Siberia and the Russian Far East contain about 75% of the country's hydrocarbon and mineral resources. These regions pose many engineering and environmental problems for economic development due to the cold climate and difficult geologic conditions, including the occurrence of permafrost. One of the major challenges in permafrost areas is to maintain the stability of both individual structures and large-scale engineering projects. The use of natural cryogenic resources of the Earth is proposed here as one possible solution.
Thawed permafrost could cause a serious stability problem for foundations and oil-wells in cold regions. A non-damage testing procedure, employing the Bender Element Method, was used for permafrost samples collected from a continuous frozen core obtained from the North Slope of Alaska, USA. The wave velocity and modulus of thawed permafrost were investigated on various isotropic confining pressure from 0 kPa to 400 kPa per 100 kPa. The received shear wave propagation was recorded, and the elastic wave theory was used to calculate shear modulus. Finally, the shear modulus affected by confining pressure, water content and dry density were analyzed and discussed, and a regression formulation of shear modulus based on the Janbu Model for thawed silty and sandy permafrost were proposed and validation.
High seismic activity, difficult permafrost and hydrogeological conditions of South Yakutia (Russia) complicate building and exploitation of engineering construction and require additional detailed and complex research. These conditions are evident within two sites. The first site is located in the middle reach of the Duray River, where it is crossed by the highway Lena. The second site is located on the right side of the Chulmakan River Valley, 400 meters to the east of the ESPO oil pipeline route. Seismic events, occurring four years ago, led to landslides in the mentioned sites. Formation of joint fissures on slopes assisted drainage of aquifers of free water exchange zone. It is worth noting that at the Duray River site, 59 cm of active soil slumping movement towards the roadbed has occurred within two summer months. Such a process is complicated by cryogenic disintegration of rocks in the base of the landslide body due to groundwater discharge and icing formation in winter.
This study is devoted to the numerical simulation of the artificial ground freezing process in a fluid-saturated rock mass of the potassium salt deposit. A coupled model of nonstationary thermal conductivity, filtration and thermo-poroelasticity, which takes into account dependence of the physical properties on temperature and pressure, is proposed on the basis of the accepted hypotheses. The considered area is a cylinder with a depth of 256 meters and diameter of 26.5 meters and includes 13 layers with different thermophysical and filtration properties. Numerical simulation was carried out by the finite-element method. It has been shown that substantial ice wall formation occurs non-uniformly along the layers. This can be connected with geometry of the freezing wells and with difference in physical properties. The average width of the ice wall in each layer was calculated. It was demonstrated that two toroidal convective cells induced by thermogravitational convection were created from the very beginning of the freezing process. The effect of the constant seepage flow on the ice wall formation was investigated. It was shown that the presence of the slow flow lead to the delay in ice wall closure. In case of the flow with a velocity of more than 30 mm per day, closure of the ice wall was not observed at all in the foreseeable time.
This paper presents various deformation-monitoring technologies employed to monitor the frost heave and thaw settlement of two mounds along the Qinghai–Tibet Engineering Corridor (QTEC), China. The QTEC is known as a critical infrastructure and passage connecting inland China and the Qinghai–Tibet Plateau (QTP). Three technologies—global navigation satellite system (GNSS), terrestrial laser scanning (TLS), and unmanned aerial vehicle (UAV)—were used to estimate the freeze/thaw–induced 3D surface deformation of two frost mounds. Our results showed that (1) the two frost mounds exhibited mainly thaw settlement in thawing periods and frost heave in the freezing period, but frost heave dominated after repeated freeze–thaw cycles; (2) different zones of the mounds showed different deformation characteristics; (3) active-layer thickness (ALT) and elevation changes were highly correlated during thaw periods; (4) integrated 3D-measurement technologies can achieve a better understanding and assessment of hazards in the permafrost area.
Concrete durability has become a hot research field in civil engineering. Concrete structures suffer salt-erosion damage to different degrees in the semi-arid region of North China. The environmental condition is one of the important factors affecting the durability of concrete constructions. To realize fully the interaction between various environmental factors, this paper researched concrete durability in the salt environment under combined actions (immersing, freeze–thaw cycles, and wet–dry cycles). According to the laboratory test data, the concrete-durability degradation law under coupling-effect factors was investigated. The results show that concrete's compressive strength decreases with the increase of salt concentration and immersion time. No matter what the environmental conditions were, the compressive strength-loss ratio increased with the test time. The compressive strength-test results indicate that sodium sulfate has the strongest corrosive effect on concrete durability, followed by calcium chloride, with sodium chloride having the weakest corrosion. Compared with the other two environmental factors, the wet–dry cycle is the key factor affecting concrete durability. Therefore, in engineering practice, the influence of environment conditions on the strength and durability of concrete should be taken into full consideration, especially in the wet–dry environment with salt conditions.
Expansive soils located in cold regions can easily endure the action of frost heaving and cyclic freezing–thawing. Cracking can also occur in expansive clayey soils under freeze–thaw cycles, of which little attention has been paid on this issue. In this study, laboratory experiment and cracking analysis were performed on an expansive soil. Crack patterns were quantitatively analyzed using the fractal concept. The relationships among crack pattern, water loss, number of freeze–thaw cycles, and fractal dimension were discussed. It was found that crack patterns on the surface exhibit a hierarchical network structure that is fractal at a statistical level. Cracks induced by freeze–thaw cycles are shorter, more irregularly oriented, and slowly evolves from an irregularly rectilinear pattern towards a polygonal or quasi–hexagonal one; water loss, closely related to specimen thickness, plays a significant role in the process of soil cracking; crack development under freeze-thaw cycles are not only attributed to capillary effect, but also to expansion and absorption effects.
This paper presents the results of long-term studies on the response of mountain permafrost in the Northern Tien Shan to changes in climate. Significant warming has been observed in the region over the past 70 years. Records from the high-elevation weather stations Tuyuksu-1 (3,450 m a.s.l.) and Mynzhylki (3,017 m a.s.l.) indicate a warming trend of 0.02 ℃/a in the mean annual air temperature during this period. Permafrost temperatures have increased at a rate of about 0.01 ℃/a over the 40-year observation period. The effects of local factors, including slope aspect, tectonic faulting, snow cover, and human activities, on the distribution of temperature and thickness of permafrost are discussed in the paper.
The strength of warm frozen soils in permafrost is fundamentally significant to estimate and predict the ground settlements from construction activities. A study was therefore initiated to assess the strength and its behaviors of undisturbed and reconstituted frozen soils at temperatures close to 0 ℃. A series of triaxial compression tests (TCT) were performed by using a developed testing apparatus and a matching specimen-preparation method. The confinement was applied from air pressure, the temperature in the specimen was maintained using two-end refrigeration, and multi-stage loading on a single specimen was adopted to determine the strength. The test results showed that the strength, both for the undisturbed and reconstituted frozen-soil specimens, was significantly dependent on the temperatures and independent of the applied confining pressures. Additionally, the strength of undisturbed frozen soils was about 1.6 times more than that for reconstituted frozen soils. These observations were closely associated with the structures existing between pore-ice and gravels with large diameters.
As an effective solution for protecting the underlying permafrost and preventing roadway damages, the block-rock embankment (BRE) has been widely used on the Qinghai–Tibet Railway, Qinghai–Tibet Highway, and Ching–Hong Road; and it will be promoted for other roadways in the future. To evaluate the adaptability of BRE, the catastrophe-progression method was adopted for the evaluation. By analyzing the factors affecting the stability of BRE and utilizing engineering experience, we were able to establish the mathematical model and divide the adaptability of BRE into five grades. After the verifying analysis of 28 practical engineering examples, the evaluation results are broadly in line with practical application effects. Therefore, the adaptability of BRE can be evaluated and predicted more accurately with this evaluation model.
Piles are the main building foundation in permafrost regions. Thawing the permafrost foundation would have a negative effect on a pile, and may cause damage to the building. This paper focuses on the effects of negative friction force due to the melt of permafrost, and presents four calculated methods for bearing capacity of a pile. An engineering station was taken as an example, where the lengths of a pile were compared based on four methods. Finally, quick field load tests were carried out, and some meaningful conclusions are presented. Thus, these analytical results can be used to design a pile for permafrost regions.
