THE IOWA DEFLECTION FORMULA: AN APPRAISAL WITH DISCUSSION

THE IOWA DEFLECTION FORMULA IS BASED ON THE ASSUMPTION THAT THE SUPPORTING STRENGTH OF BURIED CORRUGATED METAL PIPE INSTALLATIONS ARISES THROUGH THE LATERAL REACTIVE SOIL PRESSURES INDUCED AT THE SIDES OF THE PIPE. SINCE ITS INTRODUCTION MORE THAN 30 YEARS AGO, THE IOWA DEFLECTION FORMULA HAS SERVED AS A BASIC CRITERION FOR THE DESIGN OF BURIED FLEXIBLE PIPE SYSTEMS. THE FORMULA IS BASED ON AN ASSUMED DISTRIBUTION OF LOADING AROUND THE PIPE, AND CONTAINS THREE PARAMETERS THAT ARE EMPIRICAL IN NATURE. THE PRESENT STUDY EXAMINES THE SIGNIFICANCE AND POSSIBLE VARIATION OF THESE PARAMETERS IN THE DEFLECTION EQUATION. LIMITED FIELD STUDIES HAVE INDICATED THAT REALISTIC VARIATIONS IN THESE PARAMETERS CAN LEAD TO AN ALMOST THREEFOLD CHANGE IN DESIGN REQUIREMENTS. ONE OF THE MOST INFLUENTIAL PARAMETERS IN THE FORMULA IS THE MODULUS E'. VALUES OF E' AS DETERMINED FROM THE MEASURED RESPONSE OF FULL-SCALE INSTALLATIONS EXHIBIT A THIRTYFOLD VARIATION. YET THESE DATA FORM THE BASIS FOR ESTABLISHING RECOMMENDED VALUES OF E' FOR DESIGN USE. EXTRAPOLATION OF THE OBSERVED DEFLECTIONS FROM FIELD TESTS SHOWS THAT IN MOST CASES USE OF THE SUGGESTED DESIGN CRITERIA YIELDS UNCONSERVATIVE FILL HEIGHTS. THE PRESENT STUDY SHOWS NO STRONG CORRELATION BETWEEN E' AND PERCENTAGE OF STANDARD PROCTOR DENSITY FOR THE SOIL ADJACENT TO THE PIPE, THE PIPE DIAMETER, OR THE RATIO OF FILL HEIGHT TO PIPE DIAMETER. A STATISTICAL ANALYSIS COMPARES OBSERVED VALUES OF E' WITH COMMON PROBABILITY DISTRIBUTIONS, AND A LOG-NORMAL DISTRIBUTION IS FITTED. PROBABILITIES ASSOCIATED WITH VARIOUS RANGES OF E' CONFIRM THAT THERE IS NO RATIONAL BASIS FOR RECOMMENDING A DESIGN VALUE THAT IS MUCH GREATER THAN THE MEDIAN, OR CENTRAL, VALUE.

• Record URL:
  http://onlinepubs.trb.org/Onlinepubs/hrr/1972/413/413-009.pdf
• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/isbn/0309020859
• Supplemental Notes:
  • Sponsored by Committee on Subsurface Soil-Structure Interaction. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved.
• Corporate Authors:

  Highway Research Board

  2101 Constitution Avenue, NW
  Washington, DC    20418
• Authors:
  • Parmelee, Richard A
  • Corotis, Ross B.
• Discussers:
  • Spangler, M G
• Conference:
  • 51st Annual Meeting of the Highway Research Board
  • Location: Washington District of Columbia, United States
  • Date: 1972-1-17 to 1972-1-21
• Publication Date: 1972

Media Info

• Media Type: Digital/other
• Features: Figures; References; Tables;
• Pagination: pp 89-102
• Monograph Title: SOIL-STRUCTURE INTERACTION: A SYMPOSIUM
• Serial:
  • Highway Research Record
  • Issue Number: 413
  • Publisher: Highway Research Board

Subject/Index Terms

• TRT Terms: Conduits; Corrugated pipe culverts; Deflection; Earth pressure; Flexible structures; Modulus; Soil mechanics; Structural analysis; Underground structures
• Uncontrolled Terms: Modulus of soil reaction
• Old TRIS Terms: Flexible conduits
• Subject Areas: Bridges and other structures; Geotechnology; Highways; Hydraulics and Hydrology;

Filing Info

• Accession Number: 00204480
• Record Type: Publication
• ISBN: 0309020859
• Files: TRIS, TRB
• Created Date: Apr 17 1973 12:00AM