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Crossing canal and habitat with the GRUNDODRILL 18N

08.04.19 - The Kummerow lake in the Mecklenburg Lake District lies between the towns of Malchin, Dargun and Demmin, roughly 50 km north west of Neubrandenburg and about 70 km south of Stralsund. With a surface area of 33 km2, a length of 11 km and a width of 3 km, it is the fourth biggest lake in Mecklenburg-Western Pommerania. It forms the heart of the "Mecklenburgische Schweiz und Kummerower See" nature reserve together with the Malchin lake that is located south west of it. Along with the Peene river and its tributaries, the Kummerow lake is a real gem in ecological terms and worthy of protection. The lake is well frequented by indigenous and northern bird species and an important water run-off and collection area. With its wetlands, a wide reaching reed belt, a large moraine landscape and, by no means least, a 37 m high cliff on the east side, it forms a generous, ecologically valuable area.

Ready for new installation

About 60 years ago, a gas pipeline (DN 300) was built from Dargun to Malchin along the west side of the Kummerow lake. It is designed to withstand a maximum pressure of 16 bar and is operated at 7 bar. After uninterrupted operation all that time, it is beginning to age. Since 2016, it is being renewed section by section in order to safeguard the supply of natural gas to the general public in future as well. Renewal of the line on a partially adapted route means that the two Malchin districts, Salem and Gorschendorf, are now going to be connected to the natural gas network. Today, the company responsible for operation, maintenance and new installation is E.DIS AG, which is one of the biggest regional energy service providers in Germany and has its head office in Fürstenwalde/Spree. In the summer of 2018, it was time for new installation of the 11.5 km long line section from Neukalen via Gartshof, Salem, Gorschendorf to Pisede where the embankment is.
 

Planning for the environment

ECB Geo Projekt GmbH in Berlin was commissioned with planning the new installation of this pipeline section with steel pipes DN 300 PN 16 coated in plastic PE-HD in accordance with DIN 30670. Included in the order was the task of running cable protection pipes made of PE-HD DA 160 mm in sections for carrying medium-voltage cables as well as running PE-HD protection pipes DA 50 mm and DA 110 mm for carrying fibre optic cables at a later time along the entire natural gas route.
 
A great deal of attention during the planning phase of the new pipeline sections was given to crossing underneath water, canals, main roads and railway tracks. More specifically, to pass under an existing rain water channel DN 500 and subsequent crossing of a habitat, it was necessary to adhere to the strict conditions of the local water authorities! Apart from crossing a habitat, it was of course necessary in advance to ensure that the procedure and methods adopted would be as harmless as possible in an overall sensitive area in the centre of the "Mecklenburgische Schweiz und Kummerower See" nature reserve. It didn't take long to realise that the best way to cross under the rainwater channel and habitat was to choose a trenchless route for the natural gas pipeline and protection pipes using an HDD flush boring process. With this trenchless process, the CO2 emissions and the impact on the natural surroundings are reduced demonstrably to a minimum, and it is possible to pass under paths, roads, railway tracks, bodies of water and other lines cost effectively, safely and quickly. Precisely the right approach for the natural gas pipeline and cable protection pipes, for which the engineers planned a bore hole with a length of 151 m in accordance with the two areas under which the pipe and lines needed to pass.
 

Decisions for the equipment

Komesker Anlagenbau GmbH from nearby Tützpatz, a company well versed in the HDD flush boring process and well equipped with drilling plant from TRACTO-TECHNIK, was commissioned to carry out the installation. The decision was made to use a GRUNDODRILL 18N system (without rock bore drive), which is particularly well suited on account of the bore hole being in soil class 3-5 with a high silt content and ideal for the expected pulling forces. The biggest challenge here was to not exceed the bending radius of the steel pipe when passing under the canal (1.5 m beneath the bed). Once the composition of the bore flushing plant – 4000 l tank filled with 100 kg Bentonit W Plus and 15 kg PhrykoTon additive – and the necessary drilling and enlargement tools were chosen, the drilling work could commence.
 

Bore hole for the protection pipes

On the allocated route, the first step was to drill a pilot hole with a diameter of 120 mm for pulling through the PE-HD protection pipes DA 160 mm for the medium-voltage cables and the PE-HD protection pipes DA 50 mm for the fibre optic cables as a cluster. This was child's play for the GRUNDODRILL 18N plant, and it was completed in next to no time. For safe and sustainable routing of PE-HD protection pipes, two enlargement stages followed with a medium soil reamer to DA 270 mm and to DA 330 mm respectively. With the second enlargement, the protection pipes were successively drawn into the pipe cluster.
 
For reasons of safety, the contractor, E.DIS AG, sought permission to route additional protection pipes with a diameter of DA 110 mm instead of DA 50 mm for the fibre optic cables in the event of the hole being longer than 130 m. Therefore, instead of DA 50 mm protection pipes, DA 110 mm protection pipes were pulled in through this hole for the fibre optic cables.
 

Bore hole for the natural gas pipeline

Then it was necessary to drill a second hole for the natural gas pipeline. And this is where it was important not to exceed the bending radius of the steel pipes. For this purpose, it was possible to implement controls during pilot drilling with just minimum deviations. Thanks to the latest locating technology from DCI with tilt increments of 0.1 percent this was almost child's play for the drilling crew led by Enrico Hildebrandt. Just like the pilot hole for the cable protection pipes, this pilot hole was made with a diameter of 120 mm and, as expected, no problems were encountered here either. The first enlargement stage was to DA 360 mm. To compensate for the highly sensitive bending radius of the steel pipes that needed to be drawn in, Enrico Hildebrandt opted for a second enlarging process with a factor slightly greater than 1.3 (DA 450 mm). The steel pipes were draw into the bore cluster through this second enlargement without any problems, even for the bending radius. The requisite pulling force was 50 kN, the flushing volume in the extremely silty earth was 210 l/min.
 

Time for the environment

Particularly in this sensitive environment, going under rather than through was the only sensible technology for crossing a channel and a habitat. The time for routing the gas pipeline, both for the cable protection pipes and also the steel pipes, was 50 m/h – an unbeatable time compared above all with open construction. And nothing was disturbed or damaged, most importantly the habitat.
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