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Installation of drinking water lines through rock using auger boring in Neuhausen on Eck

08.04.19 - The plateaus of the Swabian Alb mountain range are characterised by rocky ground. Places such as Neuhausen ob Eck (770 m above sea level), on the plateau of the Heuberg region, located on the southwest Swabian Alb, already have rocks not very deep below the earth's surface, which makes pipeline construction more difficult. For the drinking water supply to the new industrial estate in the east of the town it was necessary to cross a former main road (B 311), which as a district road (K 5945) is now a very important access road. Because this access road cannot be damaged, the new drinking water main line could only be installed trenchless. It became apparent that the auger boring method also functions reliably in rocky ground.

DRINKING WATER LINE FOR A NEW INDUSTRIAL PARK

The town of Neuhausen ob Eck with its almost 4,000 inhabitants, located roughly 10 km east of Tuttlingen, has a high demand from business people following the construction of a bypass road. Only a few years ago an industrial park was developed to the west of the town in a section of the former air base. In the summer the area is the venue of the Southside Festival (international open-air rock concert), therefore leaving little leeway for further commercial estates. A second industrial park is now being developed in the east of the town, for which a new drinking water main line, among other things, must be laid. As was the case almost everywhere else in the town the white rocks from the Upper Jurassic era lay just a few decimetres down, which occurred from marine deposits approximately 145 million years ago. These rocks have compressive strengths between 60 - 80 megapascals. They are in the transition zone between light and hard rock.

The drinking water is supplied through a Duktus cast iron pipeline (DN 200, diameter 250 mm), which is made from long unmortared cement pipes. The cement coating is due to the rock and thus the rough soil conditions. In order to be able to cross the district road contact-free, a 22 m long drill hole is required in the rock of the limestone deposit. The town of Neuhausen ob Eck awarded the development works for the new industrial park to the company Friedrich Stingel GmbH, road construction and civil engineering, from Villingen-Schwenningen. This company in turn sought a specialist for drill holes in rock and turned to the company Krug, asphalt and sewer construction, from Langenargen on the shores of Lake Constance. Word got round that Markus Krug with his small specialist construction company can create very complex and demanding drill holes in difficult ground conditions. The Krug company has a GRUNDOBORE machine, type 200S, and for years has been realising cross drill holes and service connections in the Lake Constance region, in the Hegau and on the Swabian Alb.

GRUNDOBORE 200S WORKS RELIABLY IN ROCK

The GRUNDOBORE 200S is available as a manhole version or with a small trench box for working from starting pits. The Krug company has this pit version, which has a feed force of 200 kN and a pulling force of 250 kN. Due to the narrow dimensions of the trench box, drill rods half a metre long and with a diameter of 82.5 mm are used, pilot drill heads and expander headers with any facing can be used and the largest deployable pipe diameter is 280 mm. The Krug company has pilot drill heads for the rock application, the same also applies to the expander heads for crossing the drilled sections in the retraction. The expander heads for rock are known internationally as hole openers. With a feed force of 20 t, the GRUNDOBORE machine is well equipped to perform tunnelling work in rock.
 

DRILLING PROCEDURE AND CAST PIPE PULLING

The assembly and installation of the GRUNDOBORE machine in the starting pit was carried out on the last Monday in June 2018. The following day the entire pilot hole was made through the limestone bedrock. The drill hole was widened on Wednesday and on Thursday the pipe pulling work commenced and lasted until Friday. During the pulling work the cast pipe connection work for the tensile load-carrying socket system as well as the sealing work were carried out by the specialist company Heinrich Rack, pipeline construction, from Renquishausen. The pipe hoisting was realised by the construction company Stingel using a large excavator. After the pipe connection work the pulling work of the cast pipes could be carried out continuously, but slowly and steadily due to the rock material. The following week the annular space around the laid cast pipe was pressed with 1.5 cbm of bedding material and the linking to the new pipe network was realised. Within a good week the crossing work and the pulling of the long cast pipes in the bedrock of the hanging limestone was successfully completed to the delight of all involved.
 

SUCCESSFULLY BROKE NEW TECHNOLOGICAL GROUND

Cross holes and connecting bores can be made in rocky ground and with long fixed piping systems using the tensile load-carrying socket connection system. The high feed and retraction force of the GRUNDOBORE auger boring machines makes possible trenchless driving and expanding work in the rock. Although the limestone rock just a few decimetres below the surface in Neuhausen ob Eck would initially give the impression that trenchless cast iron pipeline installation was not possible, the planning office, the general contractor Stingel and the executing company Krug developed an innovative trenchless solution using the auger boring method. They broke new ground and applied the technical feasibility in the best possible manner with the well-considered use of the driving forces.
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