在软弱地层且不具备其他支护手段实施条件的基坑工程中，由于地层的物理力学性质差，传统锚索往往不能提供足够的抗拔承载力。为了保证施工及结构的安全，应用扩大头锚索将是一种优良、可选的施工方案。但扩大头锚索的研发及应用起步相对较晚，且其承载机理复杂，目前对于其承载机理及极限承载能力的认识不够深入，大多数工程设计依然依赖于既有工程经验，往往出现预期极限承载能力与实测值差别巨大的问题，给工程安全带来了不确定因素，甚至诱发相关安全事故；同时，目前关于基坑工程的仿真方法还不能方便地对扩大头锚索端阻力加以考虑，从而也给基坑的变形及稳定性评价带来了较大不利影响。在此背景下，本文采用数值模拟、理论分析及现场监测数据分析相结合的方法，对扩大头锚索承载机理及其在深大基坑中的模拟方法开展了较为系统的研究。论文的主要工作和研究成果如下：（1）应用数值模拟的方法，对倾斜布置下扩大头锚索的承载性能以及周围地层的响应规律进行了研究，探明了扩大头锚索侧阻力及端阻力随拉拔力的变化关系。（2）基于极限分析上限定理，构造了扩大头锚索在自由塑流阶段的两种机构破坏模式，分析了相应破坏模式下破坏土体区域的外力做功率和内部能量耗散率，进而基于虚功率原理推导了相应破坏模式下扩大头锚索极限抗拔承载力的上限解。在此基础上，通过侧阻力、端阻力及极限抗拔力理论解与相应数值解的对比，验证了上限解的正确性，并确定了更优的破坏模式。（3）基于扩大头锚索极限抗拔力的上限解，研究了扩孔直径、锚固段长度、自由段长度、杆体倾角以及埋深对扩大头锚索端阻力、侧阻力及极限抗拔承载力的影响，发现扩孔直径、锚固段长度、自由段长度以及埋深对扩大头锚索的极限抗拔承载力均有重要影响。（4）针对FLAC3D有限差分软件中锚索（cable）单元无法考虑扩大头锚索端阻力的缺陷，提出了一种可同时考虑扩大头锚索侧阻力及端阻力的数值迭代方法，而后通过该方法的数值模拟结果与未考虑端阻力的数值模拟结果以及现场实测数据的对比分析，验证了所提方法的正确性。

In the foundation pit engineering with weak stratum and without other supporting means, due to the poor physical and mechanical properties of the strata, the traditional anchor cable cannot often provide sufficient uplift bearing capacity. To ensure the safety of construction and structure, the application of extended anchor cable will be an excellent and optional construction scheme. However, the research and application of the expanded anchor cable started relatively late, and its bearing mechanism is complex. At present, the understanding of its bearing mechanism and ultimate bearing capacity is not deep enough. Most engineering design still relies on existing engineering experience, and often there is a huge difference between the expected ultimate bearing capacity and the measured value, which brings uncertain factors to engineering safety and even induces related safety accidents. At the same time, the current simulation method for foundation pit engineering cannot easily consider the end resistance of the extended anchor cable, which also brings great adverse effects on the deformation and stability evaluation of the foundation pit. In this context, this paper adopts the method of combining numerical simulation, theoretical analysis, and field monitoring data analysis to systematically study the bearing mechanism of extended anchor cable and its simulation method in a deep foundation pit. The main work and research results of this paper are as follows:(1) Application of numerical simulation method, the bearing capacity and the response law of surrounding strata of the expanded anchor cable with an inclined arrangement under different drawing forces are studied, and then the relationship between the side resistance, earth pressure before the expanded end and bearing ratio of the expanded anchor cable and the drawing force is proved.(2) Based on the upper bound theorem of limit analysis, two failure modes of the mechanism of the extended anchor cable in the free plastic flow stage generated by the ultimate drawing are constructed. The external force power and internal energy dissipation rate of the damaged soil area under the corresponding failure mode are analyzed. Based on the virtual power principle, the upper bound solution of the ultimate uplift bearing capacity of the extended anchor cable under the corresponding failure mode is derived. On this basis, the correctness of the upper bound solution is verified and the better failure mode is determined by comparing the theoretical solutions of side resistance, earth pressure before the expanded end, and ultimate uplift force with the corresponding numerical solutions.(3) Based on the upper bound solution of the ultimate uplift force of the expanded anchor cable, the effects of the diameter of the hole, the length of the anchorage section, the length of the free section, the inclination angle of the rod and the buried depth on the end resistance, lateral resistance and ultimate uplift bearing capacity of the expanded anchor cable are studied. It is found that the diameter of the hole, the length of the anchorage section, the length of the free section, and the buried depth have important effects on the ultimate uplift bearing capacity of the expanded anchor cable.(4) In view of the defect that the cable element in FLAC3D finite difference software cannot consider the end resistance of the extended anchor cable, a numerical iteration method that can consider both the side resistance and the earth pressure of the expanded cable is proposed. Then, the correctness of the proposed method is verified by comparing the numerical simulation results of this method with the numerical simulation results without considering the earth pressure before the expanded end and the field measured data.

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