Optimisation of Temporary Works in Tunnelling – Key Lessons Learned Over the Past 15 Years in New Zealand

Abstract

Abstracts should be limited to 250 words maximum. Temporary works play a critical role in the success of tunnelling projects and can often be the deciding factor for contractors in winning or losing contracts. However, their importance is frequently underestimated by clients during project commissioning. This paper shares insights of the author’s 15 years of experience designing temporary works for various tunnelling projects across New Zealand. It illustrates how advances in the understanding of soil-structure interaction— particularly as it relates to temporary works—have led to significant design optimisations, informed by onsite observations from completed projects. Key considerations for Clients and Contractors are discussed, including the establishment of realistic baseline conditions, the structuring of project consent requirements, the benefits of including provisional sum items for critical temporary works in tender documentation, as well as, how the integration of temporary and permanent works can result in substantial overall reduction in carbon. The paper also offers insights for Designers, emphasizing the importance of accounting for transient groundwater conditions, stress rotation and soil arching effects in shaft designs, and the influence of tensile strength and suction forces in various geological formations. Finally, it explores the application of the recently published Temporary Works Procedural Controls (Ref.1) and its relevance to tunnelling projects. No-Dig Down Under 2025 1 Optimisation of Temporary Works in Tunnelling Andy O’Sullivan