本文選題：水動(dòng)力彌散　切入點(diǎn)：空間尺度效應(yīng)　出處：《西南交通大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

【摘要】：水動(dòng)力彌散系數(shù)為表征污染物在含水層中遷移、分布的重要參數(shù)。國(guó)內(nèi)外大量研究發(fā)現(xiàn),該參數(shù)隨研究時(shí)間、空間范圍變化而具有尺度效應(yīng)。如果能夠準(zhǔn)確把握第四系松散巖類孔隙含水介質(zhì)水動(dòng)力彌散規(guī)律及其空間尺度效應(yīng)變化規(guī)律,無(wú)疑將有助于為該類含水介質(zhì)地下水的溶質(zhì)運(yùn)移數(shù)值模擬和污染防治提供基本參數(shù)和理論依據(jù)。本文在總結(jié)國(guó)內(nèi)外文獻(xiàn)的基礎(chǔ)上,分別采用室內(nèi)模擬試驗(yàn)、現(xiàn)場(chǎng)彌散試驗(yàn)及數(shù)值模擬方法,對(duì)松散巖類孔隙含水介質(zhì)水動(dòng)力彌散規(guī)律及其尺度效應(yīng)進(jìn)行了研究。(1)室內(nèi)彌散試驗(yàn)結(jié)果表明：①滲透性較好的松散沉積物中,溶質(zhì)濃度不是彌散系數(shù)確定的主要控制因素,當(dāng)溶質(zhì)由510mg/L增至2040mg/L時(shí),彌散系數(shù)僅增加1.1-15.7%。②調(diào)整孔隙介質(zhì)骨架構(gòu)成,試驗(yàn)柱體彌散度隨砂柱中粘土混合比例增加而降低,粒徑為0.25～0.5mm砂彌散度為4.48cm,隨混入粒徑5～50μm粘土體積比由1/9增至1/5,介質(zhì)平均彌散度降至2.97～1.845cm。③確定的孔隙含水介質(zhì)中,滲流速度為水動(dòng)力彌散系數(shù)的主要影響因素,調(diào)整彌散柱體滲流速度由0.026cm/min增至0.051cm/min,彌散系數(shù)增大了2.29～2.32倍。④彌散空間尺度效應(yīng)僅存在于非均質(zhì)孔隙介質(zhì)較遠(yuǎn)距離運(yùn)移過(guò)程中,實(shí)驗(yàn)室采用粒度分布較均勻孔隙介質(zhì)進(jìn)行的短距離彌散試驗(yàn),實(shí)質(zhì)為模擬均勻介質(zhì)的水動(dòng)力彌散過(guò)程,不會(huì)出現(xiàn)彌散空間尺度效應(yīng)。平均粒徑0.25～0.5mm砂及砂混粘土(平均粒徑5-50pmm)在運(yùn)移距離為0.8～1.2m時(shí)進(jìn)行水動(dòng)力彌散試驗(yàn),彌散度隨示蹤劑遷移距離增加基本保持穩(wěn)定。(2)現(xiàn)場(chǎng)彌散試驗(yàn)結(jié)果顯示,示蹤劑投加孔下游1m、10m和40m運(yùn)移范圍確定的縱向水動(dòng)力彌散度分別為0.069m、0.519m和0.969m。隨溶質(zhì)運(yùn)移距離增加10～40倍,彌散度增大7.5～14倍,研究區(qū)水動(dòng)力彌散空間尺度效應(yīng)明顯。(3)結(jié)合現(xiàn)場(chǎng)彌散系數(shù)隨運(yùn)移距離變化特點(diǎn),根據(jù)分維度公式確定研究區(qū)彌散度αL與運(yùn)移距離L滿足函數(shù)關(guān)系αL=10-1.122·L0.733。根據(jù)該函數(shù)關(guān)系,可估算研究區(qū)不同運(yùn)移距離彌散度,為同類型含水介質(zhì)溶質(zhì)運(yùn)移模擬參數(shù)選取提供依據(jù)。(4)根據(jù)現(xiàn)場(chǎng)水文地質(zhì)條件,采用Modflow軟件建立數(shù)值模型對(duì)現(xiàn)場(chǎng)彌散試驗(yàn)進(jìn)行模擬,結(jié)果表明：受彌散空間尺度效應(yīng)影響,以現(xiàn)場(chǎng)lm及40m溶質(zhì)運(yùn)移距離確定的彌散度作為模型參數(shù)均無(wú)法較好的模擬示蹤劑投放孔下游40m位置濃度隨時(shí)間變化的實(shí)測(cè)情況。采用研究區(qū)彌散度分維度公式求取40m運(yùn)移距離算術(shù)平均彌散度α,以α作為模型彌散度進(jìn)行溶質(zhì)運(yùn)移模擬,模擬結(jié)果可較客觀地反映溶質(zhì)運(yùn)移起始點(diǎn)下游40m位置濃度隨時(shí)間變化。由此可見(jiàn),在該類含水介質(zhì)中進(jìn)行地下水污染數(shù)值模擬時(shí),以前述函數(shù)關(guān)系先估研究范圍內(nèi)算術(shù)平均彌散度α,進(jìn)而以α作為模型參數(shù),可提高模擬結(jié)果的準(zhǔn)確性。
[Abstract]:The hydrodynamic dispersion coefficient is an important parameter to characterize the transport and distribution of pollutants in the aquifer. If we can accurately grasp the hydrodynamic dispersion law of porous water-bearing medium of Quaternary loose rock and the variation law of spatial scale effect, It will undoubtedly be helpful to provide basic parameters and theoretical basis for numerical simulation of solute transport and pollution prevention and control of groundwater in this kind of water-bearing medium. In situ dispersion test and numerical simulation method, the hydrodynamic dispersion law and its scale effect in porous porous media of loose rock are studied. The solute concentration is not the main controlling factor for determining the dispersion coefficient. When the solute concentration increases from 510mg / L to 2040mg / L, the dispersion coefficient increases only by 1.1-15.7.2, and the dispersion degree of the test column decreases with the increase of clay mixing ratio in the sand column. The particle size is 0.25 ~ 0.5mm and the dispersion of sand is 4.48 cm. With the increase of clay volume ratio of 5 ~ 50 渭 m from 1/9 to 1 / 5, the average dispersion of the medium decreases to 2.97 ~ 1.845 cm ~ (3), and the seepage velocity is the main factor influencing the hydrodynamic dispersion coefficient. When the flow velocity of dispersion cylinder is increased from 0.026 cm / min to 0.051 cm / min, the dispersion coefficient increases by 2.29 ~ 2.32 times, and the dispersion spatial scale effect only exists in the long distance migration of heterogeneous porous media. In the laboratory, the short distance dispersion test carried out by a porous medium with a more uniform particle size distribution is essentially a simulation of the hydrodynamic dispersion process of the homogeneous medium. There will be no dispersion spatial scale effect. The hydrodynamic dispersion test is carried out when the migration distance is 0.8 ~ 1.2m, and the mean diameter is 0.25 ~ 0.5 mm sand and sand mixed clay (mean diameter 5-50 pmm). The results of field dispersion test show that the longitudinal hydrodynamic dispersion is 0.069 m / 0. 519 m and 0. 969m, respectively, and increases by 1040 times with solute transport distance, the results of field dispersion test show that the range of migration of tracer is 0. 069 m ~ 0. 519 m and 0. 969m respectively, and the range of migration of tracer is 1 m ~ 10 m and 40 m downstream of the hole, respectively, and the dispersion degree is 0. 069 m ~ 0. 19 m and 0. 96 9 m. The dispersion degree increases by 7.5 ~ 14 times, and the spatial scale effect of hydrodynamic dispersion is obvious. According to the dimensionality formula, the functional relationship between dispersion degree 偽 L and transport distance L is determined. According to the function relationship, the dispersion degree of different transport distances in the study area can be estimated. This paper provides a basis for selecting the parameters of solute transport simulation in the same type of water-bearing medium. According to the hydrogeological conditions in the field, the numerical model is established by using Modflow software to simulate the field dispersion test. The results show that it is affected by the spatial scale effect of dispersion. Based on the dispersion of solute transport distance of lm and 40m in the field, it is impossible to simulate the variation of the concentration of 40 m downstream of the tracer hole with time. The dispersion dimension formula of the study area is used to solve the problem. Taking the 40m migration distance as the arithmetic mean diffusivity 偽, the solute transport simulation is carried out with 偽 as the model dispersion degree. The simulation results can objectively reflect the variation of concentration at 40m downstream of the starting point of solute migration with time. It can be seen that the numerical simulation of groundwater pollution in this kind of water-bearing medium is carried out. The accuracy of the simulation results can be improved by first estimating the arithmetic average dispersion 偽 in the scope of the study and then using 偽 as the model parameter.
【學(xué)位授予單位】：西南交通大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：X523

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