【作者】 李斌；

【导师】 刘红军； 张钊；

【作者基本信息】 中国海洋大学 ， 环境工程， 2006， 硕士

【摘要】 软弱地基开挖，流动土体对坑内桩基推移可导致桩基偏位；或者，软土由于固结、塑性屈服和流变等引起侧向移动，进而对桩基施加推力，导致桩基产生侧向弯曲，甚至发生折断，降低了桩基的竖向承载力和使用性能。如今，这类工程事故在软土地区时有发生。 软弱地层深挖基坑中工程桩与流动土体相互作用属于被动桩的研究范畴。由于难以确定流动土体作用于桩身侧压力大小，使得该类桩基与土体相互作用的研究变得较为复杂，更无法准确地通过解析方法确定桩基在流动土体作用下的反应性状、评估桩基的受损坏程度。这些都是日益突出的桩基工程事故分析和合理补强设计所要解决的问题。 分析总结国内外在相近课题上的研究成果与进展，论文着眼于理论和实践中迫切需要解决的难题，采用数值方法对以下问题进行了较系统的研究： (1)从土拱效应的角度揭示了工程桩与流动土体相互作用的过程与实质。解释了桩受流动土体作用的土压力形成机理，阐述了土压力大小与土性参数、桩布置型式的关系。根据土压力与土性参数的关系，指出了被广泛采用的Tomio塑性绕流土压力计算公式的不足。根据桩间土体成拱特征，解释了受流动土体作用下相邻桩基相互作用的机理。 对粘性土、无粘性土中的土拱形成机理及桩周土体破坏特征进行分析，并从土拱效应的四个主要方面：土拱形状、桩周土体塑性(拉裂)区分布、竖向位移等值线和桩后土体残余荷载分担比，探讨了改变土体参数、桩土接触特性、群桩排列方式对桩间土拱效应的影响及其规律。研究表明，土性不同时，土拱形成过程中土体的受力和破坏形式不同：泊松比、剪胀角、桩土接触特征对土拱效应的影响最明显。强度高、剪胀角大、桩土接触面粗糙或泊松比小的土体，易形成土拱。 根据分析得到的排桩绕流土压力与土性参数的关系发现，压力大小与土体强度参数、剪胀角、泊松比、桩土接触特征等均存在联系。而Tomio基于塑性变形理论的土压力计算公式只反映了压力大小与强度参数的关系，尚存不足。 土拱效应存在于一定桩间距之内的土层中。对于群桩，基桩的排列方式对桩更多还原

【Abstract】 Piles under the bottom of a pit are always subject to deflection due to excavation-induced soil movement on soft foundation. On the other hand, piles undergo destroy by soil lateral movement because of soil consolidation, plastic yielding, and flowing. These are all decrease vertical bearing capacity of piles and its use. Now the similar engineering accidents are prevalent on the areas of soft soil area.The interaction of piles and soil lateral movement in deep excavation on soft ground belongs to the research scope of passive piles. It is very difficult to study this kind interaction because earth pressure on piles by soil movement can’t be evaluated, and assessment of pile behavior, destroy degree and residual bearing capacity are even impossible. But these are needed to solved urgently for correct analysis of piling engineering accidents and suitable improvement methods.First literature of results and progress on close subjects at home and aboard is reviewed. Then numerical simulation is applied to study several problems as follows.(1) Mechanism of interaction of pile and soil movement is discovered at the point of soil arching effect, and relationship between earth pressure and soil properties or piles arrangement are illustrated. The deficiency of Tomio Ito earth pressure formula cited widely is pointed out according to the relationship between earth pressure and soil properties, and mechanism of pile-groups interaction are interpreted according to soil arching effect.Few researches have been studied on the mechanism and behavior of soil arching effects in passive piles, especially the comparison when soil parameters changed. Plane FEA is applied to study these problems above, and four key factors of soil arching effects, such as its shape, the vertical displacement contour, plastic or tensile area of soil between piles and remained stress behind piles are investigated by changing cohesion, internal friction angle, elastic modulus, poisson ratio, dilatancy angle, interface conditions respectively. It is found that, the yield mechanism of cohesive and cohesionless soils around piles are different when forming the soil更多还原