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stress conditions. The principles of NATM are fundamental to modern-day tunnelling, and NATM fundamentally involves specifically addressing the specific soil conditions being encountered. Most city tunnels are built at shallow depth and do not need to control the release of in situ stress, as was the
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Other designations are seen for this modern tunneling style; Sequential
Excavation Method (SEM) or Sprayed Concrete Lining (SCL) are often used in shallower tunnels. In Japan, the terms Centre Dividing Wall NATM or Cross Diaphragm Method (both abbreviated to CDM) and Upper Half Vertical Subdivision
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The NATM integrates the principles of the behaviour of rock masses under load and monitoring the performance of underground construction during construction. The NATM has often been referred to as a "design as you go" approach, by providing an optimized support based on observed ground conditions.
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case with the original NATM in the Alps. Projects in cities place a higher priority on minimizing settlement and so tend to use different support methods from the original NATM. That has led to a confusion in terminology in that tunnelling engineers use "NATM" to mean different things.
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The measured rock properties suggest the appropriate tools for tunnel strengthening, where support requirements can traditionally be estimated using the RMR or Q System. Since the turn of the 21st century, NATM has been used for soft ground excavations and making tunnels in porous
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design and construction employing sophisticated monitoring to optimize various wall reinforcement techniques based on the type of rock encountered as tunneling progresses. This technique first gained attention in the 1960s based on the work of
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More correctly it can be described as a "design as you monitor" approach, based on observed convergence and divergence in the lining and mapping of prevailing rock conditions. It is not a set of specific excavation and support techniques.
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have arisen, and alternative names for certain aspects of NATM have been adopted as its use has spread. That is partly caused by an increased use of the tunneling method in the United States, particularly in soft ground shallow tunnels.
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Exploitation of the strength of native rock mass – 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 the rock to support
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Measurement and monitoring – Potential deformations of the excavation must be carefully monitored. NATM requires installation of sophisticated measurement instrumentation. It is embedded in lining, ground, and
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There is a quick closure of the invert, that is, the bottom part of the tunnel, to create a structural ring that takes advantage of the rock or soil arc naturally created on the top part of the tunnel section.
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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,
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between 1957 and 1965 in
Austria. The name NATM was intended to distinguish it from earlier methods, with its economic advantage of employing inherent geological strength available in the surrounding
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tunnel collapse led to questions about the safety of the NATM. However, the subsequent trial blamed the collapse on poor workmanship and flaws in construction management, rather than on the NATM.
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Contractual arrangements – Since the NATM is based on monitoring measurements, changes in support and construction method are possible, but only if the contractual system enables them.
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for initial ground support of an open-face tunnel. The term NATM can be misleading in relation to soft-ground tunnels. As noted by Emit Brown, NATM can refer to both a
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The tunnel is sequentially excavated and supported, and the excavation sequences can be varied to efficiently address the specific rock conditions being encountered.
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of a tunnel are integrated into an overall ring-like support structure. Thus the supporting formations will themselves be part of this supporting structure."
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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
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NATM/SEM is generally thought to have helped revolutionise the modern tunneling industry. Many modern tunnels have used this excavation technique.
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193:. NATM enables immediate adjustments in the construction details, but requires a flexible contractual system to support such changes.
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conditions. Active rather than passive support is used and the tunnel is strengthened by a flexible combination of
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The
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NATM was originally developed for use in the Alps, where tunnels are commonly excavated at depth and in high
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must be minimised. This is achieved by applying a thin layer of shotcrete immediately after face advance.
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The permanent support is typically a cast-in-place concrete lining placed over a waterproofing membrane.
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This monitoring makes the method very flexible, even if teams encounter unexpected changes in the
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The New
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Mobilization of ground strength is achieved by allowing controlled deformation of the ground.
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mass to stabilize the tunnel wherever possible rather than reinforcing the entire tunnel.
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of the ground around a tunnel is deliberately mobilized to the maximum extent possible.
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Tunneltalk: Heathrow failures highlight NATM (abuse?) misunderstandings
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Flexible support – The primary lining is thin and reflects recent
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When NATM is seen as a construction method, the key features are:
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The
Sequential Excavation Method is very cost effective, even in
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instruments are installed to measure the later deformation of
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Analysis of controlled deformation in rocks and soils
429:. Abingdon, UK: Taylor & Francis. p. 328.
384:. Abingdon, UK: Taylor & Francis. p. 246.
359:. Abingdon, UK: Taylor & Francis. p. 288.
449:Jacobs & Associates Newsletter, Spring 2002,
248:Key features of the NATM design philosophy are:
115:protection – Loosening and excessive rock
27:Method of modern tunnel design and construction
451:NATM IN SOFT-GROUND: A CONTRADICTION OF TERMS?
228:Some engineers use NATM whenever they propose
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262:Initial primary support is installed having
30:"NATM" redirects here. For other uses, see
158:Based on the computation of the optimal
357:Sprayed Concrete Lined Tunnels – 2nd ed
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404:Zhang, D., Xiong F., Zhang L., 2016
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522:1960s establishments in Austria
427:Tunneling: Management by Design
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39:New Austrian tunneling method
47:sequential excavation method
18:Sequential Excavation Method
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177:rock consistency, e.g. by
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104:NATM has seven elements:
61:), is a method of modern
527:Rock mass classification
382:North American Tunneling
326:Rock mass classification
321:Geotechnical engineering
218:method (UHVS) are used.
152:Rock mass classification
425:Alan Muir Wood (2002).
380:Levent Özdemir (2006).
68:Ladislaus von Rabcewicz
45:), also known as the
32:NATM (disambiguation)
498:(USA), 4-8 Oct 1976.
496:Easton, Pennsylvania
355:Alun Thomas (2019).
532:Tunnel construction
517:1960s introductions
512:Austrian inventions
238:construction method
458:2013-10-17 at the
436:978-0-419-23200-1
234:design philosophy
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307:The 1994
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456:Archived
315:See also
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331:Tunnels
290:spiling
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109:itself.
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303:Safety
236:and a
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132:strata
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490:2nd
431:ISBN
386:ISBN
361:ISBN
264:load
252:The
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43:NATM
37:The
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59:SCL
51:SEM
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