水分在非饱和黄土中的运移规律及其对边坡稳定性和湿陷变形的影响

论文摘要

黄土广泛分布于我国西北干旱和半干旱地区,具有松散的亚稳态结构。其强度和刚度遇水显著降低,易触发各种地质灾害,如差异沉降,地面裂缝和滑坡等。因此,研究水分在非饱和黄土中的运移规律是研究和预防这些灾害的前提。本文的目的为研究水分在非饱和土中迁移过程及其致灾机制,具体包括:（1）探究自然降雨和多次规律加水条件下水分在非饱和土中的运移机制;（2）以甘肃黑方台塬边滑坡为例,探究多年灌溉条件下水分入渗特征和地下水位动态变化过程及其对边坡稳定性的影响;（3）探讨多年灌溉过程中,黑方台台塬灌区和非灌区湿陷变形特征随水分入渗的变化规律;（4）探究水分入渗的关键参数之一-土水特征曲线-同微观结构的关系。通过现场监测试验,模型试验和数值分析研究了水分厚层非饱和土中的迁移机制。现场监测数据包括地表7.0m内不同深度土体的温度和含水率以及监测场地的各种气候因子,如降水,气温,气压,空气相对湿度和实际蒸发量。监测时间持续一年。结果表明在表层0-1.0m内,土体温度和含水率受气候因子影响强烈,水分的气态迁移和液态流动波动较大。土体含水率整体呈先增加后减小的变化趋势,这同累积入渗量和累积蒸发量相关;1-7.0m范围内,土体含水率基本保持不变,而土体温度呈周期性变化。水分主要为液态流动,气态迁移量较少。在7.0m处,土体温度和含水率基本保持不变,水分为液态迁移。模型试验用于分析多次规律加水条件下,水分在非饱和土的运移机制。土柱高4m,上部每天加水800ml,持续0.5h。整个试验持续62天,不考虑蒸发。结果表明间断性加水使得土柱内形成两个湿润峰,第一个湿润峰持续向下迁移,第二个湿润峰仅形成于加水阶段。两个湿润峰之间存有稳态区,即基质吸力、含水率、流速和非饱和渗透系数均保持不变,水流受重力驱动。结合现场监测结果,首次提出了非饱和区吸力（或含水率）剖面的概念模型,将自然界非饱和区划分为四个区,即:活动区,稳态区,过渡区和毛细上升区。不同区域水分迁移和驱动机制不同。该分区有助于分析不同入渗条件下非饱和区土体含水率和地下水位的变化特征,并解决了降雨诱发深层滑坡的内在机理这一悬而未决的问题。对于黑方台黄土台塬滑坡的案例研究,采用数值试验分析了多年灌溉引起的该边坡水文过程变化,并探讨了边坡稳定性随灌溉的变化特征。结果表明多年灌溉条件下,黑方台地区从低含水率和无地下水的初始水力状态转变为新的水力平衡状态,即:在非饱和区土体含水率恒定,地下水水位稳定。水文过程的变化可分为四个阶段:（1）润湿锋逐渐向下移动,遇不透水黏土层形成地下水位（GWT）;（2）地下水向坡脚移动;（3）坡体内得地下水位逐渐上升并伴随部分地下水从坡脚以下降泉的形势排水;（4）新的水力平衡状态形成。边坡稳定性变化过程也可分为四个阶段,即:缓慢下降,快速下降,微弱下降和保持不变。这四个阶段分别对应于上述水文过程变化的四个阶段。对于黑方台的任一斜坡,其稳定状态必须处于四个阶段之一,不同阶段下斜坡破坏的控制因素不同。控制该区滑坡发生的最可行方法是控制或减少年灌溉水量。提出了一种简易的非饱和湿陷变形随入渗过程变化的计算模型,并进行了常含水率固结试验和增湿土水特征曲线试验中获得模型计算所需参数,分析了黑方台台塬多年灌溉过程中,灌区和非灌区湿陷变形的特征。结果表明灌溉区和非灌区之间的总沉降存在显着差异。灌溉区域的湿陷发生在湿润峰向下迁移和地下水位（GWT）形成并上升直到形成新的水力平衡状态的时期,即上述水文过边变化的前三个阶段。非灌溉区的湿陷主要与地下水变化有关。灌区和非灌区之间的总沉降差异主要发生在湿润峰向下迁移阶段。土水特征曲线为分析水分入渗的关键参数之一。为了探究土体的水力学性质同微观结构的关系,采用滤纸法测得三种击实含水率条件下黑方台黄土的增湿和减湿SWCC,并采用压汞法（MIP）和电镜扫描法（SEM）定量和定性分析土体的微观结构。三种不同的击实含水率分别为低于最优含水率（8%）,最优含水率（17%）和高于最优含水率（19%）.结果表明击实含水率影响土体的微观结构和孔隙连通性,土水特征曲线对土体的孔隙分布具有高度的依赖性。

论文目录

• 摘要
• ABSTRACT
• Chapter1 Introduction
•   1.1 Background
•   1.2 Objectives
•   1.3 Methodology
•   1.4 Layout
• Chapter 2 Literature Review
•   2.1 Water infiltration process in unsaturated soils
•     2.1.1 Conceptual models
•     2.1.2 Analytical analysis
•     2.1.3 Numerical analysis
•     2.1.4 Laboratory column test
•     2.1.5 Field investigation
•   2.2 Stability analysis of wetting-induced loess landslides
•     2.2.1 Suction decrease of unsaturated loess due to wetting
•     2.2.2 Suction loss of loess due to rise of GWT
•     2.2.3 Slide-to-flow transformation due to local failures
•     2.2.4 Static liquefaction
•   2.3 Wetting-induced collapse behavior of loess
•     2.3.1 Typical characteristics of collapse behavior
•     2.3.2 Evolution of soil structure under drying, wetting and loading
•     2.3.3 Understanding the collapse behavior within the elastic-plastic framework
• Chapter 3 Water percolation in the unsaturated loess layer considering theground-atmosphere interaction
•   3.1 Site description
•   3.2 Instrumentation system
•     3.2.1 Atmosphere monitoring
•     3.2.2 Underground monitoring
•   3.3 Results and discussion
•     3.3.1 Variation of atmospheric factors with respect to time
•     3.3.2 Variation of soil temperature with respect to time
•     3.3.3 Variation of soil water content with respect to time
•   3.4 Numerical study of the water percolation considering the ground-atmosp here interaction
•     3.4.1 Model establishment
•     3.4.2 Soil properties
•     3.4.3 Initial conditions
•     3.4.4 Boundary conditions
•     3.4.5 Numerical simulation results
•   3.5 Discussion
•   3.6 Summary and conclusions
• Chapter 4 Water flow in unsaturated soil subjected to multiple infiltration events
•   4.1 Laboratory tests
•     4.1.1 Material properties
•     4.1.2 Laboratory column test
•     4.1.3 SWCC and permeability test
•   4.2 Laboratory results
•   4.3 Numerical simulation of the column test
•     4.3.1 Numerical model
•     4.3.2 Simulation results
•   4.4 Discussion
•     4.4.1 Qualitative analysis of water flow in the unsaturated soil during wetting
•     4.4.2 Quantitative analysis of water flow in unsaturated soils
•     4.4.3 Suction profile in the unsaturated zone
•     4.4.4 Relationship between water infiltration and landslides
•   4.5 Summary and conclusions
• Chapter 5 Water flow characteristics associated with years of irrigation activities and itsinfluence on slope stability in Heifangtai
•   5.0 Study site
•   5.1 Laboratory test
•   5.2 Numerical analysis of the loess slope
•     5.2.1 Model slope establishment
•     5.2.2 Soil properties
•     5.2.3 Initial conditions
•     5.2.4 Boundary conditions
•   5.3 Numerical Simulation Results
•     5.3.1 PWP profile variation
•     5.3.2 Variation of Fs
•   5.4 Discussion
•     5.4.1 Factors that influence the hydraulic equilibrium
•     5.4.2 Slope stability characteristics
•   5.5 Summary and conclusions
• Chapter 6 Wetting induced collapse behavior associated with the infiltration process in Heifantai
•   6.1 A method of predicting collapse behavior with respect to time
•   6.2 Laboratory test and results
•     6.2.1 Laboratory test
•     6.2.2 Test results
•   6.3 Validation of the proposed model using a field infiltration test
•     6.3.1 Calculation process
•     6.3.2 Comparison between the predicted and measured results
•   6.4 Irrigation-induced collapse behavior with respect to time in Heifangtai
•     6.4.1 Numerical model
•     6.4.2 Water infiltration process associated with years of irrigation activities
•     6.4.3 Collapse deformation with respect to time
•   6.5 Discussion
•   6.6 Summary and conclusions
• Chapter 7 Influence of microstructure on the soil water characteristic curve of compacted loess
•   7.1 Background
•   7.2 Laboratory test
•     7.2.1 Soil type and sample preparation
•     7.2.2 Filter paper measurements
•     7.2.3 Microstructure observations
•   7.3 Results and interpretation
•     7.3.1 Soil water retention characteristics
•     7.3.2 Microstructure investigation and interpretation
•     7.3.3 Effect of soil structure on water retention characteristics
•   7.4 Discussion
•     7.4.1 The influence of compaction water content on the microstructure of a silt loess
•     7.4.2 The hysteresis of soil water retention behavior
•     7.4.3 Prediction of SWCC using the PSD
•   7.5 Summary and conclusion
• Chapter 8 Summary and conclusions
•   8.1 Introduction
•   8.2 Conclusions
•   8.3 Suggestions for future research
• REFERENCE
• RELATED PUBLICATIONS
• ACKNOWLEDGEMENT

文章来源

类型: 博士论文

作者: 侯晓坤

导师: 李同录,Sai.K.Vanapalli

关键词: 非饱和和黄土,水分入渗,自然降雨,蒸发,灌溉,边坡稳定性,湿陷变形,微观结构,土水特征曲线

来源: 长安大学

年度: 2019

分类: 基础科学,工程科技Ⅱ辑

专业: 地质学,工业通用技术及设备

单位: 长安大学

分类号: P642.131

总页数: 232

文件大小: 7393K

下载量: 205