The Effect of Insulation Layers on Subgrade Strength during Thaw Season

A well-known strategy for minimizing the negative effects of prolonged low temperatures on frostsusceptible subgrade is using insulation layers. It helps to mitigate the formation of ice lenses and frost heave in the subgrade and subsequently reduce the associated damage despite the presence of a shallow water table. Using insulation layers aids with the drainage of the excess water formed from melted ice lenses during thaw season, which reduces subgrade strength before it discharges out of the system.

This paper evaluates the effect of using a recently introduced by-product of power generation, bottom ash, as an insulation layer, and the commonly used Polystyrene boards on subgrade resilient modulus variations during thaw season at the IRRF test road facility of University of Alberta, Edmonton, Canada.

Using temperature data received from Time Domain Reflectometers (TDR) installed across the pavement depth over the course of two successive springs (2014 and 2015), the onset of thaw season was established. Timeline for the recovering period was based on Me-PDG recommendation. To evaluate the subgrade strength, Falling-Weight Deflectometer (FWD) testing was conducted at 10-m intervals along the test road during thaw season and the average condition. The back-calculated moduli from deflection basins were used to determine the resilient modulus of the insulated sections and the control section.

The study results revealed that using polystyrene boards as insulation layers protected subgrade soil from freezing and thawing effect since the resilient moduli were almost constant during thaw season and had greater values compared to control section. Although bottom ash layer had been affected by freeze and/or thaw, the section exhibited less variation in subgrade modulus than that of the control section during recovering period, particularly in the month of May.