Theory of a Rectangular Gravel Envelope in Drainage Design1
- Don Kirkham and
- M. Sami Selim2
A theory was developed to determine the radius of a circular drain which is equivalent to a square drain. A square drain is encountered in practice when a gravel envelope of square cross section is placed around a subsurface circular drain. The resistance of the gravel to flow was neglected. The square cross section of the envelope measured 4a2. The square drain tube was analyzed for two cases: (i) when an impermeable barrier was at great depth below the square drain tube center, and (ii) when the bottom edge of the square drain tube lay on a plane subsoil impermeable barrier. In both cases it was assumed that the length of 2a of the edge of the square drain tube was small compared with the distance from the drain's center to a water table over the drain and that the drain ran full. It is shown for Case 1 that an equivalent circular drain tube of radius 1.1772a may be used to replace the square drain tubes. If the square drains lie on the impervious layer, as in Case 2, the radius of the equivalent circular drain is 1.1037a.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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