In the original version of the New Austrian Tunneling Method, it is a tunneling concept with a set of main principles as follows:
(i) Application of thin-spayed concrete lining
(ii) Closure at invert to form a complete ring as soon as possible
(iii) Measurement of deformation until equilibrium is attained
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It is a design concept in which the ground (soil or rock) enclosing the opening becomes a load-bearing element through formation of ring-like body. It uses all available means to develop maximum self-supporting capacity to provide support of the underground opening. In essence, it makes use of geological stress of surrounding soils to stabilize the opening. Therefore, NATM is a tunneling philosophy and concept rather than excavation techniques.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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