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A BOLD ASCENT FOR STATIC PIPE BURSTING

24.10.17 - The residents of some of the localities situated above the Swiss community of Zug can enjoy the purest spring water which flows straight from their taps. The people of Zug, however, receive their spring water mixed with groundwater in two equal parts. The spring water comes from ten different headwaters having their source in the craggy Lorzental. There it is collected in so-called well houses and transported from these up a rather steep cliff into a reservoir abreast with the Tobel Bridge which crosses over the deep ravine of the Lorze. One of these spring water catchments is the "Brunnenstube Lorzental" which is connected by two lines with the Tobel Bridge reservoir higher up. The well house "Brunnenstube Lorzental", built in 1908, was completely renovated in 2004, and in 2016, the renewal of the two water mains ND 100 (fibre cement) and ND 200 (grey cast iron) was due.

New lines with greater capacity

An open-cut renewal would have been much too laborious and expensive in the steep ravine of the Lorzentobel, therefore the WWZ Energie AG opted for static pipe bursting, a trenchless pipe renewal method. This procedure allows not only the complete underground renewal of pipe lines, at the same time it is also possible to increase the pipe capacity because the nominal width of the new pipes to be pulled in can be up to two sizes larger. This killed the proverbial two birds with one stone because the hydraulic capacity of the spring water main was no longer sufficient for larger quantities anyway. In the course of pipe bursting, the old pipes were replaced by new PE-coated ductile cast iron pipes with larger diameters of ND 250 and ND 300. The WWZ AG entrusted the TPS Trenchless Piping Systems AG from Zurich with the project; this company, as a part of the Hagenbucher Group, enjoys a good reputation as a specialist for trenchless methods in Switzerland. For bursting open the old pipes and pulling in new ones, the TPS and the WWZ incorporation placed their trust in the GRUNDOBURST rig from TRACTO-TECHNIK GmbH & Co. KG; these powerful machines have no trouble even with such large pipe expansions.

Difficult soil conditions in a spectacular landscape

Not only the capacity upgrade was downright ambitious, the job-site itself, located on the foothills of the Swiss Alps, was a serious challenge: after all, the lines lead all the way up to the water reservoir, taking their course along a very steep cliff consisting of extremely weathered rocky formations which are anything but solid. "The route rises at an inclination of 45 degrees and because of its structure and the extreme weathering influences, the soil is acutely liable to slips", Plasch Depeder, the Division Manager at the TPS incorporation, describes the situation on site. If the project were going to be carried out with open trenches, the machines would have to be secured painstakingly along the precipice. The unsafe underground with a liability to slipping was also the reason why the existing access road, meanwhile badly in need of rehabilitation, was no longer able to hold out against the heavy building machinery. Therefore, a new, temporary access road had to be built before the actual project could be started at all.
 

Step by step towards the goal

The launch pit was excavated at the foot of the wooded slope and two target pits, one for each line, were set up approximately 55 m uphill. "In spite of the soil conditions, we did a relatively good job installing the concrete abutment", Depeder tells us. In the case of the smaller old line ND 100, the TBS incorporation had to work in two steps, forced upon the crew due to the extremely large expansion: at first, the old line was cut open with a GRUNDOBURST800G and the 75 mm rods pushed in; the second step was to pull in the 120 mm rods of the GRUNDOBURST1900G which was then applied because of its higher performance. As soon as the expanding tool and the new PE-coated pipe were connected, they were pulled through the old pipe while the pipe fragments were pushed into the surrounding soil in process. The GRUNDOBURST800G is able to replace pressure and water mains from ND 80 to 400 at a length of approximately 100 m without trenches, while the GRUNDOBURST1900G, which can raise a maximum traction force of 1900 kN, is used for pipes from ND 250 to ND 800 over a maximal length of 300 m.
 
The GRUNDOBURST1900G was used for the installation of the larger water main ND 200 exclusively: this time, the pipe bursting rig also pushed the bursting rods through the old pipe and up to the pulling-in pit. As soon as the cutting and expanding tools, made according to specifications by TRACTO-TECHNIK, and the new pipe were linked on, they could also be pulled through the old pipe.
 

Quick and economical performance thanks to a powerful pulling technique

On the one hand the extremely powerful and robust GRUNDOBURST pulling rigs and on the other the Quick-Lock rods, which are not screwed but simply clicked together to form a pushing- and pulling-resistant rod string, played a great part in the rapid progress of the project. Besides the short installation and equipping times, price and environmental aspects were in favour of the trenchless renewal of the lines using the static pipe bursting method. Neither time nor costs were wasted for the recovery of surfaces, the bore paths were already at hand and did not need to be cut through first before getting started, the required building space was clearly scaled down. "We believe that pipe installation with the static pipe bursting method can save 15 % to 40 % of the costs when compared to open-cut methods", believes Yves Hungerbühler, Sales Manager of TRACTO-TECHNIK Switzerland. In the case of pipe renewal in the wooded slope at the Lorzentobel in the picturesque landscape at the foothills of the Alps, the ecological benefits carried even more weight. No great masses of soil had to be excavated and moved away, thus the tree population was treated with care.
 
Rapid installation progress, ecological plus factors and great cost savings - these were the criteria which convinced the WWW Energie Incorporation. The whole building measure was successfully completed in approximately two weeks time. Since then, the spring water is flowing through the two new lines to the reservoir and from there to the households of round 30,000 people living in the community of Zug.  
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