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| NATM | |
|---|---|
| Name | New Austrian Tunnelling Method |
| Caption | Tunnel excavation with sprayed concrete lining |
| First used | 1950s |
| Developer | Karl von Terzaghi; development attributed to practitioners in Austria |
| Type | Tunnelling method |
| Materials | Shotcrete, rock bolts, steel ribs, concrete |
| Notable projects | Gotthard Base Tunnel, E18 Holmestrand bypass, Channel Tunnel (adaptations) |
NATM
The New Austrian Tunnelling Method (NATM) is a tunnelling approach that emphasizes the exploitation of the inherent strength of surrounding rock and soil through careful excavation, staged support, and controlled deformation. Originating from post‑World War II developments in Austria and associated with practitioners influenced by Karl von Terzaghi and Rudolf Henning, the method integrates sprayed concrete, systematic bolting, and monitoring to adapt supports to site conditions. NATM has been applied in major infrastructure works such as the Gotthard Base Tunnel, the E18 Holmestrand bypass, and numerous urban subway projects in Paris, Seoul, and New York City.
NATM emerged in the 1950s and 1960s as a response to earlier hard‑rock and soft‑ground tunnelling approaches used in projects like the expansion of railways in Austria and Germany. Early theoretical foundations drew on consolidation of ideas from Karl von Terzaghi and practical advances by tunnellers working on Alpine tunnels and postwar reconstruction in Europe. The method spread internationally through case studies from the United Kingdom, Japan, and United States, influencing major works such as the modernisation of the Channel Tunnel approach tunnels and upgrades to metro systems in Moscow and Hong Kong.
NATM is founded on the principle of mobilising the load‑bearing capacity of the surrounding strata by allowing controlled deformation and providing a thin, flexible support shell. Core techniques include the application of sprayed concrete (shotcrete), systematic rock bolting, and occasional steel ribs or lattice girders. Design philosophy references empirical observations from projects in Switzerland, Italy, and Norway and integrates monitoring protocols developed in conjunction with institutions such as the Austrian Society for Geomechanics and university research at ETH Zurich and TU Wien.
NATM has been used in a variety of geological and infrastructural settings: high‑speed rail tunnels like the Gotthard Base Tunnel, urban metro expansions in Paris, Seoul Subway Line 9, and complex highway tunnels such as the E18 Holmestrand bypass. Other notable implementations include extensions to the London Underground and rehabilitation works on the rail network in Japan. Case studies often highlight adaptations for mixed face conditions encountered in projects overseen by agencies such as Network Rail, Rijkswaterstaat, and municipal transit authorities in New York City.
Engineers designing NATM projects must integrate geological mapping, in‑situ testing, and observational design to select excavation sequences and support measures. Geotechnical investigations use borehole logs from projects in Switzerland and Norway, laboratory testing protocols standardised by organisations like CEN and guidelines from national agencies including British Standards Institution for shotcrete. Structural interaction between support elements and strata is modelled with finite element software employed by firms such as Atkins and AECOM, and informed by precedent from tunnelling projects managed by SNC-Lavalin and Strabag.
Proponents cite NATM's adaptability, cost efficiency in favourable geology, and reduced initial support material compared with full pre-cast lining methods used in projects by companies like Skanska and Bouygues. Critics point to challenges in weak, squeezing, or swelling grounds documented in case reports from Japan and concerns raised after incidents in tunnelling projects overseen by authorities such as Transport for London and the US Federal Highway Administration. Debate continues in academic circles at institutions like Imperial College London and Delft University of Technology over empirical versus numerical design paradigms.
A defining feature of NATM is rigorous instrumentation and observational control: convergence measurements, stress gauges, extensometers, and surface settlement monitoring. Instrumentation suites used in projects under agencies like Network Rail and Rijkswaterstaat often include automated data acquisition systems from manufacturers such as Geokon and Vibrometric and adhere to protocols developed with universities like TU Delft and ETH Zurich. Emergency response procedures are coordinated with regulatory bodies including Health and Safety Executive in the United Kingdom and national ministries of transport.
Related approaches include sequential excavation methods applied in Japan, mechanised tunnelling using tunnel boring machines as in the Channel Tunnel and Gotthard Base Tunnel construction, and hybrid techniques combining pre-cast concrete segments with NATM principles for transitional zones. Contractors and engineering consultancies such as Herrenknecht and Mott MacDonald have developed proprietary adaptations integrating NATM elements with mechanised support and ground improvement strategies used in projects across Europe, Asia, and the Americas.
Category:Tunnelling methods