二元结构岩土基坑“吊脚桩”支护设计数值分析

在山地丘陵地区，上层是土体、下层是岩体的岩土二元结构基坑非常普遍。针对此类基坑支护中常用到的“吊脚桩”的设计和施工特点进行有限元数值模拟与分析，研究了其设计方法及其安全稳定性、桩体嵌岩深度、桩脚处锚杆轴力和预留岩肩宽度等各种影响因素。分析结果表明：此类基坑设计对上层土体按传统设计计算方法进行设计施工时能够保证上层土体开挖基坑的稳定性；增加嵌岩深度或增大桩脚处锚杆预应力都能有效地控制下层岩体开挖时基坑的稳定和变形，锚杆预应力为主要控制因素，施工中要注意对其轴力进行监测；预留岩肩宽度越大，支护桩位移越小，当该宽度大于某定值时，其变化对位移和弯矩的影响作用将不再明显。

Numerical Analysis on Design of Dualistic Foundation Pit with'End-Suspended Pile'

Foundation pits with dualistic structure of soil stratum and underlying rock stratum were commonly across Qingdao area. Aiming at the characteristics of "end-suspended pile", numerical simulation with Finite Element Method(FEM) and analysis was carried out to study the design methods and other influencing factors, such as stability, depth of the pile body, axial stress of anchor and width of reserved rock shoulder. It was shown that traditional design methods were applicable for the upper soil stratum,with the excavation stability guaranteed. The increase in embedded depth of pile body or axial stress of anchor led to effective control over excavation stability and deformation of the underlying rock stratum.And the axial stress was the main controlling factor, hence intense monitoring should be carried out on the stress during the course of construction. The larger the width of the rock shoulder was, the smaller the displacement of piles would be. When the width exceeded a certain value, its influences on the displacement and bending moment of piles tended to be insignificant.