Field Experimental Investigations of Freezing and Thawing of Highway Subgrade

This paper represents and analyses the experimental data for investigation of freezing and associated temperature and moisture variations in subgrade of “Almaty-Bishkek” highway (2013–2016). Experimental data regarding temperature and moisture have been obtained by special sensors which were installed in different depths of a vertical hole, drilled in a multilayer pavement and subgrade of the highway. Measuring of temperature has been performed according to the principle of thermal resistance variation, and measuring of moisture has been performed in accordance with the principle of dielectric permeability. It was stated that temperature in points of subgrade is varied only in an annual cycle in south-eastern region of Kazakhstan, daily cycles are not available. Amplitude temperature values are decreased with the depth increase and lag in time is increased for the graphs of temperature variation with the depth increase. The character of variation and maximal value of freezing depth can be different depending on the character of air temperature variation and possible interchanging of cold and warm periods in winter. The temperature can be decreased lower than 0 ℃ in the top part of subgrade in winter periods. In such a case, sharp decrease for quantity of liquid moisture occurs, i.e. part of moisture transforms into a solid condition (ice). Quantity of moisture becomes more after thawing than it was before freezing. The value of this accumulated moisture content is connected with the duration of frozen condition for the top part of subgrade and maximal freezing depth of a highway.