静钻根植桩承载性能的试验研究以及数值分析

发布时间：2018-01-05 22:33

本文关键词：静钻根植桩承载性能的试验研究以及数值分析　出处：《浙江大学》2015年博士论文　论文类型：学位论文

【摘要】：静钻根植桩是一种由水泥土搅拌桩和高强预应力混凝土管桩复合而成的基桩,具有高承载力、适应性强、施工难度低、噪音小、泥浆污染少等优点。本文综述了水泥土、管桩、复合桩、静钻根植桩的发展简况,重点研究静钻根植桩的竖向抗压承载性能,对水平承载也作了一定的试验观察。通过两处原位静荷载试验和一处模型试验展开研究。原位试验一进行了多桩对比,原位试验二通过桩身埋设应变传感器深入了解静钻根植桩的荷载传递特性,模型试验通过消除桩端阻力来研究不同桩型在桩土接触面上的荷载传递差异。由于试验一除了竖向抗压还需做水平静荷载,不能压至破坏,试验二虽压至破坏,但却是桩头压碎而非土层达到极限,所以都未测得理想的极限承载力。为此用两种预测极限承载力的方法作了预测,弥补试验的不足。以圆孔扩张理论计算静钻根植桩的挤土效应,并与实测值对比,发现桩上部吻合得较好,下部则是错误的,原因是上部土层压缩性比较高并且对桩孔产生的围压比较小,所以能产生挤土效应,并使这部分土层中的桩侧摩阻力得到提高；下部土层压缩性又低围压又大,挤土效应难以实现。以弹性力学厚壁圆筒理论结合变形协调条件对静钻根植桩内、外部接触面进行分析,认为满足一定的条件后桩土界面是最薄弱面,芯桩与水泥土的接触面不会比之先破坏。围箍效应可以忽略不计,按内芯、芯桩、外壳单独作用的简单叠加来计算整桩的强度、刚度、承载力等。借助数值分析方法补充和完善了原位试验的不足,得出水泥土内芯和外壳的轴力、应力变化,发现即使长桩以侧摩阻力为主端阻力很小,桩端部位仍需要特别加强。除此之外,当整桩外径一定时,水泥土外壳厚度越厚(即芯桩外径越小),整桩承载力越低。水泥土对整桩的截面抗压刚度贡献不大,所以能确保其在设计荷载下不被压碎即可,无需投入额外的成本提高水泥土的掺入比。用有限元结合正交试验的方法针对芯桩直径、壁厚、混凝土强度、水泥土强度展开影响因素分析,发现芯桩直径对静钻根植桩的抗压极限承载力、桩侧摩阻力以及桩端阻力的影响最为显著,是静钻根植桩最重要的参数。芯桩直径一定后,壁厚对桩侧摩阻力的影响很大,摩擦型桩应优先选用厚壁芯桩；水泥土强度对桩端阻力的影响很大,端承型桩应注意提高水泥土的强度。对静钻根植长桩优化设计的建议是,选用大直径芯桩,芯桩直径以略小于钻孔直径为宜,且芯桩壁宜厚。又提出一种预测长桩承载力的方法：如果知道某两种桩径的桩在相同沉降时的承载力,以及其中一种桩径的端承比,就可以推断其它桩径的桩在相同沉降时的承载力和端承比,进而求得端阻力和侧摩阻力。这里所指的承载力并非仅限于极限承载力,而可以是任意加载阶段的承载力。最后通过多桩水平静荷载试验对比了静钻根植桩和钻孔灌注桩的水平承载性能,分析各自的受力特点,认为就减小侧向变形量而言,优选桩型是钻孔灌注桩,宜将静钻根植桩改为同直径的钻孔灌注桩而不宜单纯扩大静钻根植桩的桩径。但如果更重视变形恢复能力,优选桩型是静钻根植桩。
[Abstract]:The static drill rooted pile is a pile of high strength prestressed concrete pipe pile and compounded by soil cement with high bearing capacity, strong adaptability, low construction difficulty, low noise, less mud pollution. This paper reviews the cement soil pile, composite pile, static pile drilling development rooted in the key study on the static drill rooted pile vertical compressive bearing capacity of horizontal load, were also studied in some experiments. By two in-situ static load test and a model test study. In situ test of a multi pile in situ test by comparison, two pile embedded strain sensor understanding static load pile ground drill transfer characteristics, model test of pile load transfer by eliminating the difference of end resistance to study different types of pile in the pile soil contact surface. The test is required in addition to vertical compressive static load level, not pressure to damage, although two test The pressure to destruction, but the pile head crushed rather than soil reached the limit, the ultimate bearing capacity are not so ideal. This is measured by two methods to predict the ultimate bearing capacity is forecasted, make up the deficiency. The theory of cavity expansion calculation of the static drill rooted soil compaction effect of pile, and compare with the measured value the upper part of pile, found good agreement, while the lower part is wrong, the reason is the confining pressure is relatively small and relatively high compressibility of the upper soil layer of pile hole, so can produce the effect of soil compaction, and the friction of the pile side soil in this part is improved; the lower soil compressibility and low confining pressure and high it is difficult to achieve, squeezing effect. Based on the elastic theory of thick wall cylinder with coordinated deformation condition of the static drill rooted in the pile, analyzes the external contact surface that satisfies certain conditions after the pile-soil interface is the weakest surface, core pile and cement soil contact surface is no less than The first destroyed. The hooping effect can be neglected in the inner core, core pile, simple superposition shell alone to calculate the pile strength, stiffness, bearing capacity and so on. With the help of supplement and perfect the lack of in situ test numerical analysis method, the axial force of soil cement in core and shell, stress change, found that even with long pile side friction based end resistance is very small, the pile end parts still need to strengthen. In addition, when the pile diameter is constant, the thickness of the cement shell (i.e. core pile diameter smaller), the pile bearing capacity is low. Large surface compressive stiffness with cement soil on the pile section, so can ensure that it is not to be crushed under the design load, without the need to invest additional cost and improve the soil cement mixing ratio. Using the finite element method combined with orthogonal test for core pile diameter, wall thickness, concrete strength, strength of cement soil to analyze influence factors, find the core The diameter of the pile bearing capacity of compressive ultimate static drill rooted pile, influence of tip resistance of pile side friction and the pile is the most significant, is the most important parameter of the static drill rooted pile. The pile core diameter, wall thickness has great influence on the frictional resistance of the friction pile core pile of thick wall should be preferred the strength of cement soil pile; the influence of tip resistance, end bearing pile should pay attention to improve the strength of cement soil. The static drill rooted long pile optimization design is proposed, using large diameter core pile, pile core diameter to slightly less than the hole diameter is appropriate, and the core pile wall should be thick and proposes a method. A prediction of long pile bearing capacity: if you know a two diameter piles in the same settlement when the bearing capacity, and one of the end bearing pile diameter ratio, it can be concluded that the other diameter piles in the same settlement and bearing capacity of end bearing ratio, and tip resistance and friction resistance are obtained referred to here. The bearing capacity is not only the ultimate bearing capacity and bearing capacity can be arbitrary loading stage. The pile horizontal static load test comparison of the static drill rooted pile and bored pile horizontal bearing performance, analysis of the stress characteristics that reduce the lateral deformation, pile type selection is bored pile should be changed into the static drill rooted pile bored pile with diameter not only expand the static drill rooted pile diameter. But if more deformation restoring capacity, pile type selection is the static drill rooted pile.

【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU473.1

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