基于小应变特性的基坑开挖对邻近桩基影响分析方法
Small-strain behavior-based method for eflect of excavations on adjacent pile foundations
-
摘要: 越来越多的基坑紧邻既有建筑开挖,需要评估基坑开挖对邻近建筑的影响,因此基于变形控制的基坑设计已经成了必然要求。目前仍缺乏有效简单的方法去估算基坑开挖对邻近建筑的影响,特别是采用桩基础的建筑。而且当进行变形控制设计时,要求基坑变形控制在较小的范围内,此时基坑周边土体处在小应变范围内,要建立基坑开挖对周边建筑影响的分析方法必须考虑土体小应变特性。首先采用基于小应变特性计算基坑开挖引起的深层土体位移的经验计算公式计算基坑开挖引起的自由场土体三维位移,然后基于差分方法提出了基坑开挖对邻近桩基竖向和水平向影响的两阶段分析方法。通过与有限元结果的对比,验证了本方法的正确性。并分析了基坑开挖深度和桩基离基坑距离这两个因素对邻近桩基的响应的影响。研究表明开挖深度越小对桩基影响越小,基于桩基内力控制时,基坑开挖深度应避开桩底位置,且桩基在距离基坑0.5倍开挖深度距离时最为危险。Abstract: Estimating the damage potential on buildings induced by excavations is required because more and more foundation pits are excavated near the existing buildings. Thus, displacement control becomes a critical index of excavation design. Unfortunately, there is nearly no simplified method that can estimate the influence of excavation on the existing buildings and easy to be used. Small-strain behavior of soils should be considered when establishing method to estimate influence of excavation on the adjacent buildings for the strain of the soils is very small under displacement control design. In order to fit the requirement for the simplified method to estimate the influence on excavation on the existing buildings supported by pile foundation, a two-stage method is proposed herein to estimate the responses of piles adjacent to the excavation. Firstly, the empirical method based on small-strain behavior of soils proposed by Mu and Huang is employed to calculate the three-dimensional soil displacement induced by excavation. Then, a two-stage method is proposed to calculate the vertical and horizontal pile responses in layered soils. The method is verified through comparison with the results from FEM. And the influences of excavation depth and the distance between pile and retaining on pile responses are analyzed. The study shows that the additional force and deformation of piles increase with the increase of excavation depth, and the excavation base should avoid the base of the pile. It is most dangerous when the pile is 0.5H from the retaining wall.