Range of change in Fourier numbers in thermal calculations of automobile roads in the cryolithic zone

Abstract

An assessment of influence of thermal physical properties of dispersed rocks on the range of change in the values of Fourier numbers, used in thermal calculations of soil foundations of the automobile roads in the cryolithic zone, was carried out. The formulas applied in the calculation have considered the functional dependence of the thermal conductivity coefficient and the total heat capacity on the moisture (ice) content in the thawed and frozen state. A mixture of quartz sandstone with water in thawed state and ice in frozen state, with moisture (ice) content changing zero (dry quartz sandstone) to full moisture saturation, was used as an example. It was determined that the range and type of Fourier numbers for thawed and frozen dispersed rocks differs significantly, both quantitatively and qualitatively, depending on their moisture (ice) content. For thawed rocks, the Fourier number decreases as moisture content rises. For frozen rocks, it increases. It was demonstrated that in calculation of Fourier numbers for dispersed rocks it is important to properly apply the calculation models. In particular, if the model of material structure is not changed the reflect the respective contents of the binder and the filler components, above a particular concentration of the respective components, the calculation error in Fourier numbers can exceed 30%. An assessment of the possibility of averaging the thermal physical characteristics of the rocks to obtain the universal Fourier numbers was done. It was concluded that the use of universal Fourier numbers causes a significant error for both thawed and frozen rocks. Their use in thermal calculations over the yearly temperature changes is not expedient. It is correct to separate the thermal calculations into three components: calculation in the thawed state, calculation in the frozen state and calculation in the phase transition period of freezing and thawing, with corresponding calculation of Fourier numbers for every period and the aggregate state of the moisture in the dispersed rocks.