The materials for underground construction, underground construction.
The material with which to build underground structures, must have a high resistance, water resistance, erode, frost resistance and fire resistance. Due to the complexity of reconstruction of underground facilities, their service life should be longer than the land-based structures, respectively, the materials for the manufacture of such structures needs to be better. Materials which meet such requirement are: steel, cast iron, concrete and reinforced concrete. When erecting concrete structures concrete its hardness should not be less than “B15”, and the thickness of load-bearing elements not less than 20 cm. For prestressed concrete structures the concrete grade shall not be less than “B25”. Mark of concrete on water resistance should not be less than “B-6” for structures located in soil moisture hanged. Estimated supports of concrete in concrete and reinforced concrete structures take accordingly to the current normative document.
In the practice of underground construction, along with standard use and special types of concrete, which are characterized by a small moisture absorptivity, high hardness stretching, less resistance. Great value in the tunnel structure received “nabryzg-concrete”, which is applied to the surface vyrobky under the action of compressed air. The thickness of individual layers of the concrete sostavlyayushchaya 5 cm or more. When the coating thickness is more than 10cm “nabryzg-concrete” reinforced steel mesh.
When the shield tunnelling in some cases have successfully used a monolithic mount with stamped concrete. Concrete composition, which practically does not differ from that of normal concrete. Due to the push part of the water of the concrete mixture becomes water-cement ratio of 0.35 and obtained the mount is strong and waterproof. In a day the hardness of the concrete can reach 10 MPa.
For the construction of underground structures are used as polymer concrete, in which the ka used binder comprising synthetic resin. The concretes are characterized by high reliability joint, and higher than simple concrete resistance to stretching.
Promising in underground construction may be samoopredelenie concrete on cement. It is produced by a General Pamela Portland cement clinker, calcium aluminate clinker and gypsum in a ratio of 70/15/15. The cement, which is annoying, can expand after set the hardness to about 15 MPa, whereby in the concrete and the reinforcement you receive biasing voltages.
Classification of underground structures.
For the construction of underground structures in modern big cities are increasingly using underground space for transmission or saving of transport. The placement of industrial and household trade enterprises, as well as buildings for many task purposes — connection transport. engineering objects, commercial enterprises and others. The above-mentioned structures may be placed underground, in whole or in part. For example, groundwater can be a separate space ground buildings: garages, stations, airports. Shopping centers, etc.
According to the planning layout, distinguished by broaching underground structures — tunnels, whose length is much greater than the dimensions of the vertical section, and installations of limited length. Depending on the purpose of the tunnels can be transport: road, rail, metro, light rail for special vehicles, etc. for Example, in different compartments of one of the tunnel can move cars, trains, metro, the city railroad and pedestrians.
Underground transport constructions limited long, can be used for saving vehicles, metro, tram and Railways, as well as for underground highways, individual rooms or stations and airports, to create pedestrian levels and multilevel transport complexes.
When locating underground facilities at free of built-up territories, they are placed under the street expressways, under the squares, parks, and different natural piece or interference.
In most large cities there are various watercourses and ponds: rivers, lakes, canals, etc. For a permanent transport connection between the banks build not only bridges but also tunnels.
Underground transport facilities can be accommodated at different depths from the surface of the earth. Share underground structures at shallow, placed at a depth of up to 12m, and deep that is placed at a depth of more than 12m. There are half underground structure, which the upper slab is raised above the surface of the earth.