【作者】 宋广；

【导师】 宋二祥；

【作者基本信息】 清华大学 ， 土木工程， 2012， 博士

【摘要】 将微桩与土钉联合应用的复合土钉支护方式，由于微桩的超前支护，除可改善开挖面土体的自立性外，还可较好地控制基坑变形，增强基坑支护体系的稳定性，该支护方法已在我国深基坑工程中得到广泛的应用和推广。如何较准确地预测微桩复合土钉支护体系的变形，验算其整体稳定性成为工程设计中亟待解决的问题。本文采用理论分析、有限元数值模拟，结合文献调研、现场实测数据分析的研究方法，对基坑开挖问题中土体典型应力路径下的力学特性、微桩复合土钉支护体系的变形及稳定性规律进行了较系统的研究，在此基础之上提出了一种整体稳定验算方法和坑壁水平位移简化计算方法，并对土钉支护体系整体稳定验算和局部稳定验算间的关系进行了探讨。具体的研究工作如下：（1）对开挖问题中土体的典型应力路径进行分析，并指出各应力路径下土体变形及强度特性的差异。进而在介绍常见岩土本构模型特点的基础之上，通过基坑算例和工程实例的数值模拟，对几种常用的岩土体本构模型在开挖条件下数值模拟分析中的适用性进行了系统的对比分析。（2）用三维非线性有限元对超前微桩复合土钉支护和一般土钉支护基坑进行了考虑施工过程的计算和对比分析，探讨两种支护体系在坑壁水平位移、坑后地表沉降、土钉轴力分布及支护体系整体稳定性等多方面的差异，以揭示微桩复合土钉支护体系的变形受力规律；在此基础之上研究了微桩嵌固深度、微桩直径、微桩间距、土钉布置方案、土钉倾角等因素对支护体系变形及稳定性的影响。（3）依据土力学及基础工程中的有关理论结合有限元分析，对超前微桩在复合土钉支护中的抗滑作用进行了分析，进而建议了一种考虑超前微桩作用的复合土钉支护整体稳定验算方法，通过与现有规范建议的方法及有限元计算结果比较，验证所建议方法的合理性。（4）针对现行基坑支护规程中关于土钉支护的设计验算，通过概念分析及计算对比，讨论了土钉支护体系整体稳定验算与和局部稳定验算的必要性问题。（5）针对微桩复合土钉支护的坑壁水平位移，建议了一套较为简便适用的计算方法，并通过将基坑工程实例的计算结果与实测结果进行对比分析验证了所建议方法的合理可行性。更多还原

【Abstract】 The pre-installed micro piles can not only help to ensure self-stability of the soil onexcavation face, but also significantly reduce the soil deformation around the excavationpit and enhance the global stability of the supporting system. As a result, composite soilnailing with pre-installed micro piles are widely used in the deep excavationengineering in China. So it is an important topic to accurately predict the deformationand check the global stability of the supporting system. Mainly based on the finiteelement method and theoretical analysis, supplemented by literature research and fielddata, the mechanical properties of soil around the excavation pit and the deformationand stability law of the composite soil nailing with micro pile are systematically studiedin depth. And then, simplified calculation methods are proposed to check the globalstability checking and to estimate the horizontal displacement of the excavation pit.Besides, relationship between global stability checking and local stability checking forsoil nailing in design is discussed. In this thesis the following innovative conclusions orresults are made:(1)The typical stress-path in soil induced by deep excavation has been analyzed bynumerical analysis. And then the difference of the deformation and strength propertiesof the soil under various stress paths is pointed out. Several soil constitutive modelscommonly used in geotechnical numerical analysis are discussed. The suitabilities ofthese constitutive models used in numerical analysis of deep excavation are comparedthrough analyzing some typical excavation projects.(2) Three-dimensional nonlinear finite element analyses are carried out for bothsoil nailing support and composite soil nailing with pre-installed micro-piles in order toinvestigate the effect of the micro piles. The differences on horizontal displacement,settlement of excavation pit and axial force of nails between support system with andwithout micro-piles are analyzed through comparative calculations. And then severalfactors affect the deformation of support system, such as embedded length, diameter andspacing of micro pile, layout and inclination of soil nailing are studied.(3) Sliding resistance of the pre-installed micro pile in composite soil nailing isanalyzed with reference to the cutting pile force method and the elastic foundation beam method. A simplified approximate method is suggested to consider the effect of themicro pile in global stability checking for composite soil nailing. Compared with themethod suggested by the newly issued technical code on composite soil nailing andfinite element results, the proposed method is more reasonable and has a clearer idea.(4) Based on the design method of soil nailing in the current codes for excavationsupport, the need of global stability checking and local stability checking for soil nailingin design is discussed.(5)A simple and suitable method to calculate the horizontal displacement forexcavation pit of composite soil nailing support system is proposed. Compared with themeasured data, the proposed method can give good predictions of the horizontaldisplacement of composite soil nailing with pre-installed micro piles.更多还原