摘要
在桩基础现行设计方法中，当桩基础受轴心竖向力作用时，假定各桩的桩顶作用效应相同。由于在此假定下，各桩同时进入极限状态，每根桩的可靠性都代表了整个桩基础的可靠性，因此研究单桩的可靠性即可，其结果同样适用于整个桩基础。目前有关桩基础可靠性的研究成果都是在这一假定下获得的。
事实上，桩基础中各桩的桩顶反力并不相同，因而各桩并非同时进入极限状态。因此有必要对群桩的可靠性进行研究。
本文选择临近场地的四座高层建筑地基的全部勘测资料，以沿深度方向的一维平稳高斯随机场作为桩基土层土性参数的数学模型，利用相关函数法和变异函数法计算土层的相关范围，由CPT和静载试验结果综合确定钻孔灌注桩的极限承载力，进而对相同场地各试桩的承载力进行折算后检验其概率分布，并估计有关统计参数：考虑群桩效应确定桩基承载力，由桩基沉降反算其作用效应，由Monte-Carlo方法计算单桩及群桩的可靠指标。并与未采用随机场模型的计算结果相比较，对竖向荷载下桩基可靠性进行了较系统的研究，说明桩群—土—承台相互作用的特性对整个桩基础的可靠度有很大影响。
It is assumed that the effect on top of every piles are same when vertically axial load is acting on pile foundation in current design methods. Under the assumption each pile enter the limit state at the same time and the reliability of each pile represent the reliability of the pile foundation. So it is enough to study the reliability of single pile and the result is suitable for the whole pile foundation. At present the research achievements about the reliability of the pile foundation are all obtained based on this assumption.
In fact, the reaction on each pile bolck is not equivalent. So each pile doesn't enter the limit state simultaneously and therefore it is necessary to study the reliability of the group piles.
In this paper total material of the four high-rise structures near the site is selected and one-dimension stable Gaussian random field is treated as numerical model of geotechnical parameters of pile foundation. Correlative function method and variable function method are used to calculate the relevant range of soil layer. The limit capacity of bored pile is determined by the cone penetration tests(CPT) and the static loading tests and related statistics parameters are also evaluated. Considering the effects of group piles, the action effect is calculated by the settlement of pile foundation and the reliability index of single pile as well as group piles is determined by Monte-carlo method. At last, the resultes are compared with those without adoption of random field model and the reliability of pile foundation under vertical load is systematically studied. The conclusion is that the interaction of piles group-soil-pile cap has great effect on the reliability of the pile foundation.
引文
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