ESTABLISHING SUBGRADE RESILIENT MODULUS INPUTS FOR FLEXIBLE PAVEMENT REHABILITATION DESIGNS USING DARWIN-ME – A SIMPLE APPROACH

摘要

The resilient modulus (MR) of subgrade and unbound materials is significantly influenced by thechanges in the soil physical state represented by its moisture content and dry density values.DARWin-ME requires the pavement designers to input the laboratory measured resilientmodulus value at optimum moisture content for appropriate characterization of subgrade andunbound materials. The resilient modulus at optimum or near optimum moisture contentrepresents the soil physical state at the time of subgrade construction. For new flexible pavementdesigns, the resilient modulus and the optimum moisture content values are relatively easier toobtain from historical construction records. However, for flexible pavement rehabilitation orreconstruction designs, identifying the as-constructed subgrade condition is not straight forward.The field subgrade modulus derived from backcalculation of deflection basin tests or DCP teststhat reflect the “in situ” conditions at the time of overlay or reconstruction cannot be directlyused without appropriate adjustments. The pavement designs are often confronted with aquestion of what input value of subgrade resilient modulus would be appropriate for use inflexible pavement rehabilitation designs. This paper proposes a simple method to determine theresilient modulus input value from field measurements with appropriate adjustments. Theseadjustments help to establish a correspondence between the input MR value adjusted for asconstructedconditions with the “in situ” MR measured at the time of deflection testing whilekeeping the DARWin-ME simulated postcompaction profile of subgrade MR variationsunchanged.