EXIT GRADIENTS INTO SUBSURFACE DRAINS

THE EXIT GRADIENTS INTO DRAIN PIPES OF VARIOUS DIAMETERS AND AT VARIOUS DEPTHS BELOW THE PONDED SOIL WATER SURFACE AND WITH AN IMPERMEABLE BARRIER AT VARYING DEPTHS BELOW THE DRAIN WERE INVESTIGATED BY PROGRAMMING KIRKHAM'S EQUATION FOR FLOW INTO DRAINS UNDER PONDED CONDITIONS. IT IS SHOWN THAT A QUICK CONDITION OR A WEIGHTLESS CONDITION OF THE SOIL CAN RESULT ONLY UNDER THE DRAIN LINES. IT IS ONLY AT THIS POINT THAT THE UPWARD HYDRODYNAMIC SEEPAGE FORCE IS GREATER THAN THE DOWNWARD GRAVITY FORCE OF THE SOIL PARTICLE. THE SEEPAGE FORCES RESULT IN AN EXIT GRADIENT THAT IS HIGHER THAN THE USUAL CRITICAL EXIT GRADIENT OF ONE FOR A FINE SAND MATERIAL WITHOUT SURCHARGE LOAD. IN ALMOST EVERY CASE, THE CRITICAL EXIT GRADIENT IS EXCEEDED WITH DRAIN LINES LOCATED 2, 3, AND 5 FEET BELOW THE WATER TABLE AND FOR DRAIN DIAMETERS OF 0.2-1.2 FEET. THE EFFECTS OF A SURCHARGE LOAD AND THE EFFECT OF THE COHESIVE FORCES AMONG THE SOIL PARTICLES ARE DISCUSSED. AS A RESULT OF THE ANALYSIS, IT IS TENTATIVELY RECOMMENDED THAT THE GRAVEL ENVELOPE BE LOCATED BENEATH THE DRAIN RATHER THAN ALL AROUND THE DRAIN AS IS CURRENTLY PRACTICED. /AUTHOR/

  • Supplemental Notes:
    • Vol 39, No 158 PP 419-428
  • Corporate Authors:

    Hilgardia

    ,    
  • Authors:
    • Luthin, J N
    • Taylor, G S
    • Prieto, C
  • Publication Date: 1968-12

Subject/Index Terms

Filing Info

  • Accession Number: 00204212
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jul 28 1994 12:00AM