Large diameter shafts in fractured strata: Equipment and construction procedures

This paper promotes the smooth construction of large diameter shafts in fractured strata adjacent to structures by describing a novel technique that combines the use of a shaft boring extension machine (SBEM) with traditional construction methods, including details of both equipment and construction procedures. The specific construction scheme consists of several key steps: launching shaft construction, primary pilot shaft drilling, secondary pilot shaft enlargement excavation with an SBEM, and localized static blasting expansion construction for the outlet shaft. The feasibility of this approach is evaluated through a series of construction effect evaluations. The results indicate that all in situ monitoring items met the relevant requirements, and the scheme had a minimal impact on the adjacent structures and surrounding environment. Furthermore, the scheme reduced construction time by 20.5% compared to the originally planned combination scheme using an RBM and blasting and by 34.0% when excluding the equipment maintenance time. The findings provide fundamental guidance for shaft construction using an SBEM in fractured rock masses.