Seepage into drain tubes in stratified soil I ‐ Drains in the surface stratum

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Abstract
Expressions for the drain flow, the surface inflow distribution , and flow nets are derived for surface water seeping into drain tubes embedded in water‐saturated soil consisting of two horizontal strata of different permeabilities. In Part I, the drain tubes are located in the upper layer. Numerical results are presented. It is shown in the case of the flow nets how Kennelly's tables of the complex hyperbolic sine may be used to obtain numerical values for equipotentials and stream lines simultaneously. The flow nets, as well as other results, show that unless the lower layer is of high permeability compared to the upper layer, the lower layer has little effect on the flow.In Part II, the drain tubes are located in the lower layer which extends to great depth. It is shown that, unless the drain tubes are very near the upper layer, or unless the upper and lower layers are of approximately the same permeability, fee lower layer governs the flow. Quantitative results are worked out for several cases, including a flow net. The mathematical analysis in both cases is presented in some detail. This is done so that the reader will be able to work out certain details readily for himself. But the material is presented in such a way that readers not desiring to follow mathematical details may, without loss of continuity, skip all but the first few paragraphs of the Analysis and proceed to Results and Discussion.