【作者】 强小俊；

【导师】 赵有明；

【作者基本信息】 中国铁道科学研究院 ， 岩土工程， 2009， 博士

【摘要】 桩承地基由水平加筋垫层、桩体、桩帽及桩间地基土共同组成,是一种新的软基处理方法。桩承地基主要通过路堤填土中的土拱效应和水平加筋体的拉膜效应将上覆大部分路堤荷载传递到桩上,再由桩传递至下卧持力层,从而减小了路堤的总沉降和差异沉降。同时,水平加筋体的抗拉作用可减小路堤的侧向变形,提高路堤稳定性。由于桩帽的设置,可增大桩的布置间距,相比常见的复合地基,提高了桩身强度的利用率,具有良好的经济性。正因上述特点,桩承地基在国内外软基处理工程中逐渐得到了推广应用。桩承地基工作机理复杂,目前理论研究远落后于工程应用,设计理论还不完善。因此,对桩承地基体系的工作机理进行深入、系统的研究,将有助于设计方法的完善和施工工艺的改进,具有重要的理论和工程实际意义。本文首先通过模型试验研究了桩承地基在路堤荷载作用下的受力工作特性和沉降规律。具体分析了桩土沉降差、桩间土性质、桩帽大小、水平加筋体等因素对土拱效应和沉降特性的影响。其次,对模型试验进行了数值模拟,并与模型试验结果进行对比分析。着重分析了桩帽大小、路堤填土的内摩擦角和粘聚力、水平加筋体的强度和铺设层数等因素对土拱效应和土拱高度的影响。结果表明,桩帽的加大、水平加筋体的铺设、路堤填土内摩擦角和粘聚力的提高均有利于土拱效应的增强和土拱高度的减小。通过对模型试验的数值模拟,确定了土拱的大致高度和水平加筋体铺设层数的合理取值范围。然后,综合考虑了路堤填土为粘性土、水平加筋体以及桩与桩间土相互作用等因素,建立了土拱效应计算模型,并利用该模型对几组模型试验和几个具体工程算例进行了对比分析。结果表明,计算结果与模型试验结果、现场实测结果较为吻合,验证了本文分析模型的合理性。通过本文分析模型对具体工程实例进行参数分析,初步确定了路堤填土的内摩擦角、粘聚力及桩帽面积置换率的合理取值范围。最后,通过对两个桩承地基工程实例的现场观测数据的总结分析,得到了沉降、桩顶应力、桩间土应力、孔隙水压力、桩土应力比及荷载分担比等随填土高度的变化规律,并将实测结果与本文分析模型计算结果进行比较。结果表明,分析模型计算结果与现场观测结果基本吻合,进一步验证了本文分析模型的合理性。更多还原

【Abstract】 Pile-supported foundation consisting of reinforced cushion, pile, pile cap and foundation soil, and it is a new method of soft ground treatment. It is clear that there is a significant load transfer from soil to piles and to substratum due to soil arching and tension of reinforcement so that the total and differential settlements of the embankment are reduced. Simultaneously, the tension of reinforcement can reduce the lateral displacements and improve the stability of the embankment. As the installing of pile caps, the pile-supported foundation, compared with common compound foundation, which is not needed to be closely spaced, and improves the efficiency of the pile strength, and enables the pile-supported foundation a cost-effective method. Because of the above characteristics, the pile-supported foundation has been widely used in soft ground treatment engineering.The working mechanism of pile-supported foundation is complicated, and its theoretical research is lagged behind of its application, so its design theory is not perfect. Consequently, a systemic study on working mechanism of the pile-supported foundation will have theoretical significance and practical value for promoting the progress of design method and construction technology.First of all, a model test was conducted to study on the mechanical behavior and settlement law of the pile-supported foundation under the action of the embankment load. And some influences of the differential settlements between of the piles and soil, the behavior of foundation soil, the size of pile caps and the reinforcements on soil arching and settlement behavior were analyzed in detail.Secondly, the experiments were simulated by using a finite element program and the results of numerical analyses were compared with the model tests. It was emphatically analyzed that the influences of the size of pile caps, the internal friction angle and cohesion of the embankment fill and reinforcements on soil aching effect and the height of soil arching. The results showed that the increasing of the size of pile caps and the internal friction angle and cohesion of embankment fill, and the reinforcements could improve the soil arching effect and reduce the height of soil arching. The height of soil arching and the reasonable range of reinforcement were determined by numerical simulation.Furthermore, an analytical model for the transfer mechanism of embankment load was developed, which considered the influences of the internal friction angle and cohesion of embankment fill, reinforcement, the interaction between piles and foundation soil, the height of embankment and the underlying stratum. And several model tests and projects were calculated by using the analytical model. The results showed that the results from the analytical model are consistent with the actual results from the model tests and the field tests, which verified the analytical model is reasonable. The reasonable range of the internal friction angle and cohesion of embankment fill and the percentage of pile caps coverage was discussed by the analysis on the parameters of a specific project.Finally, by the analysis on the observational data from the two field tests, the variation patterns with the height of embankment were obtained for the settlements, the stresses on piles and soil, pore water pressure, pile-soil stress ratio and load sharing ratio. And the results from the field tests and the analytical model were compared. The results showed that the calculated results based on the analytical model are close to the results from the field tests, which implied the analytical model is reasonable.更多还原