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The foundation of constructions built in the permafrost areas undergo considerable creeping or thawing deformation because of the underlying ice-rich permafrost. Soil improvement may be of advantage in treating ice-rich permafrost at shallow depth. Sulphoaluminate cement was a potential material to improve frozen soil. Simultaneously, two other cements, ordinary Portland cement and Magnesium phosphate cement were selected as the comparison. The mechanical behavior of modified frozen soil was studied with thaw compression tests and unconfined compression strength tests. Meanwhile, the microscopic mechanism was explored by field emission scanning electron microscopy, particle size analysis and X-ray diffractometry. The results showed Sulphoaluminate cement was useful in reducing the thaw compression deformation and in enhancing the strength of the frozen soil. The improvement of the mechanical behavior depended mainly on two aspects: the formation of structural mineral crystals and the agglomeration of soil particles. The two main factors contributed to the improvement of mechanical properties simultaneously. The thicker AFt crystals result in a higher strength and AFt plays an important role in improving the mechanical properties of frozen soils.The study verified that Sulphoaluminate cement was an excellent stabilizer to improve ice-rich frozen soils.

Warm frozen soil has characteristics such as low shear strength and high compressibility. To improve its mechanical strength, the ionic polymer soil stabilizers (IPSS): named XRH stabilizer and acid cation exchange resin (CER) were adopted for reinforcing the warm frozen soil from the Beiluhe region of the Qinghai-Tibetan Plateau. To evaluate the effects of IPSS on warm frozen soil and analyze the mechanisms responsible, measurements were made of the physical, chemical and mechanical properties of warm frozen soil, both untreated and following treatment with IPSS. The addition of IPSS to the soil resulted in a significant decrease in the plasticity index, freezing temperature, and cation-exchange capacity of soil. The warm frozen soil were reinforced with XRH and CER, the cohesion increased by 87.9% and 43.1%, respectively, and the compressibility decreased by 44.5% and 41.1%, respectively. The trends of mechanical strength and unfrozen water content of reinforced warm frozen soil were the same, with extreme values being observed in response to treatment with an IPSS content of about 1% (optimal proportion). In addition, the curing mechanism of IPSS on warm frozen soil was analyzed. Overall, applying IPSS to the soil was an effective and feasible measure for reinforcing a warm frozen soil foundation.

In this paper, the dry cement was mixed with warm and ice-rich permafrost to improve its mechanical and physical properties. The changes of temperature of improved soil with different cement dosage were measured by in-situ test. Then, the temperature field of the improved soil in-situ test was calculated by mathematical model of heat conduction and hydration equation with consideration of temperature effect. Based on the built calculation model, we have simulated the radius of thermal disturbance and refreezing time in the process of improvement on warm and ice-rich permafrost with deep mixing method. It can be concluded from the results that, (1) heat transfer model with temperature effect can precisely calculate the changes of temperature field during the curing of cemented frozen soil; (2) in the field test, when the cement dosage is less than 15% by weight of frozen soil, the increase of temperature in cemented soil is not obvious, the peak of temperature increase appears only when the dosage is more than 20%; (3) when the dry deep mixing method with is adopted to improve the warm and ice-rich permafrost, the maximum radius of thermal disturbance increases exponentially with the decrease of mean annual ground temperature, the refreezing time decreases hyperbolically with the decrease of mean annual ground temperature.

The fragile habitat of alpine mining areas can be greatly affected by surface disturbances caused by mining activities, particularly open-pit mining activities, which greatly affect the periglacial environment. SBAS-InSAR technology enables the processing of SAR images to obtain highly accurate surface deformation information. This paper applied SBAS-InSAR technology to obtain three years of surface subsidence information based on the 89-scene Sentinel-1A SLC products, covering a mining area (tailings and active areas) in the Tianshan Mountains and its surroundings from 25th December 2017 to 2nd January 2021. The data were adopted to analyze the characteristics of deformation in the study region and the mining areas, and the subsidence accumulation was compared with field GNSS observation results to verify its accuracy. The results showed that the study area settled significantly, with a maximum settlement rate of −44.80 mm/a and a maximum uplift rate of 28.04 mm/a. The maximum settlement and accumulation of the whole study area over the three-year period were −129.39 mm and 60.49 mm, respectively. The mining area had a settlement value of over 80 mm over the three years. Significantly, the settlement rates of the tailings and active areas were −35 mm/a and −40 mm/a, respectively. Debris accumulation in the eastern portion of the tailings and active areas near the mountain was serious, with accumulation rates of 25 mm/a and 20 mm/a, respectively, and both had accumulation amounts of around 70 mm. For mine tailing pile areas with river flows, the pile locations and environmental restoration should be appropriately adjusted at a later stage. For gravel pile areas, regular cleaning should be carried out, especially around the mining site and at the tunnel entrances and exits, and long-term deformation monitoring of these areas should be carried out to ensure safe operation of the mining site. The SBAS-InSAR measurements were able to yield deformations with high accuracies over a wide area and cost less human and financial resources than the GNSS measurement method. Furthermore, the measurement results were more macroscopic, with great application value for surface subsidence monitoring in alpine areas.

The China–Russia crude oil pipeline (CRCOP) traverses rivers, forests, and mountains over permafrost regions in northeastern China. Water accumulates beside the pipe embankment, which disturbs the hydrothermal balance of permafrost underlying the pipeline. Ground surface flows along the pipeline erode the pipe embankment, which threatens the CRCOP’s operational safety. Additionally, frost heave and thaw settlement can induce differential deformation of the pipes. Therefore, it is necessary to acquire the spatial distribution of water features along the CRCOP, and analyze the various hazard probabilities and their controlling factors. In this paper, information regarding the permafrost type, buried depth of the pipe, soil type, landforms, and vegetation were collected along the CRCOP every 2 km. Ponding and erosive damage caused by surface flows were measured via field investigations and remote sensing images. Two hundred and sixty-four pond sites were extracted from Landsat 8 images, in which the areas of 46.8% of the ponds were larger than 500 m2. Several influential factors related to freeze–thaw hazards and erosive damage were selected and put into a logistic regression model to determine their corresponding risk probabilities. The results reflected the distributions, and forecasted the occurrences, of freeze–thaw hazards and erosive damage. The sections of pipe with the highest risks of freeze–thaw and erosive damage accounted for 2.4% and 6.7%, respectively, of the pipeline. Permafrost type and the position where runoff encounters the pipeline were the dominant influences on the freeze–thaw hazards, while the runoff–pipe position, buried depth of the pipe, and landform types played a dominant role in erosive damage along the CRCOP. Combined with the geographic information system (GIS), field surveys, image interpretation and model calculations are effective methods for assessing the various hazards along the CRCOP in permafrost regions.

A physical calculation model for the content of unfrozen water of silty clay was proposed with a consideration of freezing point. The freezing point of bulk water, capillary water and bound water was calculated. The freezing point of bulk water was assumed to be constant in the calculation. The Kelvin equation and the theory of water activity were used to calculate the freezing-point changes of the capillary and bound water during the volume decrease, respectively. The influence of soil-particle size on the freezing point was taken into account in the model. In the calculation, the unfrozen water content at a negative temperature was defined as the sum of the volume of capillary and bound water whose freezing point was lower than the given temperature. By using silty clay from the Qinghai-Tibet Plateau as an example, the results of the model calculations were validated by using the measured data from time-domain reflection and nuclear magnetic resonance. The calculations for four existing models as proposed by other scholars were listed for comparison with our model. The results show that the calculated results of our model are precise and reflect the hysteresis effect of the unfrozen water content during freezing and thawing. The model validated an order of freezing in soil: bulk water froze first, most capillary water froze next, and most bound water froze last. This paper explains the existence of unfrozen water from the perspective of freezing-point change and provides a theoretical basis for the calculation.

The effect of nine cement additives on the unconfined compressive strength (UCS) of warm and ice-rich frozen soils was analyzed. After 7 days of curing at −1 °C, the UCS at −1 °C, the freezing-point depression and changes in the water content of soil samples were measured to explore the additive effect and mechanism. The optimum additive dosage was determined to improve engineering applications. The conclusions were: (1) attapulgite, metakaolin, nano-silicon dioxide (SiO2), silica fume and hardener accelerator increased the UCS by reducing the water content of frozen soils; (2) sodium hydroxide (NaOH), sodium silicate (Na2SiO3) and sodium lignosulfonate thawed the ice and reduced the UCS of frozen soil samples; (3) when frozen soil with a water content of 30% and 90% was mixed with 15% cement, the optimum dosages were 2% and 8% metakaolin and 0.49% and 0.62% hardening accelerator, respectively.

A riverbank was constructed on ice-rich permafrost in the far north of China in 2015, and its performance is closely related to the thermal stability of the permafrost foundation. To investigate the thermal regime evolution of the foundation, a numerical simulation using a coupled hydro-thermal model that involves concrete hydration, heat transfer by conduction and convection is performed over 20 years in this paper. The monitored ground temperatures help confirm the accuracy of the simulation. A dramatic thaw penetration in the permafrost foundation is anticipated in the future under current geological and structural conditions. Moreover, this paper highlights the importance of concrete hydration, backfilled soil temperature, seepage and the mean annual ground temperature in effecting the geothermal evolution. These discussions suggest a requirement for some measures in construction and maintenance of hydraulic structures over permafrost.

In order to determine the long-term deformation behavior of in-situ ice-rich permafrost under natural conditions, three deformation setups utilizing a plate loading method were built in a permafrost region on the Qinghai–Tibetan Plateau. The loading plates were installed just below the permafrost table, and loads were applied via platforms that were held constant throughout. Variations in permafrost deformation and ground temperatures were recorded over a period of five years. Test results show that ground temperature at the loading plate depth fluctuated seasonally within a warm range between −3.0 °C and −0.2 °C, while the frozen ground settled over a considerable range, between 60 mm and 230 mm. Deformation was observed to be step-like in behavior, given an external load of 0.25 MPa. The amount of settlement observed during deformation was significantly influenced by ground temperature and ice content.

In the context of climate warming, damage to road pavements and embankments in permafrost regions caused by thawing of underlying permafrost severely reduces the serviceability of roads. In...

The warm and ice-rich frozen soil (WIRFS) that underlies roadway embankments in permafrost regions exhibit large compression and thaw deformation, which can trigger a series of distresses. Cement and additives were used in this study to improve the compressibility and thaw-settlement properties of WIRFS. We, therefore, selected optimum additives and studied the improvement effect on the frozen soil with 30% water content based on our previous research. Given constant load and variable temperatures, compression coefficients, thaw strains, and water content changes were obtained at temperatures of &minus, 1.0 &deg, C, &minus, 0.5 &deg, C, and 2.0 &deg, C to evaluate the effect of improvements. A scanning electron microscope (SEM) was then used to observe the microstructure of improved soils and analyze causal mechanisms. Data show that hydration reactions, physical absorptions, cement, and additives formed new structures and changed the phase of water in frozen soil after curing at &minus, C for 28 days. This new structure, cemented with soil particles, unfrozen water, and ice, filled in the voids of frozen soil and effectively decreased the WIRFS compression coefficient and thaw strain.

A series of compression experiments was conducted to observe the pore-water pressure variations of saturated warm frozen soils over time. The results indicate that saturated warm frozen soils can exhibit excess pore-water pressure when subjected to external loads. The pore-water pressure fluctuates rather than varying monotonically, and it gradually increases with increasing compressive deformation as the pores are compressed. Furthermore, the permeability of the soil allows pressure dissipation. Thus, the pore-water pressure is continuously changing because of the interactions between these two opposing processes. The peak pore-water pressure follows an exponential relationship with the soil temperature and decreases to a steady value as the temperature decreases. A dissipation trend is observed after the peak pressure is reached. This trend reflects the influence of consolidation in the deformation of warm frozen soils. As the temperature increases, the role of the consolidation becomes more significant.