兰州大学机构库 >土木工程与力学学院
黄土非饱和渗流中水盐运移规律研究
Alternative TitleResearch on the Laws of Water and Salt Transport in Loess Unsaturated Seepage
林高潮
Thesis Advisor谌文武
2017-05-01
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Keyword非饱和黄土 非饱和渗流 渗透特性 易溶盐 微观结构
Abstract

非饱和黄土广泛分布在我国西北、华北以及东北地区,明显有别于经典土力学假设下的土体,其随着土中含水率的变化而表现出不同的物理力学性质及变形特征。渗透特性作为非饱和土体最主要的性质之一,对其开展相关研究工作将推动非饱和土力学理论框架体系的完善,同时对工程建设、灾害防治等方面具有重要的理论指导意义。

本文通过设置一维黄土土柱长时间渗流模拟试验,通过埋设在土柱中的探头采集实时数据,分析总结渗透过程中水分、盐分的变化规律,并对试验结束后的土体进行易溶盐成分分析、扫描电镜观测,进一步探讨黄土的非饱和渗流性质与土体中的盐分、微观结构之间的相互关系,得到如下主要结论:

(1)水分在干燥黄土中的运移与在湿润黄土中的运移显著不同。在干燥黄土中以饱和湿润锋的形式逐渐向下推移,而在浸润后的湿润土体中,水分将以非饱和渗流的形式在黄土中迁移。

(2)黄土的干密度变化将对非饱和渗流特性有较大的影响。黄土的密实度越大,土体的孔隙度越小,孔隙结构也越复杂,渗透能力显著减弱。有限的孔隙通道将限制水分的流动,同时狭小的粒间孔隙将使微观作用力的影响大大增强。试验结果表明干密度1.4 g/cm3是黄土中水盐运移的明显分界点,当干密度大于1.4 g/cm3后,其对水分及盐分的运移影响显著。

(3)渗透过程中,黄土中的盐分将随水分发生迁移。其运移过程既受到含水率的影响,也受到干密度的控制。不同盐离子的迁移与重分布规律各不相同。但整体而言顶部10 cm范围内土体受到的淋滤作用强烈,盐分流失严重,大部分盐分将在隔水底板处富集。经渗流重分布后的盐类也将通过不同的方式反作用于黄土的非饱和渗流性质。

(4)随着渗透作用的进行,黄土土体中不同深度的颗粒形态、骨架结构、孔隙形态等都将发生一系列的变化。随着深度的增加,土颗粒的接触方式由松散堆积镶嵌向致密堆积胶结过度,土体密实程度逐渐增大,同时土体中的孔隙逐渐减小,孔隙网络变得更加复杂,从而导致黄土的渗透能力逐渐降低。

Other Abstract

Unsaturated loess widely spreads in northwest, north and northeast areas of China. Different from the saturated soil assumed under classical soil mechanics, its physical and mechanical properties and deformation features would change with the variation of moisture content. Permeability characteristic is one of the most significant characteristics of unsaturated soil, and the relative research would not only broaden and supplement the unsaturated soil mechanics theory, but also play an important role in guiding the engineering construction and the disaster prevention and control.

A one-dimensional loess pillar is designed to simulate the long-time seepage test. Probes are buried in the loess pillar at different depths to collect the data. The results would be used to analyze the change rules of water and salt movement in the loess pillar. After the seepage simulation test is over, soil samples from different depths would be collect and used for soluble salt analysis and SEM observation, which would contribute to further investigation about the interaction between unsaturated permeability characteristic and salt and microstructure. The main conclusions are shown as below:

(1) Water movement rules are quite different in dry and wet loess. In dry loess, the water will move down the pillar as saturated wetting front. But in wet loess, it moves as unsaturated seepage.

(2) Dry density of loess has great influence on the unsaturated seepage behavior. The bigger the dry density is, the smaller the porosity ratio is. The limited seepage path would impede the water movement, and the narrow pores would enhance the influence from micro acting force. The test results show that when the dry density is greater than 1.4 g/cm3, its influence on the water and salt movement is evident.

(3) During the seepage test, the salt in loess would move with the water. The salt movement rules are controlled by moisture content and dry density. During the process, different salt ions show different movement and redistribution rules. The soil within the top 10 cm range suffers great eluviations and salinity losses. Most salt ions would gather at the impervious bed. Redistributed salts have reaction on the unsaturated seepage characteristics of loess.

(4) During the seepage test, particle morphology, pore morphology and skeleton structure of loess at different depths would suffer different changes. With the increase of depth, the contact mode of soil particles changes from loose accumulation mosaic to dense accumulation cementation. So the density of soil increases gradually. Meanwhile, the pores in soil become smaller, and the porosity network become more complicated. These all result in the gradual decrease of the seepage capacity of loess.

URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/226336
Collection土木工程与力学学院
Recommended Citation
GB/T 7714
林高潮. 黄土非饱和渗流中水盐运移规律研究[D]. 兰州. 兰州大学,2017.
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