【作者】 董捷；

【导师】 张永兴；

【作者基本信息】 重庆大学 ， 岩土工程， 2009， 博士

【摘要】 悬臂桩作为一种深层抗滑支挡结构,因其具有抗滑能力强、节约建筑用地、施工便捷等优点,被广泛应用于加固岩土体切方及填方工程等领域。尽管悬臂桩的设计理论、施工技术正不断得到发展,但当前设计理论大多都基于平面假定,实际工程中常常遇到一些因设计理论简化而导致的变形破坏现象。论文依托国家杰出青年科学基金(NO.50625824)、国家自然科学基金(NO.50878218)、“十一五”国家科技支撑计划课题子题(NO.2008BAJ06B04)和国务院三峡办移民安置规划司项目(NO.2008SXG02-2),通过对悬臂桩施工进行现场调研,对悬臂桩桩间三维土拱效应及嵌固段桩身的地基反力分布展开研究,主要工作及研究结论如下:(1)在现场调查的基础上,提出采用沿法向或推力方向土压力的突变程度及突变范围替代传统的桩土承载比来衡量悬臂桩土拱效应的发挥程度及作用范围更趋合理。据此设计了悬臂桩室内推桩模型试验,重点对悬臂桩桩周土内部的应力分布特征及桩周三维土拱效应的作用程度及作用范围进行研究,深入分析了桩周摩擦土拱效应与直接土拱效应之间的联系,指出直接土拱承担了绝大部分推力作用,并对桩周土的整体稳定性起决定性作用。(2)通过对埋入式模型桩进行室内推桩试验,对比分析了上述两种结构形式桩周土的应力分布及变形破坏模式。通过调整悬臂桩间距和改变滑体材料等方式,对比分析了桩间距及滑体材料特性对桩周起拱效应的影响。在上述试验研究的基础上,进而分析了桩周土拱效应形成、发展与消散的全过程。(3)设计了柔性板桩板墙加固斜坡填方地基的室外大型试验,分别采用桩前、桩后布置柔性挡土板的方式,对比研究了柔性板桩板墙背侧的三维成拱效应及挡土板土压力的分布模式。通过摘取挡土板的手段,模拟了桩间土的卸荷过程,采用自制的简易静力贯入设备对拱脚剪切线附近的原状土进行测试,继而研究了直接土拱拱脚处的极限剪切作用厚度。将监测得到的挡土板土压力与拟化简仓法及卸荷拱法的理论计算结果进行对比,探讨了柔性板桩板墙设计时土压力的合理取值方法。(4)依据现场调查及试验结果,将拱脚确定为最不利位置,运用弹性理论对坡体切方前、后的应力状态作了分析,结合岩土强度准则建立了考虑三维土拱效应及切方卸荷效应的悬臂桩桩间土稳定性分析模型,进而探讨了土拱作用范围与桩间土局部稳定性之间的关系。在对桩间土拱整体稳定性进行分析的基础上,提出考虑桩周土自重及滑坡推力共同作用时桩间土整体稳定性与最大桩间距的分析方法。(5)引入三角级数法,通过叠加原理建立了考虑空间效应悬臂桩嵌固段地基反力计算方法。通过对桩身嵌固段的桩-岩接触压应力进行监测,分析了摩擦效应对桩-地基相互作用的影响,指出当桩嵌入较完整的岩质地基时,将桩底约束条件视为自由约束更为合理。为了检验模型计算结果的合理性,将理论计算结果与试验监测结果及普通K法计算结果进行对比。(6)论文最后分析了悬臂桩桩间土及嵌固段软弱地基的加固措施,并针对锚杆加固桩间土及钢管桩加固桩前嵌固段地基的有限差分模型进行计算。据此,对锚杆加固桩间土的立面布置方式及锚杆设计钻进深度进行分析,探讨了钢管桩与嵌固段地基之间的相互作用模式,分析了钢管桩的工作原理,并就上述两种加固措施的方案优化进行探讨。更多还原

【Abstract】 Cantilever pile is widely used in reinforcement to excavation and fill geotechnical engineering as a support structure with resistance to deep sliding because of its characteristics, such as strong resistance, reduction of land use, convenience and short-time spend about construction and so on. The design theory and construction technology of cantilever piles have been developed in many years, however, most of current methods are based on plane strain assumption. Therefore, there are some failure and deformation phenomena which occur in actual construction and application stages. This research work is being supported by grants from National Science Fund for Distinguished Young Scholars of China (NO.50625824), National Natural Science Foundation of China (NO.50878218), National Science and a subject which belong to Technique Foundation during the 11th Five-Year Plan Period of China (NO.2008BAJ06B04) and Transmigrant Allocation and Programming Department of State Council Three Gorges Project Construction Committee (NO.2008SXG02-2). The study which mainly relates to three dimensional arching effect of cantilever piles and ground resisting force acted on their build-in zone is made by survey in field engineering. The main work and research conclusions are as follow:(1) In order to more rationally account the level and range of soil arching effect, it is suggested that the mutations of earth pressure along the normal or thrust force direction should be considered to substitute for the ratio of loads on the pile and soil after investigation work has finished on site. A indoor trust-pile test is designed based on viewpoints above, and the major test is directed distribution characteristics of stress in soil and three-dimensional soil arching effects. The relationship between friction and direct soil arching effects is studied according to tesr results. It is proved that direct soil arching structure bears the most earth pressure load, and is more critical to impact on stability of soil mass between adjacent cantilever piles.(2) A indoor trust-pile test about buried piles is also design in order to comparision with the cantilever piles. The distribution of earth pressure and failure pattern of soil near the piles is analysed according to the test results. The contrast and analysis on the test results of soil arching effect are made by changing the spacings of cantilever piles and the property of soil. In addition, the formation, development and fade processes of soil arching effect are discussed. (3) A outdoor test about flexiboard sheet-pile walls used in reinforced fill foundation on inclined ramp is designed. The purpose of test is primarily to compair and analyse results of three-dimensional soil arching effect and distribution of earth pressure, when flexiboard is installed on frontal or dorsal surface of piles. In the interest of simulating the unloading process of soil between piles, the boards are taken out in test process. Subsequently, a simple static penetration device is made for evaluating solidity of undisturbed soil on shear failure line of arch spring, and ultimate shear-thicknesses of direct arch are analyzed. In addition, test analysis is made about the comparison testing results with calculation value of the simplified granary method and the unloading arch method to discuss the design method of earth pressure which acts on the board.(4) The soil near the arch springing is worst-case position, which is based on survey and analysis of cantilever piles in incised slope and testing results. The stress fields of slope in both initial and incised condition are obtained by mechanics of elasticity. Three-dimensional soil arching effect and cutting-unloading stability analysis model of soil between adjacent piles is established on the basis of geotechnical strength theory. It is discussed that there is a relation between range of arching effect and partial stability of soil between piles. Based on the analysis about integral soil stability near piles, the analysis method of maximal spacing is estabilished by considering self-weight stress and sliding thrust.(5) A calculation method which is considered space effect in cantilever’build-in zone is established by superposition principle, and this process refers to reference the trigonometric series method. Based testing results of compression stress which acts on the contact surface between pile and ground, friction effect of contact surface is analysed. It is suggested that constraint condition at bottom of pile is deem to be free, when the ground near the pile is composed of perfect rock. In order to verify the rationality of calculation model, the comparison between test results and calculation results which contain the trigonometric series and K method is made.(6) Finally, the strengthening facilities are discussed about soil mass between cantilever piles and ground near their build-in zone. The finite difference methods are established ahout soil between piles reinforced by anchors and ground in front of piles strengthed by steel-pipe piles. The elevation election and drilling length of anchors are analysed, and the interacting between steel-pipe piles and ground and their operating principle are also studied. On the basis of conclusions above, the optimum designs about two facilities are discussed.更多还原