In this study, biaxial compression tests were carried out with three plug shapes to figure out the mechanical behavior of rock-plug structure. From the results of this test, It is verified that the mechanical behavior of rock-plug structure is dependent upon the plug shape and applied stress condition, and the failure characteristics of its structure is affected by in-situ stress condition. Also, the two-dimensional numerical analysis was carried out to examine the performance of a concrete plug in underground storage cavern. When the plug was installed at a great depth, where was a tendency for the plug to be more stable with increasing in-situ stress ratio (K). The results of analysis considering the interface elements at plug-rock contact indicated that the lower asymmetric shaped plug with smooth contact condition was more stable than the symmetric or upper asymmetric shaped plug..
In construction of an underground storage cavern for crude oil, LPG, LNG, compressed air and so on, a concrete plug is mainly installed in an access tunnel or a shaft that connects the underground cavern and the ground surface after completion of the excavation and installation of facilities.
The plug prevents the stored product from leakage and the excessive inflow of underground water, so it plays an important role in construction and operation of the storage cavern. Once the plug is constructed, the cavern is isolated from the external access. And the success or failure of its function determines the technical and economical capacity of overall storage facility. Therefore, it is very important to examine the mechanical behavior of structure combined by rock mass and plug for the determination of its shape and thickness which provides the cost-saving, safety and tightness of plug structure during design and construction of storage cavern.
Most of plugs within underground storage facility have shaped like not a parallel shape but a two-cone shape excavated toward surrounding rock mass with a specific depth. According to the length ratio of upper and lower Cone in two-cone shape, it could be classified into three types: upper axi-symmetric(US; when the part of upper cone is longer), symmetric(SS) and lower axi-symmetric(LS; when the part of lower cone is longer) type. Although the plugs installed within underground oil storage facility in Korea are mainly SS and US type, there has been little research on its mechanical behavior according to plug type.
In this study, biaxial compression tests were carried out to examine the mechanical behavior of rock-plug structure with regard to three types of plug shape, wedge depth and various stress conditions. Also, we conducted numerical analyses on the mechanical behavior of the plug to find optimal shape and thickness of the plug with respect to the installation depth and the condition of rock-plug interface.
The specimens for biaxial compression test were molded as three types such as US, SS and LS which are 260 mm in width, 260 mm in height, and 60 mm in thickness.