With the aim of designing particularly slender retaining walls, dispensing with anchors to prevent uplift and draining seepage water directly into the ground, drainage concrete made of single-grain concrete with a grain size of 22 mm was used. The concrete had a fines content (0/2) of only 171 kg/m³ to better bind the cement (CEM II/ALL 32.5 R) to the coarse aggregate.
The hydraulic performance was verified mathematically in the design. During the suitability test, a compressive strength of fc = 8 N/mm², a pore space of Φ = 30 % to 40 % (depending on compaction) and a permeability of kf > 1.2 cm/s were achieved. For the acceptance test, the permeability was checked again on the structure. The method used for this purpose was specially developed, accompanied and evaluated by THP for the in-situ conditions at the dam. The required permeability was achieved and exceeded with kf = 2.5 cm/s. This corresponds approximately to the permeability of dams. This corresponds approximately to the permeability of fine to medium gravel. The results allow the assessment that the drainage effect is still given even if parts of the porespace are displaced, e.g. by sintering. Testing of fc and Φ on structural concrete was not possible due to the concrete structure, as no cores could be taken.
On massive components, it was important to keep the heat of hydration low. On the reinforced, 30 m long monolithic partition structure (TBW) with its up to 3.30 m thick bottom slab, this served to limit the required amount of reinforcement. For this reason, the bottom slab was also divided into a core zone exposed only to soil and a top zone exposed to the atmosphere. Cracks were to be completely prevented on the 7.50 m long, 6.70 m high and up to 3.80 m thick unreinforced walls of the new weft channel.
The walls of the weft channel were concreted over the entire height in one go. With the aforementioned objectives in mind, concretes with unusually low cement contents were used. The minimum cement quantities required by the standard, and in particular by the regulations of the ZTV-W and the DAfStb for solid structural elements, were undercut by 30 kg in the core zone of the TBW and by 20 kg in the walls of the weir channel. This is based on general building inspectorate approvals from Züblin. The temperature rise due to hydration heat in the core zone of the TBW was a maximum of 22.8 °C. The binder used was 210 kg/m³. The binder used was 210 kg/m³ CEM III A 32.5 NLH. The permissible crackwidths were observed. The unreinforced walls of the weft channel remain completely crack-free. The latter is due not only to the choice of cement type (CEM III A 32.5 NLH) and cement quantity (250 kg/m³) but also to the conservative choice of geometry (h/l).
Dominik Fiedler – Dresden