Abstract:

Recently suspended piles always exist in deep foundation pits, which could cause potential safety risks. In this paper, the “suspended piles” of a stripshaped foundation pit of Qingdao Metro located in hardsoft heterogeneous ground is studied. First, excavation and support scheme is proposed for the project on basis of the geological conditions and the surrounding environment; Secondly, the stability of the upper pilestrut bracing system and the lower rock slope of the foundation pit is analyzed by means of elastic resistance method and equivalent passive earth pressure method. The practice shows that: 1) In Qingdao, the “pilestrut ” support system is suitable for the upper soil strata, and the bolting and shotcreting support system is suitable for the lower rock slope; 2) The micro steel pipe piles adopted in the cutting of the vertical rock slopes of the foundation pit play the role of advance support, presplitting and vibration reduction; 3) The calculation method proposed is suitable for the design of the suspended pile support system. 

Key words: foundation pit in soilrock ground, suspended pile, foundation pit support, micro steel pipe pile, pilestrut bracing system