Widenmayer City Palace, Munich

With the support of the Seevetal branch and the dewatering department of PORR Bau GmbH Vienna, Region South was responsible for stabilising the construction pit using tie-back anchors and producing watertight underpinnings by using the jet-grouting method for constructing an underground car park beneath a historic city palace. The cluster of buildings is located on Munich’s busy Widenmayerstrasse and backs onto the Eisbach River. Both the above-ground and underground work had to be carried out in very cramped conditions. The construction site logistics were especially challenging due to the limited availability of storage and transport areas, as the access road to the underground car park provided the only means of entering the construction site.

Specialist civil engineering work in exposed surroundings

You would be hard pressed to find a more attractive residential location in Munich than Widenmayerstrasse, which runs parallel to the Isar Quay and is located directly next to the English Garden in the Lehel district. The entire street was designated a listed ensemble. The most prominent building in this ensemble is the Widenmayer City Palace, with its richly decorated Art Nouveau façades and an imposing, 6m-high entrance portal made from natural stone with a coffered vaulted ceiling. Following extensive renovations, 37 exclusive owner-occupier flats ranging in size from 45m² to 450m² have been created in the three buildings on the 950m² plot of land at number 51.

Art Nouveau gem fitted with a fully automatic multi-parking system

Since the central part of the building ensemble was not worth preserving,

it was replaced by a new building designed in the same architectural style as the two existing buildings. At the same time, a fully automatic multi-parking system for 36 cars was built. The foundation base of the underground car park is lower than that of the neighbouring buildings. The adjacent foundations were therefore underpinned by up to 11m in jet grouting. Around 230 jet-grouted columns with a diameter of 1.80m, an average borehole length of approximately 14m and average nozzle lengths of approximately 8m were required for this purpose in the Munich Quaternary gravels, Tertiary sands and marls. The work was carried out in the cramped courtyard of the existing buildings with a clear headroom, as well as under a limited clear headroom of 3m. The Tertiary soil strata contained layers of conglomerate and old tree trunks, which posed a particular challenge for the construction site. The underpinning was anchored back with two temporary layers of stranded steel anchors (about 100 anchors, each 4 x 0.6”, approximately 1,600m in total), which were manufactured in our own factory in Colbitz, in the course of the earthworks and milling for the jet grouting. As the second layer of anchors was below the groundwater level, it had to be constructed and sealed against groundwater pressure. Exposed basement walls were secured with approximately 300m of Stump-Franki Gewi nails (20mm single corrosion protection, approximately 50 nails). Special permission was granted for the groundwater to be discharged into the Eisbach via four drawdown wells. Micro-piles with Stump-Franki GEWI steel support elements (approximately 300m GEWI with 50m single corrosion protection, around 30 units) were installed below the base of the construction pit and anchored in the reinforced concrete floor slab in order to permanently secure the structure against uplift.