TPI April 2011

Civi l engineer ing products

Multiple pump shaft for the Lausitz region

The Lausitz region in Germany, between Brandenburg and Saxony, has been an important coal mining district with far-ranging commercial relevance for more than 100 years. Extensive surface mining resulted in a lunar-like landscape, with extensive pits which would not be possible to completely backfill. The plan to return the area to nature required the creation of lakeland by flooding, and Bahnsdorf, a pump station on the lakefront of the newly established Lake Sedlitzer played an important role. Bahnsdorf dewatering went into service with three pumps in 1993 to ensure the structural stability of the embankment during the long process of flooding the Sedlitz mining pit. The water level was slowly raised in dependency of the floodingof Lake Ilse, since2007.Because the three pumps are indispensible for at least the time in which the water level is raised to the intended height, the structure was refitted and a multi- pumping shaft was installed, ensuring the pumps’ long-term functionality.

Hobas prefabricated transportable units ready to be delivered

Construction work commenced in September 2010. Aggressive soil and ground-water conditions (pH-value 3.0 and sulphate content greater than 500mg/l) led to utilising CC-GRP pipes as a corrosion-resistant solution. Due to an installation depth of 18.75m, a very high ground-water level as well as multiple built-in units, structural stability was ensured with a nominal stiffness of SN 32000. DN 3000 was chosen as manhole diameter to provide enough space for the equipment and pumps, and in combination with the required nominal stiffness the pipe wall thickness resulted in a minimum of 100mm. Three 16m-long DN 700 casing pipes were vertically placed inside the manhole to host the hanging immersion pumps, which were mounted to a reinforced concrete plate laminated with GRP. 7m above the shaft bottom, a 90° bend was

flanged to the DN 1100, PN 6 inlet and fitted with a matching shut-off valve. The parts were fixed to a vertical DN 1000 pipe, and all DN 700 and DN 1000 pipes were perforated up to 1.3m in height to ensure an even water level inside the manhole. Another two intermediate plates were installed to limit the height of fall and to allow for inspections of the instruments. All pipes and plates were fabricated with GRP. Apart from the pipe material fulfilling all the tough requirements posed by site and project conditions, Hobas had convinced the client by offering a made- to-measure installation solution: Hobas engineers designed the segmentation of the manhole in transportable units, avoiding heavy-load transports and reducing assembly time and effort to a minimum. Thanks to the fast completion of the project, achieving the planned water level of the lakes has moved a step closer. Lake Sedlitzer as well as Lake Ilse will soon be used for various water sports, events and boat tours, and will above all decisively upgrade the landscape. Hobas Engineering GmbH – Austria info@hobas.com www.hobas.com

CC-GRP Shaft with three vertical perforated host pipes

Hobas CC-GRP DN 700 host pipe

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April 2011 Tube Products International