【作者】 刘力；

【导师】 郑刚；

【作者基本信息】 天津大学 ， 岩土工程， 2010， 博士

【摘要】 在软土地基上修筑高速公路、高速铁路路堤时,路堤稳定性往往成为限制路堤填土高度和填土速度的重要因素。除传统的砂桩、碎石桩外其他各种不同桩型如水泥搅拌桩、CFG桩、素混凝土桩、大直径薄壁筒桩等已在路堤下软土地基处理中得到了应用。这些其他各种不同桩型与砂桩、碎石桩在强度和刚度上有较大的差异。然而,这些不同桩型加固地基的稳定分析均采用传统的极限平衡法。已有的针对水泥搅拌桩加固路基的稳定分析已经表明,运用极限平衡法进行稳定分析,相比强度折减数值方法高估了路基稳定性。针对水泥搅拌桩加固地基的离心机试验研究表明,地基中的水泥搅拌桩并非只发生剪切破坏,在很多情况下,弯曲破坏较剪切破坏更易于发生,根据桩弯曲破坏计算的稳定安全系数能更好地符合试验的结果,而采用桩体剪切破坏的稳定计算结果高估了地基稳定性。目前各种不同桩型加固地基的稳定分析均采用极限平衡法,英国规范中提出了一种不同于极限平衡法的计算刚性桩加固地基稳定性的方法,通过本文的分析,该方法也不能完全反映刚性桩加固地基中桩的抗滑机理和破坏形式,需要对刚性桩加固地基的稳定性进行针对性的分析。本文首先对文中数值计算中采用的“桩单元”模型进行了验证,通过和参考文献计算结果的对比,明确了“桩单元”参数取值对计算桩弯矩的影响规律。关于桩加固边坡的稳定分析已有较多的研究,因此本文对桩加固边坡中加固桩位置、加固桩刚度对边坡的变形、稳定性的影响进行研究,进而有助于对位于路堤下不同位置单桩抗滑机理和破坏形式进行分析。并对路堤下单桩加固桩位置及桩体刚度对路堤稳定性的影响进行了研究。在单桩模型分析基础上建立路堤下群桩加固路堤三维数值分析模型,对路堤下不同位置桩的抗滑机理和破坏形式进行分析,然后将桩加固路堤三维问题转化为二维分析模型,根据桩发生不同破坏形式提供抗滑贡献进行稳定性分析。通过本文分析,素混凝土桩的弯曲破坏较剪切破坏更易于发生,按桩发生弯曲破坏,按桩发挥抗弯强度提供抗滑贡献进行了桩加固路堤稳定性分析。并按桩体弯曲破坏深度处桩体截面间摩擦力提供抗滑贡献进行了稳定性分析,对英国规范中由加固桩体在滑动面处的轴力提供抗滑贡献计算了桩加固路堤的稳定性。在按桩不同破坏模式,桩按不同方式提供抗滑贡献进行稳定分析时,根据桩的抗滑贡献计算桩的可使用抗剪强度,即根据桩所提供的抗滑贡献计算其按发挥抗剪强度提供相同抗滑贡献时的抗剪强度,称其为可使用抗剪强度,该可使用抗剪强度可用于极限平衡法或强度折减数值方法稳定性分析。实际工程中多在路堤底部与桩顶之间设置垫层,在垫层中设置土工格栅,因此本文也对桩顶设置土工格栅模型进行了研究。对土工格栅弹性模量、格栅层数对桩内力、桩破坏形式的影响进行了研究。结果表明桩体抗滑机理和破坏形式与桩顶无土工格栅模型相似。前面各章节基于素混凝土桩加固路堤实例模型进行了分析,论文最后对本文提出的按桩不同破坏形式进行稳定分析的思路进行总结,即介绍了按桩发生不同破坏模式提供抗滑贡献时的路堤稳定分析方法,以便于各种方法的比较和在实际工程中的应用。更多还原

【Abstract】 Due to the need of rapid construction of embankment on soft subgrade, stability of the embankment is one of the main concerns need to be considered, engineers have gradually tend to various types of rigid inclusions such as plain concrete pile and reinforced concrete pile as reinforcement elements instead of using sand column, stone column, or deep mixed column, which has been commonly used before. The stiffness and strength characteristics of rigid inclusions have significantly differences with that of traditionally used soft ground reinforcing column. However, for embankment on soft subgrade reinforced with rigid inclusions, traditional limit equilibrium method is employed when performing stability analysis.Research carried on embankment supported on deep mixed column treated soft subgrade has indicated that the deep mixed column does not necessarily subject to shearing failure. The assumption of shearing failure for DM column will lead to overestimation of the overall stability of the embankment. The centrifuge model test obout the deep mixed column reinforced subgrade indicated that the pile occurs bending failure other than shearing failure, the stability analysis basing on the bending failure of the column is more accurate and more consistent with the test results. The result of the stability analysis was overestimated by stability analysis basing on the shearing failure of pile.The stability analysis of the soft subgrade reinforced with different types of columns all use the limit equilibrium method, the British standard proposed another method to consider the reinforce mechanism of the rigid pile in a different way. The British standard can not fully discover the failure modes of the pile judging from the analysis results of this paper, the reinforce mechanism and the method of stability analysis should be carefully studied about the rigid pile supported embankment.The numerical method used to analyze the pile internal force was verified first, the results obtained using the method of this paper was compared with that of the reference’s, the rules to reasonably determine the parameters were also obtained. The numerical stability analyses about the pile reinforced slope have been thoroughly studied. Using the numerical model of the pile reinforced slope adopted in a reference paper, the effects of the pile position and the pile bending stiffness on the slope stability were studied, and then the reinforcing mechanism and the failure mode of the single pile under the embankment was studied. Furtherly, the 3D numerical model of group piles supported embankment was used to analyze the reinforce mechanisms and the failure modes of the piles, the bending failure of the plain concrete piles are more likely to occur than shearing failure. The 3D numerical model was converted to 2D numerical model to perform the stability analysis using the shear strength reduction numerical method, and the stability analysis basing on the bending failure of the pile was performed, the stability analysis basing on the anti-slip resistant moment supplied by the pile friction force at the broken points contact face of the pile was performed.The allowable shear strength of the pile computed basing on the anti-slip mechanism of the British standard was used in the stability analyses. The allowable shear strength computed basing on different anti-slip mechanism and failure modes of the pile can be used in the shear strength reduction numerical method and the limit equilibrium method in the stability analysis.The geogrid were usually established on the top of the pile in the cushion layer at the base of the embankment, the effect of the elastic modulus and the layers of the geogrid on the internal force and the failure modes of the piles were studied. The numerical analysis about the anti-slip mechanism, the failure modes of the piles, the stability analysis basing on different failure mechanism of the piles were performed using a actual model in the above chapter, then in this chapter these analysis method were summarized in general situations in order to use this method more broadly.更多还原