The New Austrian Tunneling Method (NATM), also known as sequential excavation method (SEM) or advance and smash,[1] is a modern tunnel design and construction method. The excavation is carried out in two phases, first the upper excavation is carried out (advance) and then the ground below is removed to the level of the tunnel (destroy). The method is based on using the geological stress of the surrounding rock mass so that the tunnel stabilizes itself using the arch effect "Arch (architecture)"). To achieve this, they are based on geotechnical measurements to draw an optimal section. The excavation is immediately protected with a thin layer of shotcrete. This creates a natural discharge ring that minimizes rock deformation.
This technique gained notoriety in the 1960s based on the works of Ladislaus von Rabcewicz"), Leopold Müller and Franz Pacher") between 1957 and 1965 in Austria. Its name was intended to distinguish it from the former Austrian tunnel approach. The fundamental difference between this new tunneling method, as opposed to previous methods, comes from the economic advantages available by harnessing the inherent geological strength available in the surrounding rock mass to stabilize the tunnel.[2].
NATM/SEM is generally believed to have helped revolutionize the modern tunneling industry as many have used this excavation technique.
Beginning
The NATM integrates the principles of the behavior of rock masses subjected to loads and the monitoring of the efficiency of underground construction. NATM is often cited as a "design-on-the-fly" approach, providing optimized support based on observed ground conditions. More correctly, it can be described as a "design as you monitor" approach, based on the convergences and/or divergences observed in the coating and on the study of the prevailing rock conditions. The NATM is not a set of specific excavation and support techniques.
The NATM consists of seven elements:
• - Exploitation of the strength of the native rock mass: it is based on the inherent strength of the surrounding rock mass that is preserved as the main component of the tunnel support. Primary support is intended to allow the rock to support itself.
• - Protection of shotcrete: loosening and excessive deformation of the rock must be minimized. This is achieved by applying a thin layer of shotcrete immediately after face advancement.
Primary coating
Introduction
The New Austrian Tunneling Method (NATM), also known as sequential excavation method (SEM) or advance and smash,[1] is a modern tunnel design and construction method. The excavation is carried out in two phases, first the upper excavation is carried out (advance) and then the ground below is removed to the level of the tunnel (destroy). The method is based on using the geological stress of the surrounding rock mass so that the tunnel stabilizes itself using the arch effect "Arch (architecture)"). To achieve this, they are based on geotechnical measurements to draw an optimal section. The excavation is immediately protected with a thin layer of shotcrete. This creates a natural discharge ring that minimizes rock deformation.
This technique gained notoriety in the 1960s based on the works of Ladislaus von Rabcewicz"), Leopold Müller and Franz Pacher") between 1957 and 1965 in Austria. Its name was intended to distinguish it from the former Austrian tunnel approach. The fundamental difference between this new tunneling method, as opposed to previous methods, comes from the economic advantages available by harnessing the inherent geological strength available in the surrounding rock mass to stabilize the tunnel.[2].
NATM/SEM is generally believed to have helped revolutionize the modern tunneling industry as many have used this excavation technique.
Beginning
The NATM integrates the principles of the behavior of rock masses subjected to loads and the monitoring of the efficiency of underground construction. NATM is often cited as a "design-on-the-fly" approach, providing optimized support based on observed ground conditions. More correctly, it can be described as a "design as you monitor" approach, based on the convergences and/or divergences observed in the coating and on the study of the prevailing rock conditions. The NATM is not a set of specific excavation and support techniques.
The NATM consists of seven elements:
• - Exploitation of the strength of the native rock mass: it is based on the inherent strength of the surrounding rock mass that is preserved as the main component of the tunnel support. Primary support is intended to allow the rock to support itself.
• - Measurement and monitoring - Possible deformations of the excavation must be carefully monitored. NATM requires the installation of sophisticated measurement instrumentation. It is embedded in the siding, floor and perforations. In the case of observed movements, additional supports are installed only when necessary, with an overall cost affordable for the total cost of the project.
• - Flexible support: the primary coating is thin and reflects the conditions of recent strata. Active rather than passive support is used and the tunnel is strengthened with a flexible combination of anchor bolts, wire mesh and steel ribs, not a thicker concrete lining.
• - Inversion closure: especially important in soft ground, rapid closure of the bottom (the bottom of the tunnel) that creates a load ring is important, and has the advantage of compromising the inherent strength of the rock mass surrounding the tunnel.
• - Contractual arrangements: since the NATM is based on monitoring measurements, changes to the support and construction method are possible, but only if the contractual system allows it.
• - The classification of rock masses, ranging from very hard to very soft, determines the minimum support measures required and avoids the economic waste that comes from unnecessarily strong support measures. There are support system designs for each of the major rock classes. These serve as the guidelines for tunnel reinforcement.
[2] ↑ Özdemir, Levent (2006). North American Tunneling 2006. Washington, DC: Taylor & Francis. p. 246. ISBN 0-415-40128-3.
• - Protection of shotcrete: loosening and excessive deformation of the rock must be minimized. This is achieved by applying a thin layer of shotcrete immediately after face advancement.
• - Measurement and monitoring - Possible deformations of the excavation must be carefully monitored. NATM requires the installation of sophisticated measurement instrumentation. It is embedded in the siding, floor and perforations. In the case of observed movements, additional supports are installed only when necessary, with an overall cost affordable for the total cost of the project.
• - Flexible support: the primary coating is thin and reflects the conditions of recent strata. Active rather than passive support is used and the tunnel is strengthened with a flexible combination of anchor bolts, wire mesh and steel ribs, not a thicker concrete lining.
• - Inversion closure: especially important in soft ground, rapid closure of the bottom (the bottom of the tunnel) that creates a load ring is important, and has the advantage of compromising the inherent strength of the rock mass surrounding the tunnel.
• - Contractual arrangements: since the NATM is based on monitoring measurements, changes to the support and construction method are possible, but only if the contractual system allows it.
• - The classification of rock masses, ranging from very hard to very soft, determines the minimum support measures required and avoids the economic waste that comes from unnecessarily strong support measures. There are support system designs for each of the major rock classes. These serve as the guidelines for tunnel reinforcement.