PULSE VELOCITIES IN FLEXIBLE PAVEMENT CONSTRUCTION MATERIALS

THE EFFECTIVENESS OF VIBRATORY TESTING SYSTEMS FOR ESTIMATING THE STIFFNESS AND THICKNESS OF INDIVIDUAL PAVEMENT LAYERS IN PLACE IS BEING EVALUATED. THE SHELL ROAD VIBRATION MACHINE, A HIGH-FREQUENCY ELECTROMAGNETIC VIBRATOR DEVELOPED BY THE ROYAL DUTCH SHELL COMPANY OF AMSTERDAM, HOLLAND, IS ONE DEVICE TESTED. A SERIES OF FLEXIBLE PAVEMENTS STRUCTURES DESIGNED FOR THE SPECIFIC PURPOSE OF CALIBRATING THE SHELL VIBRATORY EQUIPMENT WAS CONSTRUCTED. THIS TEST FACILITY, CONSISTING OF 27 PAVEMENT SECTIONS CONSTRUCTED IN THREE PARALLEL LANES OF NINE SECTIONS EACH, WAS STATISTICALLY DESIGNED TO FURNISH A SELECTION OF PAVEMENT SECTIONS COMPOSED OF SUBGRADE, SUBBASE AND BASE LAYERS OF VARYING THICKNESS AND TYPE OF MATERIAL WITH A VARIABLE DEPTH OF ASPHALTIC CONCRETE SURFACING. THE MODULUS OF ELASTICITY OF THE TEST SECTIONS WAS VARIED. PULSE VELOCITY MEASUREMENTS WERE MADE ON LABORATORY SPECIMENS OF THE RESPECTIVE MATERIALS. THESE VELOCITIES WERE CONSIDERED INDICATIVE OF THE RELATIVE ELASTIC MODULI AND AIDED IN THE SELECTION AND POSITIONING OF THE SUBGRADE MATERIALS AND IN DETERMINING THE AMOUNT AND TYPE OF STABILIZING AGENT TO BE USED WITH THE CRUSHED LIMESTONE FOR THE BASE AND SUBBASE LAYERS. THE PULSE VELOCITY TECHNIQUE USING BOTH SHEAR AND COMPRESSIONAL MODES OF VIBRATION SUGGESTS ITSELF AS A PROMISING POSSIBILITY FOR FINDING THE ELASTIC CONSTANTS OF FLEXIBLE PAVEMENT CONSTRUCTION MATERIALS.