上软下硬复合地层条件下深基坑支护设计探析

近年来,常出现在深基坑开挖支护中的吊脚桩存在一定的安全隐患。为此,以青岛地铁某长条形基坑为载体,对上软下硬地质条件下遇到的吊脚桩问题展开研究。首先,根据地质条件及周边工程概况,给出基坑开挖及支护思路和方案;然后,结合支护方案采用弹性抗力法和等效被动土压力法分别对上部桩撑(锚)体系和下部岩石边坡稳定性进行分析计算。实际应用结果表明:1)青岛地区上部土层适合采用桩+支撑,下部岩石边坡采用锚喷支护的组合支护方案;2)直壁开挖的岩石边坡中,微型钢管桩具有超前支护、预裂及减振作用;3)推荐算法适合于吊脚桩支护体系的设计。

Design of Support of Deep Foundation Pits in Hard-soft Heterogeneous Ground

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 practiee shows that： 1 ） In Qingdao, the ＂pile-strut ＂ support system is suitable fbr 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.