HIGHWAY DESIGNS TO RESIST SUBGRADE MOISTURE VARIATIONS

TWO MODES OF BEHAVIOR, SUBGRADE MOISTURE ACCUMULATION AND SUBGRADE MOISTURE VARIATION, WERE FOUND TO EXIST UNDER OKLAHOMA PAVEMENT SYSTEMS. COMBINATIONS OF THESE 2 MODES ALSO OCCURRED. RIGID PAVEMENTS WERE FOUND TO BE EXTREMELY SUSCEPTIBLE TO CRACKING FROM VERTICAL AND LATERAL SUBGRADE EXPANSION, WITH RESULTING INFILTRATION OF WATER TO THE SUBGRADE. HOWEVER, RIGID PAVEMENTS PERFORMED WELL UNTIL UPPER SUBGRADE MOISTURE CONTENTS APPROACHED THE LIQUID LIMIT. FLEXIBLE PAVEMENTS WERE MORE RESISTANT TO CRACKING FROM VERTICAL AND LATERAL SUBGRADE EXPANSION BUT WERE SUSCEPTIBLE TO DISTRESS WHEN SUBGRADE MOISTURE CONTENTS APPROACHED THE EQUILIBRIUM VALUE OF 1.1 TO 1.3 TIMES THE PLASTIC LIMIT. RECOMMENDATIONS INCLUDE THE USE OF A FLEXIBLE AND IMPERVIOUS BASE, SUBBASE, OR MEMBRANE COMPONENT BELOW THE WEARING SURFACE OF ANY PAVEMENT ON EXPANSIVE SUBGRADES. IMPROVED SHOULDERS AT LEAST 8 FT IN WIDTH ARE RECOMMENDED, AS IS THE ESTABLISHMENT OF EQUAL DRAINAGE BEHAVIOR ON BOTH SIDES OF THE HIGHWAY SECTION. MORE DETAILED SUBGRADE SOIL TESTING TECHNIQUES ARE ALSO RECOMMENDED. /AUTHOR/