Engineering and geocryological assessment of the impact of mineral extraction on permafrost degradation within the Arctic cryolithozone of Russia

Stupin Oleg Gennad'evich Graduate student; Department of Digital Management Technologies; Siberian Federal University 660041, Russia, Krasnoyarsk Territory, Krasnoyarsk, Oktyabrsky district, Svobodny Prospekt, 79 ipdme@mail.ru Other publications by this author     Vakhrusheva Inna Alekseevna PhD in Pedagogy Associate Professor; Department of Higher Mathematics; Russian State Agrarian University - Moscow Timiryazev Agricultural Academy 49 Timiryazevskaya St., Moscow, 127434 vakhrusheva@rgau-msha.ru Pchelintseva Svetlana Viacheslavovna PhD in Technical Science Associate Professor; Department of Applied Informatics; Russian State Agrarian University - Moscow Timiryazev Agricultural Academy 49 Timiryazevskaya St., Moscow, 127434 pchelintseva@inbox.ru

Krasovskaya Lyudmila Vladimirovna PhD in Technical Science Associate Professor; Department of Applied Informatics; Russian State Agrarian University - Moscow Timiryazev Agricultural Academy 49 Timiryazevskaya str., Moscow, 127434, Russia kraslud@yandex.ru

1. Introduction

Permafrost rocks (MMP), covering significant areas of the northern hemisphere, play an important role in the functioning of the planet's climate system, maintaining the stability of engineering infrastructure and maintaining the carbon balance. Under conditions of global warming and anthropogenic impact, the degradation of permafrost rocks is becoming one of the most pressing geoecological problems ^[1-3]. The areas of the Arctic cryolithozone are particularly vulnerable, where the processes of thermokarst, thermal erosion and thawing of frozen soils lead to irreversible changes in landscapes, disruption of the hydrological regime and destruction of economic facilities ^[4-6]. One of the most powerful sources of local heat exposure within the cryolithozone is the extraction of mineral raw materials, accompanied by the active exploitation of mining infrastructure, landfills, technological sites and heat supply networks. Against the background of high rates of industrial development of the Arctic, engineering and geocryological assessment of anthropogenic impacts is becoming an integral part of sustainable environmental management and design in permafrost conditions ^[7-10].

One of the key problems is the thermal redistribution in the mining area, which leads to a decrease in the thermal stability of frozen soils. During open-pit mining, especially in the Arctic, rocks with low heat capacity and high thermal conductivity are exposed, which contributes to rapid heating of the underlying substrate ^[11-13]. Additional thermal effects are caused by exogenous and endogenous processes, including the oxidation of sulfide minerals in landfills, the operation of heat-generating equipment and the discharge of warm drainage waters. For underground mining, the situation is aggravated by the heat transferred from the ventilation air and self-heating of the rocks. These factors together cause accelerated degradation of permafrost rocks, leading to an increase in the active layer, subsidence of soil, loss of bearing capacity of the foundations of structures and the occurrence of potentially emergency situations ^[14]. At the same time, greenhouse gas emissions from thawed areas accumulate, which further increases the negative impact on the climate system ^[15-18].

Attempts to solve this problem include both constructive and environmental approaches. At the engineering level, methods of thermal stabilization of foundations are being implemented using seasonally active or passive coolers (thermosiphons), the use of thermal insulation coatings, deep foundation laying and drainage of drainage waters beyond the permafrost zone ^[19-22]. However, these measures require significant design, operation, and maintenance costs, and they are not always economically feasible in remote Arctic areas. On the other hand, when developing mineral resources, it is allowed to introduce adaptive technological solutions aimed at minimizing thermal effects, including changing transportation routes, placing heat-loaded facilities outside cryogenically sensitive areas, and choosing the seasons of work ^[23-25]. The disadvantage of such solutions is their limited efficiency with high production volumes and the presence of permanent heat sources. In addition, in practice, there is often a discrepancy between the design and actual characteristics of permafrost rocks, which requires refined methods for assessing the condition of underlying soils ^[26-27].

In this regard, the application of engineering and geocryological methods for assessing and predicting the degradation of permafrost rocks under the influence of the thermal effects of mining is becoming increasingly relevant. The use of geothermal sensing, thermometry, long-term temperature monitoring, and numerical modeling makes it possible to more accurately determine the dynamics of the temperature field, melting boundaries, and the zone of loss of strength properties of frozen soils ^[28-30]. The combination of observational and computational methods makes it possible to take into account both local factors (mining depth, superheated reservoir capacity, dump design) and regional trends related to climate warming. The integration of such approaches into the design and operation system of mining enterprises in the Arctic opens up prospects for optimizing technological solutions and increasing the stability of infrastructure in permafrost conditions ^[31,32].

This work is aimed at an engineering and geocryological assessment of the impact of mineral extraction on the degradation of permafrost rocks within the Arctic cryolithozone of Russia. The study focuses on the analysis of the thermal effects created by the Yunyaginsky coal mine, located in the Vorkuta region, as well as a number of operating coal mines that are part of the Pechora coal basin. The purpose of the work is to determine the nature, intensity, and spatial distribution of the thermal effects of these objects on the state of permafrost soils, identify factors determining the scale of degradation, and assess potential risks to engineering structures and the environment. The conducted research covers the analysis of the temperature regime, geocryological characteristics of the area, and mining technology features, and allows us to formulate practical recommendations for reducing the anthropogenic load on permafrost rocks in the context of the development of the Arctic mining industry.

2. Methodology and methods of research.

As part of this study, a comprehensive program of field and laboratory geocryological engineering work was implemented aimed at determining the degree and nature of the thermal effects of mining activities on the condition of permafrost soils within the Arctic cryolithozone. The experimental work covered the sections of the Yunyaginsky coal mine and the adjacent mines of the Pechora coal basin, including the Vorgashorskaya, Vorkuta and Zapolyarnaya mines. The main attention was paid to the zones of direct impact of thermal sources, as well as remote background areas, which were used as control points for comparative analysis.

The instrumental part of the research included drilling engineering and geological wells with the selection of temperature, geotechnical and hydrological data. For thermometric monitoring, HOBO U23 Pro v2 digital geothermal sensors with a measuring range from -40 to +70 °C and an accuracy of ±0.2 °C were used, which were installed in wells up to 20 m deep at fixed intervals of 0.5–2 m. The measurements were carried out in automatic mode with a registration step of 1 time per hour for at least 6 months. Additionally, cable thermal probes with integrated temperature gradient recording (Geotherm-5M brands, manufactured by Technoengineering LLC, Russia) were used. These devices made it possible to quickly estimate the temperature distribution over depth in real time with a resolution of up to 0.1 °C. Drilling sites were selected taking into account lithological uniformity, distance to heat sources, and accessibility for subsequent geodetic monitoring.

The field work was complemented by laboratory studies of permafrost soil samples taken from 46 wells. The tests were carried out on automated installations IGI-3000 and TSNIIS-95M, designed to evaluate the physico-mechanical characteristics of frozen samples. The parameters obtained in the laboratory included humidity, porosity, modulus of elasticity, shear resistance, and filtration coefficient. The tests were performed at a temperature of -5 °C in thermostabilized chambers simulating the natural conditions of the cryolithozone. The content of liquid and bound moisture was analyzed separately using Sartorius MA160 moisture meters, which made it possible to determine phase changes within the transition layer of permafrost.

To simulate the thermal field, GeoStudio specialized software (TEMP/W module) was used, which provides a numerical solution of heat transfer equations taking into account phase transitions. The calculations used parameters obtained in the field and laboratory conditions, including thermal conductivity, heat capacity and latent heat of melting. The model grid had a step of 0.5 m, and the time step was 10 days, which made it possible to reliably track the development of temperature anomalies and the zone of degradation of permafrost rocks during the forecast period of up to 25 years. The results obtained formed the basis for the analysis of the spatial distribution of thermal effects and formed the basis for risk assessment for engineering structures.

3. The results of the study

In the course of this study, an engineering and geocryological assessment of the thermal effects of coal mining facilities in the Pechora coal basin was carried out, focusing on the Yunyaginsky coal mine (Fig. 1) and adjacent mines, including Vorgashorskaya, Vorkuta and Zapolyarnaya. The study was conducted on the basis of instrumental monitoring of the temperature of frozen soils, analysis of geothermal fields, thermometric drilling, seismic surveys and modeling of the dynamics of thermal effects in the zone of influence of anthropogenic load. The observation range included areas within a radius of up to 4 km from the center of the quarry, as well as control points within 8-10 km that were not affected by coal mining activities, and was used as a background for establishing a baseline temperature regime.

Figure 1. Coal mining at the Yunyaginsky coal mine.

Experimental data showed a significant increase in soil temperature within the zone of active activity of the Yunyaginsky section. Within 500 meters from the edge of the quarry, the average annual temperature at a depth of 2 meters was -0.4 °C, while in control areas of a similar geological and lithological structure it did not exceed -2.1 °C. At a depth of 5 meters, the temperature anomalies were even more pronounced: within the zone of influence, the temperature reached -0.1 °C, while the background value was -1.7 °C. The maximum penetration of positive temperatures was recorded at a depth of 7.5 meters at points located near coal depots and equipment storage sites, which is associated with heat accumulation and heat transfer through the surface layer. Additionally, at depths of 10 and 15 m, a deviation of isotherms up to +0.3 °C from the calculated values determined for permafrost was observed.

A comparative analysis of the temperature at 32 observation points showed that the average temperature increase in the Yunyaginsky quarry area compared with the control is 1.52 °C, which confirms the intense local thermal effect. There was also an expansion of the seasonal thawing zone: the average depth of the active layer increased from 1.4 m (background) to 2.8 m (zone of influence), which corresponds to an increase of more than 100%. Some areas showed signs of partial or complete thawing of permafrost soils. Thus, near the northeastern landfill zone, in an area where the average density of overburden reached 2,200 kg/m3, the disappearance of permafrost rocks at a depth of up to 4.2 meters was recorded. At the same time, the average annual temperature here ranged from -0.2 to +0.4 °C, and the liquid moisture content reached 36%, which is more than 1.5 times higher than the background values.

Figure 2. Comparative analysis of permafrost characteristics.

Analysis of samples taken from 46 drilling wells showed a change in the moisture content of permafrost rocks: if the humidity at the control points was 18-22%, then in the warming zone it increased to 30-34%, and in some places to 38%, which indicates the phase transition of ice into water. The change in the physical properties of the soil was accompanied by a decrease in the modulus of elasticity from 42 MPa to 23-27 MPa. Field laboratory tests have shown a 31% drop in shear resistance, especially in areas with humidity above 35%.

The most intense heat supply from the depths was recorded in the areas near the ventilation shafts and the depleted spaces of the mines. Thermal profiles based on the results of measurements at depths up to 20 m showed an increase in the geothermal gradient from a background of 2.9 °C/100 m to 5.3 °C/100 m near the Vorgashor mine (Fig. 3), especially in the area of ventilation outlets. Measurements of the temperature of the air emitted by the shaft fans showed that even in winter its temperature was +6.2 °C at an outdoor temperature of -29.5 °C. The flow rate of ventilation flows reached 180-220 thousand m3/h, creating a zone of stable thermal effect up to 125 meters from the mouth of the trunk. Calculations based on the model of heat transfer in permafrost rocks have shown that the horizontal impact zone of ventilation emissions can reach up to 140 meters with deep heating up to 10-14 meters over 15-20 years of operation.

Figure 3. Thermal Profile Of The Vorgashor Mine.

Numerical simulation of heat propagation using the finite difference method over a computational grid in 0.5 m increments, using thermophysical parameters (λ = 1.4 W/(m·K), C = 2.2·10⁶ J/(m3·K), L = 3.34·10⁸ J/m3), showed that complete thawing of permafrost rocks to a depth of 6-8 m near areas of intensive operation (technological roads, coal loading sites) are possible in 17-21 years. In areas of maximum heat load concentration (infrastructure nodes, heat exchange stations, pumping stations), the heating depth can exceed 9.5 m. At the same time, there was a clear correlation between the density of the heat flow and the depth of thawing: at a power of 80-100 W/m2, the degradation depth was 1.8–2.4 m, at 120-150 W/m2 — up to 3.1–3.8 m over 5 years.

An analysis of the time course of temperature according to data from automated stations (9 installations in total) for the period 2016-2024 showed a steady upward trend. The average annual temperature at a depth of 1.5 m increased from -1.6 °C to -0.7 °C, and in the upper 0.5-meter soil layer reached +0.2 °C. In the winter and spring period, the temperature in the drainage and discharge zones of mine waters increased by 1.2–1.4 °C above the background level. The recorded temperature of the drainage waters was +2.5...+4.8 °C with an average daily discharge volume of 520 m3. This thermal energy effect is equivalent to a local load of 30-35 MWh/day, which led to accelerated thawing to a depth of 4.2 m in the areas adjacent to the discharge channels.

Geodetic monitoring performed on the basis of GNSS stations and inclinometric probes revealed surface subsidence of up to 14.2 cm within the areas where the complete disappearance of permafrost rocks at depths of 2-3 m was observed. Precipitation was accompanied by local deformations of the base soils with loss of bearing capacity. The coefficient of adhesion decreased from the background value of 38 kPa to 21-24 kPa, and the modulus of deformation decreased from 22 to 13 MPa. In areas of intense thawing, an increase in porosity was recorded by 8-12%, which creates additional risks for the stability of infrastructure facilities.

Based on the results obtained, it is possible to conduct a comprehensive analysis of the temperature regime, geocryological characteristics of the studied area, technological features of coal mining, as well as formulate recommendations aimed at reducing the anthropogenic heat load on permafrost rocks in conditions of active development of Arctic territories.

The temperature regime of the Yunyaginsky section and adjacent mines is characterized not only by local warming of the upper soil layers, but also by the redistribution of heat flow in the vertical and horizontal directions. According to the model reconstruction of the thermal balance, over the past 15 years, the 0 °C isotherm has shifted downward by an average of 1.8 m, and the zone of thermal anomaly has expanded radially by 220-270 m around the main heat sources. This indicates the formation of a stable technogenic thermal field. A pattern has been revealed: with an increase in the average heat load density on the surface above 90 W/m2, an exponential increase in the depth of degradation of permafrost rocks is observed, which is associated with the nonlinear thermal conductivity of moist soils in the transition phase between the solid and liquid state.

Analysis of geocryological properties has shown that the temperature plasticity of permafrost rocks increases sharply as they approach the ice phase transition, especially in areas with a high proportion of silty particles (more than 35% in the composition). This leads to increased deformation in areas with reduced strength: in fractured and loess-like horizons. It was also found that in the zones of thermal exposure, the filtration coefficient increases by more than two times (from 1.1·10⁻⁶ to 2.5·10⁻⁶ m/s), which increases the infiltration of warm waters and contributes to the formation of secondary foci of degradation on the periphery of the active zones.

The technological features of mining also demonstrated the influence of thermal effects on the spatial structure. An analysis of aerothermographic images taken during the summer maximum of solar insolation showed that the surface temperature of rocks in the dumps reaches +22.5 °C, while in undisturbed areas it does not exceed +14 °C. At night, the dumps retain temperatures above +12 °C for more than 6 hours, while the background areas cool down to +5...+7 °C. This creates a diurnal asymmetry of heat exchange, contributing to energy accumulation and gradual warming of the underlying soils.

The greatest heat load in the mining areas is recorded in the locations of transformer substations, compressor and pumping stations, where heat generation is 35-40 kW per unit area of 100 m2. It is at these points that local temperature anomalies have been recorded at depths of 1.5–3.0 m. The analysis of temperature curves showed that not only warming is achieved near such objects, but also a long-term cycle of temperature fluctuations with low amplitude and high inertia is formed, which prevents the restoration of permafrost rocks even in winter.

One of the key results of the work was the establishment of a relationship between the structure of the engineering load and the shape of the thermal field. Linearly extended sources (technological roads, drainage channels) create oval-elongated heating zones with directed heat migration along the longitudinal axis. Point sources (fuel depots, energy facilities) form symmetrical fields with a concentrated core. This differentiation makes it possible to model the thermal regime more accurately and predict the maximum risk zones.

In order to reduce the thermal impact, it is recommended to switch to modular technological infrastructure structures with a minimized heat transfer area. For example, using insulated platforms instead of open parking lots can reduce the local heat load to 55-60 W/m2. It is also promising to introduce polymer retroreflective coatings on landfills, which reduce the surface albedo to 0.6 and lower the daytime surface temperature by 4-5 °C compared to dark man-made deposits. It is also possible to use heat recovery heat exchangers in mine ventilation systems, which allows to return up to 35% of thermal energy, reducing the temperature of emissions by 2.3–3.1 ° C. Combined with step-by-step automation of ventilation, which works depending on the thermohydraulic conditions in the exhausted spaces, this can reduce the depth of degradation of permafrost rocks by 12-18% over the next 10 years of operation.

Thus, the analysis confirmed that the thermal impact on permafrost in the conditions of industrial exploitation in the Arctic is complex and multifactorial, and its mitigation requires engineering, climatic and design solutions at the same time. Only a systematic approach combining thermohydrological monitoring, optimization of infrastructure architecture and the introduction of energy-saving technologies can ensure the sustainable development of cryolithozone mining without irreversible destruction of permafrost.

4. Conclusions.

The data obtained in the work, data for the Arctic cryolithozone of the Yunyaginsky coal mine and the Vorkuta mines confirmed that the exploitation of coal deposits is accompanied by the formation of stable man-made thermal fields, leading to a redistribution of temperature in the frozen soil. A significant increase in temperature at depths from 2 to 15 meters near industrial facilities indicates the progressive degradation of permafrost rocks, accompanied by an expansion of the active layer, an increase in humidity, a decrease in soil strength characteristics and the development of sedimentary deformations. The revealed temperature anomalies consistently correlate with the density of landfills, the power of ventilation streams, as well as the intensity of drainage water discharge. It has been established that the depth of degradation of permafrost rocks can reach 9.5 m with an average thermal load of 120-150 W/m2 and an exposure period of more than 15 years. In addition, the contribution of underground heat sources, such as mine ventilation and heat-generating equipment, to the formation of vertical heating of soils has been confirmed.

Numerical models of heat propagation in permafrost conditions have confirmed that the thermodynamic behavior of permafrost soils significantly depends on their lithological composition, the phase state of moisture and the mode of heat input. Special attention is paid to areas with a high content of silty particles and high humidity, where the most pronounced processes of thawing and loss of stability of the substrate are observed. Geodetic monitoring revealed surface subsidence of up to 14.2 cm, which indicates the need to revise design decisions when placing objects on thermoactive sites. It is also proved that the forms of propagation of thermal anomalies vary depending on the configuration of the sources: point sources form concentrated heating cores, and linear sources form elongated zones with directed heat migration. This approach to typologizing thermal effects opens up new possibilities for modeling and zoning risks.

The practical significance of the work lies in the formation of recommendations for optimizing technological solutions in cryolithozone conditions. The effectiveness of the transition to modular structures, the use of retroreflective coatings, insulated drainage channels and passive coolers (thermosiphons) in combination with automated geothermal monitoring is substantiated. The data obtained can serve as a basis for making design decisions in the field of engineering geocryology, sustainable environmental management and risk assessment for infrastructure in the Arctic.