FLEXIBLE-PAVEMENT DESIGN AS REVISED FOR HEAVY TRAFFIC

THE RATIONAL DESIGN OF A FLEXIBLE PAVEMENT INVOLVES THREE IMPORTANT FACTORS THAT MUST BE GIVEN CONSIDERATION: (1) THE MAGNITUDE AND NATURE OF THE APPLIED LOAD AND THE MODE OF ITS APPLICATION; (2) THE STRENGTH OR BEARING CAPACITY OF THE SUBGRADE SOIL AS WELL AS THE BEARING CAPACITY OF THE COMPONENTS OF THE PAVEMENT STRUCTURE (SUBBASE, BASE, AND SURFACE COURSE); AND (3) THE DISTRIBUTION OF THE PRESSURE EXERTED AT THE SURFACE OF THE PAVEMENT BY THE APPLIED LOAD. TWO METHODS FOR DETERMINING NECESSARY PAVEMENT THICKNESS ARE DESCRIBED. IN THE ORIGINAL METHOD THE PRESSURES EXERTED BY THE VARIOUS WHEEL LOADS WERE DETERMINED FROM THE INFLATION PRESSURES OBTAINED WHEN TRUCK-WEIGHT SURVEYS WERE CONDUCTED. THESE PRESSURES WERE INCREASED 10 PERCENT FOR TIRE-WALL STIFFNESS. THE AREAS OF CONTACT WERE OBTAINED BY DIVIDING THE WHEEL LOADS BY THE INFLATION PRESSURES, FROM WHICH DIAMETERS OF CIRCLES OF EQUAL AREAS WERE CALCULATED. THE REVISED METHOD OF DESIGN USES A DIFFERENT PROCEDURE FOR DETERMINING THE PRESSURES AND DIAMETER OF CONTACT AREA. THE REVISED METHOD USED THE FACT THAT DUAL WHEELS HAVE TWO CONTACT AREAS AND TOOK INTO CONSIDERATION THE SIZE OF THE TIRE AS RELATED TO LOAD-CARRYING CAPACITY. USING THE METHOD DESCRIBED, IT IS POSSIBLE TO OBTAIN THE PAVEMENT THICKNESS FOR HEAVY LOADS. /AUTHOR/