水在原状黄土中的入渗过程研究

发布时间：2018-11-11 20:20

【摘要】：我国是黄土覆盖面积最大的国家,黄土高原面积达44万km2,黄土不但覆盖面积广而且厚度大、结构松散、地质条件极其不利,其脆弱的地质环境和不当的人类工程活动(不当的坡体开挖和灌溉)、集中的降雨模式,致使该区域成为我国滑坡地质灾害发生最为频繁的区域。降雨及灌溉入渗是诱发黄土滑坡的主要因素之一,因此,开展降雨和灌溉条件下水在原状黄土中的入渗过程具有重要的理论与工程实际意义。本论文采用室内大型原状土柱试验模拟不同降雨与灌水模式条件,在高度为1米的原状土柱侧壁埋设水分计,将水分计与数采系统连接,观测水分入渗中四个深度黄土体积含水率随时间的变化,研究了原状黄土水分的运移规律,在此基础上采用HYDRUS——1D数值模拟方法模拟了水分运移过程,对于深入认识降雨型和灌溉型黄土滑坡机理具有重要的科学意义。研究发现,在雨水沿原状黄土入渗的过程中,土柱在入渗初期因为含水率比较低,而基质势又是与含水率相关的,其梯度较大,因此土柱的入渗能力相对强,体积含水率迅速提高。随着时间的增长,雨水逐渐进入到黄土土柱内,湿润峰不断向前推移,土柱下部黄土的含水率逐渐增高,其与上部黄土之间的基质势梯度逐渐减小,导致土体接受水分的能力逐渐减弱。因此,黄土土坡失去其稳定性,是与土体基质吸力减小甚至丧失密切相关的。再次灌溉入渗过程中,由于初始含水率较高,基质吸力相对较小,在上部水头压力、基质吸力及重力作用下,刚开始湿润锋的运移速率增速很快,当水分运动至土柱底部时,基质势梯度丧失,最后维持饱和入渗状态。土柱入渗试验结果与HYDRUS-1D数值模拟结果间还存在一定的误差,可能是采用小土样测定的水分特征曲线参数及非饱和导水系数与实际土柱内土体参数还存在一定的偏差,因此在模拟原状黄土水分入渗的过程中,要选择适当的土水特征曲线经典模型,考虑基质吸力与含水率之间存在滞回曲线,并且要考虑吸湿脱湿对土水特征曲线的影响。
[Abstract]:China is the country with the largest loess coverage area. The loess plateau area of 440000 km2, not only covers a wide area, but also has a large thickness, loose structure and extremely unfavorable geological conditions. Its fragile geological environment, improper human engineering activities (improper slope excavation and irrigation) and concentrated rainfall pattern make the region the most frequent area of landslide geological disasters in China. Rainfall and irrigation infiltration are one of the main factors that induce loess landslide. Therefore, it is of great theoretical and engineering significance to carry out infiltration process of rainfall and irrigation water in undisturbed loess. In this paper, the indoor large undisturbed soil column test was used to simulate the different rainfall and irrigation model conditions, and the moisture meter was embedded in the lateral wall of the undisturbed soil column with a height of 1 meter, and the moisture meter was connected with the data mining system. The changes of water content of loess in four depths with time were observed, and the water migration law of undisturbed loess was studied. On the basis of this, the process of water migration was simulated by HYDRUS--1D numerical simulation method. It is of great scientific significance to understand the mechanism of rainfall type and irrigation type loess landslide. It is found that in the process of Rain Water infiltration along the undisturbed loess, the soil column has a relatively low water content in the early stage of infiltration, and the matrix potential is related to the water content, and its gradient is large, so the infiltration ability of the soil column is relatively strong. The volume moisture content increases rapidly. With the increase of time, Rain Water gradually entered the loess soil column, and the moisture content of the loess in the lower part of the soil column gradually increased, and the matrix potential gradient between the soil column and the upper loess gradually decreased. The ability of soil to accept water gradually decreases. Therefore, the loss of stability of loess slope is closely related to the decrease or even loss of soil matrix suction. In the process of re-irrigation, the initial moisture content is high and the matrix suction is relatively small. Under the action of the upper head pressure, matrix suction and gravity, the migration rate of the wetting front increases rapidly at the beginning, when the water moves to the bottom of the soil column. The matrix potential gradient is lost and the saturation infiltration is maintained. There is still a certain error between the soil column infiltration test results and the HYDRUS-1D numerical simulation results, which may be due to the deviation between the parameters of water characteristic curve and unsaturated water conductivity measured by small soil samples and the actual soil parameters in the soil column. Therefore, in the process of simulating the water infiltration of undisturbed loess, the appropriate classical model of soil-water characteristic curve should be selected, and the hysteretic curve between matrix suction and moisture content should be considered, and the influence of moisture absorption and desiccation on soil-water characteristic curve should be considered.
【学位授予单位】：北京工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：S152.72

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