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| Facts & Figures |
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Tunnels
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Population growth, number of daily-trips
and motor-vehicles traffic, in addition to changes in the structure
of urban life all together have caused the traffic problem in
addition to its side-effects, to manifest themselves in the City of
Tehran.
This is the reason why under the ground is the only place suitable
for displacement of more passengers in a more rapid and safer
manner.
However, construction of an under-ground tunnel proved not to be an
easy task. The main difficulties in tunnel construction in this city
included the quality of the soil, which was clay, existence of
made-soil along the route of the tunnel, running-soil and also level
of the underground water tables.
In general , there are 3 different methods worldwide for excavating
metro channels as follows:
- Cut & Cover Method
- N.A.T.M Method
- T.B.M Method
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| Cut & Cover Method |
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In applying this method of tunnel construction,
initially Geo-technical survey and tests are made to determine
layers and strength of the soil along the route of tunnel
excavation. After conducting earth-moving and excavation operations,
measures are taken to clear and level the bottom of the excavated
area first and carrying-out the formwork-operation by means of
sliding-forms (dies), prior to armature working and finally, the
concrete working.
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| N.A.T.M Method |
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Geo-technical features, sliding characteristics of the
soil, in addition to underground-water tables existing at the
central part of Tehran, convinced experts of the company to conduct
extensive surveys on that zone, prior to excavation of the tunnel.
Finally, taking inspiration from the N.A.T.M Method, an excavation
method was developed to meet the requirements so far as technical
specifications and features of the soil were concerned.
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In the N.A.T.M Method of tunnel-excavation, firstly, similar to the
method of excavating underground water-channels, a shaft or ramp is
dug to reach to the intended depth and then measures are taken to
excavate the tunnel.
Then earth-moving operations are carried-out for the upper and lower
sections of the tunnel.
Following that, the tunnel is provisionally supported and then
formwork operations are carried out by means of telescopic forms
(dies).
Followed by armature working and concrete working.
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| T.B.M Method |
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Construction of tunnels by the
excavator is made at such districts that the level of
underground water-tables are rather high and also at those streets
with a high volume of traffic in applying this method, by
construction of a ramp, it would be possible for the excavator to
move deep below the ground level and then starts the excavation
operation form beneath the ground level to be followed by tunnel
construction.
The excavator is composed of a cylindrical sheet measuring 9 M. in
diameter and 6.9 M in length , equipped with a heavy-duty rotary
earth-moving machine and a number of hydraulic jacks which move in a
horizontal direction.
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The advancing-speed of the excavating-machine is 3 meters per hour.
Therefore , the machine is able to excavate a tunnel measuring 9m .
in diameter and 1.5 m . in length and transfer the soil to the rear
part of the machine.
Then , the pre-fabricated concrete segments will be installed by the
machine. Then , by means of a conveyor-bell , the excavation soil
are transferred to soil-handling wagons placed at the near part of
the excavator.
The said conveyor-belt is 45 meters and 1.5 meters , in length and
width , respectively. Its speed is 91 meters per minute , with a
soil-handling capacity of about 1600 tons per hour.
As a result , the said excavator is able to construct a tunnel
measuring 9 meters in diameter. |
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