Loads condition on underground powerhouses operated in decades could be varied due to agerelated degradation of support members and surrounding rock, and underground water condition. It brings essential concern on the soundness of the underground caverns. This paper shows an application of the continuous management method to an underground powerhouse which have been operated for about five decades and found some broken anchors. For the re-evaluation of the cavern stability, additional monitoring, stress measurement of RC beam and numerical study were conducted. The future behaviors of the cavern subject to probable risk scenarios are studied by using a simple numerical model. Comparing the results to the limit state of the structure forming the cavern, management criteria are established in line with the current state of the cavern. Finally, these studies are summarized and discussed with a view to continuous management of the cavern for existing underground powerhouses.


Since the 1940s, more than fifty underground caverns for hydropower plants have been constructed in Japan, almost all of which have been operated for the past few decades. Monitoring the deformation of the caverns and surrounding rock, as well as the forces acting on the supports, is vital to confirm the soundness of these caverns during the construction. Because the caverns are not deemed to be exposed to any additional forces, since they also incorporate reinforced concrete as inner supports, concerns over cavern stability rarely emerge after the completion of the construction.

In those one during the operation for forty-six years, several rock anchors were broken, and the stability of the cavern should be re-evaluated. For this purpose, additional monitoring and numerical study were conducted. This paper summarizes field measurement results and their interpretation, and proposes a continuous method for the stability evolution of caverns for underground powerhouses under operation.

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