【作者】 侯娟；

【导师】 张孟喜；

【作者基本信息】 上海大学 ， 结构工程， 2010， 博士

【摘要】 加筋地基就是在基础下一定深度范围土体内铺设适当的抗拉材料来改善软弱地基受力性能的一种地基形式。工程实践中,加筋地基的设计内容包括承载力、变形和稳定性计算等。伴随工程实践的增多,加筋地基的设计理论和方法也在发展。但总体来说,加筋机理的研究和加筋效果的评价还不够完善。同时,目前加筋地基的理论还远远落后于实践,描述加筋地基的设计方法也比较少。本文以新型水平-竖向加筋(horizontal-vertical,简称H-V)加筋地基为主要研究对象,通过室内模型试验、基于非连续性介质的颗粒流数值模拟及理论分析,对H-V加筋地基的承载力、影响H-V加筋地基的加筋效果和H-V加筋地基的加固机理等方面进行了系统研究。论文主要研究工作包括以下三个方面:(1)设计了水平及H-V加筋地基的模型试验方案,完成了11种工况的试验,研究了加筋层数和首层加筋深度对水平及H-V加筋地基的影响。模型试验研究结果表明,在地基中加筋能明显提高地基承载力、减小地基沉降、改善地基的受力性能。同等试验条件下,H-V筋的加筋效果较水平筋的好,对于单层H-V加筋地基,加筋效果随加筋深度的增加而减弱;加筋深度超过一定范围后,加筋对地基受力性能的改善不明显;对于多层H-V加筋地基,承载力随加筋层数的增加而增加,沉降随加筋层数的增加而减小。(2)利用PFC2D颗粒流程序对模型试验进行了模拟,得到了不同工况下不同类型加筋地基的应力分布图和颗粒位移图,并结合模型试验中观察到的加筋地基砂土滑移面的形状,深入分析了水平加筋地基和H-V加筋地基的加固机理。PFC2D的数值模拟表明,在地基中加水平筋使得地基受力性能改善的主要原因是筋材对土体起到了隔离和约束作用,加筋地基中的应力分布较无筋地基均匀,同时,筋土之间的摩擦力限制了颗粒的运动。而H-V加筋地基使得地基性能得以改善的原因除了水平筋的加强作用外,还增加了竖向筋对土体颗粒的限制和锚固作用。竖向筋约束了地基中砂粒的运动,使得颗粒更难于形成连续的滑移面,从而比水平筋具有更明显的加筋效果。(3)结合模型试验和PFC2D颗粒流数值模拟结果,基于水平及H-V加筋对地基加固的机理,以Terzaghi地基承载力理论为基础,提出了水平加筋及H-V加筋地基的承载力计算方法。并将由此计算的地基承载力和试验值进行了对比,结果吻合良好。更多还原

【Abstract】 This study aims to investigate the potential benefits of using the horizontional and H-V reinforcements to improve the bearing capacity and to reduce the settlement of shallow foundations. To implement this objective, 11 model tests were performed to study the behaviors of reinforced subsoils. The experimental results show that the reinforcement can significantly improve the bearing capacity of the soil and reduce the footing settlement. The bearing capacity of the soil reinforced with H-V reinforcements is higher than that of the soil reinforced with horizontal reinforcements under the same conditions. The effects of the location and the number of reinforcement layers on the behavior of the soil are presented. The test results show that the bearing capacity decreases remarkably by increasing the top spacing. The test results clearly identify a critical zone between 0.3 B and 0.5B (where B is the width of the footing), and thereby maximum benefits of the bearing capacity of the foundation are obtained. Laboratory tests also show an increase of 180, 290, and 410% in bearing capacity of a strip foundation when one, two, and three layers of reinforcement were used, respectively. Good agreement is observed between Terzaghi’s bearing-capacity equations and the experimental results. The test results indicate that the reinforced inclusion can redistribute the applied load to a wider area, thus minimizing stress concentration and achieving a more uniform stress distribution.Reinforcing mechanism and failure models of the soil reinforced with horizontional and H-V reinforcements were studied using PFC2D (Particle Flow Code in Two Dimensions). PFC2D analysis results indicate that reinforcement mechanisms of horizontional reinforcements are rigid boundary, membrane effect and lateral restraint effect. Furthermore, the confinement effect of vertical inclusions of H-V reinforcement can be developed. As a result, bearing capacity of the H-V reinforced soil is higher than tant using the horizontional one.Based on the tests and PFC2D results and using the limit equilibrium theory, foumlars of bearing capacity of horizontional and H-V reinforced foundations are developed for horizontional and H-V reinforced foundations. The results of proposed foumlars were compared with those obtained from the model tests. Good agreement was obtained.更多还原