Almost everyone has heard of the Cannstatter Wasen, the world’s second-biggest folk festival. The Mercedes-Benz Arena and the Hanns-Martin-Schleyer-Halle are likewise familiar names far beyond the city boundaries. But did you know that Bad Cannstatt – which merged with Stuttgart in 1905 – has also been dubbed a spa town? In fact, with 44 million litres of mineral water flowing daily from 19 springs, Bad Cannstatt is second in Europe only to Budapest by volume. The majority of these springs have been officially recognised as ‘Heilquellen’ – in other words, the water has health benefits. Such Heilquellen are legally protected by a heritage regulation established in 2002, so the planners for the NeckarPark development had to ensure the construction methods would not interfere with the groundwater in any way. It was time to call in the civil engineering experts at Stump-Franki in Stuttgart!
Groundwater protection with environmentally friendly Frankipfahl NG® piles
Length restrictions apply to the piles for the zone around the mineral waters. The water-bearing strata are covered by a protective stratum of gypsum Keuper. The challenge for the Stump-Franki team was to transfer loads to the subsoil while keeping the piles as short as possible. The 351 Frankipfahl NG® piles used have an enlarged base, which means that even with shorter lengths they can achieve the same load transfer as other pile systems, and thus do not affect the gypsum Keuper stratum.
Soft gel floor slab with optimised carbon footprint
Several sheet-pile structures in the construction pit had to be protected from vertically rising groundwater, which meant a waterproof floor slab was required. Project manager Peter Deutsch explains: “We advised the client to use a soft gel injection-grouted slab instead of the planned jet-grouted floor slab – and were awarded the contract to do just that.” This technique has an excellent carbon footprint, since it uses much less concrete and requires much less transport. In addition, no grout material flows back from the process.