TPT March 2011

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6 March 2011 ›
Industry News
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 flooding of Lake Ilse,
since 2007. 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.
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.
Hobas Engineering GmbH – Austria
Fax: +43 463 48 2121
Email:
Website:
Multiple pump shaft for the Lausitz region
Hobas prefabricated
transportable units ready
to be delivered
View from above the construction site
CC-GRP shaft with three
vertical perforated host pipes