Abstract:

In the area of deep soft soil, there are a large number of deep foundation pits conforming to the following characteristics: (1) insertion ratio of retaining wall is between 1:2.0 and 1:2.2; (2) excavation process goes smoothly; (3) basal heave stability does not meet the requirements of relevant standards. In order to reduce the inconsistency between theory and practice, based on the calculation formula of the existed foundation bearing capacity model, a basal heave stability analysis method for foundation pit considering soil stress state and shear capacity was developed by introducing the virtual foundation width. The critical width was defined as the virtual foundation width with the minimal basal heave stability in mathematics. In addition to the critical width, the width of the foundation pit and the thickness of the soft soil layer should also be considered in the selection of the virtual foundation width. A completed engineering example was given to compare the basal heave stabilities of the existed different analysis methods, and to analyze the influence of soft soil layer structure and internal friction angle on stability. The analysis results were closer to the actual situation, and showed that the influence of soil shear capacity was limited when the critical width was used as the virtual foundation width.

Key words: basal heave stability, deep excavation, soft clay, virtual foundation width, bearing capacity, foundation pit width