岩溶地区基坑支护灌注桩嵌固深度影响研究

Study on the Influence of Embedded Depth of Cast-in-place Pile for Foundation Pit Support in Karst Area

岩溶地区地质条件复杂多变,基坑支护设计难度较大,为确保岩溶基坑工程安全稳定,以岩溶地区某基坑支护工程实例,针对岩溶面起伏较大,且基岩面通常存在厚薄不均的软弱上覆土层的地质条件特点,通过理正深基坑软件计算对比分析,研究了不同支护型式下的支护灌注桩嵌固深度及桩底嵌岩深度要求,得出了存在软弱上覆土层的岩溶地区支护灌注桩嵌固深度及嵌岩深度的控制标准:对悬臂灌注桩支护,桩基嵌固长度应按最小桩长及嵌岩深度进行双控,桩基嵌岩长度约(2.5~3.0)倍桩径范围;对单支点灌注桩支护,在满足规范最小桩长时,桩基嵌岩长度约(0.33~0.625)倍桩径范围。因此,在岩溶地区施工基坑,当周边环境允许锚索施工时,宜优选灌注桩+锚索的支护型式,减少灌注桩的嵌固长度及嵌岩深度,避免支护桩触碰深层溶洞,降低灌注桩嵌岩施工难度及工程成本。

Geological conditions in karst area are complex and changeable,where the design of foundation pit support is difficult.In view of the geological conditions of large fluctuation of karst surface and uneven thickness of weak overlying soil layer on bedrock surface,the requirements of embedment depth and rock-bottom embedment depth of cast-in-place pile under different supporting types are analyzed through Lizheng deep foundation pit software calculation in this paper,which taking a foundation pit support project in karst area as an ex‐ample in order to ensure the safety and stability.The control standards of embedment depth and rock embedment depth of supporting cast-in-place pile in karst area with soft overlying soil layer are obtained:For cantilever support,the embedded length of pile foundation shall be controlled by the minimum pile length and rock socketed depth.The rock socketed length of pile foundation is about(2.5~3.0)times the pile diameter.For single support,the rock socketed length of the pile foundation is about(0.33~0.625)times of the pile diameter when the minimum pile length meets the specification.Therefore,when the surrounding environment allows the anchor cable construction,the pile an‐chor support should be optimized in karst foundation pit.Reduced the embedded length and rock socketed depth of the pile.Avoided the sup‐port pile touching the deep karst cave,and reduced the construction difficulty and project cost.