DISCUSSION OF FINITE-ELEMENT ANALYSIS OF SEEPAGE THROUGH DAMS

THE DISCUSSERS INDICATE THAT THE AUTHOR'S PAPER ON THE SOLUTION OF SEEPAGE PROBLEMS WAS OF GREAT INTEREST BECAUSE THEY ARE ALSO INVOLVED IN THE STUDY OF SEEPAGE PHENOMENA. THE USE OF CASAGRANDE EXIT POINTS IS DISCUSSED. THESE POINTS WERE DETERMINED BY THE USE OF THE SINE METHOD WITH AN ENTRANCE CORRECTION, AS PRESCRIBED BY CASAGRANDE. HIS LECTURES EMPHASIZE THAT THIS PROCEDURE IS NOT APPLICABLE IN ALL SITUATIONS. MEASUREMENTS OF THE DAM SECTIONS PRESENTED INDICATED THAT THE D/H RATIO FOR THESE SECTIONS IS LESS THAN AND EQUAL TO 1, RESPECTIVELY. THIS EXPLAINS WHY THE CASAGRANDE EXIT POINTS ARE ABOUT 10 PERCENT LOWER THAN THOSE OBTAINED BY THE FINITE-ELEMENT METHOD. ALTERNATIVE METHODS ARE DISCUSSED FOR SOLVING STEADY SEEPAGE PROBLEMS. THESE METHODS ARE: (1) THE GRAPHICAL SLOW NET METHOD ILLUSTRATED IN CASAGRANDE'S PAPER, AND (2) A NUMERICAL METHOD SUITED FOR IMPLEMENTATION ON A DIGITAL COMPUTER. LIKE THE AUTHOR'S METHOD, THE LATTER INVOLVES MODELING THE SEEPAGE REGION OF A DAM WITH AN ENSEMBLE OF DISCREET ELEMENTS. HOWEVER, THE ELEMENTS USED IN THE PRESENT METHOD ARE QUADRILATERALS INSTEAD OF TRIANGLES, EXCEPT ALONG CERTAIN BOUNDARIES. TWO EXAMPLES ARE GIVEN OF THE APPLICATION OF THIS METHOD. IN ONE EXAMPLE THE COMPUTER-GENERATED SEEPAGE RATE WAS FOUND TO DIFFER FROM THE ANALYTIC SOLUTION BY 0.6 PERCENT. MR. MAKHLOUF CONTRIBUTES A FEW REMARKS TOWARD A SIMPLIFICATION OF THE APPLICATION OF DIGITAL COMPUTERS TO THE SOLUTION OF SEEPAGE PROBLEMS. IN THE CASE OF EARTH DAMS, THE PHREATIC SURFACE MAY BE CONSTRUCTED BY ANY OF SEVERAL AVAILABLE METHODS AND USED AS A FIXED BOUNDARY CONDITION. THIS SAVES COMPUTER TIME AND EFFORT IN PROGRAMMING. THE PROPOSED METHOD DETERMINES POTENTIALS AT THE NODES BY A CLOSED FORM MATRIX SOLUTION. BY A CAREFUL CHOICE OF THE BOUNDARY CONDITIONS, HOWEVER, SOLUTION OF THE LAPLACE EQUATION BY ITERATION PROCEDURES BECOMES POSSIBLE, AND COMPUTER STORAGE MAY BE CUT DOWN TO A MINIMUM. THIS PROCEDURE HAS BEEN APPLIED TO AN ADVANTAGE IN THE SOLUTION OF SEEPAGE THROUGH EARTH DAMS OF NONHOMOGENEOUS SECTIONS. REFERENCES: FINITE-ELEMENT ANALYSIS OF SEEPAGE THROUGH DAMS, W. D. LIAM FINN, ASCE, (PROC. PAPER 5552), NOVEMBER 1967.

  • Supplemental Notes:
    • Vol 95, No SM1, PP 342 - 346, 4 FIG, 5 REF, 1 APP
  • Corporate Authors:

    N/A

    ,   USA 
  • Authors:
    • Lo, R C
    • Tillman, C C
    • Makhlouf, H M
  • Publication Date: 0

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  • Accession Number: 00232674
  • Record Type: Publication
  • Report/Paper Numbers: No SM5, Proc Paper 490
  • Files: TRIS
  • Created Date: Aug 15 2004 2:44AM