Tunnel construction
the tunnel construction makes itself often thousands of years of old realizations of the mining industry too uses. lugs were pushed forward, which became secured with stamp and sheeting. Later techniques were added from the building of Tonnengewölben.
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a condition
a condition of a tunnel construction project is the exact knowledge of the geological condition and firmness of the mountains, the rock layering and - composition and its process as well as the discharge of the rock formations, the arising pressures and the soil-mechanical analysis. Circumscription of the light area, strength of the lining, the sealing, discharge and ventilation are described in the “draft cross section”. In the modern tunnel construction fire protection topics become in the form of escape routes, emergency exits, fire-announce - and fire sprinklers promptly into planning also included.
tunnel construction devices
to the tunnel construction find as tunnel construction machines use:
- Devices for the loosening of the rock (e.g. Drilling hammers, turning impact drill presses, coal cutting machines, tunnel driving machines, shield driving machines), explosives
- of devices to the shop of the rock (e.g. Debris-hereditarychange, lug or shovel loader, wheeled loader)
- of devices for the transport of the rock (e.g. Trucks, Feldbahnen, low hollow transporter, transportation volumes)
- of devices for concreting (e.g. Concrete pumps, concrete spraying equipment (so-called. Spraying buffalos), pneumatic concrete conveyances)
building methods
the general outbreak work cover boring and blasting works, the rock loading, the Abtranpsort of the overburden, the execution of safety precautions (lug or Tunnelzimmerung) and the lining.
- With the traditional building method an arranging lug becomes as roofridge and/or. Resoling lug in the mountains pushed forward. Subsequently, the rock outbreak takes place in sections up to extending the Gesamtquerschnitts. Afterwards safety device against Nachbrechen and maximum configuration follow as further work procedures. The traditional building method requires a large expenditure of wood to the safety device.
- With the modern maximum configuration the safety device of opened surfaces takes place via spraying concrete, rock anchor, Stahlbögen and other elements. By use of fully automatic large machines the Auszimmerung can be void.
In firm rock the outbreak takes place either in “traditional building method” or continuously in the “modern maximum configuration”. With not stable rock the outbreak becomes partially. still after more traditionally, but modified building method made:
- With the “Kernbauweise” or” German building method “first two lateral resoling lugs are broken off as area for the counter bearings and a roofridge lug, before one forges ahead by the roofridges to the resoling lugs. Only after completion of the tunnel wall the massif core is out-broken.
- with the “venture building method” or” Belgian building method “begins with the development and the support of the roofridges (= Kalotte). To it the execution of the counter bearing in sections through lateral a slots closes on from an arranging lug (= Strossenbau).
- With the “old person Austrian building method “a resoling lug is advanced, which is increased. Slitting up to the roofridge follows. From there out the full outbreak takes place.
- With the “propulsion building method” or” English building method “the full outbreak takes place successively, which drawing in the Gewölbes follows directly.
- With the “disalignment building method” or” Italian building method “one begins with the outbreak of the lower third and the immediate drawing in of the lower counter bearing part and Sohlengewölbes.
In the mountains the outbreak takes place usually via blowing up (= “shooting”); the rock is removed afterwards with dismantling machines and removed by conveyances.
- To the modern building procedures the “ring building method “belongs, which begins with the outbreak and the eliminating of the Kalotte. Shifting multipart Ringschwellen follows, whereby the ring is formed by resoling or Ringschwelle, training elbow, rider and outbreak elbow. After applying spraying concrete eliminating the Strosse and the production of the Sohlgewölbes can take place.
- The “measurer building method “avails itself the roofridges of securing, steel, zugespitzter trench sheet pilings, which are pushed forward at the edge of the Gewölbes as propulsion measurers with simultaneous propulsion of the tunnel chest in the mountains. The Gewölbe is produced schubweise.
- With the “shield driving way “, which applies its in the loose rock, in as Deckschild of designated steel cylinders in the cross section of the later tunnel section with hydraulic presses one advances, which push away for their part against the finished Gewölbe. In its protection the tunnel tube can be eliminated and be fastened by rock anchors and spraying concrete by a rotary soil milling cutter in the driving process. In the next processing step the Gewölbe is lined after drawing in the presses with concrete or Stahltübbings. With water-prominent rock formations the work space can be locked by a rear wall and set in such a way under positive pressure that no water breaks in.
- With the “freezing or petrifying procedure “tubing screen covers can be used for the underrunning of heavy buildings, whereby thick steel tubes are pushed forward under the foundations and filled with reinforced concrete. Isolated water-satisfied, swimming concrete before the outbreak is frozen and/or. petrified.
- If an upward open excavation is possible, become during small cover (e.g. for Unterpflasterbahnen) tunnel in “open building method “built. The lateral sheeting walls are down-driven before or with the soil excavation.
- With the “cover building method “drilling stakes made of steel or reinforced concrete are established, between which the excavation is dug. As soon as the height is reached, in the excavators and/or. Wheeled loaders to work know, the pit for the maintenance of the traffic flowing over it are abgedeckelt. The cover building method e.g. finds. with the building of Unterpflasterbahnen application.
- For traversing of waters the “a swimming and lowering technology “are used rarely in Germany. With it ashore prefabricated Senkkästen becomes (caisson procedures) or pieces of tunnel in-swum and sunk in the rinsed out Flussbett. Example: Warnowtunnel
the new Austrian tunnel construction method (NATM or EMERGENCY)
this method was developed into the 1970ern by Austrian engineers (Leopold Mueller, Ladislaus von Rabcewicz and Franz Pacher) and soon a standard technique of the tunnel construction became.
the principle
the cavity surrounding mountain part becomes determining part of the carrying construction. In order to at all only make this possible, a semiempirical building method is necessary. The tensions and deformations become so well it go before breaking out, immediately after the installation of the first supporting means (in general. the spraying concrete bowl) and in the developed condition constantly measured. There, depending upon geological conditions, are full measurement cross-sections (tension and deformation measurement of the whole mountain part) in distances from 200 to 400 M. In extreme cases, e.g. in the urban range under buildings, the distance is only 50 M. A point net lies over which the deformations of the bowl are continuously observed. A direct tension determination is instrumentation complex, between the measurement cross-sections becomes it i.d.R. only computationally accomplished. There are problems, if the computer model of the mountains does not agree with actual geological conditions.
measuring procedures
the geological Vorwerte are determined among other things
- with
- plate loading tests
- Inklinometern
- reflection measurements
- sample drillings
settlement measurements. In the tunnel construction come then still
- radial and tangential ground pressure pressure capsules
- measuring anchors with differently long Extensometern (measurement of the shift in the mountains)
- convergence distances over the diameter (measurement of the change of the diameter)
- roofridge check measurements (laser measurement referred over the deformation to the length)
- Kalottenkontrollmessungen (laser measurement referred over the deformation to the length)
in addition.
the propulsion
the propulsion adapts to respective geological conditions, with small profiles and tension-poor zones the whole cross section at one time blown up (anticipated payment), with large cross sections or problem zones with a gradated working face is operated (Kalotte - Strosse - sole - this partitions every now and then again).
structural measures
around critical relaxations and thus a loosening of the surrounding rock to minimize take place the first safeguards immediately after breaking out.
Supporting means of the NATM are:
- high-strength spraying concrete with armouring rock nails
- set and - anchors
- injections
- distance elbows (concrete, steel)
these supporting means can be brought in both evenly over the whole cross section, and asymmetrically (dependent on the ground pressure).
The time between breaking out and the development is called period of hopping, they are determined on the one hand over with the propulsion constantly determined the measurements as well as from empirical values by other building sites. Factors of influence are the mountain class, the local tensile state, that and actual deformation degrees and the speed of the redistributions of stress which can be expected. The optimal period of hopping hangs considerably from the objective (fast propulsion, optimized redistribution of stress, minimum setting, costs with the tunnel lining). Deformations are the result of redistributions of stress, it give with active zones local cracking, partly are even possible for Verdrückungen. In order to make those flexible the spraying concrete bowl, several become up to 20 cm broad horizontal joints (contraction slots) after the anchorage as well as vertical column cut into the wall. The spraying concrete bowl takes nevertheless in connection with the surrounding mountain part approx. 70% of the forces receptible without joints up. All supporting means together form by the anchor (if necessary. Injections) with the activated mountain ring a group body, which exhibits a large ductility.
It is substantial that during the transition of the primary (=Urzustand) to a secondary (=Zustand after the outbreak) tensile state the tensions determining for the calculation of the development decrease (Fenner Pacher curve). The rigid interior bowl must take up ideally no tensions, since the sheeting with the ground pressure an equilibrium was received. In practice one changed over in addition to attach the interior bowl (development) to the avoidance of loosenings and for the increased safety actuated to the sheeting (isolating carriers). After completion of the building the tertiary tensile state is formed, depending upon geological activity is relevant a Nachbeobachtungszeitraum of up to 50 years.
area of application
the NATM can be inserted also for the underrunning by not bindigem loose rock. Examples for this are the subway railway construction in Vienna or Frankfurt. By soil improvement over injections, which transfer the function of mortar anchors in further consequence, a ring is produced around the dug cavity. A spraying concrete bowl as well as necessary tunnel elbows are applied directly in the connection. A minimization of the setting of existing founding or drilling stakes is important in the urbanen underground work.
