The fall of the Wall on November 9th, 1989, comes as a surprise to all Berliners. Thousands stream out of East Berlin to the West. Just two days later, Jannowitzbrücke subway station is opened as a provisional border crossing point. A short time later, the power lines which have been separated for decades are reconnected. However, the old water and electricity lines in the border area are utterly useless and must be completely refurbished. It’s a different story with the sewage system: by the middle of 1991, the barriers in all 52 affected sections have been removed. The deeply embedded railway tracks and iron pipes in the channel walls are removed using pneumatic hammers. Putting the other ghost stations back into operation also happens unusually quickly. When all border controls cease on July 1st, 1990, almost all former ghost stations are resurrected.
After the underground infrastructure of both halves of the city is reconnected and the gaps in the transport network are largely closed again, a new building boom takes place in Berlin. At Europe’s biggest building site in Potsdamer Platz, over half of the investment volume flows into the underground. However, before the actual construction work can begin, the “cultural debris” must be removed, some of which is a metre thick. At the same time, not only Potsdamer Platz lays bare the eventful past of the inner-city area. Time and time again, old tableware comes to light, a discarded reminder of better days. Old munitions and rusty weapons, even half of a Stalin organ, reveal the horrors of death and annihilation that raged in Berlin at the end of the war. Melted bottles and windowpanes show the consequences of the hail of bombs. When construction workers at Potsdamer Platz come across the helmet-protected skull of a young soldier, consternation prevails. The removal of rubble can usually only be carried out by excavators fitted with armoured glass.
Often, the police munitions recovery service arrives and defuses one of the countless duds. Bunker facilities also frequently come to light. As early as 1990, in the context of munitions recovery work in preparation for the rock opera performance "The Wall" by Pink Floyd bassist, Roger Waters, in the former death strip, the bunkers of the SS motor pool, which are full of weapons and live ammunition, are exposed. Above all, old wall paintings that glorify Nazi ideology cause a stir worldwide. In 1992, parts of the reinforced concrete ceiling of the “Adlon Bunker” must be broken up, as it stands in the way of the reconstruction of the historical fountains in Pariser Platz. The German Co-Operative Bank, which is planning its new building in the southern part of the square, is also unlucky. In December 1996, the completely forgotten “Speer Bunker” is found there. Missed only by a smidgen during exploratory drilling of the area, the removal of the bunker leads to significant delays in the construction process.
One year later, during the “site clearance” for the state representatives and the Holocaust Memorial, the “Goebbels Bunker” is found. Utterly oblivious to the existence of the bunker, the construction crews push through the 1.80-metre-thick reinforced concrete ceiling, instead of simply opening an access point a little further away. The interim highlight is the rather accidental exposure of a corner of the Führerbunker in October 1999, which leads to a heated debate on how to deal with this archaeological find in the future.
It is not the big investors who are the first to be active underground after reunification. While the architects are still sitting at their drawing boards, a club scene emerges in Berlin, which takes over the underground and is famous far beyond the city limits. As early as March 1991, “Tresor” opens its doors in the last remnants of the Wertheim Complex on Leipziger Strasse, once the largest department store in Europe. Of the splendour of the 20s and 30s, only the underground vault and locker facilities remain, which lend the club its unique ambience. Other locations are also rediscovered. In the old toilets under Leipziger Platz, for example, the “WMF” Club makes a guest appearance for a year, in the old Bewag substation on Wilhelm Strasse, the “E-Werk”. In the cellars of dilapidated buildings in the surrounding area, one can discover further “establishments”, most of a temporary nature. These include the “Caipirinha-Bar”, whose sparingly lit entrance is known only to insiders. However, today nothing remains of the élan of the flourishing party scene. With the arrival of the first cranes, the scene quickly relocates to other parts of the city. As the last remnant of this time, the “Tresor” must finally close its doors on April 16th, 2005. On October 29th, 1994, the ground-breaking ceremony for the new debis (a former subsidiary of Daimler-Benz) building is celebrated at Potsdamer Platz. For the major investors’ projects, several hectares of huge construction pits develop, the largest of them up to 20 metres deep. Laterally, they are secured by so-called diaphragm walls made of reinforced concrete, which are embedded up to 25 metres deep in the ground before the actual excavation. These diaphragm walls, which at the same time form the rim of the extensive foundation basins, must in turn be secured against tipping by floor anchors before dredging can begin.
Ground water, which is reached at a depth of just three metres, quickly transforms the area into a picturesque lake landscape. Not only dredgers but also divers are used, who supervise the sealing of the excavation pit floor with about 1.5-metre-thick base plates. These in turn are additionally fixed with long ground anchors in the underground. In this way, a major disaster on the construction site is prevented. Since the necessary counter-pressure is missing after pumping out the water in the excavation pits, the buoyancy of the groundwater could lift the whole foundation pit upwards again. The foundations are only deemed to be secure when the new construction has progressed so far that sufficient counterweight against the buoyancy of the groundwater has been created.
For “debis” alone, from a total surface area of 68,000 square metres, around 2.8 million tonnes of earth are removed. For the concreting of the up to four basement levels, 2,500 cubic metres of concrete are used every day. The spectacular construction site in the heart of the city quickly becomes one of the most important tourist attractions in New Berlin. Over 50 cranes are in operation. Between 1997 and 1998, over 4,000 workers are working simultaneously on 19 buildings, 10 streets, an underground regional railway station, a subway line under Potsdamer Strasse, on Federal Highway 96, on a multi-storey carpark on Köthener Strasse, as well as around 12,000 square metres of water. 2,500 of the planned 4,000 parking spaces will be housed in the extensive underground carpark. Despite the extent of this undertaking, the “debis Area” opens as scheduled after less than four years of construction on October 2nd, 1998, the 1.5 billion Deutschmark “Sony Complex” follows on June 14th, 2000.