Determination of Minimum Intermediary Hold Durations in Multistage First-Filling Schedule of Earth-Fill Dam Reservoirs

Abstract

Earth-fill dams should be monitored during the first filling of the reservoir to avoid several potential risks. Following the completion of dam construction, the primary safety check is monitoring the dam behavior during the first interaction of the earth material with water. The presented work fills the gap in the literature on the determination of intermediary hold durations of multistage filling schedule and provides insights into the first-filling process. The study investigated the behavior of a 20 m high earth-fill dam model subjected to staged reservoir filling. The durations of the intermediary holds were determined based on coupled stress and pore water pressure analyses using the finite-element method, with a particular emphasis on the transient behavior of the filling process. Hydraulic fracturing and internal erosion possibilities were evaluated based on minimum principal stress and seepage quantities at critical sections. It was observed that the minimum principal stress reaches a local minimum and tends to increase, leading to significant convergence for longer hold alternatives. In addition, seepage quantities exhibited similar behavior of decreasing with longer hold durations. A specific hold duration was recommended for the low-pool level, which resulted in a hold-to-height ratio of 2.35. At the high-pool level, it was found that further waiting has a positive effect in mitigating the risk of hydraulic fracturing and internal erosion initiation. The presented practical methodology is proposed to be used for the design of filling schedules of new dams. This study provides practical insights for design engineers to determine the first-filling schedule of earth-fill dams. The stress–pore pressure coupled finite-element model information obtained from this study can be helpful for onsite engineers who have access to instrumentation data during the first filling. These data can be used to predict the convergence of key parameters. For intermediary holds at low-pool levels, monitoring minimum principal stress and effective stress behavior over time is crucial to prevent cracking which can lead to hydraulic fracturing if filling continues. Specifically, the initially decreasing principal stress at the upstream face of the core should be closely monitored until an increasing trend is observed, to ensure that sufficient time is allowed before the dam is subjected to higher loads.