Papers by Keyword: Permafrost

Abstract: Results of pilot studies executed when strengthening foundation and tape bases of architecture monument – the building of National library of the Republic of Sakha (Yakutia) in Yakutsk are given. The article presents data on the kinetics of hardening of cement mortar with a complex additive NN+S-3 at low temperatures of permafrost soils. It is shown that the rate of hardening and strength of the solution greatly depend on the dosage of antifreeze component. A feature of the technology was also to determine the strength of cement mortar, with which possible pressure testing of the well. The strength of the mortar for re-injection should be not less than 10 MPa and not more than 20 MPa. The device technology of bored micropiles in permafrost soil is approved by the contractor – the Yakut branch “Svratka”, Czech Republic. The received results indicate an opportunity and efficiency of micropiles application in conditions of permafrost soil.

Abstract: Gas hydrate samples were collected in Muli area (Qinghai Province, China) of Tibetan Plateau permafrost, which is the first discovery of gas hydrate in Chinese permafrost and in the low to middle latitude permafrost of the world. Although the exploitation of gas hydrate in Tibetan Plateau permafrost has lots of important significance, environmental risks including permafrost and alpine meadow ecosystem degeneration, global climate influence, and environmental pollution would take place in the exploitation process. In order to avoid or decrease the risk, safe and dependable exploitation technique, carbon capture and storage technology, engineering process control, legislation and emergency preparatory scheme should be put into practice.

Abstract: The Qinghai-Tibet highway subgrade inhomogeneous deformation is very serious because of the bad climate environment and the special engineering condition of permafrost. To reveal the mechanism of subgrade diseases, based on the theory of elastic-plastic deformation, the control equation of the stress and deformation field of the subgrade is established. We analyze subgrade stress and deformation field by finite element software. Considering effect of the southern and northern slopes, the model of the inhomogeneous deformation of the subgrade was established. Then we calculated the variation characteristic of the lateral inhomogeneous deformation under different melting depth. The results showed that the melting interlayer, melting depth and the effect of southern and northern slopes were the key factors influencing the permafrost subgrade lateral inhomogeneous deformation.

Abstract: The dynamic parameters of the permafrost are very important for engineering design, also using in the numerical calculation. The dynamic parameters directly affect the correctness of engineering design and numerical simulation. Beijing Jiaotong University developed a novel dynamic load direct shear apparatus to measure these parameters. In the paper, it is analyzed Power systems, measurement and control systems of the dynamic load direct shear apparatus, and gave a verification experiment, the results show that dynamic load direct shear apparatus can complete its purpose.

Abstract: The thawing settlement related problems in 109^th national highway in Qinghai province were analyzed in this paper, experiment tests were conducted to investigate the behavior of subgrade under dynamic loading during thawing, a numerical simulation for the tests were also conducted. Both the tested and simulated results were analyzed and summarized.

Abstract: In order to study the features of permafrost in Daxinganling, based on t he methods of field investigation and borehole drilling, as w ell as theoretic analysis and the effects of frozen soil geological conditions, topography features, frozen soil type and permafrost classification the freeze-thaw depth(m),main physical indicators of the Frost soil, natural water content, plastic limit Liquid limit index were analysis .the thaw settlement and frost heave were studied in this paper.

Abstract: To investigate the effect of foundation slope on stability of embankment upon the slope in permafrost area, 3 groups of model tests with different foundation slope are designed using the mechanical similarity based on geotechnical centrifuge modeling, when the freezing-thawing depth of the embankment reaches the greatest. The results show that: (1) The foundation slope has effect on the stability of the embankment. The deformation mainly concentrates on the soil layers above the freezing-thawing interface, and the deformation mutation point takes place at the freezing-thawing interface. (2) According to fracture characteristics and failure severity of the embankment, failure modes can be divided into the cracking failure in shallow layer and in deep layer. (3) The cause of unstable failure is the deficiency of shear resistance strength of the weak belt, the soil layers above the freezing-thawing interface slips along the freezing-thawing interface under gravity load. (4) Under the experimental conditions, the critical value of the foundation slope influencing on the stability of the embankment is about 1:6 when the height of the slope embankment is 5.0 m.

Abstract: The Qinghai-Tibet direct-current transmission project crosses the high-altitude permafrost region of the Qinghai-Tibet plateau. The permafrost foundation is characterized by being poor in thermal stability, rich in underground ice, very sensitive to climate warming, and strong in water-thermal activity. The foundation of the transmit electricity engineering therefore faces great challenges including tower foundation type selection and design, permafrost protection in the process of foundation construction and long-term stability. Based on an analysis of the geological engineering conditions and principal geological engineering problems of the project, a study is carried out on the design and construction problems of the transmission tower foundations in the permafrost region, the systematic analysis is also made regarding the main solutions to these problems with consideration of tower foundations long-term stability. This study will provide a theoretical basis and technical guide for design and construction of transmission lines in the permafrost region, and a reference for construction of transmission line projects in similar regions in China or even in the world.

Abstract: For the construction of the proposed Qinghai-Tibet Express Highway in permafrost regions, it will be necessary to use the new technique of cooling the ground temperature by the coarsely crushed rock layer with a low fines content. The heat convection governing equations based on airflow function in variable permeability porous crushed rock layer are derived. Comparison of the cooling capability of winter-time natural convection in the crushed rock highway embankments with various widths of crushed rock layer and an air-permeable side slope surface were studied using a finite element method. The result indicates that the cooling capability of natural convection within the crushed rock highway embankment with a crushed rock layer width of 12 m is stronger than that with a crushed rock layer width of 10 m. Under the same temperature and pressure boundaries, the storage of cold energy in the foundation soils below the wider crushed rock highway embankment due to natural convective heat transfer is larger than that below the narrower one.

Abstract: The Qinghai-Tibet Railway(QTR) is the highest and longest plateau railway in permafrost region in the world. The Qinghai-Tibet Railway in permafrost area locates in the hinterland of Qinghai-Tibet Plateau, which belongs to a low latitude, high altitude permafrost area. In this area, that the poor thermal stability, high ice content, and many other complex factors seriously impacts survey and design of The Qinghai-Tibet Railway. Permafrost is a special soil, it has many features different from the ordinary soil. And permafrost thawing layer has seasonal freezing-thawing process every year, along with a few of adverse geological phenomenon, which results in a series of engineering problems. This paper introduces the basic characteristics of permafrost along Qinghai-Tibet Railway, expounds the permafrost hazards of railway engineering, such as frost heaving, freeze thawing, frost boiling of roadbed, thaw collapse and mud flow, bridge foundation frost heaving and thaw settlement, deformation and cracking, culvert foundation freeze-thaw deformation, tunnel lining frost heaving and so on. Briefly analyzes the influence mechanism of permafrost to railway engineering. And then, proposes a temporary prescript for the railway engineering in different type of permafrost area. It is that each engineering in different area has to adopt different design concept and different prevention measures. At last, proposes the prevention measures and suggestions for the railway engineering in the permafrost region, such as reasonable control of embankment height, rubble air-cooled embankment, crushed stone slope protection with thermal insulation subgrade, heat pipe subgrade, ventilating pipe subgrade and so on.