Abstract
The cement mixing (CM) pile is a common method of improving soft offshore ground. The strength growth of CM piles under complex conditions is affected by many factors, especially the cement and moisture contents, and shows significant uncertainty. To investigate the stochasticity of the early strength of CM piles and its impact on the displacement and stability of a seawall, a series of laboratory tests and numerical analyses were carried out in this study. Vane shear tests were conducted on the cement-solidified soil to determine the relationships between the undrained shear strength su of the cement soil curing in the seawater and the cement content ac, as well as the in situ soil moisture content w. It can be inferred that the 24 h undrained shear strength follows a normal distribution. A numerical model considering the random CM pile strength was established to investigate the deformation of the seawall. Due to the uncertainty of CM pile strength, the displacement of the seawall demonstrates a certain discreteness. The decrease of the mean undrained shear strength of CM piles causes a corresponding increase in the average displacement of the seawall. When the mean strength of CM piles is lower than a certain threshold, there is a risk of instability. Furthermore, the heterogeneity of the strength within an individual CM pile also has an impact on seawall displacement. Attention should be paid to the uncertainty of CM pile strength to control displacement and stability.
概要
目的
水泥搅拌桩桩强往往因受到原位土体含水率和水泥掺量等因素影响而存在不确定性。本文旨在基于试验所得桩强分布, 通过随机有限元数值模拟研究探讨不同形式的桩强不确定性对海堤变形和稳定性的影响, 并研究依据确定性参数进行计算和设计对结构的影响。
创新点
1. 基于十字板剪切试验, 通过蒙特-卡罗抽样和插值确定水泥搅拌桩桩强分布;2. 建立考虑桩强不确定性的随机有限元模型;3. 对比不同形式的桩强不确定性对海堤变形和稳定性的影响。
方法
1. 通过室内试验, 得到不同含水率和水泥掺量下的水泥土短期强度;2. 通过蒙特-卡罗抽样和双线性插值, 获得水泥土强度分布参数;3.建立有限元数值模型, 通过USDFLD子程序赋予随机桩强, 并通过大量算例分析桩强不确定性对海堤变形和稳定性的影响。
结论
1. 水泥土不排水抗剪强度受水泥掺量和原状土含水率影响;假设其为服从正态分布的随机变量, 则固化土体不排水抗剪强度服从正态分布。2. 水泥搅拌桩强度的提升能够显著抑制淤泥土和水泥搅拌桩桩身的塑性应变发展, 进而使海堤稳定性得到明显提升。3. 当水泥搅拌桩强度均值低于一定阈值时, 海堤存在整体失稳风险;单根水泥搅拌桩内部的强度空间变异性对海堤稳定性具有更显著的影响。4. 当桩强客观存在不确定性时, 依据确定性参数进行计算和设计将使得结构偏于不安全, 因此须留有更多的安全系数裕度。
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Acknowledgments
This work is supported by the Finance Science and Technology Project of Hainan Province (No. ZDKJ202019), the Key Research and Development Program of Zhejiang Province (No. 2021C03014), and the Natural Science Foundation of Zhejiang Province (No. LR22E080005), China.
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Yuansheng YU and Zhen GUO designed the research. Yuansheng YU and Lingling LI processed the corresponding data. Yuansheng YU and Xiangmiao KONG wrote the first draft of the manuscript. Chengyuan LI helped to organize the manuscript. Zhen GUO revised and edited the final version.
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Yuansheng YU, Lingling LI, Xiangmiao KONG, Chengyuan LI, and Zhen GUO declare that they have no conflict of interest.
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Yu, Y., Li, L., Kong, X. et al. Deformation and stability of the seawall, considering the strength uncertainty of cement mixing piles. J. Zhejiang Univ. Sci. A (2024). https://doi.org/10.1631/jzus.A2300180
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DOI: https://doi.org/10.1631/jzus.A2300180
Key words
- Construction uncertainty
- Cement mixing (CM) pile
- Strength of cement soil
- Seawall stability
- Random finite element method (RFEM)
- Monte Carlo simulation (MCS)