REMEDIES AND TREATMENTS BY THE CONNECTICUT HIGHWAY DEPARTMENT

FROST ACTION IS A MAJOR PROBLEM IN CONNECTICUT HIGHWAY WORK DUE TO THE CLIMATE, WIDESPREAD EXISTENCE OF SILTY OR CLAYEY GLACIAL TILL, AND FREQUENT SMALL AREA OF SILT AND CLAY GLACIAL LAKE DEPOSITS. THE REMEDIES AND TREATMENTS USED ARE ADEQUATE SUBBASE AND UNDERDRAINS. THE SUBBASE IS INVARIABLY CLEAN BANK-RUN GRAVEL, FOUND ABUNDANTLY THROUGHOUT THE STATE, ON NEW CONSTRUCTION OF PRIMARY ROADS, THE COMBINED THICKNESS OF PAVEMENT (SURFACE AND BASE) PLUS SUBBASE IN EARTH CUST IS FROM 20 TO 32 IN., WHICH IS 2/3 OR 3/4 OF FROST PENETRATION; THE COMBINED THICKNESS IS 32 IN. IN ROCK CUTS AND ABOUT 14 IN. IN EARTH FILLS. THE LAST MAY BE REDUCED TO 8 IN. IF CUTS EXCEED FILLS. ON SECONDARY ROADS THESE THICKNESSES OF PAVEMENT ARE REDUCED SLIGHTLY. ON TERTIARY ROADS (TOWN AID), THESE THICKNESSES OF PAVEMENT PLUS SUBBASE TOTAL 8 TO 20 IN., DEPENDING ON CONDITIONS. THESE THICKNESSES ARE INFLUENCED BY SOIL TYPES, THE GREATER AMOUNTS BEING USED IN SILTS AND CLAYS AND THE LESSER IN TILLS. IN CLEAN SANDS AND GRAVELS, SUBBASE IS GREATLY REDUCED OR ELIMINATED. ON NEW CONSTRUCTION AN UNDERDRAIN IS PLACED IN WET CUTS TO DRAIN THE SUBBASE, INTERCEPT SIDEHILL SEEPAGE, LOWER THE WATER TABLE, OR DO ALL THREE. THE UNDERDRAIN IS LOCATED UNDER THE MIDDLE OF THE SHOULDER OR UNDER THE GUTTER. DEPTH OF UNDERDRAIN DEPENDS ON FROST PENETRATION, TYPE OF SOIL AND THICKNESS OF PAVEMENT AND SUBBASE; USUALLY IT IS 5 FT. BELOW TOP OF SHOULDER IN EARTH CUTS. IN ROCK CUTS, THE UNDERDRAIN IS 4 FT. BELOW TOP OF SHOULDER, SERVING ONLY TO DRAIN THE SUBBASE. ON EXISTING ROADS, THE USUAL PRACTICE IS TO INSTALL AN UNDERDRAIN WHERE FROST ACTION HAS OCCURRED. THE UNDERDRAIN IS USUALLY CHEAPER THAN REMOVING THE PAVEMENT AND POOR SOIL AND THEN INSTALLING SUBBASE AND NEW PAVEMENT. ALSO THE UNDERDRAIN OFTEN IS NEEDED TO DRAIN THE SUBBASE AND PAVEMENT AND SOMETIMES TO CARRY SURFACE WATER AS WELL. THE SAME DESIGN FOR THE UNDERDRAIN IS USED ON AN EXISTING ROAD AS FOR A NEW ROAD, EXCEPT THAT WHERE THE EXISTING ROAD IS DEFICIENT IN SUBBASE, THE UNDERDRAIN MAY BE DEEPER. SUBBASE DEFICIENCY IN OLD ROADS IS A FREQUENT CONDITION, PARTICULARLY UNDER THE SHOULDERS. HOWEVER, WHEN THE SOIL IS PRACTICALLY PURE SILT OR CLAY, PAVEMENT AND SHOULDERS ARE REMOVED AND SUBGRADE EXCAVATED TO ALMOST FULL DEPTH OF FROST AND REPLACED WITH GOOD GRAVEL SUBBASE AND NEW PAVEMENT AND SHOULDERS. /AUTHOR/