ROADWAY FAILURE STUDY NO. II - BEHAVIOR AND STABILIZATION OF EXPANSIVE CLAY SOILS

CHANGES IN MOISTURE AND DENSITY WERE MEASURED PERIODICALLY IN AN EXPANSIVE CLAY SUBGRADE (CODY SHALE AREA) USING NUCLEAR GAGES AND LIMITED SAMPLING BENEATH THE PAVEMENT, SHOULDERS, DITCHES AND BACKSLOPE, IN BOTH CUT AND FILL SECTIONS OF I-25. IN 2 YEARS, ONLY SLIGHT CRACKING OCCURRED IN THE ASPHALTIC SURFACING, BUT THERE WAS CONSIDERABLE INCREASE IN MOISTURE CONTENT IN THE LOWER PART OF THE SUBBASE, WITH A LESSER INCREASE IN THE MEMBRANE SECTION. IT WAS CONCLUDED THAT WATER WAS ENTERING THE SUBBASE THROUGH THE SHOULDER AREAS AND SIDE SLOPES. SWELL POTENTIAL DETERMINATION OF INSITU EXPANSIVE CLAY WAS CONDUCTED WITH NUCLEAR ACCESS TUBES, ELEVATION PLATES AND WATER INJECTION INSTALLATIONS PLACED IN AN UNDISTURBED AREA UNDERLAIN BY EXPANSIVE STEELE SHALE ADJACENT TO I-80. INJECTION OF WATER, AND MOISTURE, DENSITY AND ELEVATION READINGS WERE MADE. AVERAGE ELEVATION INCREASE FOR THE AREA WAS 0.11 FT. VARIABLE AND THE MOISTURE CONTENT WAS APPROXIMATELY DOUBLED TO 24 IN. BELOW THE SURFACE OF THE CLAY SHALE (PLASTIC MEMBRANE). STABILIZERS WERE EVALUATED IN THE LABORATORY. ALTHOUGH SOME REDUCED THE SWELL CONSIDERABLY (BUT LESS THAN LIME) THEY WOULD NOT MIGRATE APPRECIABLY FROM THE POINT OF APPLICATION. SEALANTS WERE EVALUATED TO DETERMINE THEIR VALUE IN PREVENTION OF MOVEMENT OF WATER DOWNWARD INTO THE EXPANSIVE CLAY SUBGRADE. PENEPRIME AND CATALYTICALLY BLOWN ASPHALT PROVED EFFECTIVE EVEN UNDER FREEZE-THAW, WET-DRY CYCLES OF TESTING. IT WAS RECOMMENDED THAT THESE SEALANTS BE PLACED CONTINUOUSLY BENEATH THE PAVEMENT, THROUGH THE SHOULDER, ACROSS THE DITCH LINE AND A FEW FEET UP THE BACK SLOPE, TO PREVENT LATERAL INTRUSION OF WATER.