Problems of stabilizing the subgrade of railways and highways in cold regions of china

The main engineering problem associated with the degradation of permafrost and cyclic freezing-thawing of seasonal permafrost soils is a decrease in the bearing capacity of engineering structures due to the degradation of the main physical-mechanical properties of the embankment soils. The cyclical change in temperature leads to regular freezing-thawing of the soil, as a result of which such types of deformations occur as heaving during freezing and settlement during thawing. The purpose of this work is to highlight new information about complex measures to stabilize the subgrade of railways and highways in the cold regions of China. The paper considers such measures as thermosiphon stabilization, rock fill, installation of ventilation pipes and laying of thermal insulation boards. This paper also describes the disadvantages of existing measures for stabilizing the temperature regime of the embankment and its base. Considered the main transport network of the Qinghai-Tibet plateau, including the Qinghai-Tibet railway and four highways. The experimental section of the Wushu-Xining expressway on the Qinghai-Tibet plateau was chosen as the object of the study of numerical modeling; a numerical calculation of the temperature and moisture content fields of the typical embankment was carried out, as well as numerical calculation of the embankment with rock fill for the 10th year of operation. The calculations were carried out on the basis of the «Freeze-Cold» software package specially developed for engineering calculations of the freezing and thawing process in soils. The calculation showed that rock fill allows to reduce the area of the soil thawing, raising the front of frozen soil, helps to reduce the degradation of frozen soil, which ultimately has a positive effect on the bearing capacity of the entire engineering structure. Analysis of the collected data and calculated values allows to conclude that the use of rock fill of 0,8 meters depth as an insulating material to maintain the stability of the thermal regime of the embankment on frozen ground in the considered region of the Qinghai-Tibet Plateau.