DETERMINATION OF TEMPERATURE AND DEPTH OF FROST PENETRATION IN PAVEMENTS AND SUBGRADES

Remote measurement of subgrade and pavement temperature is made by means of seniconductor themoresistances. At the upper layers, measurements are made daily, but at greater depths measurements are made less frequently. Figures are presented which illustrate the results of temperature measurements in asphalt pavement surface. Such data make it possible to study temperature variations and subgrade performance in given climatic conditions. From mid-April until mid-September heat flows downward and the average rate of heating at a depth of 0.6 m from the pavement surface is 0.20 deg per day. From the end of September, the direction of heat flow changes. The rate of zero-isotherm shift at various depths and the period of transition from winter to spring, the difference between temperatures of the asphalt concrete along the road axis and its edges, and the various of the pavement temperature within 24 hours are discussed. A formula (based on field observation) is presented for determination of an average daily temperature at any point on an asphalt concrete surface as a function of its temperature conduction at an average daily ambient temperature. A nomogram is presented for the determination of the depth of frost penetration in a subgrade winter. The nomogram shows the relationship between an average maximum depth of frost penetration for a number of years, the ambient temperature a distance from the pavement surface to the ground water level, thickness of the pavement layers and their thermal characteristics. The value of the frost penetration depth is used for predicting design water content of soil. The importance is stressed of the information about minimum negative temperature of the pavement in the coldest month, positive temperature in spring, in the period of thawing when the moisture content of the subgrade soil has its highest value, and also about the maximum temperature of the warmest month.