FIELD STUDIES ON SUBGRADE MOISTURE CONDITIONS

A SUMMARY IS PRESENTED OF VARIOUS INVESTIGATIONAL STUDIES UNDERTAKEN TO OBTAIN INFORMATION CONCERNING: (1) THE SUBGRADE MOISTURE CONTENT, ITS CHANGE WITH TIME AND ENVIRONMENT, (2) THE SOURCE OF POST CONSTRUCTION SUBGRADE MOISTURE, (3) THE MEANS BY WHICH THE SUBGRADE MOISTURE TRAVELS OR ACCUMULATES, AND (4) THE POTENTIALS WHICH CAUSE SUCH FLOW. SUBGRADECORES WERE REMOVED FOR PAVEMENT THICKNESS CORE TESTS. AN INVESTIGATION WAS MADE TO TRY TO DETERMINE THE MAIN SOURCE OF SUPPLY FOR SUBGRADE MOISTURE AND AT THE SAME TIME SELECT THE MOISTURE CELL LOCATIONS WHICH WOULD BE MOST GENERALLY REPRESENTATIVE OF TGHE AVERAGE MOISTURE LEVEL IN THE SUBGRADE. DATA SHOW THAT THE MAIN SOURCE OF SURFACE MOISTURE ENTRANCE INTO THE SUBGRADE SYSTEM IS PAST THE EDGES OF PAVEMENT. IT IS CONCLUDED THAT WATER FLOW IN THE PAVEMENT-BASE SUBGRADE SURFACE SYSTEM IS NO DIFFERENT FROM ANY OTHER SYSTEM, FOLLOWING THE PATH OF LEAST RESISTANCE WHETHER IT BE OVER, INDER, AROUND OR THROUGH THE BASE MATERIALS. THE MOISTURE LEVEL OF THE SUBGRADE RISES RATHER RAPIDLY AFTER CONSTRUCTION WHERE NO SUFFICIENT PREVENTIVE TREATMENT IS PROVIDED. THERE WAS NO GRADE VARIATION IN SUBGRADE MOISTURE CONTENT AVERAGES OVER THE SEVEN YEARS OF SAMPLING. THE PREDICTION OF ULTIMATE AVERAGE MOISTURE LEVELS DOES NOT HAVE SEASONAL EFFECTS IN MISSOURI. IT IS FELT THAT THE BEST TIME TO COVER THE SUBGRADE WOULD BE WHEN THE MOISTURE DISTRIBUTION CURVE IS AT OR ABOVE THE OPTIMUM MOISTURE FOR COMPACTION AND YET REMAINS BELOW THE THEORETICAL CURVE.