WHAT SUBGRADE INVESTIGATIONS HAVE SHOWN DURING THE PAST YEAR

DURING THE PAST YEAR RESEARCH WAS CONDUCTED ON THE FOLLOWING PHASES OF THE SUBGRADE PROBLEM AND THIS WORK IA DISCUSSED UNDER THE FOLLOWING HEADINGS: (1) THE RELATIONS OF PENETRATION TO BEARING AREAS, (2) SOME EFFECTS OF TEMPERATURE AND GRANULAR MATERIALS ON SUBGRADE MOISTURE, (3) DETERMINATION OF THE PERCENTAGE OF WATER FROZEN IN SUBGRADE SOILS, (4) THE EFFECT OF GRANULAR MATERIALS IN STABILIZING PLASTIC CLAY UNDER MACADAM PAVEMENTS, (5) THE PRACTICAL FIELD TESTS FOR SUBGRADE SOILS, (6) HEAVING AND FROST BOILS. TESTS WERE CONDUCTED TO DETERMINE WHETHER ANY RELATION EXISTED BETWEEN THE SUPPORTING VALUE OF A SOIL AND THE SIZE OF THE SUPERIMPOSED AREA. IT WAS CONCLUDED THAT THE RELATIVE PENETRATION OF TUBE BEARING BLOCKS ON THE SAME UNIT INTENSITY OF LOAD IS TO EACH OTHER AS THE SQUARE ROOTS OF THEIR RESPECTIVE AREAS. THE SAMPLES TAKEN FROM THE SURFACE OF EXPOSED SOILS AND FROM THE UPPER DEPTHS OF SUBGRADE UNDER PAVEMENTS SHOW THAT THE MAXIMUM MOISTURE CONTENT DURING COLD WEATHER IS USUALLY HIGHER AT THE SURFACE THAN AT THE LOWER DEPTHS. AN EXPERIMENT WAS CONDUCTED TO INVESTIGATE THIS PHENOMENON USING GLASS TUBES FILLED WITH SOILS, THE LOWER ENDS SUBJECTED TO FREE WATER AND THE SOILS ALLOWED TO TAKE UP CAPILLARY MOISTURE UNTIL CONSTANT WEIGHT WAS REACHED. IT WAS FOUND THAT MOISTURE CONTENT IN ROAD SUBGRADE MAY BE INCRASED THROUGH: (1) INCREASED SURFACE TENSION THROUGH LOWER TEMPERATURE, AND (2) CONDENSATION OF VAPORIZED MOISTURE DUE TO LOWERED TEMPERATURE. IT IS BELIEVED THAT THE INTRODUCTION OF SUCH GRANULAR MATERIALS AS SAND, GRAVEL, CINDERS, ETC., INTO THE SUBGRADE NOT ONLY TENDS TOWARD REDUCING THE CAPILLARY TENSION IN THE SUBGRADE SOIL, BUT ALLOWS THE CONDENSED MOISTURE TO BE DEPOISTED ON A SUBGRADE MADE UP OF MATERIALS WHOSE BEARING VALUE IS NOT SO DECREASED BY MOISTURE. THE PERCENTAGE OF WATER FROZEN IN SUBGRADE SOILS WAS INVESTIGATED BY THE DILATOMETER METHOD AND THE PERCENTAGE OF MOISTURE FROZEN WAS MEASURED BY THE EXPANSION OF THE ICE CRYSTALS ON FREEZING. THE SIZE OF THE PARTICLES WAS FOUND TO BE ONE OF THE FACTOS CONTROLLING THE AMOUNT OF WATER FROZEN IN THE SOIL. THE SOIL ITSELF SHRINKS UPON COOLING AND IT IS ONLY THE WATER WHICH CRYSTALLIZES AND SEEMINGLY CAUSES THE SOIL TO EXPAND. SUBGRADE STUDIES SHOW THAT THE FIELD MOISTURE EQUIVALENT TEST SEEMS TO GIVE RESULTS PRACTICALLY IDENTICAL WITH THE STANDARD LABORATORY METHODS. OBSERVATIONS ARE MADE ON THE HEAVE OF CONCRETE PAVEMENTS.