THE DYNAMIC STRESS-STRAIN RELATION FOR A SAND AS DEDUCED BY STUDYING ITS SHOCK-WAVE PROPAGATION CHARACTERISTICS IN A LABORATORY DEVICE

A SERIES OF TESTS WAS CONDUCTED IN THE WATERWAYS EXPERIMENT STATIONS SMALL BLAST LOAD GENERATOR TO EVALUATE THE FREE-FIELD RESPONSE OF A CONTAINED SAND SPECIMEN TO DYNAMIC LOADING. THE SPECIMEN WAS A CYLINDRICAL COLUMN OF DENSE SAND 4 FEET IN DIAMETER AND 13 FEET LONG. THE SHOCK PROPAGATION CHARACTERISTICS OF THE SPECIMEN WERE STUDIED. BASED ON THE SHOCK-WAVE CHANGE AS THE WAVE PROPAGATED AND ON STRESS LEVEL MEASUREMENTS TAKEN AT VARIOUS DEPTHS IN THE SPECIMEN, A DYNAMIC STRESS-STRAIN RELATION WAS CONSTRUCTED. INDICATIONS ARE THAT THE DYNAMIC AND STATIC ONE-DIMENSIONAL STRESS-STRAIN RELATIONS MAY BE THE SAME AT HIGH STRESS LEVELS, BUT AT LOW LEVELS THE DYNAMIC CURVE APPEARS TO HAVE A POINT OF INFLECTION BETWEEN 18 AND 40 PSI. THUS, THERE IS AN INDICATION THAT IF THE MATERIAL IS STRESS-CYCLED BELOW THIS STRESS LEVEL A SHOCK WAVE WILL NOT PROPAGATE. FURTHER EXPERIMENTS ARE NEEDED TO ESTABLISH IN MORE DETAIL THE QUANTITATIVE DYNAMIC STRESS-STRAIN CURVE FOR THE TEST SAND, BUT THE RESULTS REPORTED HEREIN INDICATE THE GENERAL SHAPE OF THE CURVE. SINCE AN EXPLANATION OF THE MECHANISM OF LOAD TRANSFER IN THE FREE-FIELD IS PREREQUISITE TO DETERMINING THE LOAD TRANSFER TO A BURIED STRUCTURE, THESE RESULTS HAVE DIRECT APPLICATION TO SHALLOW-BURIED PROTECTIVE CONSTRUCTION. /AUTHOR/