EXPERIMENTAL STUDY OF PULSE VELOCITIES IN COMPACTED SOILS

Abstract

OVER 200 TESTS WERE PERFORMED ON THREE BASIC SOIL TYPES WHILE STUDYING EXPERIMENTALLY THE RELATIONSHIPS BETWEEN PULSE VELOCITY, DRY DENSITY, WATER CONTENT, AND COMPACTIVE EFFORT. LABORATORY TEST SPECIMENS WERE PREPARED BY KNEADING AND IMPACT COMPACTION METHODS IN SPLIT PROCTOR AND HARVARD MOLDS, AND IN SITU FIELD TESTS WERE PERFORMED ON THE SHOULDERS OF A RECENTLY COMPACTED HIGHWAY EMBANKMENT. ALL SOILS TESTED SHOWED A MONOTONICALLY INCREASING PULSE VELOCITY WITH INCREASES IN DRY DENSITY UNTIL THE OPTIMUM WATER CONTENT ASSOCIATED WITH A PARTICULAR COMPACTIVE EFFORT WAS ATTAINED, THEN A RAPID DROP IN PULSE VELOCITY WAS OBSERVED FOR FURTHER INCREASES IN DRY DENSITY. THE CURVE OF PEAK VELOCITIES AND THE CURVE OF MAXIMUM DRY DENSITIES WERE APPROXIMATELY PARALLEL AND LIE WITHIN PLUS OR MINUS 0.5 PERCENT WATER CONTENT OF EACH OTHER. SEVERAL FACTORS ARE DISCUSSED WHICH SEEM TO INFLUENCE THE MEASURED VELOCITIES. THESE ARE /1/ SIZE OF THE LABORATORY SPECIMEN, /2/ TYPE OF COMPACTION, /3/ SUBSEQUENT DESICCATION OF THE SPECIMEN, /4/ METHOD OF DEFINING THE FIRST ARRIVAL TIME OF THE PULSE ON THE OSCILLOSCOPE, AND /5/ THE SPATIALLY DEPENDENT ANISOTROPIC MACROSTRUCTURE CAUSED BY THE EDGE EFFECTS OF THE MOLD DURING COMPACTION. /AUTHOR/