An Investigation of Compaction Variability for Selected Highway Projects in Indiana

THE AREA OF STUDY CHOSEN FOR THIS PROJECT WAS COMPACTION CONTROL OF SUBBASE AND SUBGRADE ELEMENTS AS USED UNDER RIGID PAVEMENTS. THREE PROJECTS OF EACH WERE SELECTED FOR INVESTIGATION IN INDIANA. THE OBJECTIVE WAS /1/ TO GATHER DATA TO DETERMINE WHAT LEVEL OF COMPACTION WAS ACTUALLY BEING ACHIEVED UNDER PRESENT CONSTRUCTION PRACTICES BY STUDYING THE VARIABILITY IN COMPACTION AND THE FACTORS CAUSING THE VARIABILITY, AND /2/ TO DETERMINE HOW A STATISTICAL QUALITY CONTROL MIGHT BE DEVELOPED FROM THESE DATA. TO ASSURE A REALISTIC ESTIMATE OF THE TRUE LEVEL OF COMPACTION, ONE HUNDRED FIELD DENSITY TESTS WERE PERFORMED FOR EACH PROJECT BY SELECTING TEN UNITS OF CONSTRUCTION OF EQUAL SIZE AND MAKING FIVE RANDOMLY REPLICATED DENSITY TESTS IN EACH. REFERENCE VALUES FOR PERCENT COMPACTION WAS THE USE OF ONE-POINT FIELD COMPACTION TEST IN CONJUNCTION WITH A FAMILY OF TYPICAL CURVES. RESULTS OBTAINED INDICATED AN OVERALL LEVEL OF COMPACTION LOWER THAN THAT SPECIFIED. VARIABILITY IN COMPACTION WAS LARGE. DATA INDICATED GREATER VARIABILITY IN THE SUBGRADE COMPACTION THAN IN THE SUBBASES. THE STATISTICAL ANALYSIS INDICATED MORE TESTS FOR A UNIT WERE REQUIRED TO INSURE UNIFORM COMPACTION. A MAIN PROBLEM IS TO INSURE THAT TESTS ARE PROPERLY PERFORMED. /AUTHOR/