【作者】 李娜；

【导师】 陈昌富；

【作者基本信息】 湖南大学 ， 土木工程， 2021， 硕士

【摘要】 红黏土广泛分布于我国云贵高原、四川东部、两湖和两广等地区,是一种区域性特殊土。红黏土遇水易软化,易产生蠕变,工程中常采用增大土体密实度或加筋的方式来加固土体。此外,不同工程中土体的应力路径也各不相同。因此,研究土体密实度、加筋层数、应力路径对红黏土蠕变特性的影响具有重要的工程意义。为了揭示上述因素影响下红黏土的蠕变规律,进而为既有红土边坡的稳定性评估、新边坡的设计、红土路基的处理提供可靠的理论依据,本文通过一系列红黏土三轴蠕变试验,研究土体密实度、加筋层数、应力路径对红黏土蠕变特性的影响。论文的主要研究工作与成果如下:(1)通过一系列室内试验,获得了红黏土的天然重度、土粒比重、液塑限、颗粒级配、最优含水率、最大干密度、抗剪强度指标等基本物理力学性质指标。(2)利用自行改制的三轴蠕变仪进行红黏土排水三轴蠕变试验,获得不同干密度下红黏土三轴蠕变试验曲线。通过剖析Burgers蠕变模型参数的物理意义,并基于部分蠕变试验曲线进行模型参数辨识,建立了考虑干密度影响的红黏土Burgers蠕变模型。利用建立的考虑干密度影响的红黏土 Burgers蠕变模型对用作验证的蠕变试验曲线进行预测分析,结果表明所建模型具有较好的预测效果。(3)采用SR-6型三联式三轴蠕变仪开展了 32组加载(恒围压、加轴压)应力路径和卸载(恒轴压、卸围压)应力路径下加筋红黏土三轴蠕变试验。基于B03、B13、B23、B33(加筋层数n分别为0层、1层、2层、3层,应力路径均为卸载应力路径)四组试样的蠕变试验结果,利用引入蠕变损伤的改进Merchant蠕变模型对试验曲线进行拟合,建立了考虑加筋层数影响的红黏土卸载应力路径蠕变模型,并对B03、B13、B23、B33四组试样的蠕变试验曲线进行预测分析,结果表明模型具有较好的预测效果。(4)利用改进Merchant蠕变模型对A03、A13、A23、A33(加筋层数n分别为0层、1层、2层、3层,应力路径均为加载应力路径)四组试样的蠕变试验曲线进行拟合,建立了红黏土加载应力路径蠕变模型。结合此前已经建立的红黏土卸载应力路径蠕变模型,对比分析两种应力路径下蠕变模型参数的变化规律,分析得到:在相同偏应力条件下,红黏土在卸载、加载两种应力路径下产生的瞬时弹性应变、蠕应变、蠕变变形速率、蠕变损伤程度依次增大;在初始围压、轴压相同情况下,红黏土在卸载应力路径下比在加载应力路径下更易产生蠕变破坏。更多还原

【Abstract】 Red clay is widely distributed in Yunnan-Guizhou Plateau,Eastern Sichuan,Hubei,Hunan,Guangdong and Guangxi Provinces in China.It is a kind of regional special soil.The red clay is easy to soften and creep when exposed to water,therefore,methods as increasing soil density or reinforcement are often used to reinforce the soil in engineering.In addition,the stress paths of the soil in different projects are also different.Therefore,it is of great engineering significance to study the influence of soil compactness,number of reinforced layers,and stress path on the creep characteristics of red clay.In order to reveal the creep law of red clay impacted by these factors,and to provide a reliable theoretical basis for the stability evaluation of existing red clay slopes,the design of new slopes,and the treatment of red clay roadbeds,a series of triaxial creep tests of red clay have been carried out in this paper.The main research work and results are as follows:(1)A series of indoor tests were carried out on the red clay,where the basic physical and mechanical properties indices of the red clay,i.e.,the natural weight,specific gravity of soil particles,liquid limit,plastic limit,particle grading curve,optimal moisture content,maximum dry density and shear strength indices were obtained.(2)The triaxial creep test of the red clay under drainage was carried out by using the self-designed triaxial creep tester,and the triaxial creep test curves of red clay under different dry densities were obtained.The physical meanings of the Burgers creep model parameters were analyzed.The model parameters were identified based on part of the creep test curves,and a modified Burgers creep model considering the influence of dry density was established.The Burgers creep model considering the influence of dry density was used to predict the creep test curves used for verification.The results show that the established model has a good predictive effect.(3)In this paper,32 groups of triaxial creep test of the reinforced red clay under loading(where the confining pressure remains unchanged and the axial pressure is applied)and unloading(where the axial pressure remains unchanged and the confining pressure is removed)stress paths were carried out by using the SR-6 triple triaxial creep tester.Based on the creep test results of B03,B13,B23,and B33 samples(where the numbers of reinforcement layers take 0,1,2 and 3,and the stress paths are all unloading stress paths),the modified Merchant creep model with creep damage was used to fit the creep test curve,and the creep model under unloading stress path of red clay considering the influence of the number of reinforced layers was established.The model was used to predict the creep test curve of B03,B13,B23,and B33 samples,and the results show that the model has a good predictive effect.(4)The modified Merchant creep model was used to fit the creep test curves of A03,A13,A23,A33 samples(where the numbers of reinforcement layers take 0,1,2 and 3,and the stress paths are all loading stress paths),and the creep model under loading stress path of red clay was established.Combining with the previously established creep model under unloading stress path of red clay,the change law of creep model parameters under the two stress path was compared and analyzed.Results show that:under the same deviatoric stress condition,the instantaneous elastic strain,creep strain,creep deformation rate,and creep damage degree of red clay under unloading and loading stress paths increase in sequence.Under the same initial confining pressure and axial pressure,the creep failure of red clay is more likely to occur under the unloading stress path than under the loading stress path.更多还原