氧化铁胶体对崩岗土体抗剪特性的影响

发布时间：2018-07-27 14:01

【摘要】：崩岗土壤中含有的游离氧化铁胶体是影响土体抗剪强度变化的因素之一,这是由于其与粘土矿物的交互作用使得土壤颗粒间具有一定的结构强度。本文通过三轴剪切试验研究崩岗三个土层(红土层、砂土层、碎屑层)的土体中含有不同量氧化铁胶体时,各土层试样的抗剪强度变化情况及发生这样变化的原因。试验过程设置的四个氧化铁含量梯度的试样分别为空白试样、去除1/3Fed试样、去除2/3Fed试样和完全去除Fed试样,并从土体去除游离氧化铁胶体前后理化性质的改变、微观电镜扫描等方面分析引起土体抗剪强度的因素。经过试验研究,主要结果如下:(1)经过DCB法去除游离氧化铁后,三个土层中的粘粒含量都出现明显的增加,而大颗粒含量则有明显的减少情况,其中红土层变化最为明显。这是由于DCB处理后,大颗粒吸附的氧化铁与粘土矿物交互形成的团聚体被破坏,将原先吸附在粗颗粒表面的粘粒释放出来,成为粘粒的组成部分,使粘粒含量增加。(2)氧化铁胶体的微观胶结作用是土壤结构强度的保证之一。由于针铁矿与高岭土之间生成了氢键和静电引力,在SEM图下,土壤中游离氧化铁主要以"桥"或者"包膜"的形式与粘土矿物等颗粒之间形成联结状态并生成颗粒间引力,使之形成团聚体颗粒。由于团聚体会嵌入孔隙中,增大接触面的滑动摩擦力,也使大孔隙被填成小孔隙,孔隙度减小,使结构更加稳定。而当氧化铁胶体被去除后,胶结氢键出现断裂,导致氧化铁胶体与粘土矿物的胶结氢键断裂、颗粒间引力消失、联结状态被破坏,团聚体结构被破坏,结构强度下降。(3)从总体上分析可以得出:试样的抗剪强度为随着含水率的增加而减小,而完全去除Fed试样的抗剪强度却是随着含水率的增加,抗剪强度先增大后减小,说明了在不同含水率下,氧化铁胶体可通过影响颗粒的形态特征、排列组合结构、孔隙度等因素,使土壤的抗剪强度发生改变。而氧化铁胶体主要是通过改变土体的粘聚力与内摩擦角的大小而改变土壤的抗剪强度。在含水率一定时,三个土层试样的粘聚力和内摩擦角值随试样中含有去除氧化铁胶体土样比重的增大而呈减小的趋势,但完全去除试样中由于粘粒被完全的释放,粘粒吸附水分能力增强,毛细粘聚力增加,并且颗粒结构一致孔隙度较小,易形成分子间的引力,使部分试样在适宜的条件下粘聚力上升。(4)氧化铁胶体与粘土矿物的胶结作用对崩岗土体的结构强度具有重大作用。由土体的偏应力峰值变化情况表明:随着试样中氧化铁胶体含量的减少,空白试样、去除1/3Fed试样、去除2/3Fed试样、完全去除Fed试样的抗剪强度值总体上呈下降的趋势。但是下降趋势并非都是逐渐下降,而是与游离氧化铁胶体的发挥阶段有关,使其具有阶段性和整体性的影响能力。另外,当三个土层中游离氧化铁被完全去除后,试样的偏应力都出现增大的现象。
[Abstract]:The free ferric oxide colloid contained in the toppling soil is one of the factors that influence the shear strength of the soil, which is due to the interaction between the soil and clay minerals, which makes the soil particles have a certain structural strength. In this paper, the shear strength of three soil layers (red soil layer, sand layer, clastic layer) is studied by triaxial shear test. When different amounts of ferric oxide colloid are found in the soil mass, the shear strength of each soil layer and the reason for the change are studied. The four samples with iron oxide content gradient were blank sample, 1/3Fed sample, 2/3Fed sample and Fed sample were removed, and the physical and chemical properties of free iron oxide colloid were changed before and after the removal of free iron oxide colloid. The factors that cause the shear strength of soil are analyzed by SEM. The main results are as follows: (1) after the removal of free iron oxide by DCB method, the clay content in the three soil layers increased obviously, while the large particle content decreased obviously, among which the clay layer changed most obviously. This is because after DCB treatment, the agglomerates formed by the interaction of iron oxide adsorbed by large particles with clay minerals are destroyed, and the clay particles previously adsorbed on the surface of coarse particles are released as part of the clay particles. The clay content was increased. (2) the microscopic cementation of ferric oxide colloid was one of the guarantee of soil structural strength. Due to the formation of hydrogen bonds and electrostatic force between goethite and kaolin, in SEM diagram, free iron oxide in the soil is mainly formed in the form of "bridge" or "coating" to form a connection state between clay minerals and other particles and form the gravitational force between them. To form agglomerate particles. Because the agglomeration experience is embedded in the pores and increases the sliding friction force of the contact surface, the macropores are filled into small pores, the porosity decreases, and the structure becomes more stable. However, when the iron oxide colloid is removed, the bonding hydrogen bond breaks, which leads to the breaking of the bonding hydrogen bond between the iron oxide colloid and the clay mineral, the disappearance of the gravitational force between the particles, the destruction of the bonding state, and the destruction of the structure of the aggregate. (3) from the overall analysis, it can be concluded that the shear strength of the specimen decreases with the increase of moisture content, while the shear strength of the sample with complete removal of Fed increases firstly and then decreases with the increase of moisture content. The results showed that the soil shear strength could be changed by influencing the morphology of the particles, the arrangement of the composite structure, the porosity and other factors under the different moisture content of ferric oxide colloid. The iron oxide colloid mainly changes the shear strength of soil by changing the cohesion of soil and the angle of internal friction. When the moisture content is constant, the cohesive force and the angle of internal friction of the three soil samples decrease with the increase of the specific gravity of the sample containing the removal of ferric oxide colloidal soil, but the complete removal of the sample is due to the complete release of the clay particles. The water adsorption ability of clay particles increases, the capillary cohesion increases, and the uniform porosity of particle structure is small, which makes it easy to form intermolecular gravity. The cohesion of some samples was increased under suitable conditions. (4) the cementation of ferric oxide colloid with clay minerals played an important role in the structural strength of the rockfall soil. The results show that with the decrease of the content of ferric oxide colloid in the sample, the shear strength of the blank sample, the 1/3Fed sample, the 2/3Fed sample, and the Fed sample is decreasing as a whole. However, the downward trend is not always decreasing gradually, but is related to the stage of free ferric oxide colloid, which makes it have the ability of stage and integrity. In addition, when the free iron oxide is removed completely in the three soil layers, the deflection stress of the sample increases.
【学位授予单位】：福建农林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S157

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