Formation Mechanism of Water Level and Its Determination Method in Conventional Observation Wells for Three-Dimensional Groundwater Flow
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摘要: 对地下水三维流中常规观测孔中水位的传统计算方法提出质疑, 认为计算观测孔中水位的Hantush Бочевер方程是缺乏物理基础的纯数学方法.分析了形成观测孔中水位的机理, 提出三维地下水流中常规观测孔中只是孔口的流量为零, 而孔内却存在"抽水"和"注水"的井孔; 多层井(multilayerwell) 不一定要求"多层"的条件, 在均质单一含水层中的井孔可以具有多层井的基本特征; 混合井孔的水位并不"混合", 混合观测孔中存在符合机理的水头分布和流量分布规律等观点.普遍而言, 三维流中的观测孔不能用通常所说的线汇/线源刻画, 也不能用近几年提出的孔内为层流(线性流) 的假定来研究该问题, 然而可用笔者于1993年提出的"渗流-管流耦合模型"和"等效渗透系数"方便、有效地模拟.就说明性算例而言, Hantush Бочевер方程只能近似用于孔径大于0.2m且径距大于10~20m的条件.Abstract: The paper questions the traditional method for the calculation of the water level in the conventional observation wells for three-dimensional groundwater flow, and proposes that the Hantush -Бочевер equation, a pure mathematical method, is lacking in the basis of physics. The analysis of the formation mechanism of water level in the observation wells shows that the flux is zero only at the mouth of three-dimensional groundwater observation well, but the interior of the well contains actually "discharge" and "recharge" from the aquifers; that the water level in one homogeneous aquifer may have the same essential features as the multilayer well has; that the water level in the multilayer well is not mixed, and that the distribution of the head and flow in the multilayer well conforms to its own mechanism. Generally speaking, the observation well in the three-dimensional groundwater flow may not be described with the line sinks and line sources, nor can it be assumed that the flow in the observation well is determined by the laminar flow (linear flow) that has been proposed in recent years. However, the "seepage-pipe coupling model" and "equivalent hydraulic conductivity" (EHC) presented by the author in 1993 can be used to simulate very conveniently and effectively the three-dimensional groundwater flow. For the further illustration, the Hantush-Бочевер equation can only be approximately used in the conditions where the diameter of observation well is more than 0.2 m and that the distance between the well and the observation well is more than 10-20 m.
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图 2 检验模型有限元法与解析法对比(1~6为观测点序号)
Fig. 2. Contrast of defined element method and analytical method in test model
图 3 不同径距r观测孔中水头降深分布及Hantush-Бочевер公式计算值Sga
1.井径0.00 m; 2.井径0.02 m; 3.井径0.05 m; 4.井径0.10 m; 5.井径0.20 m; 6.Hantush-Бочевер公式计算值Sga
Fig. 3. Distribution of head drawdown in the observation well with different well distances and value of Sga calculated by Hantush-Бочевер formula
图 4 不同径距观测孔流量分布
a.径距5.19 m; b.径距21.19 m; c.径距45.01 m; d.径距65.25 m; 1.井径0.02 m; 2.井径0.05 m; 3.井径0.10 m; 4.井径0.20 m
Fig. 4. Flux distribution along vertical direction in observation well with different radius distances
图 5 不同径距观测孔中水流雷诺数的分布
a.径距5.19 m; b.径距21.19 m; c.径距45.01 m; d.径距65.25 m; 1.井径0.02 m; 2.井径0.05 m; 3.井径0.10 m; 4.井径0.20 m
Fig. 5. Re distribution in observation well with different radius distances
表 1 用于有限元解与解析解对比的观测点位置
Table 1. Position of observation spot used to compare defined element result with analytical result
表 2 完整观测孔内水位降深与Hantush-Бочевер降深对比
Table 2. Contrast of decline of complete observation well and decline of Hantush-Бочевер
表 3 径距不同时观测孔的通道效应ΔH (do, r)
Table 3. Channel effect of observation well in different radius distances
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