Three-vault metro stations

In 1971, the construction of Line A began. The implementation of excavated stations and inclined escalator tunnels was a novelty based on the fact that Line A had already been designed from the start as an underground line and its levelling alignment was designed for significantly greater depths than that of Line C, especially in the city centre.

The ring method was used to excavate the stations, i.e. the same method used to excavate tunnels in rocks with sufficient excavation stability. The three-vault stations were built by excavating three parallel tunnel tubes. The side tunnels housed the tracks for the operation of trainsets and platform edges, while the centre tube housed the bulk of the platform.

A closer look at the design of the individual three-vault stations reveals major differences between them. The first parameter is the length of the station tunnels. The side tunnels must be at least 100 metres long because of the length of a five-car metro set. The central tunnel can be built to the same length as the side tunnels, or it can be made with a shortened or extended central tunnel.

The lengths of the central vault and the side tunnels are identical, for example, at Můstek A station. Line B at Florenc station is an example of a station design with an extended central vault. Shorter central vaults can be seen at Hradčanská, Staroměstská and Jiřího z Poděbrad stations. All of these stations contain a central escalator exit at the head of the station.

The three-vault stations are also different when looking at their cross-sectional arrangement. The space between the tunnel tubes is called the rock pillar and must be sufficiently bulky. If the central and side vaults are sufficiently axially spaced and structurally independent of each other, they are called pillar stations. Pillar stations are constructed by mining each station tunnel as a self-contained unit and then mining the penetrations between them at regular intervals.

The first three-vault stations were mined using Soviet cast iron ties, which were costly. The switch was therefore made to reinforced concrete ties imported from Hungary, later produced in the local prefab plant (Hýskov). There is an example of a pillar station with reinforced concrete lining at Náměstí Míru. A patented procedure was used for the first time by Metrostav workers at the Jiřího z Poděbrad II.A station. The first step was the reduction of the axial distance between the station tunnels, which allowed the use of prefabricated steel pillars, whose dimensions corresponded to the lining segments and could be fitted with the erector directly during the tunnel excavation. Prefabricated steel pillars were fitted to these piers and activated into the segmental lining. The actual penetrations were then mined. This solution proved its worth and was repeatedly used in the construction of other metro lines.

In terms of aesthetics and passenger comfort, stations where the axial distance between the individual station tunnels is closer look much better. However, rock pillars in this case would not have the necessary load-bearing capacity. It is therefore necessary to build artificial elements - columns - at the connection of the individual tunnels. These stations are then referred to as column stations. An example of a column station is Můstek on Line A.

There are many variants of pillar and column stations and it is not our aim to exhaust the reader by going into all the various details. Nevertheless, we will mention one case that the average passenger may encounter on the Prague metro. So far, various types of three-vault stations have been discussed, and each time it has been assumed that all the station tunnels are of the same diameter. This is the case for most stations, but there are some in which the middle vault is enlarged. An example of such a station is Florenc on Line B.

Architecture is an important aspect of the Prague metro. Great attention is always paid to the architectural elements, as well as to the overall architectural design of the stations, vestibules, and surfaces related to the metro. This was the case in the past and it is still the case today. The classic three-vault stations with their characteristic cladding in the form of a combination of convex and concave lenses have become one of the hallmarks of this metro in the heart of Europe. It is notable that, for example, Staroměstská station was listed as one of the ten most beautiful metro stations in the world in the Lonely Planet international guidebook. It is thus in the select company of metros in major world metropolises such as Stockholm, Paris, or New York.