ABSTRACT
An optimized tunnel support design is one which is robust, efficient and satisfies constructability requirements. For a mined tunnel, it is often not economical to have one support type for all expected ground conditions. However, there may be situations where a prescriptive approach is economical and appropriate.When considering how many support types to provide, the main influencers are: ground conditions, the presence and existing structures, stakeholder requirements, construction and design methodology and whether the primary lining is considered permanent in the design (either fully intact or degraded to a defined level during the design life). This paper presents two examples to illustrate approaches from two different projects, with an explanation as to why this was appropriate for each.The paper concludes with a discussion on when it is appropriate to use the prescriptive approach or the ‘Support Type Selection’ approach with some guidelines which will be of benefit to practitioners.
