【作者】 尚新生；

【导师】 谢定义； 邵生俊；

【作者基本信息】 西安理工大学 ， 岩土工程， 2005， 博士

【摘要】 复合地基在我国土木工程和水利工程中得到了广泛应用,并已建立起一套比较完整的理论体系。在满足安全性条件下,为了寻求更大的经济性,多元复合地基应运而生,并已在不少工程实践中得到应用。但其理论的发展远远落后于实践。为了研究多元复合地基的承载及沉降特性,进一步完善多元复合地基的理论体系,本文主要进行了以下几方面工作: 1) 总结和分析了现有的多元复合地基的理论及设计计算方法。 2) 推导出了基于桩土相互作用原理计算多元复合地基的复合模量的解析公式。进行多元复合地基的优化设计的前提是充分了解其承载和沉降特性。复合模量作为确定沉降的关键指标,对它的研究具有重要意义。文中基于桩土相互作用原理,考虑桩体受荷时发生侧向变形,利用复合体总势能与桩和桩间土势能之和相等的原理,研究了桩一土协调变形情况下的复合模量的确定方法。通过工程实例进行了验证分析。 3) 研究了多元复合地基桩土应力比随荷载的变化规律,给出了桩土应力比随荷载变化的解析表达式。具体分析了两种桩的桩土应力比的三种组合变化:①桩土应力比均随荷载增加而增加;②桩土应力比均随荷载增加而减少;③一种桩的桩土应力比随荷载增加而增加,另一种则减少。 4) 研究了多元复合地基承载力修正系数问题。在考虑桩间土密度、含水量、凝聚力和摩擦角变化的基础上,采用后修正方法,对多元复合地基承载力进行了修正。通过工程实例进行了验证分析。 5) 系统计算了多元复合地基的三种组合:柔性桩—刚性桩、散体桩—柔性桩组合、散体桩—刚性桩组合多元复合地基,得到了每一种组合下地层条件分别为均质地西安理工大学博士学位论文口绝典口巴口巴里里粤.曰目县国曰目目砚,日.皿巴曰毕目基、双层地基(上软下硬)、双层地基(上硬卜软)的应力场、位移场、孔压场变化规律。重点研究了不同组合、地基条件下,桩体位移、应力、复合地基沉降、孔压、桩土应力比。 6)研究了多元复合地基固结问题。本文在假定散体桩底以上为径向、竖向渗流固结组合,散体桩底以下为竖向渗流固结的基础上,考虑散体桩的涂抹作用及非散体桩对下卧层渗流的减弱作用,研究了具有多元复合地基固结特征的散体桩一柔性桩组合、散体桩一刚性桩组合多元复合地基的固结理论解。这对于实际工程中常遇到的由于软弱土层较厚而散体桩未能打穿或由于_〔程需要而不需要打穿软土层的情况,研究和发展未打穿多元复合地基固结理论,具有重要的理论和实际意义。 7)系统分析了多元复合地基的作用。根据数值计算分析,认为多元复合地基具有以下作用:①护桩作用:②垫层作用;③加速固结作用;④整体作用:⑤应力均衡作用;⑥地层适应作用。 8)研究了多元复合地基的工作机理,给出了多元复合地基的优化设计方法。通过工程实例验证了文中分析结果。 9)针对本文提出的复合模量的确定、桩土应力比的确定、固结度的计算解析方法,同时采用数值方法进行了对比分析,其结果表明本文提出的复合模量的确定、桩土应力比的确定、固结度的计算解析方法是可行的。关键词:多元复合地基复合模量桩土应力比承载力修正护桩作用机理 优化设计更多还原

【Abstract】 The multi-element composite foundation has been widely applied to the geotechnical engineering. But its theory is not further than the practice. Researching the deformation and stress and pore water pressure behaviors of multi-element composite foundation has a far-reaching effect for the optimizing design. This paper expresses the following aspects of the new progress and results of multi-element composite foundation.The paper firstly generalizes the current design methods of the bearing capacity and settlement for the multi-element composite foundation, and suggests the new research contents.The determination of bearing capacity and settlement is still the key question in the multi-element composite foundation. If the composite modulus of multi-element composite foundation is determined correctly, the settlement can be calculated by the layer-wise summation method. So an analytical formula of composite modulus of multi-element composite foundation was proposed by considering the interaction between the piles and soils. In the formula the horizontal deformation of the piles and soils is concerned. The formula applying to actual engineering, it is found that the calculation results are agreement with the actual measuring data.An analytical formula reflecting the change of pile-soil stress ratio with loading is also revealed. It is valid that the pile-soil stress ratio is affected by many factors such as loading and length-diameter ratio and replacement ratio and the pile-soil relative stiffness. According to the analytical formula, three types for the pile-soil stress ratio vs. load are discussed. That are: 1) the pile-soil stress ratios of two piles all increase when the load increases, 2) the pile-soil stress ratios of two piles all decrease when the load increases, 3) the pile-soil stress ratios of one pile increases when the another decreases.Considering the change of the density, water content and cohesion of soils, the adjusting factor of the bearing capacity of multi-element composite foundation is analyzed and determined renewedly. Using the new adjusting factor the bearing capacity is calculated. It is found that the calculating results are consistent with the actual data.In order to exploring the deformation, stress and pore water pressure behaviors in the multi-element composite foundation and validating the calculation results by the analytical formula, the many kinds of multi-element composite foundation in different piles and soil layers are calculated systematically by using the FLAC program. The ground structures include three types of homogeneous soil, layer ground (the upper is weak, the lower is hard) and another layer ground (the upper is hard, the lower is weak). Also the component piles include three types of the flexible and rigid piles, the granular column and flexible pile, the granular column and rigid piles. It is discussed that the affection of five factors, which are the deformation of piles, stress of piles, settlement of composite foundation, pore water pressure and pile-soil stress ratio.An analytical method of the multi-element composite foundation is proposed by considering the daub effect of drainage pile in the radial directionand the weakening effect of un-draining pile bottom preventing the vertical drainage of lower layer. Then the consolidation behaviors of different multi-element composite foundation are discussed based on the two methods such as numerical and analytical method. It is revealed that the consolidation process of the composite foundation with drainage pile and rigid or flexible pile. The results from the analytical method are in agreement with that from the numerical method. And it was discussed that the ratio between radius of drainage and pile length and the rigidity of pile affect the consolidation degree.Numerical examples show that the multi-element composite foundation has five kinds of effect, which are retainer action, cushion action, accelerative consolidation action, integrity action, stress equilibrium action and adapting stratum action.The working更多还原