The Krakow DTW is built to last

Sep 09, 2009

Economic Microtunneling with HOBAS® Jacking Pipe Systems - Establishing the main collector of the Lower Bench of Vistula River (DTW - Dolnej Terasy Wisły) is very important for Krakow, the second largest city in Poland. The city’s growth as well as EU requirements spurred on the extension and modernization of the existing water and sewage system. A large part of the projects is funded by the EU and also the DTW collector is a so-called ISPA project.

The DTW consists of a 6.5 km pipeline of which 6 are installed by microtunneling. Once completed, it will connect two sewage systems, one of them being overloaded and one having reserves. Its function is to even out the flow to the treatment plants Kujawy and Płaszów during heavy rainfall ensuring their optimal operation. In addition to this, areas which currently use septic tanks will be connected to the new collector, preventing the soil from further contamination and improving the groundwater quality.

Construction works for the collector are conducted in three stages and in two parts regarding contractors.

DTW Collector Part I
The installation of the first part of the Vistula Lower Route collector in Krakow was initiated in March 2008, the line going into service within the next months. This part of the project is realized by a consortium consisting of Hydrobudowa 9 & PRG Metro. Microtunneling was chosen for mainly economic reasons. Since the planned pipeline route runs in 6 m depth nearby the Vistula River where water collects in layers of sand and gravel, the costs for dewatering and excavation works would have been considerably higher than for tunneling.

The pipes used for the project are HOBAS CC-GRP Jacking Pipes with outer diameters of 1,099 and 1,229 mm. Two independent microtunneling machines were utilized and the right amount of lubricant was applied to maximize the progress. The smooth and non-absorbent surface of the pipes doubled the effect of bentonite lubricant so that the installation ran smoothly over the 200 m long drives and without the help of intermediate stations. The latter would only have been activated if allowed jacking forces had been exceeded. Since their help was not needed, the installation speed was doubled.

The achieved jacking rate of up to 25 m per 24 h was the result of the contractors’ experience, the pipes’ properties and good planning. The thrust and reception pits are made of steel piles. This solution has proved its worth in the past and is now an accepted technique in Poland. Pits of any required shape can be made this way, adapted to local conditions and the optimal pipe length, which in this case is 3 m. The piles are extracted once the pipe installation has been completed. Concrete sunk shafts are utilized where intermediate stations are taken out after the pipe has been installed, to make way for a HOBAS CC-GRP Shaft. Due to the high precision of microtunneling it is possible to drill through the provided and temporarily sealed sparings in the reinforced concrete walls. Once the pipeline is laid, the intermediate jacking stations are lifted out and CC-GRP Shafts are placed in the 3 m diameter sunk shafts. Thanks to their comparatively small dimension and low weight, this is done with ease.

It was important for the contractor that all parts of the new collector, such as also manholes and fittings, were prefabricated and from one source, which together with microtunneling guarantee a complete high-quality leak tight system. It was furthermore of great importance to be able to continue installation works during the winter months. Taking the high durability of the pipeline system into account, a pressure line of the system will also be established with CC-GRP utilizing DN 500 Pipes PN 6.

DTW Collector Part II
The remaining 3.4 km line is realized under the direction of INKOP, another contractor specialized in microtunneling. Its construction was commenced in September 2008 and is expected to be completed by the end of 2009.

The works were conducted under similar soil and groundwater conditions as for Part I. Outstanding progress was achieved with installation rates up to 24 m / 12 h. The intermediate stations once again stood still during all drives, even lengths up to 208 m were easily tackled without help. Optimal technological parameters, the smooth surface of HOBAS Pipes and sufficient lubrication applied every 21 m make an efficient and economic realization of the project possible.

Year of Construction 2008 - 2009
Total Length of Pipe 6500 m
Pressure Class PN 1, PN 6
Diameter DE 530, 1099, 1229
Installation Microtunneling, Open trench
Application Sewer®, ShaftLine®
Client Krakow Waterworks
Contractor Hydrobudowa 9, PRG Metro, INKOP.
Advantages Ideal for microtunneling, low friction, durability

HOBAS System PolskaSp. z. o. o.
Koksownicza Str. 11
41-300 Dabrowa Górnicza
PH.: +48.32 639 04 50
Fax: +48.32 639 04 51

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