The restoration was moving along quickly – until frequent high levels of water damaged the auxiliary gravel dam in the Wertach river. The dam had been constructed in agreement with the responsible nature conservation authority. All attempts to keep the water away from the weir system failed using “big bags” – gravel-filled plastic sacks one cubic metre in size. More flood water caused the water level to rise so much that the floodgates were opened and the drainage took on further damage.

All further work on the part of the weir facing the Bärensee had to be put on hold. Meanwhile, pillars and walls in the direction of the Bachtelsee surrounding the turbine inlet had to be restored. The challenges presented by the floodwater were overcome by VWEW-energie, the operator and client, by erecting a new reinforced concrete wall at the suggestion of the engineering firm Dr. Ing. Koch Bauplanung GmbH and with the support of the commercial diving company Kerlen Taucher GmbH. The wall was connected to the current dam wall and is 2 m thick and 9 m long. Together with a needle valve the reinforced concrete wall will separate the Wertach river from the working areas once it has been “raised”.

The professionals constructed the wall by attaching B 500B reinforced concrete with the fischer injection mortar FIS EM 1500 S in combination with 20mm-diameter connection sleeves to an existing ground plate. The material used meets ISO and Swiss SIA standards and is highly ductile, enabling it to deform plastically under load before yielding.

“Our fischer injection mortar FIS EM is approved for water-filled boreholes according to anchor theory, which makes it suitable for this application”, explains Bernd Wetzel, fischer Application Engineer. The boreholes with a diameter of 25 cm were therefore successfully filled with the injection mortar while the concrete was secured with the system. “Further advantages include the fact that alongside other system components the solution is particularly suitable for reinforce-ment connections of between 8 to 40 mm in diameter in concrete, therefore providing high load values”, the certified civil engineer adds. “The system temperature of up to 5° is also suitable for underwater installation”.

The subsurface of the construction did not consist of standard concrete. Bernd Wetzel carried out a series of preliminary tests together with employees of the contracted firm Xaver Lutzenberger GmbH & Co. KG. The experts examined the load-bearing capacity of the system consisting of injection mortar FIS EM, reinforcement bar and concrete using a rock anchor testing device set at a tensile force of 200 kN, which was determined in coordination with the engineering firm Konstruktionsgruppe Bauen AG. In order to do this, employ-ees of the Lutzenberger GmbH took a boat out above the fastening points where anchors had been placed. They lengthened the rods by using a reinforcement sleeve as a connection and attached a steel pipe to it. The testing device was attached to this pipe and was then pulled on.

The FIS EM is heated before its installation in order to prevent the risk of it becoming viscous through the low water temperate. The commercial divers of Kerlen Taucher GmbH who created the boreholes then informed Bernd Wetzel by radio if they required any further mortar. fischer’s expert then responded by injecting the mortar through a tube, enabling the construc-tion divers to fill the boreholes. The weir facility was success-fully drained and reinforced using this procedure. “In general we only use fischer products for underwater installations”, Karl Kerlen from Kerlen Taucher GmbH emphasises. “By using the fischer injection mortar system in order to strengthen the reinforced concrete wall in the Wertach river we can be absolutely certain that it will withstand the extreme conditions”.

The result was a robust reinforced concrete wall that enables the restoration and continued functionality of the 1960s facility, and therefore the generation of green electricity through water.

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