Abstract
Q-system is a preferred alternative method of rock mass classification for underground oil storage caverns where stable lithological rocks are widely distributed. In this paper, correspondences between important input rock mechanics parameters (friction angle, cohesion, tensile strength, Poisson’s ratio, deformation modulus) and Q values were investigated, thereby bringing convenient to rapidly obtain available parameters when it’s hard to collect measured field data in underground storage projects basically with similar lithology. The proposed correlations were verified through numerical simulation and on-site monitoring measurement. In addition, comparison of different criteria among Q-system and other codes for rock mass classification has been made to help for making a preliminary evaluation of rock mass quality in the practical engineering. Finally, the behaviours of surrounding rock deformations under different Q values were analysed by using FLAC3D code with the calculating parameters suggested in this paper, and the calculation results match well with measured values in situ. Above results will not only guide the construction but also could be relevant to other underground storage engineering under similar geological conditions.
Highlights
At present, water sealed underground petroleum storage caverns in rock is the main way used for strategic petroleum reserve
Based on fitted empirical equations for estimation of rock mass modulus summarized by Hoek [25], we tried to correlate deformation modulus with Rock Mass Rating (RMR) values (Q and RMR systems are based on very similar properties [20]), when we found it’s hard to make a direct way to connect deformation modulus with Q values
Correlations between friction angle, cohesion, tensile strength, deformation modulus, Poisson’s ratio and Q were suggested by means of regression method with different mathematic models, thereby rapidly obtaining available parameters when it’s hard to obtain the measured field data, which were recommended to use in underground storage projects basically with similar lithology
Summary
Water sealed underground petroleum storage caverns in rock is the main way used for strategic petroleum reserve. Correlations between different rock mass classification systems and Q-system, especially RMR system [16,17,18,19,20], some have concentrated on improving [15] and correcting misuse [21] of Q-system, while there have been few studies with regard to the relationships of Q values with general rock mechanics parameters. While there is few study on relationships among Q values and friction angles, cohesion, tensile strength, Poisson’s ratio, deformation modulus, which are very useful for initial estimation when field parameters are hard to acquire in underground storage projects. This paper aims to investigate the correspondences between Q values and general rock mechanics parameters (friction angles, cohesion, tensile strength, Poisson’s ratio, deformation modulus), to find some correlations which can be used in underground storage projects basically with similar lithology
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