Agapito Associates, Inc. (Agapito) conducted a variety of design and project management tasks for PBESS related to the design and construction of a large underground gas storage complex on mainland China, southwest of Hong Kong. Located near the city of Zhuhai, Guangdong Province, the facility includes two storage caverns, one for butane and one for propane, each having a volume of approximately 7 million cubic feet (ft3) (1.25 million barrels). The caverns consist of multiple galleries that are approximately 650 ft long, 65 ft high, and 60 ft wide. The butane cavern has a minimum cover depth of 330 ft, and owing to the higher vapor pressure, the propane cavern is located at twice that depth. Because the caverns are constructed in permeable host rock (fractured granite), a water curtain system is used to ensure that hydrostatic pressure within the fractured rock exceeds the pressure of the Liquid Petroleum Gas (LPG) products, providing a pressure barrier for product containment. Construction access was via a decline, while operation access is via shafts. The facility was constructed to replace ship-based offshore gas storage, which the Chinese government required to be eliminated due to safety concerns.
During the design phase, Agapito developed rock mass classification procedures, evaluated cavern shape alternatives, and developed ground support requirements for varying ground conditions. Numerical modeling was used for the geotechnical analyses, including confirmation of cavern stability, and the stability of access ramps, water curtain galleries, and the intervening pillars. Agapito played a key role in the design process by providing advice to PBESS regarding excavation and support practices specified by the owner, and evaluating the viability of detailed construction plans. Throughout the construction phase, Agapito provided on-site inspections to observe construction practices and verify that proper excavation and ground support methods were employed. Agapito monitored changing ground conditions and developed site-specific support plan modifications as needed during construction. Agapito’s involvement spanned about 3 years, from 2004 to cavern commissioning in 2007.