Fujita Research is a company with a simple mission - to create harmony between people, the environment and technology through sustainable development in construction. We already market several innovative products and, together with industry partners, are working to develop real solutions to the problems of the 21st centruy construction industry. Fujita Research was founded in 1989 in California and now has branch offices in Bangkok, Tokyo and Brighton, England. We are the primary R&D division of Japan's 7th largest construction company, the Fujita Corporation. Whilst every effort is made to ensure these reports are accurate, we cannot be held liable for any errors or omissions. You should verify any information contained herein with independent third parties before making any commercial decisions. Click here to access other reports from Fujita Research Click to access the Fujita Research homepage

Tunnelling - 'The State of the Art'

Last updated: 05/97

1. Introduction

Tunnelling is a huge industry in Japan, worth several trillion yen in any year (see fig.1). Tunnelling in Japan is also a highly conservative and highly regulated industry, with high costs. This report looks at the state of tunnelling in Europe, with emphasis on developments to reduce costs. For this reason, it focuses on NATM (New Austrian Tunnelling Method) and NMT (Norwegian Method of Tunnelling). Both of these methods are very flexible (engineering decisions are made on-site as the tunnel is constructed), and both employ shotcrete, either as a primary or final lining of the tunnel.

The report also briefly discusses immersed tube tunnels, which may be of interest Fujita, and submerged floating tunnels (SFTs) - although very little information is available about SFTs.

2. New Austrian Tunnelling Method (NATM)

One of the main attractions of NATM is its cost, which is 10-30% less than shield methods (Ground Engineering, April 1995). The key feature of NATM is the use of a sprayed concrete lining (shotcrete) to stabilize exposed soil faces, prior to the installation of a permanent lining.

2.1 Safety of NATM and Tunnel Collapses

NATM is a safe method if properly applied. Proper application requires:

•Good theory and Calculations
•Experience of Engineers
•Good Labor Skills
•Excellent Monitoring/Instrumentation.

If any of these four factors are poor, a tunnel may collapse. In Europe in 1994 there were a number a number of highly publicized collapses. All the falls were due to bad implementation of NATM rather than NATM itself, but gave NATM bad publicity.

Date	Tunnel	Details of Collapse
31 July-01 Aug	Montemor Tunnel, Portugal	45m section of Northbound Tunnel collapsed 7.30 pm,31 July, creating 20m hole on the surface (14m above). Collapse in Southbound Tunnel 4am, 01 August. Caused by burst water pipe which created a saturated clay layer.
unknown	Subway, Munich, Germany	1-2 impermeable marl was overlaid with a sandy gravel layer with 12 m free water. TBM entered an area with no marl cover
21 October	Heathrow Airport, London	Few details available. Damage estimates were UKP50M

The collapse at Heathrow led to reviews of the use of NATM in the UK, and presented problems for the London Jubilee Line extension (subway tunnel), the largest NATM project then underway in the UK. A trial tunnel was completed in 1992, and it showed NATM to be a viable method in the London Clay. After the collapse of the Heathrow tunnel in 1994 however it was thought possible that NATM tunnelling would be suspended throughout the UK and preparations were made to use a 7.7 m diameter shield. In the end SGI segments were used as an additional safety measure, but the shield was never assembled. This successful work on the Jubilee Line Extension is widely regarded as having restored faith in NATM in Britain.

A final result of the Heathrow collapse, was the publication (in 1996) of two reports on the use of NATM in the UK: one by the Health and Safety Executive (a government department) and the other by the Institution of Civil Engineers. The second report examined the use of NATM under sub-optimal ground conditions (soft ground). I have not yet been able to obtain this report (Institute of Civil Engineers, A guide to sprayed concrete linings in soft ground in urban areas (1996)). However, from summaries I have read, it appears to recommend increasing use of numerical analysis prior to construction. But, more importantly, it does it find any problem with NATM in itself - providing it is properly supervised by experts.

2.2 Large Current and Planned NATM Projects

[source ‘Project Round Up’, Tunnels and Tunnelling, Dec. 1995&1996]

Location	Details
South Korea	Taegu Metro
Sweden: Haland Ridge	8.6km, 9.1m, through soil ranging from Hard Rock to Clay
Ireland: Dublin	2.4 km twin-bored tunnel sections, planned for 1998
Southern England	High speed Channel Tunnel Link (3.2 km rail tunnel (possibly NATM, possibly shield)
Austria : Semmering	22.1 km rail tunnel, 900 m pilot tunnel to be completed Dec. 97 (some NATM - some other techniques)
Australia: Melbourne	6 km city link tunnel, budget $AUS 2billion
Spain: Madrid	Metro (length unknown, will use NATM and tunnelling, planned for 1998-2001)

3. Norwegian Method of Tunnelling (NMT)

The Norwegian Method of Tunnelling (NMT) is most suitable in jointed rock which tends to overreach. By 1984 (in Sweden, Norway etc.), NMT had replaced NATM in such ground conditions. NMT does not use mesh-reinforced concrete or S(mr), instead it uses S(fr) (fiber reinforced shotcrete). NMT is often used with drill and blast tunnelling, but can be used in conjunction with TBMs in clay zones.
One of the advantages of NMT is use of S(fr) as the final tunnel lining. Over 160km of Norwegian road-tunnel uses shotcrete or S(fr) as the approved final lining. Temporary rock reinforcement and permanent tunnel support can be any of the following:

•Reinforced Ribs of Shotcrete
•Systematic Bolting
•Spot Bolts

The simplicity of NMT allows drill and blast driving rates of 0.6 m/hr. Use of S(fr) and bolting in fault zones and clay-bearing rock is eliminating the need for use of cast concrete, and leads to costs being 50% lower. Use of S(fr) and RRS used as permanent support in soft-jointed rocks and over-consolidated fissured clays (such as London Clay), will probably result in similar savings. The benefits of NMT mean Norway uses 60-70 000 m3 of S(fr) per year, the highest use in the world - despite the small population of the country.

When NMT was introduced it was not certain if the steel fibers used to reinforce shotcrete would corrode (rust). However if precautions are taken (using high-grade concrete with platicizers, super plasticizer and hydration control) no corrosion seems to occur, not even in undersea tunnels. The Norwegian government recommends strength class C45 and environmental class MMA S(fr) for saltwater environments, with a shotcrete layer at least 70 mm thick. In addition an update for the Q-system has been developed for NMT, based on over 1000 road tunnels.

4. Other Information

4.1 Excavation Costs - Drill&Blast vs. TBMs

[source: Tarkoy, P.J., Tunnels and Tunnelling, Oct. 1995]

Use of TBMs has increased dramatically over the last twenty years and now 90% of the tunnels in north America are created using tunnel boring machines. Technological developments have made it possible for TBMs used in increasingly hard rock. But few comprehensive studies have been made, directly comparing the costs of drill-and-blast against the use of TBMs. The conclusions of the study show that TBMs are cheaper, but for slow rates of advance, the cost benefits over drill+blast are only because of the need for less temporary support structures. One of the major cost factors against TBMs is the lead time for starting tunnelling. These can of course, be minimized by placing orders early, or (as is becoming increasingly common) using refurbished (second-hand) TBMs.

4.2 Immersed Tube Tunnels and SFTs

Immersed tube tunnels and submerged floating tunnels (SFTs) are two relatively novel developments in Europe. The first type are useful in river crossing where the soil conditions are too poor to allow for tunnel boring and are becoming increasingly common in the UK and in Europe. The second type are planned for use in deep water crossings where a tunnel is moored above the seabed.

Immersed Tube Tunnels:

An example of an immersed tube tunnel is the River Medway crossing which includes a 260m immersed tube. The immersed tube consisted two concrete-only units of 126 m each made of 6x21 m sections connected by a dilatation joint with groutable water, and neoprene ends. The sections (with steel bulkheads) are floated into the river, sunk into a dredged trench, and connected to cut-and-cover tunnel approaches using a rubber seal - a seal improved by tidal pressure. This approach results in a final tunnel which is flexible enough to allow for differential settlement. A number of other such tubes are used in the Netherlands.

Recently, Parsons Brinckerhoff have developed a new system of constructing concrete tubes on floating pontoons. By removing the need for casting basins on the river or canal (where the tubes are normally made) costs are reduced by 20-30%, and the process is made much more environmentally friendly. First of all the base slab is constructed on a pontoon. Next, outer walls are built and the ends of the tube are closed by steel bulkheads. The pontoon sinks more slowly than the walls rise, and eventually the tube is buoyant without the pontoon, which can then be removed. Following slip-forming of the walls, and application of a waterproof membrane the roof is added. The tube element is then sunk, and connected to the previous element.

Submerged Floating Tunnels (SFTs)

The first SFT is still to be built, but there is much interest in the concept. Unlike immersed tube tunnels the tunnel is not an embedded structure, but is suspended above the sea floor. It seems likely that for some crossings SFTs will be cheaper than a suspension or an undersea tunnel and they are being aggressively promoted in Europe. On May 29-30 1996 the Norwegian Public Roads Administration held the first conference devoted to SFTs, and over 100 engineers attended (conference proceedings are available).

The conditions which favor SFTs are:
Water depth greater than 50 m
Crossing length Greater than 1 km
Preservation of scenic beauty required.
Limited currents.

In Norway, the Høgsfjord pilot SFT project, designed to connect Lauvvik and Oanes, has been underway for 10 years. Høgsfjord is 1400 m wide and 155 m deep, with an 0.6 m/s current, and a significant wave height of 1.5 m. Tenders for construction are due to be submitted in 1998, with construction starting in 1999, and the tunnel opening in 2001 or 2002. Four different tunnel plans are being considered: three concrete tunnels (one tethered to the seabed; two supported by pontoons) and one steel tunnel (supported by pontoons). Estimated cost is $US128 million.

Two other SFT projects in Europe are in the planning stage, a crossing of the Messina Straits in Italy, and a crossing of Lake Lugano on the Swiss-Italian border. However, interest in the concept is much wider, and the EU has commissioned a report (the SFT Analysis Project) to further examine the feasibility and benefits of SFTs (completion was due in Dec 1996). The following table lists possible SFT sites in Europe.

There is also considerable interest in the use of SFTs in Japan. In the North, there is interest in a possible SFT crossing between Hokkaido and Honshu (Funka bay), and also several crossings within Hokkaido itself (including Uchiura Bay). On Honshu there are plans to develop an SFT between Kansai International Airport (KIX) and Kobe Airport. The SFT component of the 30 km crossing is 11 km (the rest of the crossing being buried SFT or immersed tube).

4.3 Developments in Shotcrete, Rockbolting, Grout, and Computation

[source Greywell, C., ‘Maintaining Ground Stability’, Tunnels and Tunnelling, Jan 1997]
[source 2 Page, M., ‘Supporting Tunnels at Lower Cost’ Tunnels and Tunnelling, Jan. 1995]

Bunder Cement (Netherlands) has developed a proprietary shotcrete of finely ground cement significant silica fume content and lower than average gypsum content (named Buandrier Tunnel Cement). The result is a shotcrete which remains workable for a long period yet quickly develops high strength. The cement was first used in 1994, and has been successfully employed in the 19.1 km Vereina rail tunnel.

Increasingly companies are beginning to use shotcrete which includes steel fiber reinforcement S(fr) as developed for use in NMT to save both time and money Several tunnels under construction in Australia are using 150 mm Steel Reinforced Shotcrete (S(fr)) as the primary support. Tunnels include the 6 km Melbourne City Link Project (mentioned above), the Sydney Airport-City rail link and Homebash Link. One example of reinforcing used is BHP EE Fibresteel which is widely used in Australian mines, and the Tai Lam tunnel. It is mixed to shotcrete at rates of 40-75 kg/m3.

Fibre Technology, based in Nottingham, UK, has developed a ‘Melt Overflow’ technique to incorporate metals than steel in S(fr). The company has already used aluminum-bearing stainless steel, nickel alloys, and copper alloys. Some of these materials have resulted in increases of fracture toughness of up to 400%.

Developed in Norway in 1993 the Ingersoll-Rand CT bolt can save money by being installed initially as a temporary rockbolt and grouted later. The bolt has a rigid polythene sleeve between bolt and rock which keeps water away from the bolts. The sleeve also allows grout to flow to the end of the bolt and returns outside the sleeve to the bearing plate, thereby completely enclosing the bolt.

Atlas Copco have developed two new bolts. The first may reduce the number of bolts needed in a tunnel. Connectable Swellex bolts can be joined to give any length of rockbolt, although practical considerations (hole drilling) will likely limit the length to 15-20 m. The other bolt, Swellex stainless is made of stainless steel and is of use in corrosive environments. It should prove particularly durable over the long term. All swellex bolts offer immediate full-column rock reinforcement, and can accomodate large ground movements. They are also said to be non-sensitive to blast vibrations.

Ischebeck of Germany have developed a one-step rockbolt. The rock bolt is a hollow drill bit, which is left in the rock. It is filled with grout, which is injected at the same time as the drilling. Such rockbolts have been used in the Penyclip tunnel in Wales.

In silty sandstone, grouting is often used as pre-support before tunnelling. If a surface right-of-way exists, then grouting is simple. If not construction can be slowed. Hayward Baker has used horizontal directional drilling with tube-a-manchette grouting on a 4.4 km section of a 6.1 km tunnel. Nineteen million liters of chemical grout in lengths up to 244 m were installed, with the result that stand-up time for the tunnelling was increased.

A research team in Italy [at Politecnico di Torino, International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts Vol.33 No.5] has developed a new procedure for the computation of convergence-confinement curves of bolted tunnels. The model allows the effects of the following to be calculated:
distance of the bolted section to the tunnel face
increasing the lateral spacing between bolts
the influence of the different bolt-end plate response curves

Comparisons of the new procedure with those derived from numerical simulation and performance monitoring show similar results.

4.4 Japanese-language references unavailable in the UK

Title: A Design Method of Rock Bolts in Jointed Rock Masses
Authors: Hojo, A. et al.
Journal: Dobuku Gakkai ronbushu No.533 Pg. 143

Title: Application of SK-steel-bar-mesh unit to tunnel inner-lining reinforcement
Authors: Kurokawa, K.et al.
Journal: Sumitomo Metals Vol. 48 No.2 pp.109-114 (April 1996)

Title: Attempting a new three-dimensional support system for NATM
Authors: Kamori-Hiroshi et al.
Journal: Tsuchi-To-KisoVol. 43 No.8 pp.34-36 (1995)

5. Summary

This report has covered new developments in tunnelling which may reduce costs, and looked at a number of innovative techniques. Further, and more detailed investigation can be undertaken into areas of most interest to Fujita staff. As with other reports on the web this study will be updated, as and when new information comes is available.

also see the list of Major European Tunnelling Contractors

Major European Tunnelling Contactors (Feb 1997)

Company	Address/Fax	Interests	Current Projects
AMEC Tunnelling	Cold Meece, Swynnerton, Stone, Satffs, ST15 0QX, UK. Fax +44.1785.760022	NATM	Jubilee Line Extension, London
Angleglobe	3 Lord's Close, Sewards End, Saffron Walden, Essex, CB10 2EN, UK. Fax+44.1799.513.544	NATM	Størebelt Tunnel, Denmark
Ballast Nedam	Laan van Kronenburg 2, PO Box 500, 1180 BE Amstelveen, The Netherlands. Fax +31.20.6473000	TBM Operation	Heinenoord Tunnel (Rotterdam, Netherlands)
Baresel	Nordbahnhofstrasse 135, D-70191 Stuttgart, Germany. Fax+49.711.2584.402	TBM Operation	Rail Tunnels in Greece
Barhale Construction	167 Imperial Drive, Harrow, Middlesex, HA2 7HD,UK Fax +44.1818.868.6822	Microtunnelling Pipejacking Segmental Tunnels	?
Beton- und Monierbau	A-6020 Innsbruck, Bernhard-Hefl-Strasse 11, Austria. Fax+43.512.33110	NATM	German Railways
CMC di Ravenna	Via Trieste N.76, 48100 Ravenna, Italy. Fax+39.544.428.186	?	Several projects in the Netherlands.
DCT Civil Engineering	Prospect House, George St., Shaw, Oldham, OL2 8DX, UK	TBM Operation Microtunnelling	Rail tunnels in Scotland
Dyckerhoff & Widmann	Erdinger Landstrasse 1, Postfach 810 280, D-81902, Munich, Germany. Fax+49.89.9255.3688	Shield?	Størebaelt Rail Tunnel (Denmark), Mekka-Taif water tunnel (Saudi Arabia)
Dielmann-Haniel GmbH	Postfac 13 01 63, 44311 Dortmund (Kurl), Germany. Fax+49.231.2891.492	Mining Shafts	?
Edmund Nuttal	St. James House, Knoll Rd, Camberley, Surrey, GU15 3XW, UK. Fax+44.1276.66060	Immersed Tube Shield	Cairo Wastewater Project, Medway Tunnel (Kent, UK)
Ed Züblin	Albstadtweg 3, D-70567 Stuttgart, Germany. Fax+49.711.7883.261	Shield NATM	Niederhausen Tunnel (Germany)
Heilit + Woerner	Klausenburgerstrasse 9, Postfach 860680, 81633 Munich, Germany. Fax+49.89.93993.216	Shield NATM	Hofberg Road Tunnel, Germany
Heitkamp	Bauunternehmung E Heitkamp GmbH, Langekampstrasse 36, D-44652, Herne, Germany. Fax+49.2325.574336	Microtunnelling TBM Operation drill+blast	?
Jaeger Baugesellschaft	Batloggstrasse 95, A-6780, Schruns, Austria, Austria. Fax+43.5556.7181.31	Shield Microtunnelling	24.9 km water supply tunnel (Greece)
Kier Construction	Tempsford Hall, Sandy, Bedfordshire, SG19 2BD, UK Fax+44.1767.640.002	Immersed Tube Soft Ground	Lantau and Airport Railway (Hong Kong)
Marti-Inter	Freiburgstrasse 133, CH-3000 Berne 5, Switzerland. Fax.+41.31.381.9262	TBM Operation	Rail Tunnels
Mosmetrostroy	17 Tsvetnoy Bulvar, 103051 Moscow, Russia. Fax+7.95.925.3842	Shield NATM	Metro Tunnels (Moscow)
NV Denys	Industrieweg 124, 9032 Wondelgem, Belgium. Fax+32.9.254.0111	TBM Manufacture/Use Pipejacking	?
Phillip Holzmann	HN Tunnelbau, Kaltenbornweg 2, D-50679 Koln, Germany. Fax+49.2219810040	NATM Shield	?
Recchi	Via Montevecchio 28, 10128 Torino, Italy. Fax+39.1153.2474	?	Taipei-Ilan Expressway, Taipei
Soletanche	Prospect Place, Mill Lane, Alton, Hants, GU34 2SX, UK. Fax+44.1420.543566	TBM Operation Pre-cutting Techniques	Projects in France, UK, Hong Kong
Spie Batignolles	10 Avenue de l'Entreprise, 95862 Cergy Pontoise Cedex, France. Fax+33.1.34243918	?	Over 40Km of Subway Tunnels throughout Europe
Tarmac Civil Engineering	Roadstone House, 50 Waterloo Rd, Wolverhampton, WV1 4RU, UK. Fax+44.1902.316165	Rail Tunnels Tracklaying Immersed Tubes	Copenhagen Metro (Denmark), Medway Tunnel (Kent, UK)
Taylor Woodrow Civil Engineering	Taywood House, 345 Ruislip Rd, Southall, Middz, UB1 2QX, UK. Fax+44.181.575.4098	NATM Shield	Jubilee Line Extension, London
Universale-Bau	Zweigniederlassung, Untertagebau, A-5022 Salzburg, Austria, Fax+43.662.458.302	TBM Operation drill+blast	?
Walter-Bau	Postfach 10 25 47, D-86015 Augsburg, Germany, Fax+49.821.5582.517	Shield Driving	?

©1997 Fujita Research