Editing Tunnel (section)

=== Sprayed concrete techniques ===
The [[New Austrian tunneling method|new Austrian tunnelling method]] (NATM)—also referred to as the Sequential Excavation Method (SEM)<ref name=tbm20181205/>—was developed in the 1960s.
The main idea of this method is to use the geological [[stress (physics)|stress]] of the surrounding [[Rock (geology)|rock]] [[mass]] to stabilize the tunnel, by allowing a measured relaxation and stress reassignment into the surrounding rock to prevent full loads becoming imposed on the supports. Based on [[geotechnical]] measurements, an optimal [[cross section (geometry)|cross section]] is computed. The excavation is protected by a layer of sprayed concrete, commonly referred to as [[shotcrete]]. Other support measures can include steel arches, rock bolts, and mesh. Technological developments in sprayed concrete technology have resulted in steel and polypropylene fibers being added to the concrete mix to improve lining strength. This creates a natural load-bearing ring, which minimizes the rock's [[Deformation (mechanics)|deformation]].<ref name=tbm20181205/>

[[File:Hill 60 illowra battery port kembla.jpg|thumb|[[Illowra Battery]] utility tunnel, Port Kembla. One of many [[Template:Barracks Batteries Bunkers and Forts in Sydney|bunkers south of Sydney]].]]

By special [[Condition monitoring|monitoring]] the NATM method is flexible, even at surprising changes of the [[geomechanics|geomechanical]] rock consistency during the tunneling work. The measured rock properties lead to appropriate [[tool]]s for tunnel [[Strength of materials|strengthening]].<ref name="tbm20181205">
{{cite news |date=5 December 2018 |title=Understanding the New Austrian Tunnel Method (NATM) |url=https://tunnelingonline.com/understanding-the-new-austrian-tunnel-method-natm/ |access-date=27 December 2018 |work=Tunnel Business Magazine |publisher=Benjamin Media}}</ref>