非饱和黄土入渗试验研究

发布时间：2018-06-02 03:33

本文选题：非饱和黄土 + 渗流　；参考：《长安大学》2016年硕士论文

【摘要】：野外调查表明,黄土地区地下水位一般高于临河水位,地下水没有临近河流水源的补给,因此大气降水(局部灌溉)成为黄土地区地下水仅有的补给来源。通过天然降雨剖面、人工降雨剖面、灌溉剖面观测不同深度的含水率,发现地表水在黄土中的浸润深度有限,难以到达地下水位,因此黄土中的地表水是如何运移并补给地下水是人类一直感兴趣的课题。本文拟通过现场观测和试验的方法,揭示降雨在非饱和黄土中入渗规律及补给地下水的机理。考虑到以往试验观测深度小、时间短,且降雨在黄土中的入渗规律和影响深度尚不明确。本文在甘肃省正宁县设立监测站,开挖一口深96.0m,直径1.0m观测井,用以监测黄土塬区地表水入渗补给地下水的完整过程。地面设置雨量计、气压计、空气温度计及空气湿度计;井壁插入土壤水分计;井底水位面以下设置水位计。结果显示:降雨引起土体含水率增大,最大浸润深度不超过4.0m;降雨量越大,土壤含水率增幅越大,含水率增大的响应时间越快,影响深度越大,随着深度增加,增幅减小,时间上渐有滞后;非饱和黄土中,水分入渗主要以非饱和渗流或水汽形式迁移;地下水位受气压的影响明显,和当前降雨无明显联系。针对现场监测得出的规律,在室内做了一个小型土柱模型试验,取塬边L1马兰黄土,人工加水模拟降雨,测量加水过程中含水率与基质吸力的随时间的变化。通过测得的含水率与基质吸力,结合黄土中应用最广泛的Gardner、van Genuchten和FredlundXing三种理论模型拟合试验数据,得到重塑马兰黄土的土水特征曲线,结果表明FredlundXing模型的拟合度最高。马兰黄土重塑样中,湿润锋扫过的土壤含水率不变,最大值与饱和含水率的比值为0.74。同时,基于非饱和理论建立监测井和土柱试验模型,利用Geo-Studio软件结合试验测得的土水特征曲线及渗透性曲线,模拟降雨和土柱试验中水在黄土中的入渗过程。模拟结果与现场监测结果、室内试验结果相吻合。说明水在黄土中的渗流属于非饱和渗流,对非饱和渗流理论在实际工程中的应用提供了依据。
[Abstract]:The field investigation shows that the groundwater level in loess area is generally higher than that in the adjacent river, and there is no recharge of groundwater near the river source, so the atmospheric precipitation (local irrigation) is the only source of groundwater recharge in loess area. Through the observation of water content at different depths through natural rainfall section, artificial rainfall section and irrigation section, it is found that the infiltration depth of surface water in loess is limited and it is difficult to reach the groundwater level. Therefore, how the surface water in loess is transported and recharged is a subject of human interest. This paper intends to reveal the infiltration law of rainfall in unsaturated loess and the mechanism of recharge of groundwater by means of field observation and test. Considering the small depth and short time, the infiltration law and influence depth of rainfall in loess are not clear. In this paper, a monitoring station was set up in Zhengning County, Gansu Province, and an observation well with a depth of 96.0m and a diameter of 1.0m was excavated to monitor the complete process of surface water infiltration and recharge of groundwater in the Loess Plateau. Set rain gauge, barometer, air thermometer and air hygrometer on the ground; insert well wall into soil moisture meter; set water level meter below bottom water level. The results show that the soil moisture content increases and the maximum wetting depth is not more than 4.0 m, the larger the rainfall, the larger the increase of soil moisture content, the faster the response time of water content increase, the greater the influence depth, and the smaller the increase with the increase of soil moisture content. In the unsaturated loess, the water infiltration is mainly in the form of unsaturated seepage or water vapor, and the groundwater level is obviously affected by the pressure, and has no obvious relation with the current rainfall. A small soil column model test was carried out in the laboratory according to the law obtained by field monitoring. The L _ 1 Ma Lan loess was taken from the edge of the tableland to simulate rainfall with artificial water, and the variation of water content and matrix suction with time was measured. The soil-water characteristic curve of remolded Ma Lan loess was obtained by combining the measured moisture content and the suction of matrix, combined with the experimental data fitted by the most widely used three theoretical models of Gardnervan Genuchten and FredlundXing in loess. The results show that the FredlundXing model has the highest fitting degree. In the remolded Ma Lan loess, the moisture content of the soil swept by the wetting front was unchanged, and the ratio of the maximum value to the saturated moisture content was 0.74. At the same time, the model of monitoring well and soil column test is established based on unsaturated theory. The infiltration process of water in loess is simulated by combining the characteristic curve of soil and water and permeability curve measured by Geo-Studio software. The simulation results are in good agreement with the field monitoring results. It shows that the seepage of water in loess belongs to unsaturated seepage, which provides the basis for the application of unsaturated seepage theory in practical engineering.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TU411.4

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