Theoretical analysis of screw pile under individual thread shear failure pattern
Article Text (Baidu Translation)
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摘要: 为解决高铁路基工程中螺纹桩临界螺距及单螺牙式剪切破坏形态下螺牙所提供极限承载力如何计算的问题，以螺纹桩展开后的局部区域作为研究对象，对极限荷载作用下单螺牙式剪切破坏形态展开研究；根据螺牙结构受力特点建立了一种理论破坏模型，将螺牙周围土体划分为弹性压密区、被动破坏区及过渡区，通过分析不同区域的应力和变形的协调关系，推导螺牙提供的极限承载力；根据螺牙理论破坏模型提出对应临界螺距和极限承载力计算方法，通过与既有破坏模型对比分析，并结合大直剪试验结果验证了理论破坏模型的有效性及准确性。研究结果表明：提出的单螺牙式剪切破坏形态比Meyerhof破坏形态更契合螺牙实际破坏模式；螺纹桩临界螺距主要由螺牙高度及土体内摩擦角决定，其数值随螺牙高度近似线性变化，随摩擦角近似成指数性增加；单螺牙式剪切破坏形态下螺牙提供的承载力优于圆柱式剪切破坏形态，而承载力提高程度主要由土体破坏面形状及土体抗剪强度决定；螺纹桩设计阶段，在保证螺牙自身结构安全的前提下宜适当增加螺牙高度及螺牙间距，使桩周土体恰处于单螺牙式剪切破坏形态，该状态下螺纹桩极限承载力将达到峰值。研究结果可为粉土、黏土地质条件下高铁路基工程螺纹桩极限承载力的优化设计提供理论参考。Abstract: To address the problems of calculating the critical pitch of screw piles and the ultimate bearing capacity provided by threads under an individual thread shear failure pattern in high-speed railway subgrade engineering, the locally unfolded region of screw piles was taken as the research object. Research on the individual thread shear failure pattern under ultimate load was carried out. Based on the structural stress characteristics of the thread, a theoretical failure model was established by dividing the surrounding soil into an elastic compaction zone, a passive failure zone, and a transition zone. Through analysis of stress-deformation compatibility relationships in different regions, the ultimate bearing capacity provided by the thread was derived. Corresponding calculation methods for critical pitch and ultimate bearing capacity were developed according to the proposed theoretical failure model of the thread. The validity and accuracy of the model were verified through comparative analysis with existing failure models and large straight shear experiments. Research results show that the individual thread shear failure pattern proposed by the research demonstrates better agreement with the actual failure mode of the thread compared to the Meyerhof failure pattern. The critical pitch of the screw pile is primarily determined by the height of the thread and the internal friction angle of the soil, exhibiting nearly linear variation with the height of the thread and approximately exponential growth with the friction angle. The bearing capacity provided by the thread under the individual thread shear failure pattern surpasses that of the cylindrical shear failure pattern, with the improvement magnitude mainly governed by soil failure surface geometry and shear strength. During screw pile design, appropriately increasing the height of the thread and pitch while ensuring the structural safety of the thread can optimize the surrounding soil to achieve the individual thread shear failure pattern, thereby maximizing the ultimate bearing capacity of the screw pile. The research results provide a theoretical reference for the ultimate bearing capacity optimization design of screw piles in high-speed railway subgrade engineering under silt and clay geological conditions.
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图 8 螺纹桩极限承载力变化曲线
Figure 8. Variation curves of ultimate bearing capacity of screw pile
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