Abstract: Storing oil in large underground caverns by water sealed is an important way of strategic oil reserve in the world. It needs to optimize the layout of caverns for the stability of such a large-scale unlined underground cavern. Based on the analysis of the engineering geological characteristic of an underground project in Shandong province, the numerical model was established. And the mechanical parameters of rock mass were estimated by the generalized Heok-Brown failure criterion with the integration of rock sample triaxial test and rock mass classification of rock mass rating (RMR) system. Choosing the depth, axial direction and space as factors, and calculated the displacement of the caverns by the FLAC3D code in different schemes, determined by the orthogonal design. The visual analysis of the results of the evaluating index, key point displacement and plastic zone area was done. The axial direction is the significant factor, and the influence on the stability was studied separately. The optimized layout of the underground caverns is that the depth is -60.0 m, axial direction is N30°W and space is 25 m. It has some values for the layout of the underground oil storage caverns.

Key words: water sealed underground oil storage caverns, caverns optimization, orthogonal design, generalized Hoek-Brown failure criterion