Limiting cavity depth for spudcan foundations penetrating clay
Limiting cavity depth for spudcan foundations penetrating clay
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DOI：
10.1680/geot.2005.55.9.679
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发表时间：
2005-11-01
期刊：
影响因子：
5.8
通讯作者：
White, DJ
中科院分区：
文献类型：
--
作者：
Hossain, MS;Hu, Y;White, DJ
进行了离心机模型试验和有限元 (FE) 分析，以研究标称强度随深度恒定的均匀粘土中桩桩基础的渗透性。特别是，已经研究了浅渗透（土壤隆起到地表）和深渗透（具有局部流动机制）之间的过渡。这种过渡控制回流的开始，从而控制安装的桩桩上的土壤深度，这反过来又影响承载能力以及吸力发展的潜力，从而影响地基的举升能力和力矩阻力。因此，在任何回流之前，桩桩上方的最大空腔深度是粘土中桩桩评估的关键问题。在离心机模型测试中，使用穿透透明窗口的半桩桩模型来可视化穿透过程中桩桩周围的土壤流动机制。离心机建模和有限元分析揭示了桩锤上方空腔的形成。研究发现，桩钉安装过程中存在三种不同的穿透机制：在初始穿透过程中，形成一个具有垂直壁的开放空腔；随着进一步渗透，土壤在桩棒周围部分流入空腔；在深度渗透过程中，桩筒完全嵌入，土壤流动机制完全局部化。在探索的各种标准化土壤强度中，第二阶段的土壤回流被证明是由于桩桩穿透引发的流动破坏，而不是由墙体破坏（即土腔垂直侧的塌陷）引起的。这一观察结果得到了有限元分析的支持。由于流动失效而产生的空腔深度比当前设计指南中包含的壁失效标准浅得多。相反，建议采用新的设计图表和表达式，将标准化空腔深度表示为土壤抗剪强度的函数，并通过土壤的有效单位重量和桩桩直径进行标准化。
Centrifuge model tests and finite element (FE) analysis have been conducted to study the penetration of spudcan foundations in uniform clay with nominally constant strength with depth. In particular, the transition between shallow penetration, with soil heaving to the ground surface, and deep penetration, with a localised flow-round mechanism, has been investigated. This transition governs the onset of back-flow and hence the depth of soil lying on the installed spudcan, which in turn influences the bearing capacity and also the potential for suction to develop and hence the uplift capacity and moment resistance of the foundation. The maximum cavity depth above the spudcan prior to any back-flow is therefore a critical issue for spudcan assessment in clay. In the centrifuge model tests, a half-spudcan model penetrating against a transparent window has been used to visualise the soil flow mechanisms around the spudcan during penetration. The formation of a cavity above the spudcan is revealed by both centrifuge modelling and FE analysis. It is found that there are three distinct penetration mechanisms during spudcan installation: during initial penetration, an open cavity is formed with vertical walls; with further penetration, soil flows partially around the spudcan into the cavity; during deep penetration, the spudcan is fully embedded and the soil flow mechanism is entirely localised. Over the wide range of normalised soil strengths explored, the soil back-flow in the second stage was shown to be due to a flow failure that was triggered by the spudcan penetration and not by wall failure, that is, the collapse of the vertical sides of the soil cavity. This observation is supported by FE analysis. The cavity depth due to flow failure is much shallower than the criterion for wall failure that is incorporated in current design guidelines. Instead, a new design chart and expression is suggested with the normalised cavity depth expressed as a function of the soil shear strength, normalised by the effective unit weight of the soil and the spudcan diameter.