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