Studies on the Validity of Darcy's Law for Flow in Natural Sands.

摘要

Well entrance losses are commonly assumed to be due,in part,to non-Darcy flow near the well,but concrete evidence for non-Darcy flow of water in natural sands at any reasonably large macroscopic flow velocity does not appear to exist. On the other hand,at very low flow velocities,the permeability of sands varies with macroscopic flow velocity in a very complex way,and some earlier studies purporting to support the validity of Darcy's Law at very low flow velocities actually support this view. Changes in flow resistance appear to be related,in part,to the surface chemistry of quartz. Experiments at high flow velocities showed no dramatic change in permeability in the range of one to two cm/sec,but,because of problems with piezometry,the results are not considered conclusive. One basic cause of 'well entrance losses'probably is over estimation of the average permeability of the aquifer,either because gas permeameters are used,or because tests with water are conducted in the first three flow regimes. (Modified author abstract)