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| Deformation characteristics analysis of free single pile in soft clay induced by dewatering in confined aquifer |
Hongwei YING1,2( ),Guan LIU1,Huiying GAO1,Lisha ZHANG1,3,Yifan XIONG1 |
1. Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, Hohai University, Nanjing 210024, China
2. Research Center of Coastal and Urban Geotechnical Engineering, Zhejiang University, Hangzhou 310058, China
3. Department of Civil Engineering, Hangzhou City University, Hangzhou 310015, China |
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Abstract The confined water dewatering leads to consolidation in the overlying aquitard, subsequently affecting the operational performance of the current pile foundation and potentially resulting in catastrophic outcomes. A pile equilibrium equation was derived using the load transfer method, based on existing research on soil layer consolidation induced by instantaneous dewatering in the aquifer. The semi-analytical solutions for the deformation characteristics of a free single friction pile in a homogeneous aquitard caused by instantaneous pressure-relief pumping were obtained, and the solution was verified by the degeneration to “virtual soil pile” and the comparison with the FEM numerical solution. Based on a pile foundation project case, the development process of aquitard settlement with time and depth, the stress and deformation characteristics of a free single pile induced by pumping down confined water were revealed, and a parametric impact analysis was carried out. Results show that the consolidation of the aquitard induced by instantaneous dewatering in the underlying confined aquifer and its impact on free single piles develop from bottom to top, contrary to the traditional understanding in pile foundation engineering of a “top-down” progression. The larger the pile diameter, the smaller the pile head settlement, but the greater the pile axial force. The greater the drawdown of confined water, the faster the development of skin friction, leading to increased axial force and pile head settlement. As the pile length increases, the axial force also increases. The depth of the neutral point exhibits a relative downward trend with increasing pile length, and an increase in pile length significantly reduces settlement for unpierced single piles.
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Received: 20 December 2023
Published: 25 April 2025
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| Fund: 中国博士后科学基金资助项目（2021M690883）；国家自然科学基金资助项目（51678523）；中央高校基本科研业务费资助项目（B200201012）. |
降承压水引起的软黏土中自由单桩变形特性分析
抽降承压水引起上覆弱透水层发生释水固结沉降，影响既有桩基础服役性能甚至导致灾变. 在大面积瞬时减压降水引起土层固结沉降研究的基础上，采用荷载传递法建立桩体平衡方程，解得瞬时减压降水引发均质弱透水层中自由摩擦单桩受力变形的半解析解，通过退化至“虚土桩”及与有限元数值解的对比验证半解析解的合理性. 以实际工程为背景构建算例，揭示减压降水作为诱因时弱透水层沉降随时间和深度的发展过程以及自由单桩的受力变形特性，并进行参数影响分析. 结果表明，抽降承压水引起的弱透水层固结和对自由单桩的影响均自下而上发展，与桩基工程传统认识的“上部先于下部发展”不同；桩径越大，桩顶沉降越小但桩身轴力越大；承压水降深越大，桩侧摩阻力发展越快，桩身轴力和桩顶沉降越大；桩长越长，桩身轴力越大. 中性点深度随桩长增加有相对下移的趋势，增加桩长可显著减小未打穿弱透水层的单桩沉降.
关键词：
固结,
荷载传递法,
负摩阻力,
承压水降水,
轴向受荷单桩
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