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Pump Station Altjessnitz

Innovative foundation pit sealing

The pump station of the basin in Altjessnitz in the vicinity of Bitterfeld-Wolfen/Germany was to be entirely reconstructed.
With the exception of the rakes in front of the pump chambers, the entire landside part of the basin's pump station was to be retreated. A reliable sealing method was required in order to protect the working area from penetrating water, i.e. to retain any water in the basin exceeding the 2 m water level.
The sealing had to be in place for at least one year which means that it had to be resistant to alternating frost and thaw.

The traditional solution would have been a sheet pile wall erected in the foundation pit. Alternatively it was possible to use the space between the rakes and the open weir as a sealing level. The sealing material was to be installed between the rakes at full water level and be reversible after the construction work. All soiling with sealing material had to be avoided. After testing several sealing methods, WEBAC® 240 was opted for. This polyacrylic gel was filled with sand to obtain a stable, mechanically resistant sealing material.
The open weir's rakes were first provided with wooden boards and PE foil and then lowered again making for a space between the two rakes suitable for the sealing method with a mixture of gel and sand. This way the space could be filled with the gel-sand mixture even at full water level. Due to its density of > 1.8 kg/dm³ the mixture sank to the ground and could be easily installed layer by layer up to 30 cm above the highest water level to be expected. After pumping off the water, any remaining leaks were sealed by injecting the pure WEBAC® 240. This way the pump station could be retreated and the new construction be implemented in the area behind the sealing. Once again the sealing effect of the acrylic gel WEBAC® 240 proved worthwhile.
The approx. 15 cm thick gel-sand mixture prevented all pressing water exceeding the water level of 2 m from penetrating the building site for an entire summer and winter season. Following the construction work, the gelsand body was removed from the space between the rakes without any problem. Compared to the erection of a sheet pile wall this innovative solution was much more cost-effective.

This innovative use of polyacrylic gels opens new horizons for economical solutions in the field of foundation pit sealings.