Excavation cycle times recorded during sinking of a deep shaft in crystalline rock – A case example at Ventilation Shaft of Mizunami URL, Japan

Abstract

Realistic and properly planned excavation cycle times developed prior to tunnel construction are an important issue for dependable project management, including cost estimation and time saving. Existing design studies, conducted to estimate the total cost for geological disposal, have been limited to estimates of approximate construction total time schedules. There were no case studies which compared the detailed excavation cycle time used in design studies with the actual results from an excavation taking into account each excavation cycle operation and task. In this paper, analyses of actual cycle time recorded during the sinking of the Ventilation Shaft of the Mizunami Underground Research Laboratory and comparison with the planned cycle time developed in the design stage are intended for an evaluation of the baseline work plan and schedule and for optimization of the calculations for application to shaft construction in any future repository in Japan. Actual times to perform three operations, drill and blast, muck removal and concrete lining emplacement were much larger than expected and represent the largest portion of the total excavation cycle time and had the largest impact on the efficiency of the excavation cycles and schedules. Operating at increasingly greater depths and excavating harder, more competent rock combined to significantly affect the shaft sinking speed. The underlying reasons for increases in actual times for the excavation cycle operations compared to their design estimates fall into three categories: constraints on construction; to ensure safety; and maintenance.