SUBDRAINAGE DESIGN

A pavement drainage system must be designed; using rules-of-thumb is simply not adequate. There are two criteria for establishing minimum required permeabilities of materials to be used in drainage systems: the quantity of water that might enter such a system and the permeability needed to carry that water out, and the permeability that is needed to get the water out fast enough so that there is inadequate time for freezing. To calculate the needs of systems, it is necessary to work with reasonable values for permeability factors, hydraulic gradients, and cross-sectional areas. Darcy's Law, although not used much for the purposes of designing pavement drainage systems, is an excellent way to determine an order-of-magnitude numerical solution to the kind of materials needed. Guidelines recommend that the designer assume some percentage of rainfall intensity is coming through the pavement surface or joints. The direction of flow of this water in the drainage layer is in the direction of the maximum gradient or perpendicular to the contour lines, as the water makes its way to the drain. It is generally more economical to go to a higher permeability material down to the point where it becomes not practical to build anything that thin. The drain capacity required to accommodate intercepted groundwater can also be determined from the application of Darcy's Law. If direct and indirect costs are included in an economic analysis, drains and drainage systems are not an expensive luxury. A chart is appended for determining the coefficient of transmissibility in inch feet per day.

  • Supplemental Notes:
    • This paper was presented at three 1973 workshops on Water in Pavements sponsored by the Federal Highway Administration, held in Albany, New York; Des Moines, Iowa; and Denver, Colorado.
  • Corporate Authors:

    Federal Highway Administration

    Office of Research, Development, Engineering and Highway Operations, 1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Authors:
    • Cedergren, H R
  • Conference:
  • Publication Date: 1973-11

Language

  • English

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: p. 146-164

Subject/Index Terms

Filing Info

  • Accession Number: 00792249
  • Record Type: Publication
  • Files: TRIS, USDOT
  • Created Date: May 3 2000 12:00AM