A PRACTICAL APPROACH TO FLEXIBLE PAVEMENT DESIGN

THIS PAPER DESCRIBES TWO POPULAR APPROACHES TO THE FLEXIBLE PAVEMENT DESIGN PROBLEM, THE THEORETICAL AND THE EMPIRICAL, AND POINTS OUT SOME OF THE MANY LIMITATIONS OF EACH WITH REGARD TO THE EVERYDAY JOB OF DESIGNING PAVEMENTS IN DIFFERENT PARTS OF THE COUNTRY. THE RESULTS OF THE AASHO ROAD TEST ARE DISCUSSED WITH EMPHASIS ON THE VARIABILITY IN PUBLISHED EQUIVALENCY VALUES FOR THE SEVERAL TYPES OF MATERIAL INCLUDED IN THAT EXPERIMENT. IN SPITE OF THIS VARIABILITY, CERTAIN WEIGHTED AVERAGE VALUES HAVE BECOME CONSIDERED AS CONSTANTS AND ARE USED AS COEFFICIENTS OF RELATIVE STRENGTH IN PAVEMENT DESIGN PROCEDURES PATTERNED AFTER THE 1961 AASHO INTERIM GUIDE. EMPHASIS IS GIVEN TO THE FALLACY OF SELECTING AN OVER-ALL AVERAGE THICKNESS INDEX RELATIONSHIP FROM THIS ONE LIMITED EXPERIMENT, USING IT TO SET UP AN EMPIRICAL GUIDE FOR THE UNIVERSAL APPLICATION TO DESIGN PROBLEMS. THE FACT IS CITED THAT EVEN ON THE SAME PROJECT, THE RELATIVE STRENGTH RATIO BETWEEN THE SAME TWO MATERIALS VARIES WITH THE MAGNITUDE OF LOAD AND, MOST PARTICULARLY, WITH DEPTH BELOW SURFACE. THE IMPROBABILITY OF DEVELOPING CONSTANT COEFFICIENTS OF RELATIVE STRENGTH THROUGH SATELLITE TEST PROJECTS IS EXPLAINED. SINCE IN THE MEANWHILE PAVEMENT DESIGNS HAVE TO BE MADE, A MORE PRACTICAL APPROACH TO A UNIVERSAL DESIGN PROCEDURE IS PROPOSED. EVERY DESIGN WOULD INCLUDE PROVISIONS FOR' /1/ PERMANENTLY FIRM, NON-RESILIENT SUPPORT AT THE SUBGRADE LEVEL, TO BE ASSURED WHERE NECESSARY BY MEANS OF CHEMICAL STABILIZATION, /2/ A BASE COURSE AFFORDING STABILITY WITHOUT BRITTLENESS, AND /3/ A BINDER-SURFACE COMBINATION OF HIGH STABILITY WITH ADEQUATE COHESION TO RESIST HORIZONTAL SHEAR STRESSES FROM ACCELERATION AND DECELERATION. THICKNESSES WOULD BE ESSENTIALLY STANDARD WITH STANDARD MATERIALS UNDER STANDARD RANGES OF TRAFFIC LOADING. ALTHOUGH MINOR THICKNESS ADJUSTMENTS MIGHT BE MADE WHERE ONLY NON-STANDARD MATERIALS ARE AVAILABLE, ALL THREE COMPONENTS SHOULD STILL BE PRESENT, AND OVER-ALL THICKNESSES SHOULD BE GREAT ENOUGH TO PREVENT OVERSTRESSING THE ROADBED SOIL BENEATH THE LOWEST IMPROVED LAYER. /AUTHOR/

• Supplemental Notes:
  • Preprint VoL, PP 641-651, 5 TAB, 12 REF
• Authors:
  • Nichols, F P
• Conference:
  • Intl Conf Struct Design Asphalt Pvmts
• Publication Date: 1967-1

Subject/Index Terms

• TRT Terms: Base course (Pavements); Binders; Empirical methods; Flexible pavements; Loads; Pavement design; Stability (Mechanics); Structural supports; Subgrade (Pavements); Theory; Thickness
• Old TRIS Terms: Supports; Thickness design
• Subject Areas: Highways; Pavements;

Filing Info

• Accession Number: 00205494
• Record Type: Publication
• Files: TRIS
• Created Date: Aug 1 1994 12:00AM