Salt from the earth: new model will facilitate the construction of mines beyond the Arctic Circle

Engineers have developed a new method for calculating the freezing of soils and rocks, which for the first time takes into account the influence of dissolved salts on the freezing processes. The resulting model will make it possible to predict soil behavior in difficult climatic conditions much more accurately and identify risk zones for dangerous swelling, deformation and loss of stability in advance. It will enable designers and builders to more accurately assess the reliability of foundations and choose safe parameters for mine construction. For more information about the calculation methodology, see the Izvestia article.

How salt changes the behavior of frozen soils

For the first time, scientists have studied in detail how small concentrations of dissolved salt affect soil freezing and moisture migration in frozen rock. The study was conducted by specialists from Perm Polytechnic University, the Mining Institute of the Ural Branch of the Russian Academy of Sciences and the Institute of Environmental Management of the National Academy of Sciences of Belarus.

The problem of frost heaving remains one of the key issues in construction in the northern regions and the development of underground workings. When freezing, the water moves to cold areas, turns into ice and increases in volume. This causes rock deformation, which can lead to subsidence of foundations, destruction of roads and damage to pipelines. Such processes are particularly dangerous during the construction of mine shafts and potash mines, where soils often contain natural brines.

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Until recently, the effect of salt on the behavior of frozen soil was studied mainly empirically. Engineering calculations usually assumed that salinization reduces the effect of frost heaving. However, a new study has shown that this process is much more complicated.

For the experiments, the scientists used clay, chalk and loam, the most common types of soils in permafrost and potash mining areas. The samples were placed in special installations with a controlled temperature gradient simulating natural freezing. Then various concentrations of table salt were added and the movement of moisture, as well as changes in the rock structure, were analyzed.

— The analysis showed that at low concentrations of salt — up to 0.0035 kg per 1 kg of soil — heaving does not weaken, but, on the contrary, increases by 17-40%. At higher concentrations, the effect becomes the opposite: moisture migration slows down," said Mikhail Semin, Doctor of Technical Sciences, Head of the Laboratory of the Mining Institute of the Ural Branch of the Russian Academy of Sciences, Professor at PNRPU.

According to him, the key conclusion of the study is that salt affects the process not only through chemical reactions, as previously thought, but primarily through changes in the hydraulic permeability of the soil. With a small amount of salt in the pores, the volume of unfrozen water increases, which makes the moisture move more actively towards the freezing front. At high salinity, the filtration properties of the soil, on the contrary, deteriorate.

Photo: Global Look Press/Jon G. Fuller/Vwpics

Mikhail Semin noted that the work is primarily focused on the tasks of mine construction and artificial rock freezing technology. In the future, the results obtained can be applied to the development of territories in conditions of natural permafrost.

— It is possible to more accurately assess the contribution of frost heaving during the freezing of soils and rocks containing dissolved salt. This is a rather acute problem when drilling potash mines, and previously it was not always possible to pass through such areas without problems due to the brines encountered," he explained.

Based on the results of the work, the scientists also prepared a methodology for calculating the parameters of artificial freezing of rocks under conditions of mineralized moisture transfer. In fact, we are talking about a new internal regulatory document for engineering calculations, the authors added. The study itself was conducted within the framework of the "Priority 2030" program.

Technology for the Arctic and industrial infrastructure

The development can significantly increase the reliability of construction in the northern regions and reduce the risk of accidents at infrastructure facilities, experts believe. Leonid Drobyshevich, NTI technology expert, believes that the new technique makes construction more predictable in difficult climatic conditions.

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According to him, engineers will be able to take into account the influence of soil salinity, which acts as a kind of antifreeze and changes the freezing processes of rocks under foundations, roads and pipelines. This will make it possible to more accurately predict deformations and reduce the likelihood of destruction of engineering structures.

"Such a development is especially relevant for the Arctic: where there is permafrost and extreme conditions, any inaccuracy in calculations can be very expensive," the expert noted.

He also added that such techniques can be used in conjunction with drones and digital terrain models. This will make it possible to create digital soil twins, monitor their condition in real time and identify potentially dangerous changes in advance.

The new technology is of strategic importance for the northern territories of Russia, added Alexander Vorotnikov, coordinator of the expert council of the expert center of the Arctic Development Project Office, PhD, Associate Professor at the Institute of Social Sciences of the Russian Academy of Sciences. According to him, about 60% of the country's territory is located in the permafrost zone, which requires a special approach to the construction of residential facilities, roads, railway infrastructure and pipelines.

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— Many accidents that were previously considered technical are actually related to the degradation of permafrost. Changes in the soil condition lead to deformation of foundations and destruction of engineering structures. One of the most famous examples was the accident in Norilsk," said Alexander Vorotnikov.

The expert emphasized that the new technique will allow predicting the behavior of the soil in advance, more accurately estimating the service life of structures and reducing the likelihood of emergencies. In his opinion, additional opportunities will be provided by the use of artificial intelligence and digital models capable of calculating various scenarios of permafrost changes in advance.

In the context of the active development of the Arctic and the development of northern infrastructure, such technologies can become an important tool for reducing accidents and reducing the cost of restoring facilities.