New Austrian Tunnelling method

The New Austrian Tunnelling Method (NATM ) uses the natural carrying capacity of the mountain for safe and economical production of tunnels. It has been developed in the 1950s as the time new development concept and combined geological and rock mechanical foundations with special imaging process to secure and expand a tunnel cavity. These technological advances have also led to lower construction costs, so that the method prevailed quickly and has since been continuously developed.

In English-speaking labeling New Austrian Tunneling Method ( NATM ) is in use. In German-speaking countries, the term NATM has become customary in connection with tunneling in recent years. In common parlance, is often the coupling shotcrete according to NATM to find as a demarcation for use of the shotcrete surface to fuse.

A duty cycle during tunneling according to NATM comprises the steps of:

• " Outbreak " (with hammer, excavator, Fräsvortrieb or drilling and blasting ),
• "Save" (primarily shotcrete, if necessary complementary measures such as anchors and shield vault )
• " Mucking " (promotion of the outbreak, usually in the dry state ).

Protecting the shotcrete is ( drilling and blasting, tunneling with tunnel boring machine or shield tunneling machine ) also applicable to other propulsion methods.

History

In the traditional tunneling methods, the basic idea consisted in the creation of the tunnel cavity therein, securely receive the prestigious unavoidable rock pressure by constructive methods, such as interceptions and extensions. These methods, such as the German core construction and the old Austrian Tunnelling Method, were common until the middle of the last century.

This is offset in the New Austrian Tunnelling Method of thought in the foreground, or not at all allow this rock pressures only to a small extent and to obtain the self- sustainability of the mountains largely. For this, the local geological and geomechanical conditions must be observed, so this method goes beyond a pure design with schematic procedures for the outbreak and for securing the tunnel cavity.

This fundamental change in thinking was possible through the interaction of theoretical considerations and practical insights: When creating the first tunnel cavities of Ladislaus of Rabcewicz 1944, the importance of the influence of time between onset of the cavity and its subsequent backup was detected. To this end, gave Franz Pacher 1964, the rock mechanical explanations as an interplay between rock pressure and support resistance. On the practical side the cavity backup was simplified by the variable applied shotcrete, its application has been significantly expanded and improved in the period. More multi-way support and expansion elements were added, such as skewers, pipe screens, anchor and support arches.

Steps

The essential steps in the New Austrian Tunnelling method are the onset and securing with the following details:

For outbreak are used:

• In soft ground: excavator with bucket, fangs or hydraulic chisel,
• At intermediate rock strengths and fractured rock: part - or full -face machines with rotating cutting rollers, the mill off with applied chiseling the rock material. According to the mode of action of the cutting rollers is divided into axial (rotating in the direction of the support arm ) and radial ( transverse to the arm with two rolls ) cut machines. The latter are harder rock used or
• Loosening blasting.

With the subsequent Backup as an essential feature of the NATM a void -free, non positive connection of the fuse into the mountains to be achieved. The core is the application of shotcrete, bringing the mountain surface -treated and an appropriate composite construction between the mountains and the concrete shell of the Endausbaus is achieved. The spray concrete can be applied in two different methods:

• In the dry process, water is added to a dry mixture ( cement, aggregates, admixtures ) only at the spray nozzle.
• In the wet spray process, the finished concrete is already being promoted and mixed at the spray nozzle with air and admixtures.

Depending on the rock mass properties assurance systems are incorporated into the mountains or the shell addition. They are installed to improve the sustainability in loose soils or fractured rock ahead of haste before the actual outbreak of the mountain: Pfändbleche, skewers, pipe screens, jet - injection and umbrellas. Their common characteristic is that they are supposed to or secure a composite action in the rock, so as to form the rock supporting ring around the tunnel cavity and to keep steady.

After the outbreak anchors ( steel or girder with different profile shapes ), if need be installed as dowelling between mountains and concrete that also support the formation of the rock supporting ring, or support arches erected, which form the core of a rotating concrete reinforcement and also to protect against falling rock fragments serve.

Pfändbleche and (steel) skewers are simple mechanical fuses that are star-shaped driven or drilled around the excavated cross-section with 10 to 20 degree slope to the tunnel axis into the rock. Pfändbleche ranging from about 2 to 4 feet deep, skewers, usually tubes with diameters up to 22 mm, up to 5 meters long and with each other 30 to 50 cm apart. They can also be used in conjunction with injections being perforated pipes are used, in which grout is pressed into the surrounding ground, so that an injection element for sound is generated.

Pipe umbrellas are made from longer, up to 15 meters long pipes with diameters of 140 to 200 mm. Only the front, up to 4 meters long section is exposed later. Tube screens are often used to limit settlements at the ground surface.

Jet screens display a similar structural behavior such as pipe screens, however, consist of pressed wells. First, a bore hole is produced and the slow retraction of the floor is cut and pressed to a Verpressdüse in the head under constant rotation of the drill string. This results cylindrical solidified zones of 50 to 100 cm in diameter.

To stabilize and peripheral injections can be used by the pore spaces are compressed, so that the bearing capacity of the subsoil increased and the permeability is reduced.

Ice shields can be used in groundwater as anticipatory hedging, if only a temporary increase in the carrying capacity is required or the permeability of the soil should be temporarily reduced. The production of ice bodies - mostly with brine or liquid nitrogen - requires a high level of logistics and is therefore associated with considerable costs.

The NATM is associated with permanent metrological verification, on the one hand to examine the assumptions on which the advance is based, and on the other hand to control stresses and deformations after installation of the first proppant (usually the shotcrete shell ) and in the expanded state. Full measurement cross-sections with stress and deformation measurements are arranged depending on the geological conditions at intervals of 200 m to 400 m in urban areas under structures also significantly lower, and sometimes only 50 m. In between is a point network over which the deformations of the shell are monitored constantly.

Principles and definition

The principles of the New Austrian Tunnelling Method have been written in 1979, together with a definition of the working group " tunneling " of the Research Society for Highways in the Austrian Engineers and Architects Club.

The New Austrian Tunnelling Method ( NATM ) follows a concept that makes the mountains surrounding the cavity (rock or soil) by activation of a mountain ring to a load-bearing components. Here, some principles must be observed, such as:

• Consideration of the geomechanical rock mass behavior,
• Prevention of less favorable stress and deformation states by the timely installation of suitable support measures
• In particular, in time of introduced, static effective Sohlschluss, which gives the mountain support ring the static function of a closed tube,
• Optimization of the extraction resistance as a function of the allowable deformations and
• Metrological monitoring and control optimization.

For this purpose, 22 principles both in text form as well - particularly illustrative - designed with characteristic sketches and concise summaries ( see table ).

Application of the method of tunneling

The first practical application of the New Austrian Tunnelling Method using shotcrete in 1955 at tunnel construction of the hydroelectric plant Prutz -Imst in Austria. As a first application in the Federal Republic of Germany, the 308 meter-long twin tunnels Schwaikheim in Latvians and Gipskeuper was produced 1963-1965.

Between 1969 and 1971, followed by U -Bahn Frankfurt, Lot 25, for the first time a near-surface tunnel that was created in the Frankfurt clay under development. In the following years the tunnel are in ever shorter intervals created by this method, such as 1970-1971 the Hasenbuck tunnel and from 1973 to 1975, the metro Los A2 in Bochum.

In the following years the New Austrian Tunnelling Method won in different modified forms increasingly important. In the tunnels by mining produced the track share in 1983 was already two-thirds.

In the 1980s, the New Austrian Tunnelling Method in the construction of main-line railway and highway tunnel has replaced the conventional, formerly standard construction methods as far as possible. On the high-speed line between Hanover and Würzburg, the first major new railway line of the German Federal Railroad, nearly all of the 61 tunnels have been built with a total length of around 121 km to the NATM, including the ridge Tunnel ( 10,779 m ) and the Mündener Tunnel ( 10,525 m), the two longest tunnel in Germany.

Process development related to the tunneling

The need for tunnels increased greatly with the onset of railway construction in the first half of the 19th century. The tunneling method with expansion and release techniques have been largely taken over from the mining industry, which presented to the durability of the structures but significantly lower requirements.

The stabilization of the exposed tunnel walls was not until the mid-20th century, mostly with the help of wooden fixtures that claimed a significant portion of the newly created cavity, so that the final finishing work with masonry of hewn or unhewn stone, occasionally also of brick, much more difficult were.

The purpose, in frequent reaction of the supports led, along with their resilience and the lack of extensive contact with movements in the surrounding rock and in many cases to a resolution of the Mountain Association in cavity nearby. This structure loosening caused, the surrounding mountains were thus " softens " and would make the final expansion by its extra weight.

An engineering- treatment of the tunneling and underground construction began with the first major reference work textbook of the tunneling art by Franz Rziha in a 1867 ( Volume I ) and 1874 ( Volume II ). He asked even then fundamental and pioneering firm:

"The art of the engineer is to keep large rock pressure, that is, not to give rise to a far greater art than those to cope once existing rock pressure. "

More fundamental findings published Ernst Wiesmann in the years 1909 and 1912 he was the first to the stress transfer to the new tunnel cavity formed basically correct and drew the conclusion. :

" So the tunnel builder has not the task of supporting the cavity against superposition pressure, this causes the sleeve, but he must be concerned only with their conservation. "

Ladislaus of Rabcewicz in 1944 together his own experiences as well as the findings of other professionals in the past few decades, which had contributed to a better understanding of the geomechanical processes in tunneling. For two core areas of the tunnel, he summarized the findings as follows:

For loosening pressure:

"The cause of loosening pressure is mainly due to the defects in our discrimination and temporary Ausbaues used here, which favors settlement and cavitations. "

He pointed to the decisive influence of the time between creating the tunnel cavity and the final expansion for:

"One of the most important factors for the generation of the loosening pressure ... is the time. The sooner a cavity is closed, the lower the settlement .... When loosening pressure is always to denote the most appropriate those tunneling and operation, which closes the open as quickly as possible quickly and with minimal cross-section ratios again by an incompressible, final installation. "

For genuine rock pressure he was:

" The Primary -true for overlay printing is a compression of the elms with elastic Dodge against the cavity. Is this the rock strength is not exceeded, nothing happens, the tunnel needs no lining .... At the moment, however, when it comes to destruction, the voltage image changes. In the elms, the voltage will drop to 0, and the pressure rise is shifted further into the mountain. "

A change in practical tunneling held about 1947 anchorages catchment, which are built into the surrounding rock to secure the final tunnel extensions. This as the " Roof bolting " or anchorage designated method was first used later in the U.S. and Sweden, also in Central Europe.

At the same time shotcrete has been increasingly used, which has evolved from the " Gunite ", an injection grout for renovation, developed and has been further developed for use in tunnel by the Austrian tunnel engineer Anton Brunner. The theoretical foundations for the new field at the time rock mechanics have been compiled by Leopold Müller and Franz Pacher along with geomechanical findings in Austria by the so-called " Salzburger circle" and systematized. Ladislaus of Rabcewicz used from 1956 to 1958 for the first time the use of systematic tunnel and shotcrete as the sole supporting means in the construction of highway and railway tunnel in Venezuela.

The breakthrough of the New Austrian Tunnelling Method in Europe succeeded in 1963, when it was used after a cave-in in the mountain tunnel mass as a remedial measure. Ladislaus of Rabcewicz changed as a consultant, the expansion method fundamentally, used shotcrete, perforations and anchoring a relatively rapid ring closure. The stabilization process was observed by systematic measurement, the effect of the Sohlschlusses clearly showed. The construction of the tunnel was then completed without problems.

Example Structures

The following prominent tunnel - in addition to the pilot projects mentioned above - are constructed in this construction:

• About control center in the English part of the Euro tunnel: ( " probably one of the most impressive buildings, which has been built according to the principles of the NATM " )
• Himmelberg Tunnel ( a railway tunnel in the high-speed line Cologne-Rhine/Main at Montabaur )
• Sitina tunnel ( a highway tunnel in Slovakia)
• Dietershantunnel ( a railway tunnel in the high-speed line Hannover- Würzburg)
• Inntaltunnel ( a twin-track railway tunnel between the Inn Valley and the Wipptal in Tirol)
• Devil's Slide Tunnel ( a tunnel during the California State Route 1 )
• Tunnel Vomp - Terfens ( in early construction of tunnel Unterinntalbahn )