Abstract
Rock-embedded foundations with good uplift and bearing capacity are often used in mountains or hilly areas. However, there are soil layers with a certain thickness on the rocks in these mountainous areas, and the utilization of those soil layers is a problem worthy of attention in foundation construction. Considering construction- and cost-related factors, traditional single-form foundations built on such sites often cannot provide sufficient resistance against uplift. Therefore, an anchored pier foundation composed of anchors and belled piers, specifically constructed for such conditions, can be invaluable in practice. This paper introduces an experimental and analytical study to investigate the uplift capacity and the uplift mobilization coefficients (UMCs) of the anchored pier foundation. In this study, three in-situ monotonic pullout tests were carried out to analyze the load–displacement characteristics, axial force distribution, load transfer mechanism, and failure mechanism. A hyperbolic model is used to fit the load–displacement curves and to reveal the asynchrony of the ultimate limit states (ULSs) of the anchor group and the belled pier. Based on the results, the uplift capacity can be calculated by the UMCs and the anchor group and pier uplift capacities. Finally, combined with the estimation of the deformation modulus of the soil and rock, the verification calculation of the uplift capacity and UMC was carried out on the test results from different anchored pier foundations.
目的
山区广泛存在上覆土层下卧岩层的地质情况。在基础工程建设上,为了满足抗拔和下压承载力要求,在这种场地采用传统单一形式的挖孔桩基础往往需要嵌入岩层,施工难度大,且经济性差,而采用岩石群锚基础又会导致土层大开挖,浪费土体承载力,且破坏环境。因此,一种由墩基础和群锚基础组成的锚墩基础被提出。在土层中采用墩基础、在岩层中补充群锚基础的方式,适用于山区“上土下岩”地质。该方式不仅能满足承载要求、优化传力机制,且施工难度小、经济性好。然而,锚墩基础属于新型基础,目前关于其上拔承载机理的研究还较少。本文旨在通过三个全尺寸锚墩基础现场单调上拔试验,分析承载机理,探究破坏模式,并提出承载力和承载发挥系数计算方法,为工程应用提供参考。
创新点
1. 通过分析现场试验结果,提出锚墩基础上拔承载传力机理和破坏模式;2. 基于荷载传递微分方程和变形协调,提出锚墩基础上拔承载发挥系数计算方法。
方法
1. 通过试验结果分析,得到锚墩基础上拔承载力-位移曲线,确定极限承载状态和服役极限状态,并基于切线法确定抗拔承载力;2. 通过现场试验现象分析,结合国内外已有桩基础、墩基础、群锚基础的研究结论,提出锚墩基础传力机理和上拔承载极限状态破坏模式;3. 通过理论推导,基于荷载传递微分方程和变形协调,提出锚墩基础上拔承载发挥系数k值的计算方法,并结合本研究现场试验结果和国内外已发表的类似基础试验结果,验证方法的可行性和有效性。
结论
1. 锚墩的抗拔承载力主要由墩和群锚基础两部分提供;2.率先达到极限抗拔承载力的部分是锚墩基础服役极限状态的控制因素;3. 锚墩基础在上拔承载极限状态的破坏模式是墩和群锚基础的破坏模式组合;4. 可根据地质条件对锚墩基础的设计进行灵活调整,且设计应包括荷载分担分析,以确定服役极限状态和设计抗拔承载力;5. 通过将地质条件和工况代入本文所提理论方法计算得到的承载发挥系数与实测结果吻合度较好,可为锚墩基础的抗拔承载力计算和设计提供参考。
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Acknowledgments
This work is supported by the National Natural Science Foundation of China (No. U2006225) and the European Union’s Horizon 2020 Marie Skłodowska-Curie Research and Innovation Staff Exchange Programme (No. 778360).
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Yizhou SUN designed the research and wrote the first draft of the manuscript. Honglei SUN helped to organize the manuscript. Chong TANG, Yuanqiang CAI, and Feng PAN revised and edited the final version.
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Yizhou SUN, Honglei SUN, Chong TANG, Yuanqiang CAI, and Feng PAN declare that they have no conflict of interest.
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Sun, Y., Sun, H., Tang, C. et al. Monotonic uplift behavior of anchored pier foundations in soil overlying rock. J. Zhejiang Univ. Sci. A 24, 569–583 (2023). https://doi.org/10.1631/jzus.A2200446
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DOI: https://doi.org/10.1631/jzus.A2200446