Abstract: At present the theoretical calculation of the stope floor failure depth simplifies the floor as elastomer or plastomer for analysis. However, the application conditions for the two methods are not specified. Meanwhile, this calculation approach cannot reflect the layered structure of the stope floor. Therefore, the limit equilibrium failure mode of the floor under abutment pressure is regarded as a circular-arc sliding. The Swedish slice method is used to search for dangerous sliding surfaces and to obtain the stability coefficient as well as the maximum depth of the sliding surface. Based on the safety factor value given by the foundation design code, the homogeneous soft and hard rock floor is taken as an example for comparisons to be made between the calculation results with existing theoretical solutions and elastic-plastic numerical solutions. The article discusses the influence of several factors, such as slab combining soft and hard rocks and strata inclination on the base slab stability coefficient and sliding thickness. The research shows that the hard rock floor mainly experiences local plastic failure, and generally demonstrates high stability coefficient. Therefore, it can be solved with the elastic solution. The soft rock floor has large plastic zone, and can even involve plastic sliding phenomenon, it requires the use of limit equilibrium method to reduce errors. In slab combining soft and hard rock, when the thickness of the hard rock reaches a certain value, the base slab stability coefficient will be greatly increased and the plastic zone in the floor will be controlled. In the top region of the coal face, the floor with high dip angle can easily experience shallow sliding failure while the lower part undergoes opposite act. The application example shows that the circular sliding solution considers the non-uniformity of the strength parameters of layered floor and the floor’s failure mode, which is more consistent with the actual situation.

Key words: floor failure, layered rock mass, mining stability, circular sliding