Justification of the subgrade design features from draining soils in the cryolithic zone using heat engineering calculations

Abstract

   During the construction of transportation facilities in the cryolithozone, the temperature regime of permafrost soils is radically disturbed. During the operation of the Baikal-Amur Mainline for several decades, the so-called thawing bowls were formed at the base of the subgraid in some sections in the areas of high-temperature frozen soils. These are zones of thawed perennially frozen ground located directly under railway embankments, even when the first principle of construction is used. This applies mainly to embankments with drainage soils. In this case, the formation of such bowls is primarily promoted by infiltration of atmospheric precipitation into the body of the subgrade. It is very problematic to estimate the effect of precipitation on the warming effect of the subgrade because of the chaotic nature of filtration processes occurring in the body of the subgrade.
   In this paper an attempt is made to use a non-traditional approach to solving this problem, namely, it is proposed to introduce a correction to the summer values of the coefficient of thermal conductivity, taking into account the heat exchange of filtered warm atmospheric water with solid particles of the draining soil. To determine the correction to the thermal conductivity coefficient, an empirical approach was used. It consists in correcting the heat conductivity coefficient in the process of numerical calculations, focusing on the real depth of the upper boundary of permafrost under the embankment, obtained during geotechnical surveys. The heat conductivity coefficient thus selected can be used for further calculations under similar conditions.
   Using the proposed approach, an effective embankment design from draining soils was justified. It is also shown that the use of such a technique to prevent degradation of the embankment base soils is effective in the construction of the earth bed for the second tracks in the cryolithozone.