Minimizing the use of concrete in tunnels and caverns: comparing NATM and NMT

Minimizing the use of concrete in tunnels and caverns: comparing NATM and NMT For many decades, a tunnelling method has been in use which effectively minimizes the use of concrete, which should be one of the goals in our CO2-producing planet. We call the method NMT (Norwegian Method of Tunnelling) and emphasize its ‘single-shell’ characteristics, to distinguish it clearly from double-shell NATM (the so-called New Austrian Tunnelling Method), which is recommended to have (ASG, NATM: the Austrian practice of conventional tunnelling 2010): shotcrete, mesh, lattice girders, rock bolts (if in-rock), drainage fleece, membrane, and the final load bearing and often steel-reinforced concrete lining, including the invert when in poor rock conditions. This tunnelling method is inevitably several times more expensive, uses many times the volume of concrete, takes longer to build, and requires at least a ten times larger labour force than single-shell NMT. The single-shell tunnels for road or rail or hydropower or water transfer, or for large caverns for storage of oil or food, or for hydropower machine and transformer halls, can be made stable by judicious application of a well-used (>2000 case record based) the so-called Q-system of rock mass quality estimation. The latter encompasses a rock mass quality scale from 0.001 (equivalent to a serious fault zone, where we also may need a local concrete lining) to 1000 (equivalent to massive unjointed rock) where careful blasting will remove the need even for shotcrete. In general, rock masses where we need tunnels or caverns will lie closer to ‘mid-range’ (i.e. closer to Q = 1 which is described as ‘poor quality’). Here we would need combinations of corrosion-protected rock bolts and high quality fibre-reinforced shotcrete, with stainless steel or polypropylene fibres. We may also need systematic high-pressure pre-injection of micro-cement and micro-silica, which may add 20% to the (low) starting cost of the NMT excavation. Written as B + S(fr) in short-hand, NMT has rock bolt c/c spacing in metres and shotcrete thickness in centimetres, as specified by the range of Q values and excavation dimensions. The details are also affected by the planned use. For instance, at our record-breaking Olympic cavern of 60 m span (for housing 5400 spectators or later concert goers), B = 2.5 m c/c + S(fr) 10 cm were (and remain 25 years later) the stabilizing and permanent measures of support and reinforcement. Deformation monitoring and distinct element (jointed rock) numerical verification showed 7–8 mm of maximum deformation in the arch. The moderate Q value range of quality of 2–30 (poor/fair/good) and RQD = 60–90 indicated a well-jointed gneiss, which had only moderate UCS = 90 MPa compressive strength. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Innovative Infrastructure Solutions Springer Journals

Minimizing the use of concrete in tunnels and caverns: comparing NATM and NMT

Loading next page...
 
/lp/springer_journal/minimizing-the-use-of-concrete-in-tunnels-and-caverns-comparing-natm-l6KamYcIUp
Publisher
Springer International Publishing
Copyright
Copyright © 2017 by Springer International Publishing AG
Subject
Earth Sciences; Geotechnical Engineering & Applied Earth Sciences; Environmental Science and Engineering; Geoengineering, Foundations, Hydraulics
ISSN
2364-4176
eISSN
2364-4184
D.O.I.
10.1007/s41062-017-0071-x
Publisher site
See Article on Publisher Site

Abstract

For many decades, a tunnelling method has been in use which effectively minimizes the use of concrete, which should be one of the goals in our CO2-producing planet. We call the method NMT (Norwegian Method of Tunnelling) and emphasize its ‘single-shell’ characteristics, to distinguish it clearly from double-shell NATM (the so-called New Austrian Tunnelling Method), which is recommended to have (ASG, NATM: the Austrian practice of conventional tunnelling 2010): shotcrete, mesh, lattice girders, rock bolts (if in-rock), drainage fleece, membrane, and the final load bearing and often steel-reinforced concrete lining, including the invert when in poor rock conditions. This tunnelling method is inevitably several times more expensive, uses many times the volume of concrete, takes longer to build, and requires at least a ten times larger labour force than single-shell NMT. The single-shell tunnels for road or rail or hydropower or water transfer, or for large caverns for storage of oil or food, or for hydropower machine and transformer halls, can be made stable by judicious application of a well-used (>2000 case record based) the so-called Q-system of rock mass quality estimation. The latter encompasses a rock mass quality scale from 0.001 (equivalent to a serious fault zone, where we also may need a local concrete lining) to 1000 (equivalent to massive unjointed rock) where careful blasting will remove the need even for shotcrete. In general, rock masses where we need tunnels or caverns will lie closer to ‘mid-range’ (i.e. closer to Q = 1 which is described as ‘poor quality’). Here we would need combinations of corrosion-protected rock bolts and high quality fibre-reinforced shotcrete, with stainless steel or polypropylene fibres. We may also need systematic high-pressure pre-injection of micro-cement and micro-silica, which may add 20% to the (low) starting cost of the NMT excavation. Written as B + S(fr) in short-hand, NMT has rock bolt c/c spacing in metres and shotcrete thickness in centimetres, as specified by the range of Q values and excavation dimensions. The details are also affected by the planned use. For instance, at our record-breaking Olympic cavern of 60 m span (for housing 5400 spectators or later concert goers), B = 2.5 m c/c + S(fr) 10 cm were (and remain 25 years later) the stabilizing and permanent measures of support and reinforcement. Deformation monitoring and distinct element (jointed rock) numerical verification showed 7–8 mm of maximum deformation in the arch. The moderate Q value range of quality of 2–30 (poor/fair/good) and RQD = 60–90 indicated a well-jointed gneiss, which had only moderate UCS = 90 MPa compressive strength.

Journal

Innovative Infrastructure SolutionsSpringer Journals

Published: Aug 21, 2017

References

You’re reading a free preview. Subscribe to read the entire article.


DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Search

Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly

Organize

Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.

Access

Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

DeepDyve

Freelancer

DeepDyve

Pro

Price

FREE

$49/month
$360/year

Save searches from
Google Scholar,
PubMed

Create lists to
organize your research

Export lists, citations

Read DeepDyve articles

Abstract access only

Unlimited access to over
18 million full-text articles

Print

20 pages / month

PDF Discount

20% off