【作者】 张婧；

【导师】 高广运； 冯世进；

【作者基本信息】 同济大学 ， 岩土工程， 2008， 硕士

【摘要】 随着我国工程建设的发展,大直径扩底桩应用越来越广泛,然而对其竖向承载机理的研究却远不够。我国不少软土地区的桩基工程常遇到有薄硬夹层的地质条件,该硬层能否作为大直径扩底桩的持力层一直是工程界非常关注的问题,若能合理利用则可减少桩长、节约基础造价。为分析存在软弱下卧层的大直径扩底桩的竖向承载性状,本文利用有限差分程序建立三维非线性有限差分数值模型,将计算结果与实测数据进行对比,验证了计算模型与参数选取的合理性。在此基础上,分别研究持力层厚度、桩端入持力层深度和土层参数的变化以及桩身尺寸的变化对存在软弱下卧层的大直径扩底桩竖向承载性状的影响。可以发现,大直径扩底桩承载力随持力层厚度的增加而增大,且在持力层厚度较小时持力层厚度的变化对承载力及桩端阻力所占比例影响显著。桩侧土层模量与持力层模量比为0.2时,桩端入持力层深度的变化在持力层厚度较小时对大直径扩底桩的极限承载力影响较大。相同持力层厚度下,桩侧土层模量的变化对大直径扩底桩承载力的影响较大,模量越大承载力越高;大直径扩底桩承载力随持力层模量的提高而显著增大;下卧层参数的变化对大直径扩底桩承载力的影响很大。桩体尺寸变化对存在软弱下卧层的大直径扩底桩承载性状的影响与无软弱下卧层时的规律类似。本文分析结果对实际工程具有指导作用。更多还原

【Abstract】 With the development of municipal engineering, large diameter belled piles are used more and more widely, but the study on vertical bearing mechanism of it is not enough for the practice. In quite a good deal of foundation engineering in soft soil region, there is a kind of geologic condition that a thin hard stratum lays between soft soils. Sometimes the thin hard stratum can support the pile, it will decrease the pier’s length and the cost of foundation. So, quite high value has always been put on that if the thin hard stratum is suitable for supporting course or not.In order to analyze vertical bearing behavior of large diameter belled pile in soft substratum, three-dimensional non-linear finite-difference numeric models are established with finite-difference program, calculated and measured results are contrasted, and it proves that the calculation models and the chosen parameters are rational. Based on the previous manner, the effect of soil parameters such as thickness of supporting course, depth of embedded and pile dimension on vertical bearing behavior of large diameter belled pile in soft substratum are studied.It is found that the bearing capacity of large diameter belled pile will increase with the increment of thickness of supporting course, bearing capacity and proportion of bottom-resistance are affected more notably by supporting course thickness when the supporting course thickness is small. When the ratio of modulus of surrounding stratum and supporting course is 0.2 and the supporting course thickness is relatively small, the ultimate bearing capacity of belled pier with large diameter is affected notably by depth of embedded. With the same thickness of supporting course, the bearing capacity of belled pier with large diameter is affected notably by modulus of surrounding stratum. The greater the modulus of overlying stratum is, the greater the bearing capacity. The bearing capacity of belled pier with large diameter will increase with the increment of modulus of supporting course, and the bearing capacity is greater affected by modulus of substratum. The affection of vertical bearing behavior of belled pier with large diameter in soft substratum by pier dimension is similar to the no soft substratum. The results are instructional to practices.更多还原