The history of Berlin’s built-up underworld is, in contrast with Paris or Moscow, still very young. The high ground water level and ancient glacial deposits are the reason that only since the second half of the 19th century could the deeper soil levels be penetrated. The centre of Berlin lies in the Warsaw-Berlin glacial valley, a former marshy and swampy lowland. If you dig a hole here, you will reach the ground water after two or three metres. But above all, unpredictable layers of sludge, peat and moor soils and fine, barely workable alluvial sandstones, which act like subterranean quicksand, make all construction projects a difficult undertaking to this day.
The breweries are the “pioneers” of the Berlin underground. As early as 1840, they built the first major underground structures, mainly in Prenzlauer Berg and Kreuzberg. Only here can up to 18-metre-deep storage cellars for the fermentation and cooling of beer be built, without coming into contact with the ground water. The construction of an urban water supply system starts in 1852, work begins on the sewage system in 1873. This is urgently needed as the hygiene standards are catastrophic and the wastewater flows untreated into the rivers and canals. Cholera and typhoid epidemics are the result. Not only the first sections of the sewage system go into operation in 1876; the Berlin pneumatic post is also handed over to the public for faster inner-city communication. Just five years later, the construction of the telephone network follows, but this does not detract from the popularity of the Berlin pneumatic post. In 1888, the first electric street lighting is switched on – by 1895, most of the urban supply systems are finally under the ground.
After the German-French war comes the founding of the German Empire in 1871. Berlin, the new imperial capital, experiences an unprecedented construction boom. The population doubles then triples and the city rapidly expands far beyond its old borders. As land prices are rising sharply, plots in backfilled waterways and former swamp areas are now being developed. For larger structures in Berlin, the so-called pile foundation method is often used. Logs are sometimes driven in side by side up to 15 metres deep, until they finally reach a viable subsoil. Once this pile is constructed, the actual foundations can be built. Thus, for example, the floor of the dome of the Reichstag building stands on 2232 such piles, which were driven into the ground with steam hammers in order to stabilise the subsoil.
The traffic flow is also partly moved underground. To relieve the congested streets, at the end of the 19th century, two electrical companies, AEG and Siemens, compete against each other to build an underground transport network in Berlin. As early as 1891, AEG wants to run a low-lying tube railway through the Berlin underground based on the London model, and even builds the first two test tunnels - the AEG test tunnel and the Stralauer Spree tunnel, which were innovative masterpieces at the time. Ultimately, however, Siemens wins the contract to build the subway in 1899. Berlin receives its first subway station at Potsdamer Platz, which opens on February 18th, 1902.
With the introduction of new construction techniques, the urban underground can soon be used even more intensively. Many commercial buildings and hotels being built in the inner city after the First World War have, in addition to a normal basement, a cellar that houses the building services and storerooms. Existing buildings are often retrofitted with a second basement level by their owners. For economic reasons, investors are forced to use their properties as optimally as possible. The expansion of underground capacities is now possible almost everywhere thanks to the use of modern construction methods which can lower the ground water level. Berlin’s development is repeatedly interrupted by political or economic cutbacks. The consequences of the First World War and, from 1930, the effects of the global economic crisis, leave their mark in the form of unfinished tunnels in the Brandenburg countryside. After recovering from inflation, a real tunnel boom starts in the middle of the 1920s. Four new subway lines go into service by 1930 – existing tracks are extended. For a planned urban subway between Treptow and Moabit, tunnel carcasses are installed at Potsdamer Platz and under Moritzplatz as so-called preliminary construction work. Similarly, more “blind tunnels” are built around Alexanderplatz for a subway between the districts of Weissensee and Steglitz. However, due to the global economic crisis, these plans are postponed and also not realised later.