海岸带含水层系统中海潮引起的地下水流的荷载效应和密度效应的数值模拟研究

发布时间：2018-06-04 02:16

本文选题：滨海含水层 + 数值模拟　；参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：海潮引起的海水水位的周期性波动必然会引起下部含水层压力的变化,这种压力变化势必会对含水层地下水动态造成一定的影响,即海潮荷载效应。在过去的60多年里,各国的许多专家学者对海潮引起水位波动进行了解析研究,其中有很多涉及到这种作用机制。但是,目前所有的地下水数值模拟软件中,即使是很出名的,如MODFLOW、FEFLOW等软件,都没有考虑这种效应。本文运用已拓展的数值模拟程序MARUN进行数值模拟研究。MARUN程序考虑了盐分对液体粘度和密度的影响,能模拟非饱和带空隙介质中水流和溶质运移。拓展后的MARUN程序添加了海潮荷载效应,本文利用其参照文献中关于海潮荷载效应的解析模型,考虑了两种滨海多层含水层系统：第一种含水层系统包括上部潜水含水层、中间的弱透水层以及下部的承压含水层,其中弱透水层及承压含水层在海底延伸一段有限距离；第二种含水层系统包括上部的隔水层、下部的承压层以及在海底露头处隔水的淤泥覆盖层,其中隔水层及承压含水层在海底延伸一段有限距离。模拟了荷载系数在0-1范围内的几种典型情况。对于第一种含水层系统,在考虑地下水密度效应时,承压含水层中文献解析解与本文数值解水头波动之间的误差不超过海潮波幅的0.21%,在弱透水层中的海岸带附近区域误差较大,在弱透水层的其他区域,数值解和解析解水头波动吻合情况较好。在第二种含水层系统中,在考虑地下水密度效应时,文献解析解与本文数值解误差不超过海潮波幅的0.12%。海水和地下淡水之间的密度差异必然会影响地下水动态,本文利用数值模拟程序MARUN,对比了考虑和忽略密度效应两种情况的数值解,模拟了单一潜水含水层和复杂多层含水层两种类型,分别取不同海滩坡度研究密度效应对水头波动的影响。数值模拟对比结果表明,对于单一潜水含水层,在潮间带下部的含水层中,坡度为0.1时,考虑和忽略密度效应两种情况的数值解之间的最大误差为2.5%,该误差随海滩坡度的增加而增大,当坡度达到0.86时,潮间带下部含水层中误差达到百分之十几,说明在单一潜水含水层中,密度效应在影响水头波动的同时会受到坡度的影响。对于多层结构含水层,在不同坡度情况下,弱透水层与承压含水层中最大误差均为2.50%,且在水陆界面上达到,说明密度效应几乎不受坡度的影响。
[Abstract]:The periodic fluctuation of the sea water level caused by the sea tide will inevitably lead to the change of the pressure of the lower aquifer, which will inevitably have a certain effect on the groundwater dynamics of the aquifer, that is, the tidal load effect. In the past 60 years, many experts and scholars of various countries have made analytical research on the fluctuation of water level caused by sea tide, many of which are related to this mechanism. However, even well-known software, such as MODFLOWFEFLOW, does not take this effect into account. In this paper, the extended numerical simulation program MARUN is used to simulate the fluid flow and solute transport in unsaturated porous media, considering the effect of salt on the viscosity and density of the liquid. The expanded MARUN program adds the tidal load effect. In this paper, two kinds of coastal multilayer aquifer systems are considered by referring to the analytical model of the tidal load effect in the literature. The first aquifer system includes the upper submersible aquifer. The intermediate weak permeable layer and the lower confined aquifer, in which the weakly permeable layer and the confined aquifer extend a limited distance from the seabed; the second aquifer system includes the upper aquifer, The bottom of the confined layer and the silt cover that separates water at the outcrop of the seafloor, in which the water-isolated layer and the confined aquifer extend at a limited distance from the bottom of the sea. Several typical cases with load coefficient in the range of 0-1 are simulated. For the first aquifer system, when the groundwater density effect is considered, the error between the analytical solution in the confined aquifer and the numerical solution in this paper does not exceed 0.21 of the tidal wave amplitude, and the regional error is larger in the coastal zone near the weak permeable layer. In other regions of the weakly permeable layer, the numerical and analytical solutions are in good agreement with the water head fluctuation. In the second aquifer system, when the groundwater density effect is considered, the error between the analytical solution and the numerical solution in this paper is not more than 0.12 of the tidal wave amplitude. The density difference between seawater and fresh water will inevitably affect groundwater dynamics. In this paper, the numerical solutions of considering and neglecting the density effect are compared by using the numerical simulation program Marun. Two types of submersible aquifer and complex multilayer aquifer were simulated. The effects of density effect on the water head fluctuation were studied with different beach slopes. The numerical simulation results show that for a single aquifer, the slope of the aquifer in the lower part of the intertidal zone is 0.1, The maximum error between the numerical solutions considering and ignoring the density effect is 2.5, which increases with the increase of the beach slope. When the slope reaches 0.86, the error in the lower aquifer of the intertidal zone reaches more than ten percent. It is concluded that in a single aquifer, the density effect will be affected by the slope as well as the water head fluctuation. For the multi-layered aquifer, the maximum error between the weakly permeable aquifer and the confined aquifer is 2.50 at different slopes, and the maximum error is achieved at the water-land interface, indicating that the density effect is almost independent of the slope.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P641;P731.23

【共引文献】