Abstract: The circular sliding method is one of the most important methods for calculating safety factor of heave-resistant stability in China. Most commonly, the traditional methods assume the position of center of the slip arc are placed at the intersection of the bottom support and retaining wall, which means the support system will not be destroyed and the calculated result is obviously insecure. To solve this problem, the center of slip arc is not fixed in this paper. Through several calculations, the minimum safety value is adopted as the final safety factor of heave-resistant stability. Besides, a new method which considering the width of the foundation pit is also proposed in this paper. The analysis of the example shows that the center of slip arc may be located at the bottom support or above the bottom support for the insertion type of traditional subway foundation pit. It shows the stability of the support system has a significant impact on the safety factor. When the ultimate axial support force is large enough, the new method can be turned into the traditional circular slip method. Further analysis shows that the ultimate center of the slip arc is located inside of foundation pits. The proposed method is an important improvement to the traditional circular slip method, which is suitable for design and construction of foundation pit.

Key words: foundation pit, heave-resistant stability, circular slip center, insertion ratio, excavation width