METHOD OF EXCAVATION OF TUNNELSWhen beginning the excavation of
a tunnel, you find the lot in a status of equilibrium. As a
consequence of the advance of the excavation, this status of
equilibrium is seen altered and a decompression of the lot is
produced.For this motive, it will be necessary to embrace
constructive methods that they enable avoiding and to limit to the
full the effects of the aforementioned decompression at the
excavation's zone.
This decompression of the lot matches accompanied of an effect
of dilatation and of an irremediable loss of his characteristics
geomechanics, of such form, than at a decompressed lot, the
stability of the set only can be assured by means of the execution
of a support of the lot made suitable to its behavior
tensodeformational.
The excavation of tunnels has matched evolving in the course of
time clearing the way for new systems and methods developed
regionally in terms of the characteristics geomechanic of the
existent materials.
That way for example, as to tunnels played by phases, the
Austrian New Method of construction of tunnels ( NATM ), the German
Method can tell apart themselves, and the Belgian Method, the ones
the complete section splits in in smaller sections, the fact that
they excavate themselves and they stabilize to cause the complete
section at a later time.
They have an important potential of development as to the
tunnels excavated to complete section ( TBM ), the partial systems
or totally mechanized.
2,1 Austrian New Method ( NATM )
You are based on the integration of the lot that surrounds the
excavation in the structural ringSelf-supporting formed
surroundings to the cavity, so that you form the lot depart Member
in him. The aforementioned method intends to relax the status
tensional of the rocky mountain massI close a little bit the
tunnel, permitting his deformation to one point of equilibrium in
than theSupport controls the aforementioned deformation, anchoring
this to the very lot. This himselfGet by means of techniques of
auscultation and measure of convergences, to controlDeformations
all the times and avoiding that these be excessive ( looking up
themeInteraction tunnel support ); For which the tunnel with a cost
can be sold offMinimum and a maximum certainty.
The following basises will have to have NATM themselves in
account within the system: The adverse statuses of tension and
deformation at the lot, they will have to correct themselves by
means of a method of support adapted for each kind of lot. In
unfavorable cases, the execution of a counter-vault will contribute
the resistant desired arch, I grasped obtained, some static similar
properties to give them a tube. The kind of support will match
itself optimizing according to the maximum admissible deformations
that you show the lot. You will have to get an exhaustive tracking
of the general measurements of control ( convergences ),
accomplishing constant tests of optimization of support. As a
consequence of everything it, the NATM's correct utilization
involves :
1. Careful execution of procedures of excavation.2. Election of
the best section of possible excavation, allowing to his adaptation
besides to the conditions specific mechanical of the rock and the
distribution of tensions.3. The system of excavation will be
supposed to become adapted to the found lot's properties. The
stability of the front without support, the correct election of the
blowing-up and the length of the advance, they play an important
role to elect the operational method more feasible and
economic.
2.2.Excavation of tunnels with machines tuneladoras
The excavation of tunnels with integral machines to complete
section ( Tunnel Boring Machine ) divides itself fundamentally in
two groups, in terms of the kind of material to excavate, and of
the needs of support.In the first place, the Moles would be,
designed fundamentally for hard and half a rocks, and in addition,
Shields, employees at soft rocks and grounds. A later development
would be twice the amount Shield, capable to work with the two
typologies of lot described.
Moles, tuneladoras or TBM ( Tunnel Boring Machine ):The tunnel,
retirann excavate the scrap and apply the coating.
Shield EPB Roll of court of one mixhield MOLEI shield of
pressure of lands EPB ( pressure of land ) Commendable
stops:Cohesive lots, the job of a shield is commendable EPB ( Eartg
Preasure Balance )His advantages: A lofty performance of
extractionThe profitability of his functioning and his in relation
to the midwayAcclimatize.
The shield mixshieldIt is a very polyvalent shield Perforate in
different kinds of geology with a same machine.Different operating
modes:Like hidroescudoAs I shield with control of pressure of lands
EPBWith compressed air or open shieldHe is the but used in the
contruccion of tunnels at cities for lines of meter, railroad,
roads, etc.
I shield twice the amountDrills with mixed characteristics
between the mole and the shield
Use two independent systems of propulsion: Proulsion of shield
The mole's propulsion
Tiene un sostenimiento continuo del terreno durante el avance
del tnel.
Board 18 moles' scaleof utilization in terms of the needs of
supportRMRRQDPerformance
ValueClassroom
80-100I>90 Excellent grades
60-80II70-90 Good.
50-60IIIa50-70 Adequate
40-50IIIb40-50 Not much adeacuado
20-40IV25-50 Tolerable at short stretches
0-20V