滤纸法测定膨胀土基质吸力试验及数值模拟

发布时间：2018-02-15 05:04

本文关键词： 膨胀土基质吸力土水特征曲线滤纸法数值模拟　出处：《南昌航空大学》2017年硕士论文　论文类型：学位论文

【摘要】：膨胀土主要以非饱和土的形式存在,基质吸力是影响非饱和土的重要参数之一,因此,研究基质吸力对非饱和土的影响十分必要。本文以宜春地区膨胀土为研究对象,采用滤纸法量测了不同干密度、干湿循环条件下非饱和膨胀土的基质吸力与总吸力,并基于试验结果,进行了干湿循环条件下基坑渗流与稳定性分析。取得了如下主要成果:(1)采用滤纸法开展了不同初始条件下土体总吸力与基质吸力试验研究,结果表明:相同初始条件下,滤纸与土样表面距离对总吸力影响较大,3cm时所测得的总吸力离散程度较小,可考虑将3cm作为滤纸法测定总吸力时的标准测试距离;通过引入伪基质吸力的概念,根据总吸力-距离拟合公式求得了不同初始条件下土体伪基质吸力值,并与由试验得到的真基质吸力进行比较,认为土体伪基质吸力与真基质吸力之间表现较好的线性关系;并据此提出了测量土体基质吸力的预测方法。(2)采用Fredlund和Xing三参数模型对干湿循环条件下膨胀土土水特征曲线进行拟合,获得了拟合参数与循环次数n之间的变化规律,建立了一个与干湿循环次数n有关的经验模型,并对其合理性进行了初步验证。(3)基于干湿循环条件下膨胀土土水特征曲线经验模型,采用有限元分析软件Geo-Studio对干湿循环条件下基坑的渗流与稳定性进行数值模拟。结果表明:相同含水率条件下,随着循环次数的增加,土体基质吸力逐渐下降,基坑安全系数总体呈下降趋势,且降低的幅度越来越小。因此,在基坑渗流与稳定分析时宜考虑干湿循环对其影响。
[Abstract]:Expansive soil mainly exists in the form of unsaturated soil, and matrix suction is one of the important parameters affecting unsaturated soil. Therefore, it is necessary to study the effect of matrix suction on unsaturated soil. The matrix suction and total suction of unsaturated expansive soils with different dry densities and dry and wet cycles were measured by filter paper method, and the results were based on the experimental results. The seepage and stability analysis of foundation pit under dry and wet circulation conditions is carried out. The main results are as follows: 1) the experimental study of soil total suction and matrix suction under different initial conditions is carried out by filter paper method. The results show that under the same initial conditions, the soil total suction and matrix suction are tested under the same initial conditions. When the distance between the surface of filter paper and the soil sample has a greater influence on the total suction, the dispersion of the total suction measured is relatively small, so we can consider using 3cm as the standard test distance when the total suction is measured by the filter paper method, and by introducing the concept of pseudo matrix suction, According to the formula of total suction and distance fitting, the pseudo matrix suction values of soil under different initial conditions are obtained, and compared with the true matrix suction obtained from the test, it is concluded that the relationship between pseudo matrix suction and true matrix suction is better. Based on this, a prediction method for measuring the suction of soil matrix is proposed. The Fredlund and Xing three-parameter models are used to fit the characteristic curves of expansive soil and soil under dry and wet cycles, and the law of variation between the fitting parameters and the number of cycles n is obtained. An empirical model related to the number of dry and wet cycles n is established, and its rationality is preliminarily verified. The seepage and stability of foundation pit under dry and wet circulation were simulated by finite element analysis software Geo-Studio. The results show that the suction of soil matrix decreases with the increase of circulation times under the same moisture content. The safety factor of foundation pit is decreasing, and the extent of decrease is becoming smaller and smaller. Therefore, the influence of wet and dry circulation on the seepage and stability of foundation pit should be taken into account in the analysis of foundation pit seepage and stability.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU443

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