COMPACTION: THE ART ADVANCES BUT MISCONCEPTIONS LINGER

THE ECONOMICS OF SUCCESSFUL EMBANKMENT COMPACTION IS REVIEWED. THE VALUES OF OBTAINING ADEQUATE SOIL DENSITIES THROUGH GOOD COMPACTION ARE SELF-EVIDENT. HOWEVER, THE PROBLEM OF OBTAINING CONSISTENTLY HIGH DENSITY IS COMPLICATED BY INCONSISTENCY OF TEST RESULTS. USING STANDARD AASHO TESTS, DIFFERENT LABORATORIES OBTAINED A RANGE IN READING FOR OPTIMUM MOISTURE CONTENT OF NEARLY 12% AND VARIATIONS IN MAXIMUM DENSITIES UP TO 26.6 LBS/CU. FT. A SPECIALIZED COMPACTING EQUIPMENT IS DISCUSSED. THE SHEEPSFOOT ROLLER HAS LONG BEEN ACCEPTED AS AN IMPORTANT COMPACTION MACHINE. A TEST OF SHEEPSFOOT CONFIGURATIONS COMPARED VARIOUS PRESSURES RANGING FROM 125 TO 750 PSI. MAXIMUM DENSITIES WERE MEASURED AFTER 6, 12 AND UP TO 24 PASSES AT SIMILAR MOISTURE CONDITIONS. THE DIFFERENCES IN RESULTS WERE NEGLIGIBLE. TEST RESULTS INDICATE THAT SOMETHING OTHER THAN THE ACTION OF THE SHEEPSFOOT WAS ACCOMPLISHING THE NEEDED COMPACTING FORCE. RECENT LABORATORY FINDINGS INDICATE THAT THE DEPTH OF EFFECTIVE SOIL COMPACTION IS A FUNCTION OF THE SMALLEST DIMENSION OF THE COMAPACTION FOOT WHICH IN TURN MEANS THAT A SQUARE FOOT WILL PROVIDE BETTER COMPACTION THAN A RECTANGLE, AND FLAT BETTER THAN POINTED OR CHISELED SHAPED FEET OF EQUAL SIZE. AN IMPORTANT FACTOR IN THE EFFORT TO INCREASE COMPACTION PRODUCTION IS TRAVEL SPEED; REDUCED COMPACTION AT HIGHER SPEEDS ONLY OCCURS WITH VIBRATORY COMPACTORS. UNDER ALMOST ALL CIRCUMSTANCES WITH CORRECT MOISTURE RANGES, 4 TO 6 PASSES WILL BE SUFFICIENT.