Abstract: Numerical model based on project example was established to analyze the influence of pit-in-pit on the stability of foundation pit. The influence of excavation depth, slope angle and width of platform on the displacement of pile top was analyzed. Results showed that with the increase of excavation depth and slope angle and the reduce of platform width, the displacement of support pile tended to increase. In the presence of different platform widths and excavation slope angles, a critical excavation depth existed; and when the excavation depth was determined, a critical platform width existed. With the increase of area ratio, the displacement of supporting pile decreased gradually, and while the area ratio reached a certain value, the displacement of pile no longer decreased. It is concluded that as long as the width of platform is enough, the pit-in-pit has almost no effect on the stability of foundation pit. Analysis results can be referenced for stability design of pit-in-pit in similiar projects.

Key words: foundation pit, pit-in-pit, excavation platform, critical depth, area ratio