The New Austrian Tunneling method (NATM) was developed between 1957 and 1965 in Austria. It was given its name in Salzburg in 1962 to distinguish it from old Austrian tunnelling approach. The main contributors to the development of NATM were Ladislaus von Rabcewicz, Leopold Müller and Franz Pacher. The main idea is to use the geological stress of the surrounding rock mass to stabilize the tunnel itself. Year 1957 (MCMLVII) was a common year starting on Tuesday of the Gregorian calendar. ... 1965 (MCMLXV) was a common year starting on Friday (the link is to a full 1965 calendar). ... Salzburg is a city in western Austria and the capital of the federal state of Salzburg (population 150,000 in 2006). ... 1962 (MCMLXII) was a common year starting on Monday (the link is to a full 1962 calendar). ... A disused railway tunnel now converted to pedestrian and bicycle use, near Houyet, Belgium A tunnel is an underground passage. ... Stress is the internal distribution of force per unit area that balances and reacts to external loads applied to a body. ... The rocky side of a mountain creek near Orosí, Costa Rica. ...

Principles

The NATM is an approach of philosophy integrating the principles of the behaviour of rock masses under load and monitoring the performance of underground construction during construction. The fact is that the NATM is not a set of specific excavation and support techniques. For other uses, see Philosophy (disambiguation). ...

There are seven features on which is NATM based:

• Mobilization of the strength of rock mass - The method relies on the inherent strength of the surrounding rock mass being conserved as the main component of tunnel support. Primary support is directed to enable rock support itself.
• Shotcrete protection - Loosening and excessive rock deformation must be minimised. This is achieved by applying thin layer of shotcrete immediately after face advance.
• Measurements - Every deformation of excavation must be measured. NATM requires installation of sophisticated measurement instrumentation. It is embedded in lining, ground, and boreholes.
• Flexible support - The primary lining is thin and reflects recent strata conditions. Used is rather active than passive support and strengthening is not by thicker concrete lining but by a flexible combination of rock bolts, wire mesh and steel ribs.
• Closing of invert - Quickly closing of invert and create load-bearing ring is imporant. It is crucial in soft grounded tunnels where no section of tunnel should be left open even temporarily
• Contractual arrangements - Since the NATM is based on monitoring measurements, changes in support and construction method are possible. This is possible only if the contractual system enables those changes
• Rock mass classification determines support measures - There are main rock classes for tunnels and corresponding support. These serve as the guidelines for tunnel reinforcement.

Based on the computation of the optimal cross section, just a thin shotcrete protection is necessary. It is applied immediately behind the Tunnel boring machine, to create a natural load-bearing ring and therefore to minimize the rock's deformation. Additionally, geotechnical instruments are installed to measure the later deformation of excavation. Therefore a monitoring of the stress distribution within the rock is possible. Shotcrete and gunite are two commonly used terms for sprayed concrete. ... In geometry, a cross section is the intersection of a body in 3-dimensional space with a plane, or of a body in 2-dimensional space with a line, etc. ... Shotcrete and gunite are two commonly used terms for sprayed concrete. ... A tunnel boring machine that was used at Yucca Mountain. ... In engineering mechanics, deformation is a change in shape due to an applied force. ... Geotechnical engineering is concerned with the engineering properties of earth materials. ... The term archaeological excavation has a double meaning. ... To monitor or monitoring may mean: to observe a situation for any changes which may occur over time, using a monitor or measuring device of some sort: Baby monitor, medical monitor, Heart rate monitor Biomonitoring Condition monitoring Network monitoring Election monitoring to observe the behaviour or communications of individuals or...

This monitoring makes the method very flexible, even at surprising changes of the geomechanical rock consistency during the tunneling work, e.g. by crevices or pit water. Such (usual) problems are not solved by thicker shotcrete, but the reinforcement is done by wired concrete which can be combined with steel ribs or lug bolts. Geomechanics is the study of the engineering behaviour of soil and rock. ... In operant conditioning, reinforcement is any change in an organisms surroundings that: occurs regularly when the organism behaves in a given way (that is, is contingent on a specific response), is contiguous with the behaviour (associated in time and space), and is associated with an increase in the probability... A wire is a single, usually cylindrical, elongated strand of drawn metal. ... A bolt may be one of the following things: For bolts and capscrews, see Bolted joint. ...

The measured rock properties lead to the appropriate tools for tunnel strengthening. Therefore in the last decade NATM was also applied to soft ground excavations and to tunnels in porous sediments. The flexible NATM technique enables immediate adjustments in the construction details, but this requires a flexible contractual system, too. A modern hammer is directly descended from ancient hand tools A tool or device is a piece of equipment which typically provides a mechanical advantage in accomplishing a physical task. ... Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of water or other liquid. ... A contract is a legally binding exchange of promises or agreement between parties. ...

Philosophy and controversial names

When tunneling engineers talk on NATM, they often mean different things because some of them define it as a special technique, but others as a sort of philosophy. Recently the scene has been complicated by new terms and even alternative names, when discussing certain aspects of NATM. This is partly caused by an increased use of the method in the USA, particularly in soft ground conditions (see External links). For other uses, see Philosophy (disambiguation). ... The word term refers to either a word unit or a time unit with specified boundaries or limits. ...

Besides the official name New Austrian Tunneling Method other designations are used in the last years, e.g. Sequential Excavation Method (SEM), or Sprayed Concrete Lining (SCL). In Japan sometimes other names were used, e.g. Centre Dividing Wall NATM, or Cross Diaphragm Method (both abbreviated as CDM), and even Upper Half Vertical Subdivision method (UHVS). Evidently, the scientists and the tunneling industry cannot find an unified name for this wide-used method. In mechanics, a diaphragm is a sheet of a semi-flexible material, anchored at its periphery, and most often round in shape. ...

As defined by the Austrian Society of Engineers and Architects, the NATM constitutes a method where the surrounding rock or soil formations of a tunnel are integrated into an overall ring-like support structure. Thus the supporting formations will themselves be part of this supporting structure. This article is about the military unit. ... The word support has several specialized meanings: In mathematics, see support (mathematics). ...

But many engineers already refer to as NATM, when shotcrete is proposed for initial ground support of an open-face tunnel. Especially with reference to soft ground, the term NATM can be misleading. As noted by Emit Brown, NATM can refer to both a design philosophy and a construction method. Shotcrete and gunite are two commonly used terms for sprayed concrete. ... Design, usually considered in the context of the applied arts, engineering, architecture, and other such creative endeavours, is used as both a noun and a verb. ... In large construction projects, such as skyscrapers, cranes are essential. ...

Key features

According to E.Brown (Weblink 2), the key features of the design philosophy refer to:

• The strength of the ground around a tunnel is deliberately mobilised to the maximum extent possible.
• Mobilisation of ground strength is achieved by allowing controlled deformation control of the ground.
• Initial primary support is installed having load-deformation characteristics appropriate to the ground conditions, and installation is timed with respect to ground deformations.
• Instrumentation is installed to monitor deformations in the initial support system, as well as to form the basis of varying the initial support design and the sequence of excavation.

When NATM is seen as a construction method, the key features are: It has been suggested that Tensile strength be merged into this article or section. ... Look up Control in Wiktionary, the free dictionary. ... Load is what is carried, or a force. ... Timing refers to how events are spaced in time. ... Instrumentation is defined as the art and science of measurement and control. Instrumentation can be used to refer to the field in which Instrument technicians and engineers work, or it can refer to the available methods of measurement and control and the instruments which facilitate this. ... The term archaeological excavation has a double meaning. ...

• The tunnel is sequentially excavated and supported, and the excavation sequences can be varied.
• The initial ground support is provided by shotcrete in combination with fibre or welded-wire fabric reinforcement, steel arches (usually lattice girders), and sometimes ground reinforcement (e.g. soil nails, spiling).
• The permanent support is usually (but not always) a cast-in-place concrete lining.

Some experts note that many of these construction methods were used in the US and elsewhere in soft-ground applications, before NATM was described in the literature.

In an article of 2002 Romero states the major difference between the viewpoints of design and of construction: The deformation of the soil (rem.: at soft-ground tunnels) is not easily ‘controlled’. Therefore it can be concluded that the excavation and support planned for sequentially excavated, shotcrete-lined tunnels .. utilises NATM construction methods but not necessarily NATM design methods. These details are less essential at tunnels in solid or fair rock. Perspective in theory of cognition is the choice of a context or a reference (or the result of this choice) from which to sense, categorize, measure or codify experience, cohesively forming a coherent belief, typically for comparing with another. ...

See also

• Tunneling
• Geotechnical engineering

The word tunneling (also spelled tunnelling) has more than one meaning. ... Bostons Big Dig presented geotechnical challenges in an urban environment. ...

Further reading

• Johann Golser, The New Austrian Tunneling Method (NATM), Theoretical Background & Practical Experiences. 2nd Shotcrete conference, Easton (USA), 4-8 Oct 1976.

Shotcrete and gunite are two commonly used terms for sprayed concrete. ...

External links

• Insight into the New Austrian Tunnelling Method (NATM)
• NATM in Soft-Ground: A Contradiction of Terms?
• 19 NATM-Tunnels in Europe and Japan (length 1-13 km)