Abstract

Japan Oil, Gas and Metal National Corporation has constructed one of the world's largest hydraulic containment type LPG storage caverns in Kurashiki, Japan and have launched the operation in March, 2013 to provides 400,000 tons stockpile capacity. Compared with conventional caverns for traffic tunnels and hydraulic power stations, the construction of hydraulic containment type storage caverns should maintain the hydraulic potential during excavation. Therefore, the authors have applied a new observational construction method to control the hydraulic behaviors during the cavern excavation.

In this study, concerning the hydrogeological characteristics of Kurashiki site, the authors design the artificial water curtain system and grouting works surrounding the cavern wall as two countermeasures for hydraulic behaviors control. For the water curtain system, the authors designed the vertical/horizontal boreholes to enclose the storage caverns and applied high water pressure from boreholes prior to the cavern excavation. Meanwhile, the authors designed 10m thick grouting zone surrounding the cavern wall and conducted in-field grouting tests to decide the proper grouting methods for better grouting efficiency.

For the purpose on hydraulic behaviors control, the authors applied the 3-dimensional groundwater simulation model to estimate the hydraulic behaviors (e.g. pore-pressure dropping, seepage) while excavation and compared with the monitoring data for evaluation. The evaluation results were applied for deciding the necessity of additional water curtain boreholes and grouting works. Further, in order to evaluate the hydraulic behaviors with high precision, the authors established and upgraded the 3-dimensional groundwater simulation model based on investigated and measured permeability data derived in excavation. After the construction was completed, the storage caverns were taken into the acceptance test obligated by High Pressure Gas Safety Act. As the result, the air-tightness of the storage caverns and the hydraulic containment ability of the water curtain system have been verified.

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