斜坡地区大直径嵌岩桩承载机理及其安全性评价

Large-diameter rock-socketed piles are the main foundation form in mountain areas for bridge construction of highways and railways, the specific boundary-condition of mountain slopes has considerable effects on the bearing behaviors and stability of large-diameter rock-socketed piles. Since its bearing mechanism is not clear so that the design is out of order, it is necessary to carry out the research on the bearing mechanism of large-diameter rock-socketed pile and its reliability at slope areas. At first, the distribution characteristics of the shaft resistances, tip resistance, shear force and bending moment of large-diameter rock-socketed piles at slope areas and their quantitative relationship are researched through field static load test and the advanced technology of distributed optical-fiber temperature sensor; Second, the effects of parameter change such as slope's degree, rock covering thickness and the position of pile on the bearing behavior, deformation and rock-socketed depth of large-diameter rock-socketed piles are explored on the basis of centrifuge model tests; And then, the effects of slope parameter variations on pile’s resistance, shearing force, bending moment, deformation and their regularity are analyzed according to the results of indoor-field tests and three dimensional finite element simulation, and the optimal rock-socketed depth are explored as well; At last, the safety analysis and evaluation of large-diameter rock-socketed piles at slope areas are carried out on the basis of the analysis of influencing factors. The research results will enrich pile theory and have guidance for actual engineering.

大直径嵌岩桩是山区高速公路与铁路等大型基础设施的桥梁工程中最主要的基础形式，山区斜坡特殊的边界条件对其承载特性与稳定性均有较大影响。鉴于大直径嵌岩桩承载机理不明而致使设计无章可循，本项目拟开展斜坡地区大直径嵌岩桩承载机理及其安全性研究。首先，通过现场静载荷试验和分布式光纤等综合测试技术，研究斜坡地区大直径嵌岩桩侧阻与端阻、剪力与弯矩分布特征及其随上部荷载变化间的量化关系；其次，通过离心模型试验，研究斜坡坡度、覆盖层厚度、桩所处位置等参数的变化对大直径嵌岩桩承载特性、变形及其嵌岩深度的影响及其变化特征；然后，根据现场和室内试验结果，采用三维有限元模拟分析斜坡地区各相关参数变化对大直径嵌岩桩侧阻与端阻、剪力与弯矩、变形的影响及其变化规律，探索其最佳嵌岩深度；最后，通过斜坡地区影响因素变异性与敏感性分析，进行斜坡地区嵌岩桩安全性评价理论研究。本研究成果丰富完善桩基理论，同时对实际工程有指导作用。

大直径嵌岩桩是山区高速公路与铁路等大型基础设施的桥梁工程中最主要的基础形式，山区斜坡特殊的边界条件对其承载特性与稳定性均有较大影响，本项目拟开展斜坡地区大直径嵌岩桩承载机理及其安全性研究。首先，通过现场静载荷试验，研究斜坡地区大直径嵌岩桩侧阻与端阻、剪力与弯矩分布特征及变化规律；其次，通过离心模型试验，研究斜坡坡度、覆盖层厚度、桩所处位置等参数的变化对大直径嵌岩桩承载特性、变形及其嵌岩深度的影响；然后，根据现场和室内试验结果，采用三维有限元模拟分析斜坡地区各相关参数变化对大直径嵌岩桩受力、变形的影响及其变化规律，探索其最佳嵌岩深度；最后，通过斜坡地区影响因素变异性与敏感性分析，进行斜坡地区嵌岩桩安全性评价理论研究，获得以下结论：.1. 自平衡法是解决斜坡山区大直径嵌岩桩静载荷试验最有效的方法，精细的滑动测微计和先进的分布式光纤测试技术能够精确完整地测到斜坡地区嵌岩桩的的受力与变形等相关数据；.2. 斜坡山区的覆盖层厚度与斜坡坡角对嵌岩桩的受力与变形性状产生较大的影响，尤其对嵌岩桩的最佳嵌岩深度也有显著的影响；.3. 随着斜坡山区的覆盖层厚度和斜坡坡角的增加，嵌岩桩的受力分布规律发生较大的变化，桩端阻力所占荷载比呈现递增趋势；.4. 斜坡山区覆盖层厚度、斜坡坡角的变化对嵌岩桩水平受力有显著影响，嵌岩桩所受的水平剪力和弯矩随其值的增大而增大，且弯矩最大值位置也随坡角增大而沿桩身下移；.5. 斜坡山区嵌岩桩存在围压不对称性，即桩体迎坡面的侧压力大于背坡面的侧压力，嵌岩桩迎坡面桩侧的侧摩阻力高于背坡面桩侧的摩阻力，这种差值随覆盖层厚度和坡度的增大而逐渐增大；.6. 斜坡山区嵌岩桩所处位置对其受力性状也有明显影响：坡底处影响效应最强烈，其次是坡中，坡顶处受力和变形都较前两者低；.7. 斜坡山区嵌岩桩的较一般场地嵌岩桩的影响因素复杂，其不利因素也较多，其风险安全系数也随斜坡倾角增大而减小。