黄土非饱和湿陷变形特性研究

发布时间：2018-07-09 17:49

本文选题：黄土 + 湿陷性　；参考：《长安大学》2015年硕士论文

【摘要】：黄土的湿陷变形通常是通过室内试验测得湿陷系数计算或原位浸水试验直接观测获得。现场浸水试验结果准确,但成本高,时间长。绝大部分工程是根据规范,使用室内试验湿陷系数来计算。然而计算值和实测值之间往往存在很大差异,这一方面是由于湿陷系数是在饱和状态下测得,而实际上土体含水量增加到某一值时即可发生湿陷;另一方面原位浸水试验结果表明湿陷变形总量会随时间变化,停渗期也有沉降变形,表明湿陷变形同水分在土体中的入渗有关,忽略时间因素也会造成差异。黄土是一种典型的非饱和土,本文根据非饱和渗透和非饱和变形理论,提出了一种非饱和湿陷变形随时间变化的计算模型。用此模型计算了黑方台地区自1967年灌溉以来的年沉降量和累积沉降量,并同相关文献资料的得到的沉降量进行了对比。此外还利用显微镜对原状和不同含水率压缩后的土样进行了细观结构分析,探讨了细观结构同宏观物理力学性质的关系。在黑方台非灌区挖井取样测定了土体的基本物理参数沿深度的分布情况,据此对该黄土分层,每层取样进行了不同含水率土样的侧限压缩试验和土水特征曲线的测定,获得计算模型所需参数。建立了非饱和渗透模型,得到每年不同灌溉阶段土层孔隙水压力沿深度的分布情况,获得差值,进行沉降变形的计算。结果表明自1967年灌溉以来,累积沉降变形达1.91m,同取样点位置处台面的下降量2.01m接近;地下水水位上升前,年沉降量较大,其中1967年的沉降变形最大,高达0.4m,之后逐渐降低;地下水水位开始上升后后年沉降量在20-40mm之间波动,2007年以来年沉降量在20-30mm之间,这同相关文献资料研究成果相一致借助显微镜得到了到每层土体原状样和900kPa压力变形稳定后不同含水率土体的细观结构。原状样的孔隙大小和数量直接决定了土样的孔隙比和干密度,而孔隙分布特点则影响土体的土水特征曲线,体积含水率相同,大孔隙和中孔隙含量百分数越大,土体基质吸力越小。900kPa压力下变形稳定后,随着含水率的增大,百分数最大的孔径减小,微孔隙增多。每层不同含水率土体压缩变形稳定后具有相同的孔隙分布特征。反映土体变形的参数主要受原状样孔隙分布影响,大孔隙和中孔隙含量越高,湿陷系数越大。
[Abstract]:The collapsing deformation of loess is usually obtained by calculating the coefficient of collapsibility measured by laboratory tests or by direct observation of in-situ soaking test. The results of field immersion test are accurate, but the cost is high and the time is long. Most of the projects are based on the code, using indoor test to calculate the coefficient of collapsibility. However, there is often a great difference between the calculated value and the measured value, which is due to the fact that the coefficient of collapsibility is measured under saturated condition, but in fact, when the water content of soil is increased to a certain value, the collapsibility can occur. On the other hand, the in-situ immersion test results show that the total amount of collapsing deformation will change with time, and there will also be subsidence deformation in the impervious period, indicating that the collapsing deformation is related to the infiltration of water in the soil, and neglecting the time factor will also cause the difference. Loess is a typical unsaturated soil. Based on the theory of unsaturated permeability and unsaturated deformation, a calculation model of unsaturated collapsing deformation with time is proposed in this paper. The annual and cumulative settlement in Heifangtai area since 1967 has been calculated by using this model and compared with the results obtained from relevant literatures. In addition, the microstructures of soil samples with different moisture content were analyzed by microscope, and the relationship between microstructures and macroscopic physical and mechanical properties was discussed. The distribution of the basic physical parameters of soil along the depth was measured by well sampling in Heifangtai non-irrigated area. According to the stratification of loess, the lateral limit compression test of soil samples with different water cut and the determination of soil water characteristic curve were carried out in each layer. The required parameters of the calculation model are obtained. The unsaturated permeation model was established, and the distribution of pore water pressure along the depth of soil layer was obtained at different irrigation stages every year. The difference value was obtained and the settlement deformation was calculated. The results show that since the irrigation in 1967, the cumulative settlement deformation has reached 1.91 m, and the decrease of the Mesa at the same sampling point is 2.01m, and the annual subsidence is larger before the groundwater level rises, in which the settlement deformation of 1967 is the largest, up to 0.4 m, and then decreases gradually. After the groundwater level began to rise, the annual settlement fluctuated between 20-40mm, and in 2007, the annual settlement was between 20-30mm, This is consistent with the research results of relevant literature and materials. The microstructures of soils with different moisture content are obtained by means of microscope after each layer of soil is undisturbed and stabilized by pressure deformation at 900kPa. The pore size and quantity of the undisturbed sample directly determine the porosity ratio and dry density of the soil sample, while the pore distribution characteristics affect the soil-water characteristic curve of the soil, the volume water content is the same, the percentage of the macroporosity and the middle pore content is larger. With the increase of water content, the pore size of the largest percentage decreases and the micro-porosity increases after deformation and stabilization under the pressure of .900kPa when the suction of soil matrix is smaller. Each layer of soil with different moisture content has the same pore distribution characteristics after compression deformation and stability. The parameters reflecting soil deformation are mainly affected by the distribution of undisturbed pores, and the higher the content of macropores and mesoporous pores, the greater the coefficient of collapsibility.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU444;TU411

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