SUBGRADE MOISTURE VARIATIONS: EVALUATION OF COLLECTED DATA 1966-1968

A SIX-YEAR SUBGRADE MOISTURE VARIATIONS PROJECT IS BEING CONDUCTED IN OKLAHOMA TO : (1) REVIEW PREVIOUS WORK ON SUBGRADE MOISTURE BEHAVIOR BY THIS PROJECT AND BY OTHER AGENCIES, (2) RELATE MEASURED SUBSURFACE MOISTURE CONDITIONS TO SOIL, CLIMATE AND PAVEMENT, AND (3) DISCUSS OBTAINED RELATIONSHIPS AS THEY APPLY TO OKLAHOMA HIGHWAY DESIGN. FIFTY FIELD RESEARCH SITES WERE INSTALLED THROUGHOUT THE CENTRAL AND NORTH CENTRAL/ NORTH EASTERN PARTS OF OKLAHOMA. THE SITES WERE LOCATED ON HIGHWAYS OF VARIOUS AGE, CONDITION RATINGS, CROSS-SECTION, AND PAVEMENT TYPE. PROCEDURES USED TO COLLECT RESEARCH DATA AT THE 50 FIELD RESEARCH SITES ON EXISTING PAVEMENT FOR A 3-YEAR PERIOD ARE DESCRIBED. PROCEDURES USED FOR EVALUATION OF DATA AND OBSERVED TRENDS IN SUBGRADE MOISTURE BEHAVIOR AND RELATED FACTORS ARE PRESENTED. EFFECTS OF SUBGRADE MOSITURE ON VARIOUS HIGHWAY DESIGNS ARE DESCRIBED. TWO MODES OF SUBGRADE MOISTURE BEHAVIOR OCCUR IN OKLAHOMA: SUBGRADE MOISTURE ACCUMLATION AND SUBGRADE MOISTURE VARIATION. DATA STUDIED AND EVALUATED INDICATE THE FOLLOWING CONCLUSIONS: (1) SUBGRADE MOISTURE ACCUMLATION OCURRED AFTER HIGHWAY CONSTRUCTION AND/OR OVER LONG PERIODS OF DROUGHT, (2) SUBGRADE MOISTURE VARIATIONS ARE EITHER PRECIPITATION OR WATER TABLE-DEPENDENT, (3) HIGHWAY PAVEMENT RATINGS ARE EVIDENT IN IMPERVIOUS PAVEMENTS WITH WIDE SHOULDERS, IMPERVIOUS AND INFLEXIBLE BASE MATERIAL, AND GRADE OR CUT SECTION, (4) HIGHWAYS WITH WIDE SHOULDERS EXHIBITED MORE NEARLY CONSTANT MOISTURE CONDITIONS AND REDUCED MOISTURE CONTENT INCREASE-DECREASE BENEATH THE PAVEMENT WHILE MOISTURE CONDITIONS BENEATH SHOULDERS VARIED SOMEWHAT MORE, (5) SUBGRADE MOISTURE CONTENTS WERE FOUND TO FLUCTUATE SEVERELY BENEATH SHOULDERS IN FILL AND TRANSITION SECTIONS, BUT FLUCTUATE LESS IN GRADE OR CUT SECTIONS, (6) WET-DRY INTERFACE BEHAVIOR SEEMS TO BE THE CAUSE OF LONGITUDINAL CRACKING IN SHOULDERS, (7) SUBGRADE SOILS ENCOUNTERED WERE FOUND TO BE EXPANSIVE, (8) LATERAL AND VERTICAL SWELLING OF EXPANSIVE OKLAHOMA SUBGRADES WERE FOUND TO CAUSE MOST DAMAGE TO SOIL-CEMENT BASE MATERIAL AND TO PAVEMENTS WITHOUT BASE MATERIAL, AND (9) FLEXIBLE, IMPERVIOUS BASE MATERIALS SUCH AS STABILIZED AGGREGATE BASE COURSES OR SAND-ASPHALT BASE COURSES, REDUCED INFILTRATION AND RESISTED CRACKING BETTER THAN SAND CUSHION OR SAND-CEMENT BASE MATERIALS.