【摘要】：黃土高原是滑坡、崩塌等地質(zhì)災(zāi)害易發(fā)地區(qū)。自然降雨和灌溉都是滑坡的主要誘發(fā)因素。黃土區(qū)地下水位一般很深,水分在土體中的運(yùn)移屬于非飽和滲流。因此,研究降雨或灌溉條件下黃土邊坡的穩(wěn)定性,或水分在黃土中的分布運(yùn)移,都需要利用非飽和滲流理論。非飽和滲透系數(shù)是非飽和滲透方程的基本參數(shù),與飽和滲透系數(shù)不同,它是含水率(或基質(zhì)吸力)的函數(shù),需要用特定的量測(cè)方法。本文通過(guò)室內(nèi)滲透試驗(yàn),選用瞬態(tài)剖面法測(cè)定甘肅正寧地區(qū)重塑馬蘭黃土(Q3)的非飽和滲透系數(shù)。試驗(yàn)裝置為一高2m,外徑25cm的圓柱形有機(jī)玻璃桶。土樣碾壓風(fēng)干,用0.5mm的篩篩入玻璃桶,一系列EC-5土壤水分探頭按5cm的間距預(yù)埋到土柱中。試驗(yàn)開(kāi)始前,土樣頂部補(bǔ)給2500ml的水量,密封玻璃桶。然后每隔一段時(shí)間采集數(shù)據(jù),記錄不同時(shí)刻土柱不同深度的含水率。同時(shí)在制樣盒中單獨(dú)配制土樣,其干密度與玻璃桶土柱相同,選擇張力計(jì)來(lái)測(cè)定基質(zhì)吸力。分別采用FredlundXing、Gardner和Van Genuchten三種理論方程來(lái)擬合該土水特征曲線。不同時(shí)刻土樣的總水頭剖面由實(shí)測(cè)的體積含水率和土水特征曲線計(jì)算得到�；谝陨先N擬合的土水特征曲線方程,利用瞬態(tài)剖面法分別計(jì)算獲得了相應(yīng)的非飽和滲透性曲線。同時(shí),直接采用土水特征曲線法估算出相應(yīng)的非飽和滲透性曲線。并對(duì)以上兩種方法獲得的滲透性曲線進(jìn)行了比較。結(jié)果表明:基于FredlundXing和Gardner的土水特征曲線方程,兩種方法的結(jié)果相差較大;而基于Van Genuchten的土水特征曲線方程,二者趨勢(shì)相同,數(shù)值最接近。根據(jù)室內(nèi)滲透試驗(yàn)建立SEEP/W數(shù)值模型,選用試驗(yàn)得到的非飽和滲透性曲線作為模型的參數(shù)。設(shè)與室內(nèi)滲透試驗(yàn)相同的邊界條件,模擬土柱中水分的運(yùn)移,模擬結(jié)果與試驗(yàn)實(shí)測(cè)數(shù)據(jù)吻合,表明瞬態(tài)剖面法測(cè)非飽和滲透系數(shù)是可行的;改變數(shù)值模型的邊界條件,研究土體中水分的運(yùn)移。結(jié)果發(fā)現(xiàn)模型中,邊界條件和土性一定的條件下,遠(yuǎn)離邊界一定距離存在一個(gè)平衡區(qū)域,當(dāng)平衡區(qū)域形成后,上部入滲不會(huì)改變其含水率,但會(huì)使底部隔水邊界處水位上升。這和黃土區(qū)所觀察到的現(xiàn)象基本一致。對(duì)非飽和滲透系數(shù)及土體中水分運(yùn)移研究,為應(yīng)用非飽和滲流理論研究降雨或灌溉型滑坡機(jī)理提供了基礎(chǔ)。
[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.
【學(xué)位授予單位】：長(zhǎng)安大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：P642.131

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本文編號(hào)：2216608