PRELIMINARY EXPERIMENTS ON THE DISTRIBUTION OF WHEEL LOADS THROUGH FLEXIBLE PAVEMENTS

A TYPE OF APPARATUS FOR MEASURING THE PRESSURE DISTRIBUTION UNDER STATIC WHEEL LOADS ON FLEXIBLE PAVEMENTS IS DESCRIBED, WHICH GIVES PROMISE OF MAKING POSSIBLE AN EXTENSIVE STUDY OF THE EFFECTS OF VARIOUS CHARACTERISTICS OF FLEXIBLE PAVEMENTS AND SUBGRADES UPON PRESURE DISTRIBUTION. THE APPARATUS CONSISTS OF A SERIES OF STAINLESS STEEL RIBBONS ARRANGED TO SLIDE BETWEEN THIN STAINLESS STEEL STRIPS. THESE RIBBON ASSEMBLIES ARE PLACED IN THE PLANE BETWEEN THE FLEXIBLE PAVEMENT AND THE SUBGRADE, AND ARE PULLED HORIZONTALLY TO MEASURE THE TOTAL PRESSURE ON THE RIBBONS. THEN THE RIBBONS ARE SHORTENED BY DECREMENTS OF ONE INCH AND THE PULL MEASURED FOR EACH LENGTH OF RIBBON. THE DIFFERENCE BETWEEN THESE PULLS IS PROPORTIONAL TO THE DIFFERENCE IN PRESSURE ON THE RIBBONS AT THE VARIOUS LENGTHS, AND WITH THE COEFFICIENT OF FRICTION DETERMINED, PROVIDES A MECHANICAL DIFFERENTIATION OF THE PRESSURE. OBSERVATIONS WERE MADE ON FLEXIBLE PAVEMENTS IN WHICH ALL CHARACTERISTICS WERE HELD CONSTANT EXCEPT THE THICKNESS, WHICH VARIED BETWEEN 3 AND 15 IN. LOADS WERE APPLIED THROUGH A PNEUMATIC TIRE. THE MAXIMUM PRESSURE ON THE SUBGRADE OCCURED DIRECTLY BENEATH THE APPLIED LOAD AND DISTRIBUTED LATERALLY IN AN ELONGATED BELL SHAPE. THE MAXIMUM UNIT PRESSURES ACCOMPANYING A 3,000 LB. LOAD WERE: 65 LB. PER SQ. IN. AT 3 IN. THICK, 35 AND 44 LB. AT 5 IN., 24 LB. AT 7 1/2 IN., 18.5 LB. AT 10 IN. AND 13 LB. AT 15 IN. THICK. /AUTHOR/