HOBAS Multiple Pump Shaft for the Renaturation of the Lausitz Region, Germany

The region Lausitz between Brandenburg and Saxony has been an important coal mining district with far-ranging commercial relevance for more than 100 years. Extensive surface mining, however, left its traces and resulted in a lunar-like landscape with extensive pits which would not be possible to completely backfill. The intended renaturation therefore comprises the creation of lakeland by flooding. Bahnsdorf, a pump station on the lakefront of newly established Lake Sedlitzer, thereby plays an important role. Bahnsdorf dewatering went into service with 3 pumps in 1993 to ensure the structural stability of the embankment during the longtime process of flooding the Sedlitz mining pit. The water level is slowly raised in dependency of the flooding of Lake Ilse since 2007. Because the 3 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. Construction works commenced in September 2010. Aggressive soil and ground-water conditions (pH-value 3.0 and sulfate content >,500mg/l) led to utilizing CC-GRP Pipes as corrosion-resistant solution. Due to an installation depth of 18.75 m, 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 100 mm. Three 16-m-long casing pipes DN 700 were vertically placed inside the manhole to host the hanging immersion pumps that are mounted to a reinforced concrete plate laminated with GRP. Seven meters 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 pipe DN 1000 and all pipes DN 700 and DN 1000 are perforated up to 1.3 m 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, thus avoiding heavy-load transports and reducing assembly time and effort to a minimum – the contractor was very pleased to save on costs and installation time. Thanks to the fast completion of the project, achieving the planned water level of the lakes has moved yet a step closer. Lake Sedlitzer as well as Lake Ilse can soon be used for various water sports, events and boat tours and will above all decisively upgrade the landscape.