Mechanical analysis of circular liners with particular reference to composite supports. For example, liners consisting of shotcrete and steel sets

This paper describes a methodology for the mechanical analysis of composite supports, such as liners consisting of shotcrete and steel sets. The methodology presented here is based on an established technique of structural analysis commonly referred to as the 'equivalent section' approach. This technique consists in treating the composite section of a straight beam as a homogenized section of equivalent mechanical properties. The equations presented in this paper have been derived from application of the theory of elastic shells (or curved beams) and therefore are more appropriate for the analysis of circular tunnel liners. The proposed methodology for the design of liners is based on the construction of capacity diagrams, another established technique of structural analysis and concrete design that can be conveniently extended to the analysis of composite sections for tunnel liners. When applying the theory of elastic shells to derive the equations that conform to the proposed methodology, the problem of determining the mechanical response of semi-circular arches treated with the theory of thin and thick formulations has been re-visited. Observations of practical interest arising from the comparison of results obtained with both approaches are discussed.