Permafrost prevention pipes installed under road embankment
A team of researchers conducted a permafrost-geological survey to determine the cause of road damages near Buraat Pass from June 18 to July 15, 2021. Geophysical electrical tomography measurements were made in the damaged sections of the road in Tolbo soum of Bayan-Ulgii Province, and holes were drilled to confirm the measurements, take samples, and measure the permafrost temperature. Buraat Pass is in the continuous and intermittent permafrost area, reported the team. Drilling and geophysical measurements revealed high permafrost in the damaged sections of the road embankment.
The study found that permafrost with high ice content under the road embankment was thawing, and that the road embankment surface was sagging. To this end, thermosyphon, which has been tested and put into practice in Mongolia for more than 10 years, was installed under the road embankment. In other words, permafrost prevention pipes were installed under the road embankment.
A thermosyphon tube is a passive cooling device that transmits cold water deeper into the soil when the air temperature is colder than the soil temperature. Carbon dioxide (CO2) is used in the coolant. If the sealing of the thermosyphon pipe is not lost, the pipe can operate for decades in the winter without the need for any additional power. In other words, a thermosiphon tube is a device that works in the cold of winter and uses renewable energy.
Mongolia has a total of 112,414 kilometers of road, of which 14,918.7 kilometers belong to the international and national road network. Of this, 48.5 percent, or a total of 7,227 kilometers are paved roads. Among them, 1,424 kilometers of roads pass through the permafrost region, but permafrost conditions have not been considered while designing and constructing roads.
The “Permafrost Survey along Some Roads” survey was conducted in Arkhangai, Khuvsgul, Zavkhan and Bayan-Ulgii provinces between 2017 to 2019 with funding from the Science and Technology Foundation. Implemented by researchers from the Mongolian Academy of Sciences, the survey found that roads built without considering the characteristics of permafrost and the design and technology of road embankments on permafrost soils can get damaged in one to five years. The road surface is bent up to 20 to 40 centimeters and cracks have formed along some parts. This subsidence varies depending on the amount of ice contained in the permafrost.
Mongolia ranks fifth in the world in the prevalence of permafrost, with 29.3 percent of the total area covered by permafrost. Permafrost is soil or rock that has been frozen for two years or more at a temperature of zero or less. Permafrost accounts for 24 percent of the total land area of the northern hemisphere and is distributed to some extent in 48 countries. About 95 percent of the total permafrost region is in the territory of five countries, namely Mongolia, Russia, Canada, China and the USA.