EFFECT OF DEGREE OF SATURATION ON BEARING CAPACITY OF FLEXIBLE PAVEMENTS

IN THE U.S.A. THE BEARING CAPACITY OF FLEXIBLE PAVEMENTS IS OFTEN REDUCED DURING THE SPRING THAW, PARTLY BECAUSE BASE AND SUBGRADE MATERIALS HAVE EXPANDED BY FROST HEAVE AND PARTLY BECAUSE THE SOIL HAS BECOME SATURATED AND THERE IS EXCESS OF PORE PRESSURE CAUSED BY RAPID MELTING OF ICE LENSES. IN 1963 THE AUTHOR PROPOSED A DESIGNED METHOD FOR FLEXIBLE PAVEMENTS BASED ON THE ASSUMPTION THAT FAILURE TAKES PLACE IN A FULLY SATURATED SUBGRADE. THE PRESENT PAPER CONCERNS THE EFFECT OF DEGREE OF SATURATION ON BEARING CAPACITY WHICH IS A FUNCTION OF THE APPARENT ANGLE OF INTERNAL FRICTION AND OF THE APPARENT COHESION AS EVALUATED BY UNDRAINED TRIAXIAL OR DIRECT SHEAR TESTS. THE APPARENT FRICTION ANGLE DECREASES RAPIDLY WITH INCREASING PORE PRESSURE COEFFICIENT AND THE APPARENT COHESION INCREASES RAPIDLY WITH INCREASING DEGREE OF SATURATION AND PORE COEFFICIENT. THE EFFECT OF OTHER FACTORS IS SMALL WHEN THE APPARENT COHESION OF THE SOIL EXCEEDS 400 LB/FT2. CALCULATIONS OF THE ULTIMATE BEARING CAPACITY OF FLEXIBLE PAVEMENTS ON SUBGRADES OF /A/ SILT OF LOW COMPRESSIBILITY AND /B/ CLAY OF MEDIUM PLASTICITY FOR DIFFERENT PAVEMENT THICKNESSES, TYRE CONTACT PRESSURES AND SUBGRADE SATURATION SHOW THAT THE DEGREE OF SATURATION GREATLY AFFECTED THE BEARING CAPACITY OF THE PAVEMENT. /RRL/