软黏土中刚性桩复合地基的失稳研究

发布时间：2018-03-12 22:23

本文选题：刚性桩复合地基　切入点：数值模拟　出处：《浙江大学》2014年硕士论文　论文类型：学位论文

【摘要】：刚性桩复合地基技术因具有施工方便、承载力高、稳定性好等优点而被广泛应用于软弱土地区的工程实践中,但整体失稳事故时有发生。研究其失稳破坏机理以防止类似事故的发生,是工程界亟待解决的问题。本文主要研究内容如下： (1)结合已有离心机试验模型,采用大型通用有限元软件ABAQUS建立考虑桩-土接触的刚性桩复合地基支承路堤的三维有限元分析模型。将有限元模拟结果与离心机试验及已有研究成果进行了对比,验证了本文有限元模型的合理性与可行性。 (2)对刚性桩复合地基的失稳临界点进行讨论,发现特征点位移-加载曲线变化情况与土体塑性区发展变化的规律较为一致,将特征点位移突变结合塑性区贯通作为失稳判据较合理。 (3)分析了桩身抗弯刚度、桩端嵌固条件、桩间距对路堤下刚性桩复合地基桩土受力变形的影响,并选取典型算例分析了上述不同条件下的失稳破坏规律,研究表明：在一定范围内增大桩抗弯刚度能有效提高复合地基的稳定性,但桩身刚度过大时易发生桩间土绕流破坏；桩端嵌入持力层的深度为桩径的3～6.25倍时增加桩长能有效提高复合地基的稳定性,过大的嵌固深度会造成不必要的浪费,而桩端未打穿软土层或嵌固深度不足时桩体易发生倾覆破坏,不能充分发挥桩的强度；桩间距为桩径的2.5～7.5倍时减小桩间距能有效提高复合地基的稳定性,桩间距的增大会影响桩体的破坏模式,桩体在第一次弯曲破坏面以上可能发生二次弯曲破坏,桩间距过小则桩间土不能充分发挥其强度。 (4)建立了桩承加筋土复合地基支承路堤的三维有限元模型,分析了铺设土工格栅后复合地基的失稳破坏规律,并研究了格栅刚度、垫层厚度、加筋位置等因素对桩承加筋土复合地基稳定的影响,研究表明：土工格栅调节了桩土应力,减小了土体塑性区范围和深度,影响了滑动区的形状,显著提高了复合地基的稳定性,但铺设土工格栅后复合地基的失稳破坏模式与未加筋的情况相似;格栅刚度处于2000-4000kN/m、垫层厚度为0.4m～0.6m、土工格栅位于桩顶时复合地基的稳定性最好。
[Abstract]:The technology of rigid pile composite foundation is widely used in engineering practice in soft soil area because of its advantages of convenient construction, high bearing capacity and good stability. However, the overall instability accidents occur from time to time. It is an urgent problem to study the failure mechanism to prevent the occurrence of similar accidents. The main contents of this paper are as follows:. 1) combined with the existing centrifuge test model, A three-dimensional finite element analysis model of embankment supported on rigid pile composite foundation considering pile-soil contact was established by using ABAQUS, the finite element simulation results were compared with the results of centrifuge test and existing research. The rationality and feasibility of the finite element model are verified. 2) the critical point of instability of rigid pile composite foundation is discussed. It is found that the change of displacement-loading curve of characteristic point is consistent with that of soil plastic zone. It is reasonable to take the abrupt displacement of the characteristic point and the transfixion of the plastic zone as the criterion of instability. This paper analyzes the influence of bending stiffness of pile body, the condition of pile end embedding and the spacing of pile on the stress and deformation of pile and soil in rigid pile composite foundation under embankment, and selects a typical example to analyze the law of instability and failure under the above different conditions. The results show that the stability of composite foundation can be effectively improved by increasing the flexural stiffness of piles in a certain range, but the soil flow around piles is easy to occur when the pile body is over large. When the depth of the bearing layer embedded at the end of the pile is 3 ~ 6.25 times of the diameter of the pile, increasing the length of the pile can effectively improve the stability of the composite foundation, and if the depth of the embedded layer is too large, it will cause unnecessary waste. However, when the pile ends do not penetrate the soft soil layer or the embedded depth is insufficient, the pile body is prone to overturn and destroy, and the pile strength can not be brought into full play, and the stability of the composite foundation can be effectively improved by decreasing the pile spacing when the pile spacing is 2.5 or 7.5 times the diameter of the pile. The increase of pile spacing will affect the failure mode of pile body. Second bending failure of pile body may occur above the first bending failure surface, but if the pile spacing is too small, the strength of soil between piles can not be fully exerted. 4) the three-dimensional finite element model of supported embankment on pile-supported reinforced soil composite foundation is established, and the instability failure law of composite foundation after laying geogrid is analyzed, and the stiffness of grid and the thickness of cushion layer are studied. The influence of reinforcement position on the stability of pile-supported reinforced soil composite foundation is studied. The results show that the geogrid adjusts the stress of pile and soil, reduces the range and depth of soil plastic zone, and influences the shape of sliding zone. The stability of composite foundation is improved obviously, but the instability failure mode of composite foundation after laying geogrid is similar to that of unreinforced ground, the stiffness of grid is in 2000-4000kN / m, the thickness of cushion is 0.4mand 0.6m. the stability of composite foundation is the best when geogrid is located at the top of pile.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU470

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