【作者】 鹿宏伟；

【导师】 葛忻声；

【作者基本信息】 太原理工大学 ， 岩土工程， 2009， 硕士

【摘要】 近几年,随着复合地基理论和技术的发展,许多新型的复合地基被应用到工程的设计和实践中去,长短桩复合地基就是其中的一种。长短桩复合地基的优势就是通过褥垫层的应力协调作用充分发挥桩间土的承载力,从而最大限度的发挥复合地基的承载力,以减少桩量,并满足工程的承载力和沉降要求,因此具有良好的经济性。这种地基处理方式,实际上是我国的工程技术人员结合我国的国情,在不断总结以往的工程经验而发展起来的一种新型的地基处理方式。鉴于此,本文依托国家自然科学基金资助项目“长短桩复合地基的变形性状分析及其试验研究”(项目号:50678110),通过在砂土中进行的一系列模型试验,包括不同桩数、不同桩间距、不同厚度的垫层,对长短桩复合地基的工作机理进行了研究,得到如下结论:1.在本试验长短桩相间布置的情况下,复合地基承载变形特性主要体现在长桩上,长桩不仅在承载方面发挥重要作用,而且是控制沉降的主要构件。短桩作为辅助桩,其桩身变形较大,上部荷载不能有效地向下传递,与长桩相比在承担荷载及控制沉降方面的作用较小。2.不同位置长桩与短桩桩身轴力的发挥程度,依次为角桩最大、边桩次之、中桩最小。3.带褥垫层的复合地基,不同位置长桩与短桩桩侧负摩阻力的发挥程度为中桩最大,土反力的分布为中部大、边部小;而在无褥垫层的情况下,桩侧负摩阻力的发挥程度为角桩最大,土反力的分布为中部小、边部大。4.随着桩间距的减小,复合地基的沉降、桩侧摩阻力和桩间土承担的荷载减小,长桩和短桩的桩身轴力、桩土应力比和桩的荷载分担比增大。5.随着垫层厚度的增大,复合地基的沉降、桩侧摩阻力和桩间土承担的荷载增大,长桩桩身轴力、桩土应力比和荷载分担比减小,短桩桩身轴力、桩土应力比和荷载分担比先增大后减小。更多还原

【Abstract】 Recently, with the theoretical and technologic development of composite foundation, many new types of composite foundation have been used in design and construction. The long-short-pile composite foundation is one of them. Its advantage is that, the capacity of soil between piles has been developed through the stress coordination of cushion, in turn, bearing capacity has been satisfied, the number of piles has been reduced, capability and settlement has been satisfied, so it is economic. As a new ground treatment method, it is developed by our engineer, according to local conditions and engineering experience.In response to these circumstances, this subject relies on the National Natural Science Foundation Project " The Long-short-pile Composite Foundation Deformation Behavior Analysis and Experimental Study" (project number: 50678110), a series of model experiment on the sandy soil has been done, including a number of different piles, different pile spacing, different thickness of cushion, the long-short-pile composite foundation’s work mechanism has been conducted, the following conclusions have been made.1. In this experiment, the long pile plays an important role in the capability and deformation characteristics of long-short-pile composite foundation, it not only occupies an important position in the bearing capability, but also control settlement. As the auxiliary pile, short pile has more deformation, the upper load can not pass down effectively, compared with the long pile, short pile’s effect on bearing capability and settlement is small.2. The axial force’s level of long pile and short pile with different position is different, the corner pile is biggest, the side pile is next, the center pile is smallest.3. The negative skin friction’s level of long pile and short pile with different position of composite foundation with cushion is that, the center pile is biggest, and the distribution of soil stress of composite foundation with cushion is that, the middle of soil stress curve is big, side is small. But without cushion, the conclusion is opposite, the negative skin friction’s level is that, the corner pile is biggest, the distribution of soil stress is that, the middle of soil stress curve is small, side is big.4. With the pile spacing decreases, the settlement of composite foundation, the skin friction and the soil between piles bearing capacity decrease; the axial force, the pile-soil stress ratio and pile-soil load-sharing ratio of long pile and short pile increase.5. With the cushion thickness increases, the settlement of composite foundation, the skin friction and the soil between piles bearing capacity increase; the axial force, the pile-soil stress ratio and pile-soil load-sharing ratio of long pile decrease, these factors of short pile increase at the beginning and then decrease.更多还原