【作者】 李剑强；

【导师】 温晓贵；

【作者基本信息】 浙江大学 ， 岩土工程， 2010， 硕士

【摘要】 大直径薄壁筒桩内土芯的贡献对桩竖向承载力影响很大,这也是该桩有别于其他桩的一个重要特点。现有开口桩承载力研究对土芯的认识和研究还很肤浅,导致计算结果与实测相差较大,开展土芯性状及对竖向承载力贡献研究非常重要,这是合理进行筒桩设计的理论基础。本文从土芯闭塞定义入手,研究土芯闭塞影响因素,提出考虑土芯贡献的筒桩竖向承载力计算新方法,本文主要研究成果有：1)对比分析现有国内外土芯闭塞定义后发现,现有的各种定义方法非常混乱,考虑因素也各有侧重。研究认为从土芯静力平衡条件出发给出的土芯闭塞定义适用于静压式开口桩,而且桩径不是很大的情况；2)大直径开口桩打桩引起的土芯惯性力不容忽视,桩径越大,打桩时土芯闭塞高度越大,而且该高度与打桩加速度密切相关。混凝土筒桩与大直径钢管桩相比,打桩时土芯闭塞的可能性大很多；3)静载下土芯闭塞影响因素研究表明,桩径越大,土芯越不容易闭塞；同样桩径下,壁厚越大,土芯越容易闭塞；土体性质及分布对土芯闭塞影响非常大,土体强度越低,越不容易闭塞；贯入深度越大,土体性质的影响越大；4)现有国内开口桩计算方法无法准确估算打桩前后开口桩桩侧摩阻力的变化,及土芯闭塞引起桩端阻力的提高,因此计算结果并不理想。比较而言,ICP(Imperialco1lege pile)方法计算方便,结果准确；5)本文基于ICP计算思路,提出考虑土芯贡献的筒桩竖向承载力计算新方法,并用工程实例进行了验证。该方法综合考虑我国东南沿海土体的特点,比ICP方法简单,实用,预测效果更好。更多还原

【Abstract】 Soil plug is one of the most important features of large-diameter cast-in-situ tubular pile, and has great effect on its vertical bearing capacity. Present studies on soil plug fall behind the application, and lead to unsatisfied predictions. Therefore, it is very important and urgent to do more investigation since it is the basis of pile designing.Starting from the definition, all the factors on soil plugging were studied. The paper put forward a new approach to include the influence of soil plugging in the bearing capacity calculation. The main achievements of this paper are as the following:1) After comparing all the different definitions of soil plugging, it has been found that there is a great confusion in the definition and each definition has its own emphases. Study results show that present definitions, deduced from the static equilibrium, can only be used for jacked pile of small diameters.2) The inertia force on soil plug caused by pile driving is very important for large diameter open-ended piles. The larger the diameter, the higher the plug will be, and the hight is also very related to the acceleration. Soil plugging can be more often occured in concrete pile than in steel pipe pipe.3)The research on influencing factors under static loading shows that the inside soil is not easy plugged when pile diameter increases, but will be when the wall-thickness increases. The influence of soil properties and soil distribution on plugging is much greater than pile geometires. Compared with stiff soil, soft soil is easier to get plugged. And the influence of soil distribution is greater with the penetration.4) Present domestic calculation method for open-ended pile can not predict the changes of shaft friction before and after pile penetration. It can not well estimate the increment of ending capacity either. So the prediciton is far behind satisfaction. Instead, Imperial College Pile (ICP) method can get good results.5) The paper put forward a new proproach, which the contribution of soil plug is considered. The verified results proves that this new method is beter and simpler than ICP method and can be used for this tubular pile in south-east China.更多还原