Abstract
Japan Oil, Gas and Metals National Corporation (JOGMEC) has constructed the world’s largest hydraulic containment type underground LPG storage caverns in Kurashiki from 2002. The construction was completed and the operation was launched at 2013.For the hydraulic containment type underground LPG storage caverns, despite seepage rate is control in the cavern excavation stage, the stable water pressure is also demanded to ensure the air-tightness of storage cavern. Therefore, the authors have designed the water curtain system to enclose the storage cavern to provide artificial water pressure continuously and also have applied grouting works at the cavern vicinity to reduce the seepage. Considering the rock mechanical stability at the fractured zone in the cavern vicinity, the authors have applied pre-grout prior to the cavern excavation to derive better efficiency by high grouting pressure.After the grouted zone was excavated, the authors measured the seepage and surrounding pore pressure to evaluate the efficiency of water curtain and the ground improvement. The derived geological and hydrogeological data are also applied on the following excavation stages to determine the construction method and the improvement criterion for pre-grout based on the observational construction method. After excavation was completed, the authors have compared the measured seepage and pore pressure with estimated values. If the seepage or pore pressure is unsatisfactory with the criterion, we applied post-grout as countermeasure.Finally, we compressed the water curtain system and evaluate the water curtain efficiency from groundwater behaviors.
