The hydraulic fracturing technology is adopted to define in-situ stresses in a region where underground water-sealed oil storage will be built. The measurement result shows that the maximum horizontal principal stress is approximately 10.0 MPa and the minimum horizontal principal stress is about 6.0 MPa at the cavern burial depth. The possibility of rock burst is analyzed with the Project Rock Mass Classification Criterion (GB50218–94), Norway Barton criterion, Hou Faliang criterion and Hoek criterion. The results indicate that the rock burst will not happen due to the underground excavation disturbance. However, such a conclusion is only based on experiences, which needs further validation. Because the analytic solution of induced stresses around the cavern complex cannot be obtained, and it is difficult to judge the possibility of rock burst during the excavation precisely, the FLAC2D software is used to simulate the excavation process and to obtain the characteristics of redistributed stresses. According to the corrected Barton rule and the characteristics of redistributed stress, the analytic result indicates that the possible medium rock burst phenomenon may happen in some region where extreme stress concentration occurs. It also indicates that the typical rock burst criterion is fit for the whole cavern well but has some errors locally in judging rock burst possibility.
Underground water-sealed oil storage cavern is a crude cavern which is built in intact rock mass at definite depth. "Water-sealed" means that oil overflowing paths are obturated by the underground water in the surrounding rock mass or the artificial water screens. Since underground water-sealed oil storage cavern has good obturation and stableness, it requires much better engineering geological and hydro-geological conditions. The requirement of rock condition is intact-lightly weathered crystal rock mass. Structure conditions are that faults and folds do not exits and joints and fissures are not present or present moderately [1]. By the water-sealed requirement, underground cavern always locates in intact-brittleness granite which is largely below sea level, with long axis, large span and multiple single caverns. For much elastic strain energy releases instantly during the excavating course, the rock burst easily happen. Hence, using actual measurement data to analyze the rock burst possibility is of an important practical significance. After R. S. Lieurace (American)[2] had measured the original rock stress successfully in a tunnel cavern under Hoover Dam in 1932, experts have used in-situ stress data from different stress measurements to study rock burst possibility in excavating underground cavern, and have created multiplicate criterions. These criterions are:
Project Rock Mass Classification criterion [3];
Norway Barton criterion [4];
Hou Fa-Liang criterion [5];
Hoek criterion [6] and so on. Most of above are summarized via lots of practices and have preferable practicability. Considering the watersealed oil storage cavern's large span, high wall and multi-cavern characteristics, in the paper, we study the rock burst possibility during excavating underground cavern via combining above four criterions using the in-situ stress measure data.
