THE INFLUENCE OF FROST ON HIGHWAY FOUNDATIONS

SOME OF THE MOST FREQUENTLY ENCOUNTERED TYPES OF CON- DITIONS ALONG SOME OF THE HIGHWAYS IN THE STATE OF NEW YORK WHERE DAMAGE HAS BEEN CAUSED BY FROST ACTION ARE DESCRIBED AND RECOMMENDATIONS MADE FOR PRACTICAL MEASURES TO CORRECT THESE CONDITIONS. SOME HEAVING OCCURS WHEN THERE IS A CONCENTRATION OF WATER IN THE SUBGRADE NEAR ENOUGH TO THE SURFACE TO BE SUBJECT TO FROST. THE CAUSES ARE TOO MUCH WATER AND NOT ENOUGH DRAINAGE. BOULDERS EMBEDDED IN THE FOUNDATION SOIL AT DEPTHS WITHIN THE FROST RANGE PENETRATION HAVE A WAY OF WORKING TO THE SUBSURFACE WHERE THEY EVENTUALLY CAUSE BUMPS IN THE PAVEMENT. THIS PROBLEM HAS BEEN MET IN DESIGN BY UNDERCUTTING THE PROPOSED PAVEMENT AREA FOUR FEET BELOW THE FINISHED CENTERLINE GRADE AND THEN BACKFILLING AND RECOMPACTING. THIS DESIGN METHOD IS NOW STANDARD PRACTICE THROUGH KNOWN BOULDER AREAS. IN THE NORTHERN AND EASTERN SECTIONS OF NEW YORK STATE, CONSIDERABLE PORTIONS OF THE HIGHWAYS ARE LAID THROUGH ROCK CUTS. ONE OF THE HIGHWAY DISTRICTS IS PLANNING TO MEET THIS PROBLEM IN DESIGN BY ESTIMATING A BACKFILL CONSISTING OF A FINE-GRAINED BITUMINOUS MIX. SUCH BACKFILL IS TO BE BUILT UP SUFFICIENTLY WITH WELL-TAMPED LAYERS TO FORM A SMOOTH TOP-SURFACE GRADIENT WHICH WILL DRAIN ANY WATER SEEPAGE FROM UNDER THE PAVEMENT. IT IS RECOMMENDED THAT A CUSHION OF RUN-OF-BANK GRAVEL, HAVING A MINIMUM THICKNESS OF 12 IN. BE PLACED BETWEEN THE PAVEMENT AND THIS BACKFILLED AREA. SUGGESTIONS ARE MADE TO AID IN SUBSURFACE DRAINAGE FOR SIDE-HILL CUTS. FIELD OBSERVATIONS PROVIDE EXAMPLES OF FROST DAMAGE FOLLOWING THE USE OF SILTY SOILS IN EMBANKMENTS. BY PLACING A LAYER OF GRAVEL BETWEEN THE HIGHEST WATER TABLE AND THE FROST LINE, THE CAPILLARY FLOW IS CUT OFF, AND THE FROST HEAVE CAN USUALLY BE HELD WITHIN REASONABLE LIMITS.