Construction of an excavation pit in the tightest of spaces

Bauer Spezialtiefbau GmbH was tasked with the construction of the excavation pit for a residential building by FGF Verwaltungs KG.

In the trendy Glockenbach district, not far from the Munich city center, a new residential building with a two-story underground parking garage is being constructed.

One might imagine that this is nothing out of the ordinary, but this project packs a punch: The site is situated in a rear courtyard, where buildings have recently been demolished, and is only accessible via a single house entrance. Material and equipment cannot be transported via a site entrance as is usual, but must instead be lifted into the rear courtyard by crane.

As part of the inner-city project, Bauer Spezialtiefbau GmbH was tasked with the construction of the excavation pit for the residential building by FGF Verwaltungs KG. “A total of 348 piles with lengths between 8 and 13 m are constructed as a pile wall for the retaining structure,” reports Stefan Ferstl, Operations Manager at Bauer Spezialtiefbau.

The work is carried out using the Front-of-Wall (FoW) method. This means that the piles are installed adjacent to the existing buildings. In addition to this, Bauer is responsible for the pit excavation, the single-layer strut for the excavation pit, and for dewatering. Before work could commence, the required material as well as a drilling rig – a Bauer BG 20 H weighing 42 t – needed to be lifted over the adjacent buildings and into the rear

courtyard. To be able to realize this at all, the mast of the rig first needed to be dismantled – in total, a BG 20 H generally weighs around 54 t including the mast. A 500 t truck-mounted crane was deployed for the backyard lifting task. “Our works will take around six weeks; completion of the pit including subcontractor services is scheduled for spring 2021”, concludes Stefan Ferstl.