EVALUATION FOR CBR AND PAVEMENT DESIGN TESTING BASED ON FIELD COMPACTION CONDITIONS, WITH DISCUSSION AND CLOSURE

THREE SUBGRADE STRENGTH TESTS WERE EVALUATED FOR A REPRESENTATIVE SAMPLE OF SOIL TYPES ENCOUNTERED AROUND CANBERRA. SUBGRADE EVALUATION IS EXPEDITED BY THE ADOPTION OF SEVERAL TECHNICAL MODIFICATIONS OF THE CALIFORNIA TEST: CONTROLLING MOISTURE CONTENT IN THE FIELD AND IN THE LAB, REPLACEMENT OF PLASTIC LIMIT DETERMINATION BY A LINEAR SHRINKAGE TEST, DRY SIEVING, GRADATION ANALYSIS FORM LIQUID LIMIT AND PLASTICITY INDEX ANALYSIS FOR FRACTION PASSING THROUGH A NO. 200 SIEVE, MINIMUM CURING IN CASE OF LIQUID LIMIT, LINEAR SHRINKAGE, AND MAXIMUM DENSITY DETERMINATIONS. ON THE BASIS OF GRAPHIC AND TABULAR COMPILATION OF RESULTS, IT IS CONCLUDED THAT (1) THE SOAKED CBR TEST IS MOST SUITABLE FOR HEAVY CLAY SUBGRADES, PARTICULARLY WHERE APPRECIABLE CHANGES IN MOISTURE ARE LIKELY TO OCCUR; (2) THE UNSOAKED CBR TEST IS SUITABLE FOR TESTING GRAVELS AND ALL SOILS EXCEPT CLAYS AND GRAVELS CONTAINING COARSE FRAGMENTS; (3) THE EQUIVALENT CBR TEST IS SUITABLE FOR ALL SOILS EXCEPT GRAVELS AND CLAYS SUBJECT TO INUNDATION. IT IS RECOMMENEDED THAT ALL SUBGRADES BE CONSTRUCTED TO 95% COMPACTION (HEAVY) IRRESPECTIVE OF EVALUATION METOD.