MEASUREMENT AND PREDICTION OF FROST PENETRATION IN HIGHWAYS

Knowledge of the depths of frost penetration in highway roadbeds is essential to determining the safe location of structural foundations, sewers, pipelines, and water mains. Most of the current knowledge of frost penetration is limited to sparsely documented information gained from studying boreholes and excavations, even though a method exists for predicting the relationship of frost penetration to air freezing index. Through a 5-year program of measuring frost depth by use of frost depth indicators at 62 locations in Ontario, a body of data has been acquired and used to make the relationship between frost penetration and air freezing index more appropriate to Ontario. To further assist the user of this relationship, a freezing index map of the province has been created from published temperature data observed at 224 locations during the period from 1941 to 1970. The map was prepared by using a method recently developed by the National Research Council of Canada that calculates the air freezing index from mean monthly temperatures. Although the method is simple to use, local factors such as soil type and moisture content influence the actual depth of frost penetration. To enable such effects to be evaluated and to provide the capability of examining the effects of insulation and frost retaining layers, a computer program to solve the heat flow relationships was developed for the Ministry by Carleton University. The program can predict the maximum frost penetration and ground temperatures from information that is, in most cases, readily available. Computer predictions at several sites have been favorably compared with measurements of actual frost penetration and time profiles. (Author)