Corrugated Plastic Drain Tubing Used as Underground Conduit

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Agricultural and Biosystems EngineeringSeed Science Center
Model studies were made to investigate the effect of high water velocity on the extent of soil movement when corrugated plastic drain tubing is used as conduits for underground terrace outlets on steep slopes. No significant amount of sediment was drawn into the tubing, even when the slope was 10 percent and velocity approached 9 ft per sec. The magnitude of the flow from the tubing to the soil was low in cohesive soils. But, with less cohesive soils this outflow was greater and there was considerable movement of soil from around the tubing. Corrugated plastic drain tubing has been used extensively in water disposal systems in recent years. Thus, there is a need for research to determine its performance and limitations. This study was undertaken to evaluate the effect of velocity of flow on the performance of such tubing when it is used as a conduit in underground terrace outlet systems. A successful method of controlling surface runoff combines a system of terraces and underground outlets to remove the excess water. The basic concept of such a system is to store the runoff temporarily in the terrace chan-nel and gradually drain it off through an underground conduit. Because of the detention storage, small diameter conduits can be used to carry the runoff. The underground terrace outlet system consists of a vertical intake riser located in the terrace channel, an underground conduit and an outlet section. Clay or concrete farm drain tile, clay sewer pipe, asbestos cement pipe or corrugated plastic tubing is used for the outlet conduit. In areas where excess groundwater is a problem, it is desirable that the system provides subsurface drainage in addition to removal of surface runoff. When drain tile is used, groundwater enters the drain at the joint between the tiles. When the velocity in the tile line becomes excessive on steep slopes, the turbulence causes movement of soil near the opening between the tiles, which re-sults in misalignment of the tile line. When misalignment occurs, the flow is obstructed and the turbulence increases which, in turn, causes greater misalignment and causes debris to enter the line. Design recommendations by ASAE (1974) to prevent the misalignment, include maximum permissible velocities in tile drains when protective measures are not used. The velocities range from 3.5 to 9.0 ft per sec depending on soil texture. On sites where the grade exceeds 2.0 percent or the design velocities exceed the given value, special protective measures are recommended. For continuous pipe with perforations, the recom-mended protective measure is to com-pletely enclose the pipe with filter mate-rials. In most occasions an underground conduit used as a terrace outlet must be installed on much steeper slope than 2.0 percent and the water velocity in the conduit becomes quite high. Misalignment is not a problem with corrugated plastic drain tubing since the tubing is flexible and continuous. Nevertheless, in some areas the velocity limitations specified for drain tile are also used for corrugated plastic drain tubing (Griessel and Beasley 1969). No research has been cited to show the validity of these velocity limitations as applied to the corrugated plastic drain tubing. Corrugated plastic drain tubing has a number of perforations per foot of length. Therefore, it is possible that some water escapes to the soil from the tubing. This outflow may establish a flow along the sides and beneath the tubing. The flow may cause movement of soil along the sides of the tubing or undermining the tubing.
This article is published as Misra, M. K., and R. P. Beasley. "Corrugated Plastic Drain Tubing Used as Underground Conduit." Transactions of the ASAE 18, no. 2 (1975): 0260-0262. DOI: 10.13031/2013.36568. Copyright 1975 ASABE. Posted with permission.