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https://nap.nationalacademies.org/catalog/27432/critical-issues-in-transportation-for-2024-and-beyond

OBSERVED AND CALCULATED STRAINS AT VARIOUS DEPTHS IN ASPHALT PAVEMENTS

IN THE YEAR OF THE FIRST CONFERENCE IN ANN ARBOR, JONES PUBLISHED IN THE FORM OF TABLES SOLUTIONS OF STRESS EQUATIONS FOR A WIDE RANGE OF THE PARAMETERS INVOLVED IN THREE-LAYERED SYSTEMS. THESE TABLES CONTAINED THE RADIAL AND VERTICAL STRESSES PREVAILING AT THE INTERFACES OF THE STRATIFIED SYSTEMS UNDER THE CENTRE OF A LOADED CIRCULAR AREA. THEY CONSTITUTE THE BASIS OF THE SHELL DESIGN CHARTS. RECENT WORK HAS ENABLED US TO CALCULATE THE STRESSES OCCURRING AT ANY DEPTH IN THE CONSTRUCTION AND AT RADIAL DISTANCES FROM THE CENTRE OF LOADING IN ANY NUMBER OF LAYERS. IF WE ARE TO USE ELASTIC THEORIES WE MUST KNOW THE ELASTIC CONSTANTS OF THE CONSTRUCTION MATERIALS, AND THESE HAVE TO BE DETERMINED UNDER CONDITIONS SIMILAR TO THOSE GENERATED BY TRAFFIC. PHASE VELOCITY MEASUREMENTS SHOULD SERVE THIS PURPOSE. THE APPENDIX PRESENTS A GRAPHICAL METHOD FOR INTERPRETING THE RESULTS OF SUCH MEASUREMENTS AT HIGHER FREQUENCIES. IN THE PAST THE ROAD VIBRATION MACHINE ENABLED DEFLECTIONS TO BE MEASURED UNDER TRAFFIC CONDISTIONS, WHICH DEFLECTIONS COULD THEN BE COMPARED WITH THOSE CALCULATED BY MEANS OF ELASTIC THEORY. IT WAS FELT, HOWEVER, THAT DIRECT MEASUREMENT OF STRESSES OR STRAINS AT VARIOUS LEVELS IN THE CONSTRUCTION WOULD BE AN EVEN BETTER MEANS OF CHECKING THE USEFULNESS OF THE ELASTIC THEORY. AFTER TENTATIVE LABORATORY EXPERIMENTS ON A MODEL ROAD INVESTIGATIONS WERE STARTED ON SOME ROADS IN HOLLAND WITH THICK ASPHALT PAVEMENTS, ELECTRIC RESISTANCE STRAIN GAUGES BEING ATTACHED TO THE SURFACE OF THE VARIOUS ASPHALT LAYERS. MOST OF THESE GAUGES SURVIVED APPLICATION OF THE NEXT LAYER UNDER HIGH TEMPERATURES AND HEAVY ROLLER WEIGHTS. THEY NOW ENABLE US TO DETERMINE HORIZONTAL STRAINS AT VARIOUS DEPTHS IN AN ASPHALT PAVEMENT UNDER THE ROLLING WHEELS OF A TRUCK OF WHICH WHEEL LOAD, INFLATION PRESSURE AND TYRE PRINT ARE KNOWN. THE QUANTITIES OBTAINED EXPERIMENTALLY CAN ALSO BE CALCULATED, PROVIDED THE DYNAMIC MODULUS IS KNOWN AS A FUNCTION OF TEMPERATURE AND TRUCK SPEED. THEREFORE IT WAS NECESSARY TO DETERMINE THIS RELATIONSHIP IN THE LABORATORY AND TO MEASURE THE TEMPERATURE AND SPEED IN THE FIELD. STRAINS MEASURED AT VARIOUS LEVELS IN FLEXIBLE PAVEMENTS, UNDER VARYING CONDITIONS OF TEMPERATURE AND VEHICLE SPEED, ARE COMPARED WITH STRAINS CALCULATED ON THE BASIS OF ELASTIC THEORY. THE TECHNIQUE DESCRIBED PROVED TO BE SUCESSFUL TO DETERMINE THE HORIZONTAL STRAINS IN A PAVEMENT UNDER MOVING TRAFFIC. THE STRAINS MEASURED SHOW IN GENERAL A REASONABLE AGREEMENT WITH THOSE CALCULATED. A BETTER AGREEMENT IS OBTAINED AT LOWER THAN AT HIGHER TEMPERATURES (GREATER THAN 25 DEGREES C) AND MORE ACCURATE MEASUREMENTS CAN BE CARRIED OUT AT THE BOTTOM INTERFACE OF AN ASPHALT LAYER THAN AT THE ROAD SURFACE. THIS CONCLUSION JUSTIFIES THE USE OF ELASTIC THEORIES FOR CALCULATIONS OF RADIAL STRAIN AT THE BOTTOM OF AN ASPHALT PAVEMENT AS HAS BEEN DONE TO DEVELOP THE SHELL DESIGN CHARTS 1963. (AUTHOR)

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Filing Info

  • Accession Number: 00206652
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Aug 1 1994 12:00AM