Curved pipe successfully installed IN ITS first curved pipe jacking project in Poland, HOBAS has installed almost 1150 m of centrifugally-cast glass reinforced plastic (CC-GRP) sewer pipe. For the Zielona G6ra project, Hobas used DE 1099 and
1229 and SN 128000 pipes. Incorporated into the system were two curved sections with radii of 350 m and 175 m. The system needed curved sections to direct the pipes around building foundations and to avoid other under-
ground networks o n the route of the sewer. Engineers installed the pipe using micotunnelling, a technique where pipes are pushed into place using a hydraulic jack. The biggest challenge, explains Hobas, was to install
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the curved sections without damaging them. W h e n straight sections are installed using microtunnelling, it says compressive forces are distributed evenly along the length of entire pipe. But when curved sections are installed this way, the compressive forces are uneven and there is a risk that the pipe will exceed its allowable stress and become damaged. Therefore it was important to choose pipes that would be stiff enough to cope with the load conditions involved during installation. A lower jacking force was used to install the curved sections than for the straight ones (3000 kN for the curved and 4660 kN for the straight sections). But despite the difficulties with installing the curved sections, Hobas says the smooth surface of the pipes meant that they could be easily installed at lower forces than had been allowed for. For the curved section, 1 m long pipes were used, while the straight sections consisted of 3 m long pipes. Up to eight lengths were installed each day. A laser guidance system was used to ensure the pipes were following the correct route. According to Hobas, the deviation from the path is no more than a few centimetres anywhere on the route.
Corina Unterkofler, Hobas; tel: +43-463-482424-16; fax: +43463-482121; e-mail: corina. [email protected]
; website: www.hobas.com.