【作者】 王志良；

【导师】 王秀艳；

【作者基本信息】 中国地质科学院 ， 地质工程， 2013， 硕士

【摘要】 湿陷性是黄土内部特征的综合体现,受成因、地质营力、水成作用以及人为因素的影响巨大,不同地区黄土湿陷特性都具有其独特的特征,黄土产生湿陷的受控因素及其湿陷机理存在着区域性差异,本文以湿陷性比较典型的河南黄土作为研究对象,分别从土的物理特性指标、土的颗粒组成、塑性状态、沉积年代、微观结构以及可溶性盐等几方面查明本地区黄土湿陷的影响因子,并在此基础上总结本地区黄土的湿陷机理。本文通过黄土湿陷性试验以及土常规实验,对黄土湿陷性的受控因素进行研究,发现研究区内黄土在共同满足含水量w<12%或饱和度Sr<40%、孔隙比e>0.95或低干密度ρd<1.39、粘粒含量<17%以及液限约为28%四个条件时才具有强烈湿陷性,否则黄土不具有强烈湿陷性。同时黄土湿陷特性与压力的关系受初始含水量、孔隙比的影响,低含水量(<10%)时湿陷系数随压力的增加而增大,高含水量(>20%)时,湿陷系数随压力的变化幅度逐渐降低直至趋于某一定值;高密实土体在低压力下不具有湿陷性,随着压力的增大其湿陷程度逐渐由非湿陷向轻微湿陷转化,低密实土体在较低压力下就具有一定的湿陷性,但在高压力下其湿陷系数的变化幅度相比高密实土体变幅较低。利用能谱分析测定的黄土中易溶盐离子含量,湿陷系数随易溶阴离子含量的增多而增大,CO32-(或HCO3-)是对湿陷程度贡献最大的阴离子；同时湿陷系数与部分易溶性阳离子(Na+、K+、Mg2+)存在着线性单调递减关系,且Ca2+是黄土中含量最大的易溶性阳离子,CaCO3是黄土胶结程度的主要成分。使用扫描电镜分析了天然状态下以及不同等级压力下黄土湿陷后的微结构,通过低倍镜下全貌分析以及高倍镜下的局部定点分析发现土体骨架体系与湿陷性有着明显的相关关系,颗粒排列疏松且大孔隙较多的黄土湿陷系数显著较高,否则相反,高倍镜下强烈湿陷性黄土与非湿陷性黄土的土颗粒排列方式及走向、颗粒与极小孔隙的分布特征基本相似,极小孔隙与颗粒排列方向对黄土产生湿陷没有贡献,利用分形几何原理确定强烈湿陷性黄土中大孔隙与“大团聚颗粒”的分维数分别为2、2.3。本文采用灰色关联以及层次分析相结合的方法来确定各种因了对湿陷性的贡献度,其中易溶盐胶结对湿陷性影响最大且贡献度达到45%,多孔性是次要主控因子,贡献度为30%,其次依次为压缩模量、粘粒含量以及含水量。同时在此基础上选取孔隙比、含水量以及易溶盐含量、粘粒含量两组指标利用MATLAB软件分别做出黄土湿陷等值线趋势图,明确了两种因子对湿陷特性的综合影响。本地区黄土胶结物以钙质胶结为最主要胶结,其中碳酸氢钙与部分碳酸盐胶结对黄土湿陷性影响最大,是影响本地区黄土湿陷的主控因素,多孔性是本地区黄土湿陷的次要主控因素,而其中的大孔隙骨架结构是强烈湿陷性黄土的主要结构;天然含水量及压力对黄土湿陷性也有一定的贡献,作为条件参数影响着黄土湿陷。从而可以对本地区黄土湿陷机理进行描述：黄土湿陷是钙质胶结、欠压密土体受水侵润,胶结易溶盐逐渐发生溶解,土体抗剪强度相应变弱,大孔隙骨架结构从而发生“塌陷”,团粒或集粒滑入孔隙之中,土体结构发生二次重组的过程。更多还原

【Abstract】 Collapsibility of loess is the comprehensive embodiment of the internal characteristics, enormously impacted by the cause, geologic forces, water into effect and the influence of the artificial factor. Collapsibility of the collapsible loess in certain part has its unique characteristics, and the controlled factors and mechanism of collapsible loess have regional differences in different part. This paper chooses the Henan loess as the research object, where have less collapsible mechanism researches. We research fist control factors of loess collapsibility, on this basis to sum up the loess collapsible mechanism of the area.Through researching the influence factors of collapsibility by the collapsible test and conventional test, we found that physical indicators of strong collapsible loess must meet water content<12%or saturation<40%, void ratio>0.95or low dry density<1.39, clay content<17%and liquid limit about28%, otherwise the loess don’t have strong collapsibility; The relationship between pressure and collapsibility coefficient is affected by void ratio and water content, under low water content(<10%) collapsibility coefficient increase with the increase in pressure, under high water content(>20%) collapsibility coefficient changes gradually until tends to a certain value, the soil in different load pressures only has a collapsible degree; high compacting soil has no collapsibility under low pressure, but which will have a slight collapsibility with the increase of the pressure, under low pressure low compacting soil has certain collapsible, but there only have slight variations with the pressure increasing; Through spectrum analysis, coefficient of collapsibility increases along with the increase of soluble anion content, and CO32-(or HCO3-) has the largest contribution to the degree of collapsibility; There is a monotone decreasing linear relationship between collapsibility coefficient and some soluble cationic(Na+, K+, Mg2+), and Ca2+accounts for the largest component of soluble cationic of loess; Through the analysis of the natural conditions and pressured conditions under different level of loess soil using scanning electron microscopy, it found that microstructure has a very obvious correlation with collapsible coefficient, if the particles conglomerate looser and the big pore is more, loess collapsible coefficient is significantly higher, or on the contrary, particle pattern and trend, particles and tiny pore distribution are similar between strong collapsible loess with the non-collapsible loess at high magnification, so soil tiny pore and the particle conglomerate’s direction have basically no contribution to the collapsibility, and the fractal dimension of strongly collapsible loess are2,2.3by fractal geometry principle.Based on the grey correlation and hierarchical analysis method this article determine contribution to collapsibility of various factors, we found that contribution of soluble salt content is the biggest and achieves45%above, and porosity is secondary master control factor, the contribution of30%,followed by modulus of compression, clay content and water content. At the same time on the basis of porosity ratio and moisture content, soluble salt content and clay content, we make the contour trend surface of collapsibility of loess by using MATLAB software, and there has been clear about the relationship between collapsible characteristics with the two kinds of index.The main cementation of loess in Henan region is calcareous cementation, in which calcium bicarbonate and part calcareous cementation influence on the collapsibility of loess largest, and that is the main control factor affecting the collapsibility. Porosity is secondary main control factor of loess collapsibility in this region, and the big pore skeleton structure is the main structure of strong collapsible loess; Natural water content and pressure also have certain contribution, affecting the loess collapsibility as condition parameters. According to the above conclusion, the author summarizes the collapsible loess mechanism of Henan region:under-compacted loess with low moisture content occur that cementing soluble salt is gradually dissolved after inundation, corresponding the soil shear strength weaken, then big pore skeleton structure lead to the "collapse" and crumb or set grain slip into pore of soil, structure occur secondary restructuring process.更多还原