For the voestalpine AG in Donawitz (Leoben, Austria), a more than 100 m long HOBAS GRP Pressure Pipeline De 1720 has been installed by means of curved jacking. Despite challenging circumstances, the installation has been successfully completed within two months only.
An internationally renowned steel company, voestalpine places highest demands not only on the company’s products, but also on the plant infrastructure. When it turned out that a cooling water pipeline had to be replaced, the company looked for a solution that would match the claimed quality criteria and challenging conditions on site. The installation had to be implemented in limited space, with a trenchless method, and in a curve. The new pipeline was to pass beneath a road and some rails, past old foundations and pipelines underground, and further obstacles along the pipeline route had to be expected.
Since the soil did not contain any groundwater, it was decided to realize the curved trenchless installation with open shield tunneling technology. This would allow for a flexible approach to all sorts of challenges along the planned pipeline route. In terms of an adequate top-quality pipe material, voestalpine found what they required at HOBAS. Thanks to their small outside diameter in relation to their inside diameter, HOBAS Jacking Pipes are in fact ideally suited for restricted space conditions, featuring a low weight at maximum compressive strength. A smaller outer diameter requires a smaller borehole, which in turn means less soil to excavate and dispose of.
The original plan to provide the new landfill with a concrete pump shaft for drainage water were rejected very quickly: Among others, the project schedule was too tight and the manpower available for construction works limited. However, it didn’t take the construction company Polytrade Construction Ltd. very long to come up with an alternative solution – which was HOBAS. HOBAS Experts from Bulgaria, Romania and Austria conducted all technical calculations and custom-tailored the shaft according to the project specifications. The resulting HOBAS GRP Pump Shaft has a diameter of DN 2200 and features optimal hydraulic properties as well as perfect leak-tightness. With a stiffness class of SN 10000, it has the required properties for the maximum installation depth of 12 m. All necessary connections for valves, stainless steel accessories and fasteners were also precisely calculated and provided.
Challenging installation: The new pipeline De 1720 was jacked in limited space, beneath a road and some rails, and past old foundations and pipelines underground.
Another significant advantage concerns the fact that the pipes’ smooth outside surface ensures low friction and resistance during jacking and whenever jacking is (re-)initiated, for instance after standstill periods. In view of the partly unforeseeable soil conditions and necessary adaptations in the course of tunneling works, this was an essential benefit. Thanks to the elasticity of the GRP material, allowing for an optimal transmission of jacking forces without timber packing rings and a high steering precision, HOBAS Jacking Pipes are also ideal for curved trenchless installations.
In early 2016, more than 100 m centrifugally cast HOBAS GRP Pressure Jacking Pipes in 2 m length, with a stiffness of 100000 N/m² and a pressure class of PN 6, were delivered to the voestalpine AG in Donawitz. The construction companies Max Bögl and Hinteregger & Söhne successfully completed the open shield jacking installation, including a curve with a radius of 300 m, within two months’ time. With an expected lifetime of up to 100 years, the HOBAS Cooling Water Pipes now ensure a reliable and successful service of the steel plant.