EFFECT OF MECHANICAL MANIPULATION ON THE PLASTICITY OF SOILS

A SERIES OF LABORATORY TESTS WERE PERFORMED ON FIVE SOILS: TWO FROM VERY SILTY MATERIALS, THE OTHER THREE WERE CLAYS. A SERIES OF TESTS WERE PERFORMED TO DETERMINE WHAT CHANGES IN THE PLASTICITY CONSTANTS MIGHT OCCUR AS A RESULT OF PROLONGED PHYSICAL MANIPULATION OF THE SOILS. EXPERIMENTS CONFIRM THE OBSERVATION THAT EXTENDED MANIPULATIONS SUCH AS MIXING AND KNEADING OF SOILS IN A WET CONDITION MAY CHANGE THE PLASTICITY CONSTANTS TO GIVE LARGER VALUES OF THE PLASTICITY INDEX. THE ACTION IS MOST PRONOUNCED ON SOILS WITH HIGH SILT CONTENTS WHICH ORIGINALLY WOULD BE JUDGED AS BEING ONLY SLIGHTLY PLASTIC. FIELD TESTS SUBJECTED SOILS TO THE ACTION OF TRAFFIC UNDER A FLEXIBLE MAT AND SHOWED VERY SLIGHT INCREASES IN PLASTICITY INDEX. LIQUID LIMIT AND PLASTIC LIMIT DETERMINATIONS WERE MADE. THIS STUDY MAY HELP TO EXPLAIN INCONSISTENT TEST RESULTS OBTAINED IN INVESTIGATIONS ON SOILS MANIPULATED REPEATEDLY IN THE COURSE OF EXTENSIVE TESTING.