BAUER Spezialtiefbau GmbH involved in the rehabilitation of the Berlin State Opera

The most elaborate rehabilitation project in the history of the Berlin State Opera has been in progress since 2010: respecting the features of the listed building, structural defects are being rectified while the obsolete equipment is being upgraded to a new technical standard, along with the stage technology. Disabled access, the air conditioning and fire protection are also being improved. The external fabric is being preserved and restored.

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The general rehabilitation involves a whole series of specialist foundation engineering works under a contract awarded by the Berlin Senate to BAUER Spezialtiefbau GmbH and its consortium partner, Keller Grundbau GmbH. The specialist foundation engineering has particularly focused on building an underground structure which will in future connect the opera house to the new rehearsal center built on the premises of the former warehouse building; this link runs through the opera house 's main technological artery. The client specified that a complex trough excavation pit should be constructed for this purpose. Since June 2011, BAUER Spezialtiefbau GmbH has been executing this work in the technical director role together with its consortium partner. The specialist foundation engineering will be completed by about mid-2015.

Constructing the trough excavation pit about 3,300 square meters in size involves a wide range of individual works. Amongst other things, the joint venture constructed 1,300 square meters of reinforced concrete diaphragm wall, 720 square meters of diaphragm cut-off wall with inserted sheet piles and 5,200 square meters of secant pile wall with diameters of up to 1,200 mm. In addition, 1,020 linear meters of foundation piles were sunk to depths of as much as 30 meters. Among others two BAUER BG 28 drilling rigs, two Klemm drilling rigs KR 806-2B and 806-7 as well as a Bauer diaphragm wall grab on an MC 64 duty-cycle crane were used.

It was known from earlier building works that the site contained historical architectural remains; as a result, several exploratory bores were undertaken with a BG 28 rotary drilling rig at the start of the build. These revealed that the course of the diaphragm wall in particular contained many more architectural remains that had previously been assumed. Encountering several obstacles – including the strongroom of a bank destroyed by bombing – and the discovery of various wooden and later steel structural foundations meant that the original plans had to be adapted several times. For example, extensive jet grouting bodies were incorporated for shoring the opera house. Furthermore, parts of the shoring area for the stage house were sealed by freezing the ground for nine months.