Fload and coastal protection

Ohra dam extraction tower and intermediate structure, production of standardised reliability

Talsperre Ohra
Talsperre Ohra

Reliability deficits were identified at the extraction tower of the drinking water dam built between 1960 and 1966. The standardised load-bearing capacity could not be demonstrated under the exceptional impacts, failure of the existing drainage under full damming as well as failure of the ice-free system at the operating damming target and one-sided ice pressure. The operational safety of the entire dam was therefore not given in the rare load case combination.

To ensure reliability, the base plate of the extraction tower was anchored in the ground with a total of 16 tension members. Eight prestressed strand anchors and eight slack micropiles with a total cross-sectional area of approx. 300 cm² were used. An additional strand anchor was used as a test anchor. The load-bearing capacity was designed in such a way that reliability is also ensured when the invert water pressure relief systems are taken out of service as planned, i.e. in the permanent design situation. The tension members serve to increase the overturning safety. To increase the sliding safety, dowel tubes were provided, which were installed in the same borehole as the tension members. In this way, the intervention in the heavily reinforced floor slab could be minimised. The measure was implemented during ongoing operations under extremely cramped conditions at the installation sites. Access was only possible via the inspection corridors of the hearth walls. To ensure stability during the realisation of the measure, an extensive procedure for flushing and monitoring the invert water pressure relief was planned.

Client: Thüringer Fernwasser­versorgung

Processing period: 2018 – 2021

Main data:
Main dam:
Total storage capacity: 18.4 million m³
Height above foundation base: 59 m
Crown length: 260 m
Withdrawal tower:
Construction: Reinforced concrete
Height above foundation base: 64 m
Shaft diameter: 8.60 m

Project planning LP 1 to 9 HOAI
Structural design LP 1 to 2 and 4 to 6 HOAI
Local construction supervision