VEREINIGTE Energiewerke AG (VEAG) is erecting its new pumped storage power station, Goldisthal, in the eastern part of Germany’s Thüring Forest. Originally planned in the days of former East Germany to lessen reliance on lignite-fired and nuclear power stations, the plant is designed to impound the river Schwarza in a lower reservoir and pump water to the upper reservoir, situated 300m above, during off-peak hours.

Upon completion in 2003/4, Goldisthal will generate up to 1060MW from its four turbines in the underground power house, and will take over the supply of energy in peak load areas. The scheme will be one of the largest and most modern plants of its kind in Germany and will consist of an:

• Upper reservoir with intake construction.

• Upstream gallery.

• Machine cavern with access gallery.

• Transformer cavern with energy diversion gallery.

• Underwater gallery with outlet structure.

• Operational building and secondary construction.

Upper reservoir

One thousand metres wide, 935m at its longest part, and located at a height of approximately 850m, the upper reservoir will store up to 12M m3 of water. Both the reservoir floor and the fill slope on the water side are fully sealed by asphalt concrete. To attain a controllable seal against mountain water, an extensive drainage system is to be installed, the main part of which is a 14cm thick filter base which has to be placed over a total surface of almost 200,000m2. The filter material consists of 28,000m3 of crushed stone (grain size 2/40) which is delivered to the slope by German company, Putzmeister’s, Telebelt. The mobile delivery belt has a feed belt system and a telescopic delivery belt extension /boom with a 32m reach. In daily practice the construction site succeeds in completing sections up to 3600m2.

Pressurised water galleries

The two 817m and 828m long pressurised water galleries connect the inflow construction at the upper reservoir to the pump turbines in the machine cavern lying 350m below. The upper water galleries were driven at an angle of inclination of 26°. To be able to lower the heavy steel pipe segments onto a rail-bound transport wagon, the travelling bases of the rails were concreted. Concreting was carried out from top to bottom by a stationary PM concrete pump (BSA 1408 E) with a slump of 34cm. After the reinforced pipeline (steel pipes with a wall thickness of up to 57mm) had been installed, the ring space between the gallery excavation (diameter of 7m) and the pressure line (exterior diameter of 6.2m) had to be backfilled with concrete. This was done by two Putzmeister BSA 1400 concrete pumps with electric drives. They were set up in the mountain near the machine cavern and conveyed the concrete upwards from below. If concreting had been carried out in the reverse direction, the concrete would have segregated with at least 57cm of slurry.

The machine cavern is the largest underground cavity at Goldisthal. It is set deep in the mountain with inner dimensions of 138m long x 26m wide x 50m high. The dimensions of the neighbouring transformer cavern are 122m long x 15m wide x7m high. Both caverns can be reached via a 1.3km long access gallery.

The extensive concreting work in both cavities is being carried out by a Putzmeister BSA 2110 HD pump with a 200kW drive performance, as well as a 167kW BSA 2110 HD. In numerous operations they are conveying concrete manufactured according to different specifications for the turbine platforms, base plate walls, ceilings, etc. Here the amounts of concrete to be conveyed fluctuate between 50-1000m3.

Concrete delivery is carried out via a ZX pipeline, up to 170m long, which is anchored on one of the long cavern faces, with access via a gallery for foot traffic. Three vertical delivery lines lead from their main line to the individual cavern sections. The flow of concrete can be interrupted by two hydraulically actuated gate valves which each have a separate 7.5kW hydraulic unit and can be controlled by remote control. Two stationary Putzmeister placing booms are also used in the machine cavern. These have a 22m horizontal reach which is an ideal working range for such concreting work. On average concrete is being placed at 40m3/h.

Underwater gallery

The pressurised water piping from the upper reservoir consists of reinforced steel pipes but the underwater galleries, as well as the pertinent branching galleries, are lined with a concrete coat which on average is 70cm thick. The galleries link the pump turbines to the discharge construction at the lower reservoir. After under-crossing the transformer cavern, two branching galleries are combined with an underwater gallery which then leads to the discharge construction via a 14° inclination.

The underwater galleries were driven with an excavated cross-section of approximately 9.6m. A full round formwork with an 8.2m inside diameter is being used at present to concrete the gallery. The concrete placing is being carried out in 10m sections. Between 280m3 and 300m3 of concrete is required per section for the concreting of the vault and base. This is placed in a continuous working cycle of 12-13hours. A total of over 27,000m3 of concrete is pumped to line the underwater gallery and the outlet structure.