Constructional features of Saint Petersburg metro

For Saint Petersburg as a big city it had always been being transport problem. Nowadays the Metro (or metropolitan in Russian) is the most claimed type of transport. Improvements and innovations in construction of underground railway are relevant for residents and guests of the city. The first objects like this were constructed at the end of the XIX century in European capitals. In Russia the metro projects were implemented only in the middle of XX century (Moscow, Leningrad). Proposed engineering solutions facilitated tense traffic situation on city’s streets [2].

The main task of this research is explore fundamental difficulties which arise during laying of the underground railways, detect outstanding characteristics and find new decision and methods which could be used in practice.

After construction of Moscow Metro was completed in 30th of XX century, it was raised the issue of building underground lines in Leningrad. In 1938 Chairman of the Executive Committee of the Leningrad City Soviets of Working People's Deputies Alexei Kosygin made a proposal for the design modern underground metro. This work was started in 1941, however was interrupted and continued only in 1946. In 1955 the first stage of the Leningrad Metro was officially put into operation [1].

The first difficulties had already appeared on the design stage. «Choice of the metro laying depth determines on hydrogeological conditions and building density among the track» [2]. The city was founded by Peter the Great «on the swamp», therefore it was discovered in the study of soils that construction of underground railways in most parts of Saint Petersburg just impossible, except the opportunity to build in Cambrian clay layers (it is about 100 meters depth). Moreover, ground under Leningrad is heterogeneous and there are risks to face with groundwater and quicksand. Also a mixture of rock and clay much obstructed construction because of need extra calculations and people’s efforts for tunneling. In addition, conditions required to build metro almost only deep foundation [2].

Features of the soils were not the only difficulty. Former capital of Russian Empire was densely built up by historical importance houses. As mentioned above, it became another one problem. Many structures had already built before October Revolution and much of them needed major overhaul not only by reason of time but due to destruction of War. It was necessary to took into consideration subsidence and vibration exposure of future metro. Moreover, there was a problem to find entry point for stations. In many case there were no place for egress near projected track. Constructors had to solve complex engineering problems during building of shafts. By the way, it is specialty of Saint Petersburg Metro: you should pass a long labyrinth of crossing and escalators to reach some stations. On the surface initially separate grandiose lobby were built for station of deep foundation and were not for shallow station. Afterwards in order to save money many entries were constructed direct in buildings (in central part of the city) or just in typical ground lobby which cannot characterize especial architectural extravagances. The process of searching place for entry became reason for existence in a certain period such ghost-station as Admiralteyskaya and Obvodny Kanal (stations before and after them had already opened but here trains did not stop) [3]. Exactly local complicated hydrogeological conditions most trouble task of construction metro in Saint Petersburg.

In our opinion, there are some ways to solve problems, those mentioned above. To increase underground railways network coverage for whole city it could be used so called «premetro» - underground tram-train lines. Such technological decisions used in many European countries such as Belgium, Poland, Portugal, Germany, Austria and so on. In Saint Petersburg these lines could be shallow and laying under major highways. It allows saving cash while tunneling and easing traffic situation in the city by reducing tramways volume. These decisions will likely possible in new and emerging districts, where there are not so much big rivers and channels, because the tunnels will be slightly adapted to passage under them. Moreover, we think, that construction of radial rings which could unload central interchange node would be most appropriate.

The laying depth of tram-train lines would not be more than this characteristic of underground crossing. As we now there many such structures in Saint Petersburg and in our opinion this project could be realized without great investment as for metro. It is cost-effective proposal for solving many of city’s problems. It saves people and natural resources and the most important thing it saves money.

As the results of this article, it is possible to note next features that should be key moments in construction such structure in Petersburg:

• 1.    There is extreme necessity to avoid overpasses, because of their completely destructive impact on streets’ views;

• 2.    Rejection from combining rail and tram ways is the best way to save both transport types speed characteristics;

• 3.    Tunnels must be only shallow in depth, as it was mentioned above, otherwise sources spending will rapidly grow up.

• 4.    Acceptable construction method is cut-and-cover.

In conclusion, we would like to say that world is in permanent motion and changes are amplified from year to year. What was the norm in soviet times already feasible nowadays (we mean the pace of metro construction [3]), therefore searching of alternative solutions represent promising activity in many scientific fields, including technical.