Drain Tube Opening Effects on Drain Inflow

Abstract

Laboratory tests were conducted to determine the effects of total opening area, location of openings and gravel envelope on radial flow to 100 mm (4 in.) diam corrugated plastic drains. Radial flow theory was used to evaluate the effective drain tube radius, re, and the drainage transfer coefficient for the corrugated tubes. The effective radius increased with total perforation area as expected, but the location of the drain tube perforation had little effect on re. The greatest increase of effective radius for an increase in perforation area occurred between areas of 38-75cm2/m where re increased from 5 mm to about 21 mm. Use of a 50 mm thick gravel envelope resulted in an increase in the effective drain radius for a 100 mm diam pipe from 5–36 mm. Experimental results for the effective radius were compared to theoretical values obtained from an earlier solution for circumferential openings. The experimental results were in close agreement with predicted values for a 1.0 mm opening width.