非饱和黄土渗透性函数的试验研究
发布时间：2018-09-01 08:12
【摘要】：黄土高原是滑坡、崩塌等地质灾害易发地区。自然降雨和灌溉都是滑坡的主要诱发因素。黄土区地下水位一般很深,水分在土体中的运移属于非饱和渗流。因此,研究降雨或灌溉条件下黄土边坡的稳定性,或水分在黄土中的分布运移,都需要利用非饱和渗流理论。非饱和渗透系数是非饱和渗透方程的基本参数,与饱和渗透系数不同,它是含水率(或基质吸力)的函数,需要用特定的量测方法。本文通过室内渗透试验,选用瞬态剖面法测定甘肃正宁地区重塑马兰黄土(Q3)的非饱和渗透系数。试验装置为一高2m,外径25cm的圆柱形有机玻璃桶。土样碾压风干,用0.5mm的筛筛入玻璃桶,一系列EC-5土壤水分探头按5cm的间距预埋到土柱中。试验开始前,土样顶部补给2500ml的水量,密封玻璃桶。然后每隔一段时间采集数据,记录不同时刻土柱不同深度的含水率。同时在制样盒中单独配制土样,其干密度与玻璃桶土柱相同,选择张力计来测定基质吸力。分别采用FredlundXing、Gardner和Van Genuchten三种理论方程来拟合该土水特征曲线。不同时刻土样的总水头剖面由实测的体积含水率和土水特征曲线计算得到。基于以上三种拟合的土水特征曲线方程,利用瞬态剖面法分别计算获得了相应的非饱和渗透性曲线。同时,直接采用土水特征曲线法估算出相应的非饱和渗透性曲线。并对以上两种方法获得的渗透性曲线进行了比较。结果表明:基于FredlundXing和Gardner的土水特征曲线方程,两种方法的结果相差较大;而基于Van Genuchten的土水特征曲线方程,二者趋势相同,数值最接近。根据室内渗透试验建立SEEP/W数值模型,选用试验得到的非饱和渗透性曲线作为模型的参数。设与室内渗透试验相同的边界条件,模拟土柱中水分的运移,模拟结果与试验实测数据吻合,表明瞬态剖面法测非饱和渗透系数是可行的;改变数值模型的边界条件,研究土体中水分的运移。结果发现模型中,边界条件和土性一定的条件下,远离边界一定距离存在一个平衡区域,当平衡区域形成后,上部入渗不会改变其含水率,但会使底部隔水边界处水位上升。这和黄土区所观察到的现象基本一致。对非饱和渗透系数及土体中水分运移研究,为应用非饱和渗流理论研究降雨或灌溉型滑坡机理提供了基础。
[Abstract]:Loess Plateau is prone to landslide, collapse and other geological disasters. Natural rainfall and irrigation are the main inducing factors of landslide. The groundwater level in loess area is very deep, and the water migration in soil belongs to unsaturated seepage. Therefore, it is necessary to use unsaturated seepage theory to study the stability of loess slope under rainfall or irrigation, or the distribution and migration of water in loess. The unsaturated permeability coefficient is the basic parameter of the unsaturated permeability equation. It is a function of water content (or matrix suction), which is different from the saturated permeability coefficient. In this paper, the unsaturated permeability coefficient of remolded Ma Lan loess (Q3) in Zhengning area of Gansu Province is determined by using transient profile method through laboratory permeation test. The test device is a cylindrical plexiglass barrel with a height of 2 m and outer diameter of 25cm. The soil sample was compacted and air-dried and sifted into glass barrel with 0.5mm sieve. A series of EC-5 soil moisture probes were embedded in the soil column according to the spacing of 5cm. Before the test starts, the top of the soil samples recharge the 2500ml water and seal the glass barrel. Data are collected every other time to record the moisture content of the soil column at different times and at different depths. At the same time, the dry density of soil sample is the same as that of glass barrel soil column in the sample making box. FredlundXing,Gardner and Van Genuchten equations were used to fit the soil-water characteristic curve. The total head profile of soil samples at different times is calculated from the measured volume water content and soil water characteristic curve. Based on the above three fitting characteristic curve equations of soil and water, the corresponding unsaturated permeability curves are obtained by transient profile method. At the same time, the unsaturated permeability curve is estimated by the method of soil water characteristic curve. The permeability curves obtained by the two methods are compared. The results show that the results of the two methods differ greatly based on the characteristic curve equations of soil and water based on FredlundXing and Gardner, while the characteristic curve equations of soil and water based on Van Genuchten have the same trend and are most close to each other. According to the indoor permeability test, the SEEP/W numerical model was established, and the unsaturated permeability curve was selected as the parameter of the model. With the same boundary condition as the indoor permeation test, the water migration in the soil column is simulated. The simulation results are in agreement with the measured data, which shows that the transient profile method is feasible to measure the unsaturated permeability coefficient, and the boundary conditions of the numerical model are changed. The movement of water in soil is studied. The results show that in the model, there exists a equilibrium region at a certain distance from the boundary under certain boundary conditions and soil properties. When the equilibrium region is formed, the upper infiltration will not change its water content, but it will make the water level rise at the bottom barrier boundary. This is basically consistent with the observed phenomena in the loess area. The study of unsaturated permeability coefficient and water migration in soil provides a basis for the application of unsaturated seepage theory to study the mechanism of rainfall or irrigated landslide.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P642.131
本文编号：2216608
[Abstract]:Loess Plateau is prone to landslide, collapse and other geological disasters. Natural rainfall and irrigation are the main inducing factors of landslide. The groundwater level in loess area is very deep, and the water migration in soil belongs to unsaturated seepage. Therefore, it is necessary to use unsaturated seepage theory to study the stability of loess slope under rainfall or irrigation, or the distribution and migration of water in loess. The unsaturated permeability coefficient is the basic parameter of the unsaturated permeability equation. It is a function of water content (or matrix suction), which is different from the saturated permeability coefficient. In this paper, the unsaturated permeability coefficient of remolded Ma Lan loess (Q3) in Zhengning area of Gansu Province is determined by using transient profile method through laboratory permeation test. The test device is a cylindrical plexiglass barrel with a height of 2 m and outer diameter of 25cm. The soil sample was compacted and air-dried and sifted into glass barrel with 0.5mm sieve. A series of EC-5 soil moisture probes were embedded in the soil column according to the spacing of 5cm. Before the test starts, the top of the soil samples recharge the 2500ml water and seal the glass barrel. Data are collected every other time to record the moisture content of the soil column at different times and at different depths. At the same time, the dry density of soil sample is the same as that of glass barrel soil column in the sample making box. FredlundXing,Gardner and Van Genuchten equations were used to fit the soil-water characteristic curve. The total head profile of soil samples at different times is calculated from the measured volume water content and soil water characteristic curve. Based on the above three fitting characteristic curve equations of soil and water, the corresponding unsaturated permeability curves are obtained by transient profile method. At the same time, the unsaturated permeability curve is estimated by the method of soil water characteristic curve. The permeability curves obtained by the two methods are compared. The results show that the results of the two methods differ greatly based on the characteristic curve equations of soil and water based on FredlundXing and Gardner, while the characteristic curve equations of soil and water based on Van Genuchten have the same trend and are most close to each other. According to the indoor permeability test, the SEEP/W numerical model was established, and the unsaturated permeability curve was selected as the parameter of the model. With the same boundary condition as the indoor permeation test, the water migration in the soil column is simulated. The simulation results are in agreement with the measured data, which shows that the transient profile method is feasible to measure the unsaturated permeability coefficient, and the boundary conditions of the numerical model are changed. The movement of water in soil is studied. The results show that in the model, there exists a equilibrium region at a certain distance from the boundary under certain boundary conditions and soil properties. When the equilibrium region is formed, the upper infiltration will not change its water content, but it will make the water level rise at the bottom barrier boundary. This is basically consistent with the observed phenomena in the loess area. The study of unsaturated permeability coefficient and water migration in soil provides a basis for the application of unsaturated seepage theory to study the mechanism of rainfall or irrigated landslide.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P642.131
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