Abstract: In this study, a block instability risk assessment method based on catastrophe theory is proposed to tackle the difficulty of block failure risk assessment of underground caverns under complex geological conditions. Firstly, the finite element mesh modeling technology and the method of element reconstruction-aggregation technique are used to identify the rock blocks around the complex caverns. Then the influencing factors of block instability and failure are analyzed, starting from two aspects of internal and external factors of block with 6 elements, including the development trend, spatial location, structural block property, external load, structural surface characteristics and environmental factors. Eleven factors are selected as the underlying evaluation index, on which the mutation model of block instability risk assessment is constructed. After that, the normalized formula is used to seek the solution of the mutation state variables layer by layer, and the membership degree of the obtained total mutation series is converted to improve its clustering and finally the risk state of the block is determined. The analytical results of engineering example show that the method is simple in calculation and high in reliability. It allows comprehensive consideration for the influence of various factors on block stability and avoids the limitations of rigid body limit equilibrium method. The law revealed from the calculation results is basically consistent with the known law, which better reflects the real occurrence state of cavern block. It provides a new way for risk assessment of cavern block under complex geological conditions.

Key words: underground cavern, rock block, catastrophe progression method, risk assessment, index system