Abstract
In recent years, the importance of reasonable tile drainage has increasingly recognized. The soil of paddy fields lies generally not in homogeneous but in layered conditions. In such soil layers, the tile drainage should be designed reasonably with the consideration of the layered conditions of soil.
Amoung the various analytical methods for the studies on the flow of water in soil, the resistance network analogue seems to be a usefull one from the practical point of view and high accuracy solving data on numerical analysis by electrical analogue.
For the reasons mentioned above, the authors have preliminarily constructed the resistance network for the fundamental studies on the tile drainage in layered soils and considered on the accuracy of this network.
When the resistance network analogue is applied to the tile drainage investigations, determination of boundary condition at the drain perimeter becomes a problem.
In this paper, the writers assumed that the water in the vicinity of the drain is flowing radially toward the drain and that the equipotentials form concentric circles. From this assumptions, the boundary condition at the drain perimeter can be estimated by a simple equation as follows:
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where RAQ is the resistance at the drain perimeter, s is the net spacing, r is the drain radius and R0 is the basic resistance.
In order to assure the above equation, the tile drainage in homogeneous soil was experimented, and its results were compared with the theoretical solutions by Kirkham (1949). As a result, if the above equation was used, the accuracy of this network was ascertained to be satisfactory enough for practical use.
