whole pulling-
in process. In the final section of the bore length, at around 140 m, it reached an unbelievable 1,900 kN, which equals the maximal pulling force for the machine! The pulling speed reduced itself strongly, but was still sufficient to complete the pulling-in task over the total bore length of 160 m.
In the starting pit and the seven intermediate pits for the installation of the house connections, a Bentonite-Water-Emulsion was applied to reduce the friction between the old pipe and the new pipe.
All the described working steps were completed in only one day. Due to the perfectly tuned equipment with machine and accessories, as well as an experienced and perfectly co-ordinated “Top-Team-Rettberg”, the GRUNDOBURST 1900G managed to burst an old sewer pipe ND 1,000 for the very first time and install a new PE-pipe with outer diameter 990 mm over a bore length of 160 m. A premiere with quite a few extreme values.
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