Berlin , January 1998- In the heart of Berlin, subsurface specialists and divers have teamed up with civil engineers to fight water and creeping sand with concrete, steel and brains. At a cost of over twenty billion Deutschmarks, the scars left by the Second world war, the iron curtain and the Cold War are being healed along the line of the former Berlin Wall. Today, every spot in the centre of the German capital can be pinpointed with an accuracy better than four millimetres by applying state-of-the-art survey techniques such as GPS.
The south-to-north axis between the Potsdamer Platz, the Brandenburg Gate, the Reichstag and the site of the future main rail station is four kilometres long and is one enormous construction site. The main problem is: water. Any project which goes down more than three metres hits the gigantic area of ground water which saturates Berlin's sandy subsurface. Tunnels have to be designed to resist lift; their foundations need concrete tanks. The tunnel system can involve 28'000-ton caissons, six parallel pipes created by shield tunnelling, or colossal concrete troughs the footwalls of which have to be formed under water. Here, construction is an art all of its own.
The international architectural panorama of the next century
The centre of Berlin, now a city with a population of three and a half million, contains many construction sites, of which the largest at present is the Potsdamer Platz. Here, in early 1998, the longest finger of the Debis skyscraper already extends 75 metres above the frenetic building activity on the ground below. Several stories of a building which one day will be the 110-metre high, glass-fronted headquarters of the Sony centre are already rearing up. Other imposing structures are taking shape on the plots owned by other investors. Together with the rail stations for the German State Railways, and for the rapid-transit and underground rail systems, and with the new subsurface highways, they will form the nucleus of a new Berlin, transformed after more than half a century.
The architects reshaping the Potsdamer Platz include Renzo Piano (for Debis), Helmut Jahn (for Sony) and Giorgio Grassi (for ABB). Other famous names include Arata Isozaki, Richard Rogers, Josè Moneo, Jürgen Sawada and Hans Kollhoff. Frank O. Gehry and Gunter Behnisch are building right next to the Brandenburg Gate. Sir Norman Foster is active beneath the Cupola of the Reichstag, and Santiago Calatrava is busy with a bridge over the Spree. A kilometre east of the Potsdamer Platz, Jeoh Ming Pei and Jean Nouvel have already made their architectural marks.
Tunnels and Building excavations all round the new government centre
600 million Deutschmarks are being invested in the conversion of the Reichstag building. It will be the future seat of the German Bundestag, and it must be largely complete by the end of 1998. All around the huge steel structures of the new cupola there are deep excavations and also tunnelling operations, including sections of the 3.4km-long railway tunnels to the future Berlin main station. The six tunnels will accommodate road and rail traffic, including the underground rail system. To build them, it will be necessary to divert part of the River Spree for a time. Until the centre of Berlin gets its new skyline in time for the millennium, it resembles a permanent outdoor exhibition of modern construction technology.
In the loop of the Spree, right up against the tunnelling operations, the new chancellery is under construction. The office buildings of the Government and Parliament will take shape within the immense complex of the Dorothea, Luise and Alster blocks. The modern new centre of power within the loop of the river will also extend beyond it, but involves only short distances and will have rapid -transport links. In a few years, the most populous state in the European Community will be governed from this place.
Sixteen square kilometres, and everything accurate to better than four millimetres
For this ambitious project, the survey authorities and land registries had to provide precise location and height data for all interested parties, at a very early stage. The Berlin Senate Administration and the German Railways assigned to the Messmer survey office the responsibility for establishing triangulation points over an area 2 kilometres by 8 kilometres. This task was being carried out with Leica Instruments; with TC2002 total stations, with NA3003 digital levels and with GPS systems. Now, the location of every point within the grid is known with an accuracy of 3.3 millimetres. Land valued at 25000 Deutschmarks per square metre is being covered by construction projects which strain technical ingenuity to its limits, but it is reassuring to know that these developments are founded on a technical survey of the highest quality.
Monitoring the construction: the greatest challenge
Fractions of a millimetre can be important in construction engineering. Enormous excavations are right next to existing tall buildings and to the underground rail system. It is therefore very important to monitor the position and height of the new structure as its development progresses, and to detect any deformations in good time. Karsten Braun, an engineer from the Messmer survey office, says: ''Wherever possible, we like to carry out our demanding deformation surveys on Sundays, when there is less vibration from the heavy construction plant''. For example, the rapid-transit rail station on the Potsdamer Platz are lined by construction sites, and specialists from Solexperts AG have installed there an automatic monitoring system for the immediate detection of subsidence in the existing rapid-transit and underground rail systems. One kilometre to the east there are Leica NA3003 digital levels which are integrated into this monitoring system. They monitor the tilt and subsidence of a 16-storey building next to which there is yet another construction site.
When this ambitious project is complete, the skyline of Berlin will have changed beyond recognition. The enormous subsurface structures will be largely out of sight, but the survey experts in the Berlin Senate Administration, in the German Railways and in the large construction companies will still be keeping their sights on them.
