【作者】 杨洁；

【导师】 韦秉旭；

【作者基本信息】 长沙理工大学 ， 交通运输工程， 2023， 硕士

【摘要】 膨胀土的膨胀特性对实际工程产生极大危害,在降雨工况下,膨胀土边坡易出现失稳、滑坡等不良地质现象,采用刚性挡土墙对边坡进行防护时,挡土墙除承受土压力外,还需承受膨胀土吸水膨胀后产生的侧向膨胀力,然而现行规范对挡土墙进行设计计算时未考虑侧向膨胀力的作用,这就导致挡土墙支护设计无法满足工程需求。对此,本文结合室内试验、数值模拟和理论计算的方法对降雨条件下膨胀土路堑刚性挡土墙墙背侧向膨胀力进行分析与计算,将理论计算与数值模拟的结果进行对比验证,分析两者的差异性。接着采用数值模拟的方法对膨胀土-EPS缓冲层-挡土墙支挡体系进行研究,探讨降雨条件下不同弹性模量和厚度的EPS缓冲层对侧向压力的折减效果。本文的主要研究内容和成果如下:(1)本文对广西宁明膨胀土工程特性进行研究,通过压力板试验、双环渗透试验和直剪试验、固结试验得到膨胀土水力特性参数、力学参数和变形参数,利用弹性力学有关理论推导了侧向膨胀系数表达式,其关键参数基于可测侧向压力有荷膨胀试验得到。接着利用常规有荷膨胀试验得到试件竖向膨胀系数,在此基础上确定侧向膨胀系数。建立了各参数随含水率、上覆荷载变化的拟合公式,为后续数值模拟和理论计算提供基本参数。(2)利用FLAC3D模拟降雨条件下膨胀土堑坡的渗流情况,得到了不同降雨历时时挡土墙墙后填土孔压场和湿度场的分布规律,根据湿度场计算墙后各深度土层含水率,并分析计算出墙背侧向压力和侧向膨胀力,发现距堑坡表面深度0.5 m时,侧向膨胀力达到最大值为20.78 kPa,表层2 m范围内的土体因雨水入渗而产生了膨胀变形,表层0.75m范围内土体达到饱和。(3)提出一种侧向膨胀力的计算方法,结合有荷膨胀试验数据、各向异性增湿膨胀系数表达式和数值分析的湿度场结果对侧向膨胀力进行计算,得到侧向膨胀力随土层深度增加呈现先增大后减小的分布形式,于0.5 m深度处达到最大值21.0 kPa。并得出理论计算出的侧向膨胀力结果与数值模拟分析结果相差不大,分布规律趋势一致。(4)通过对膨胀土-EPS缓冲层-挡土墙支挡结构进行一系列数值模拟,研究了降雨条件下不同厚度和弹性模量EPS缓冲层的折减效率与最大压缩量的关系,得出最大压缩量受厚度的影响程度比弹性模量更大,为保证较高折减效率,避免高压缩量,本文提出了EPS缓冲层的材料参数选择的相关建议:低弹性模量避免高厚度,高弹性模量需结合高厚度,而较低的弹性模量可以对应选择较高厚度或高厚度。更多还原

【Abstract】 The swelling characteristics of expansive soil are extremely harmful to the actual project,and under rainfall conditions,the slope of expansive soil is prone to instability,landslide,and other adverse geological phenomena.The design of retaining wall support cannot meet the engineering requirements.In this paper,the lateral expansion force at the back of the rigid retaining wall of expansive soil graben under rainfall conditions is analyzed and calculated by combining indoor test,numerical simulation,and theoretical calculation,and the results of theoretical calculation and numerical simulation are’ compared and verified to analyze the difference between them.Then,numerical simulations were used to investigate the effect of different moduli of elasticity and thickness of the EPS buffer layer on the lateral pressure reduction under rainfall conditions.The main research contents and results of this paper are as follows:(1)In this paper,the engineering characteristics of swelling soil in Ningming,Guangxi are studied,and the hydraulic characteristics parameters,mechanical parameters,and deformation parameters of swelling soil are obtained through pressure plate test,double-ring penetration test,and straight shear test,consolidation test,and the expression of lateral expansion coefficient is derived by using the relevant theory of elasticity mechanics,and its key parameters are obtained based on the measurable lateral pressure loaded expansion test.Then,the vertical expansion coefficient of the specimen was obtained by using the conventional load expansion test,and the lateral expansion coefficient was determined on this basis.The fitting equations for the variation of each parameter with moisture content and overlying load were established to provide the basic parameters for the subsequent numerical simulation and theoretical calculation.(2)Using FLAC3D to simulate the seepage of swelling soil riffle slopes under rainfall conditions,we obtained the distribution rules of pore pressure and moisture field of the fill behind the retaining wall at different rainfall calendars,calculated the moisture content of the soil layer at each depth behind the wall according to the moisture field,and analyzed and calculated the lateral pressure and lateral swelling force behind the wall.The soil within 2 m of the surface layer was swollen and deformed by the infiltration of rainwater,and the soil within 0.75 m of the surface layer reached saturation.(3)A calculation method of lateral expansion force is proposed,and the lateral expansion force is calculated by combining the loaded expansion test data,the expression of anisotropic hygroscopic expansion coefficient and the moisture field results of numerical analysis,and the distribution of lateral expansion force increases and then decreases with the increase of soil depth,and reaches the maximum value of 21.0 kPa at the depth of 0.5 m.It is also concluded that the theoretically calculated lateral expansion force results do not differ from the numerical simulation results.The theoretically calculated lateral expansion force results are similar to the numerical simulation results,and the trend of distribution law is the same.(4)Through a series of numerical simulations of the swelling soil-EPS buffer layer-retaining wall support structure,the relationship between the discounting efficiency and the maximum compression of EPS buffer layer with different thicknesses and elastic modulus under rainfall conditions is investigated,and it is concluded that the maximum compression is influenced by the thickness to a greater extent than the elastic modulus.To ensure high folding efficiency and avoid high compression,this paper proposes the following recommendations for the selection of material parameters of the EPS cushioning layer:low modulus of elasticity avoids high thickness,high modulus of elasticity need to be combined with high thickness,while the lower modulus of elasticity can correspond to the selection of higher thickness or high thickness.更多还原