山西省临汾市黄土崩塌地质灾害特性及冻融成因分析

发布时间：2018-04-17 11:23

本文选题：黄土高原 + 原状黄土　；参考：《太原理工大学》2017年硕士论文

【摘要】：黄土崩塌是黄土高原地区较为普遍,致灾后果较严重的一类地质灾害。近些年来,随着气候环境的恶化以及人类在黄土区工程活动的日益加剧,严重影响了黄土地区的地形地貌及黄土自身结构,加之黄土具有的大孔隙、垂直节理发育、遇水易出现湿陷变形等特殊性质,在外界环境变化以及人为因素的诱发作用下极易引发黄土地质灾害。据调查统计,我国西北部的黄土高原地区是黄土类地质灾害多发的区域,本文所研究的山西省临汾市正处于此范围内,且是崩塌易发及多发区域。黄土是在风的搬运堆积作用下形成的土状沉积物,多分布在干旱半干旱地区,颗粒较小,质地较疏松,在干燥条件下可表现出直立特性,土质较坚硬,具有较高的粘聚力,但遇水易表现出湿陷特性,土体的结构易被软化引发崩塌灾害。诱发黄土崩塌除了土体自身的特殊性质外,还有降雨、冻融循环作用、河流冲蚀、动植物的生物活动及人类工程干预等,排除人为因素干预的条件下,在自然环境中,降雨及冻融是引发黄土崩塌的最重要诱因。降雨的破坏性在于土体内含水量会突然上升,导致颗粒间孔隙水压力相应增大,有效应力出现减小,随着土体自重的不断加大,土体抗剪强度不足以支撑增大的土体质量,引起土体崩落下坠;冻融循环的破坏性在于土颗粒孔隙内存在的水体受冻结冰过程中会出现体积膨胀变形,升温消融的过程中又会出现融沉变形,在反复的冻胀与消融作用下,土颗粒间原本的稳定排列次序被打破,抗剪强度出现减弱,最后在人为活动或者环境变化等作用的激发下,出现崩塌灾害。对于本文黄土崩塌的冻融成因分析,采取对崩塌灾害点进行现场取样,将取样土体用保鲜膜包裹密实放入低温试验箱中以模拟土样在封闭系统下的冻融循环条件,并对冻融前后的试样做直剪抗剪强度试验,分别比对冻融前后土样的抗剪强度、粘聚力、内摩擦角、含水量等物理力学指标,对比后发现:封闭系统下,受到冻融循环作用的土样含水量会减少,粘聚力会下降;在直剪试验中施加的垂直压力较小时受到冻融循环作用后的土样内摩擦角小于原始黄土,在垂直压力增大到一定程度后冻融后土体的内摩擦角变大并大于原始黄土;在一级垂直荷载增加至另一级垂直荷载时对应土体的抗剪强度值会相应增长,在初始垂直压力较小时抗剪强度的增长量原始土大于冻融后土体,随着垂直压力的增大冻融后土体的增长量大于原始土;造成土体冻融破坏的重要因素是土体内孔隙水的含量,孔隙水含量大则受冻时结冰膨胀大,消融时冰体融化收缩大,这些因素都影响了原始土自身的整体结构性,造成土体的强度降低;若孔隙内水量较少则受冻冰体膨胀量相对较小,对原始土体的结构性影响也较小。
[Abstract]:Loess collapse is a kind of geological hazard in the Loess Plateau.In recent years, with the deterioration of climate and environment and the intensification of human engineering activities in loess area, the topography and geomorphology of loess area and the structure of loess have been seriously affected, in addition to the large porosity and vertical joint development of loess.The special properties such as collapsing deformation and so on are easy to occur when the water is in the water. It is easy to cause the loess geological hazard under the external environment change and the human factor induced action.According to the investigation and statistics, the Loess Plateau area in the northwest of China is the region where the loess geological hazards occur frequently. The Linfen City of Shanxi Province is in this range, and it is prone to collapse and frequent area.Loess is a soil-like sediment formed by the action of wind transport and accumulation, mostly distributed in arid and semi-arid areas, with smaller particles and looser texture. Under dry conditions, loess can exhibit vertical characteristics, the soil is hard and has high cohesion.However, the soil structure is easy to be softened and the collapse is caused by water.In addition to the special properties of the soil itself, loess collapses are induced by rainfall, freeze-thaw cycles, river erosion, biological activities of animals and plants and human engineering interventions.Rainfall and freezing and thawing are the most important causes of loess collapse.The destructiveness of rainfall lies in the sudden increase of soil moisture content, which leads to the corresponding increase of pore water pressure between particles and the decrease of effective stress. With the increasing of soil weight, the shear strength of soil is not enough to support the increased soil mass.The destructiveness of freeze-thaw cycle lies in the volume expansion deformation in the frozen and frozen water body in the pore of soil particles, and the thawing deformation in the process of heating up and ablation, under the action of repeated frost heaving and ablation.The original stable order of soil particles is broken, shear strength is weakened, and finally collapse disaster occurs under the excitation of human activities or environmental changes.Based on the analysis of the cause of freezing and thawing of loess collapse in this paper, the site sampling of collapse disaster point is adopted, and the sampling soil is packed with plastic film to simulate the freezing and thawing cycle conditions of soil samples under closed system, so as to simulate the freezing and thawing cycle conditions of soil samples under closed system.The results of direct shear strength tests before and after freezing and thawing were compared with those of soil samples before and after freezing and thawing, such as shear strength, cohesion, internal friction angle, water content and so on.The moisture content of soil sample subjected to freeze-thaw cycle will decrease and the cohesive force will decrease, and the internal friction angle of soil sample subjected to freezing and thawing cycle will be smaller than that of the original loess after the vertical pressure applied in the direct shear test is smaller than that of the original loess.When the vertical pressure increases to a certain extent, the internal friction angle of the soil becomes larger and larger than the original loess after freezing and thawing, and the shear strength of the corresponding soil increases when the first vertical load increases to the other vertical load.When the initial vertical pressure is small, the increase of shear strength is larger than that of frozen and thawed soil, and with the increase of vertical pressure, the increase of soil mass is larger than that of original soil, and the important factor causing freezing and thawing failure of soil is the content of pore water in soil.When the pore water content is large, the frozen swelling is larger and the ice body melts and shrinks greatly. These factors all affect the whole structure of the original soil and cause the strength of the soil to decrease.If the amount of water in the pore is less, the expansion of frozen ice body is relatively small, and the influence on the structure of the original soil is also small.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P642.21

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