黏弹性地基中基坑开挖对邻近桩基变形影响的时域解

Time-domain solution for influence of excavation on adjacent pile deformation in visco-elastic foundation

目前就软土基坑开挖卸荷对邻近桩基变形影响的研究一般是基于瞬时开挖工况,很少考虑时间效应对桩-土相互作用的影响,但实际工程中软土在开挖情况下具有较为明显的流变效应。从地基黏弹性角度出发,采用两阶段法研究了黏弹性地基中基坑开挖与邻近桩基相互作用的时域问题。第1阶段基于Boltzmann黏弹性模型推导出Mindlin时域解,用于分析黏弹性地基中基坑开挖引起的邻近桩基处的土体附加应力;第2阶段采用Pasternak地基模型分析桩基与黏弹性土体之间的相互作用,并求得考虑流变效应的桩基水平变形的简化时域解。最后,采用大型有限差分软件对相关工况进行数值模拟,并将数值模拟结果与简化时域解进行对比分析,得到了较好的一致性。此外,也针对Boltzmann黏弹性模型参数(体积模量、剪切模量、黏性系数)、桩径、基坑开挖深度、桩与基坑间距和基坑开挖尺寸进行了影响因素分析。分析结果表明,所得出的简化时域解能较好地反映基坑开挖对邻近桩基水平变形的影响,以及桩基变形随时间的发展趋势,可为相关实际工程提供一定理论依据。

At present, the studies of adjacent pile deformation caused by foundation excavation in transient case are common. Less attention has been paid to the influences of time behavior on the pile-soils interaction. The disturbed soils show the rheological properties during excavation. A two-stage method considering the soil visco-elasticity is proposed to obtain the time-domain solution for the interaction between adjacent pile and foundation pit excavation. On the first stage, based on Boltzmann visco-elastic model, a Mindlin＇s time-domain solution is derived to analyze the influence of excavation on soil additional stress at the position of adjacent pile in visco-elastic foundation. On the second stage, a Pasternak＇s two-parameter foundation model is adopted to simulate the interaction between pile and soils. A simplified time-domain solution of pile horizontal deformation is derived in consideration of rheological effects. Finally, the simulation results from finite difference software are compared to simplified time-domain solution with good agreements. The parameters of Boltzmann visco-elastic model（bulk modulus, shear modulus, viscosity coefficient）, pile diameter, excavation depth, distance between pile and foundation pit and excavation size are analyzed to investigate the influences on pile deformation. It is shown that the presented simplified time-domain solution can reflect the influence of excavation on adjacent pile deformation and the development trend of pile deformation with time. It may provide certain theoretical basis for practical projects.