Effective Radius of Corrugated Drainage Pipes Wrapped with a Thin Geotextile Envelope

Abstract

Entrance resistance occurs when water flows into a perforated subsurface drainage pipe, making the effective radius smaller than the real radius. Accurately calculating effective radius is essential for drainage calculation. No effective radius formulas for corrugated drains wrapped with thin geotextile are applicable. In this study, new effective radius formulas were proposed by dividing the entrance resistance into corrugation and perforation resistance. The accuracy of the formulas was verified by experiments. Sensitivity analysis was conducted, indicating that corrugation was the main factor affecting drainage efficiency. When the radius and structure of the drain wall were determined, the opening area exhibited high sensitivity with interactivity between it and drainage discharge. The effect of the opening area and position of the perforations on the effective radius was evaluated for different drainage discharges. Placing more rows of perforations on the lower half of the pipes was better for drainage efficiency. For small drainage discharge of less than 0.1 cm3 s−1 cm−1, the opening area was not significant, and an opening area of 15 cm2 m−1 was sufficient. However, for greater drainage discharge, an opening area of 60 cm2 m−1 would be required.