Abstract
Tunnels excavated by the New Austrian Tunnelling Method (NATM) are traditionally supported by a double-shell lining. The primary lining is generated from reinforced sprayed concrete with rockbolts, the secondary lining is generated from in-situ cast concrete and it is protected by a waterproof membrane. The static evaluation of the long term behaviour generally assumes full degradation of the primary lining (the primary lining impact is not considered). Some investigations of tunnels constructed in past indicated that the primary lining degradation is slower than expected. This paper discusses possibilities of partly damaged primary lining consideration in static calculations of the secondary lining. Various options were verified by numerical modelling, and its results were compared and discussed.
Highlights
Tunnels excavated by the New Austrian Tunnelling Method (NATM) are traditionally supported by double-shell lining [1]
The primary lining is generated from reinforced sprayed concrete with rockbolts, the secondary lining is generated from in-situ cast concrete and it is protected by a waterproof membrane [2]
Designers only assume that the primary lining can be damaged during a tunnel lifetime and the primary lining is not considered during the secondary lining evaluation
Summary
Tunnels excavated by the New Austrian Tunnelling Method (NATM) are traditionally supported by double-shell lining [1]. The primary lining is generated from reinforced sprayed concrete with rockbolts, the secondary lining is generated from in-situ cast concrete and it is protected by a waterproof membrane [2]. The full degradation of the primary lining is normally considered during the secondary lining design and evaluation [1, 2], this approach is assumed to be reasonably conservative. The use of spray-applied waterproofing membranes [3, 4] is an associated topic, as it offers to use the primary lining for a permanent purpose. The spray-applied waterproofing membranes bond to the substrate and structurally connect the primary and the secondary lining, resulting in the so-called composite lining, which can bring a lining thickness reduction due to the primary lining contribution. It would indicate a possibility to consider partly decomposed primary lining for the secondary lining evaluation.
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