UTAH'S USE OF DYNAFLECT DATA FOR PAVEMENT REHABILITATION

DEFLECTION MEASUREMENTS ARE USEFUL IN DETERMINING THE STRUCTURAL ADEQUACY OF PAVEMENTS BEFORE UNDERTAKING RESURFACING OF AN EXISTING PAVEMENT. UTAH IS NOW USING A DRESSER-ATLAS (FORMERLY LANE-WELLS) DYNAFLECT FOR DEFLECTION MEASUREMENTS. THE SYSTEM CONSISTS OF A SMALL TRAILER TOWED BEHIND A VEHICLE WITH A CONTROL UNIT LOCATED IN THE VEHICLE BESIDE THE OPERATOR. THE DYNAMIC DEFLECTION IS MEASURED BETWEEN TWO RIGID STEEL WHEELS THAT ARE SUBJECTED TO AN OSCILLATORY LOAD OF 1,000 LB PEAK-TO-PEAK VARYING SINUSOIDALLY AT THE RATE OF 8 CYCLES PER SECOND. THE MAGNITUDE OF THE DEFLECTIONS ARE SENSED BY MEANS OF 5 GEOPHONES SPACED AT 1-FT INTERVALS BEGINNING WITH ONE PLACED BETWEEN THE FORCE WHEELS. THE SHAPE OF THE DEFLECTION BASIN IS DETERMINED BY UTILIZING THE VALUES FROM ALL GEOPHONES. THE DEFLECTIONS ARE READ ON THE METER IN THE CONTROL UNIT IN THE TOW VEHICLE. THERE IS GOOD CORRELATION BETWEEN THE DATA OBTAINED WITH THE BENKLEMAN BEAM AND THOSE OBTAINED WITH THE DYNAFLECT. PERFORMANCE-DEFLECTION RELATIONSHIPS WERE ESTABLISHED AS PART OF THE AASHO ROAD TEST AND EQUATIONS FOR FALL OR SPRING NORMAL DEFLECTIONS WERE DEVELOPED. THESE EQUATIONS WERE MODIFIED FOR THE DYNAFLECT AND USED TO DEVELOP TWO FAMILIES OF CURVES CORRELATING DYNAFLECT DEFLECTIONS, DAILY EQUIVALENT 18-KIP LOADS, AND PAVEMENT LIFE. THE SURFACING CAN THEN BE DETERMINED FOR REHABILITATION WHICH IS THE AMOUNT REQUIRED TO REDUCE THE ACTUAL DEFLECTION TO THE ALLOWABLE DEFLECTION. DATA ARE PRESENTLY BEING DEVELOPED FOR DETERMINATION OF THE THICKNESS OF A NEW SURFACE COURSE REQUIRED TO REDUCE THE DEFLECTION TO A POINT AT WHICH IT WILL MEET THE DESIGN-LIFE CRITERIA.