Study On Analysis And Evaluation To The Stability Of Slope Embankment In Permafrost Regions Of Qinghai-Tibet Railway In Operating Period

The study relies on the topic of "the evaluation and treatment measures researchon the stability of slope embankment in permafrost regions (2006BAC07B02)" whichis one of sub topic of "the research on engineering measurement and disease treatment in permafrost regions." which is also one of national "Eleventh Five Year" science and technology support projects "Qinghai Tibet railway security operating system research", and emphasis on analyzing the stability of slope embankment structurein the Qinghai Tibet railway in permafrost regions during the operation period morecomprehensively. Through the methods of on site investigation, theoretical analysis,the actual monitoring, physical modeling, numerical simulation etc. to study its deformation and failure mechanism, the stability can be analyzed and evaluated fromboth thermal and mechanical aspects. On this basis, the methods and standards ofanalysis and evaluation the stability of slope embankment in permafrost regions wasproposed, and the strong technical support is provided to give priority to the stabilityof slope embankment and take appropriate measures. The research results can be directly used in the operation and maintenance on Qinghai Tibet railway, and it is important reference value for other construction projects on the stability research in thepermafrost regions. Main research results can be summarized as follows:1. It is explicitly put forward that the range of angle of repose in slope embankment in permafrost regions. When the embankment whose angle of repose is≥1:10,its failure mechanism is different from the situation of the flat slope or a gentle slope(1:10). Under the action of gravity, the part or all of the soil of slope embankment slipforward and down along a certain weakness, which is a principal factor of its stability.And the differential settlement that caused by the heat balance differences of thefreezing and thawing in yin and yang slope is a induce factor of it.2. Through studied methods such as theoretical analysis, physical modeling andfield monitoring etc., the deformation and failure mechanism of slope embankmentcan be illustrated. The main water in the embankment fill is the atmosphere precipita tion, and the location and morphology of artificially table affected the water field distribution in slope embankment. The important impact factors of the stability of slopeembankment are the moisture content conditions, temperature and moisture field distribution. The trouble with the stability of slope embankment appears not in the highembankment, but rather in a low embankment frequently.3. According to the characteristics of the stability of slope embankment in permafrost regions, combined with the current level of theoretical and experimental status, the stability analysis method that from both thermal and mechanical stability ofthe respective of which can be put forwarded. The temperature field analysis methodof two field coupling theory can be used in the thermal analysis by considering themigration and phase change of water. Based on the thermal analysis, the critical slipfield method can be used in mechanical stability analysis to calculate the mechanicsstatus of slope embankment. Based on the relationship between the mechanics statusof soils and temperature field which transformed in time, the whole mechanics stabilities of slope embankment in different time are be calculated, and we can treat theworst case as its stability eventually.4. Because the temperature field of slope embankment is changed with the time,its status of stability is also showed a dynamic characteristic. Through having analyzed the respective stability of two slope embankments sections of K1139+070 andK1152+370 in permafrost regions in different months, from the changes of stability itcan be pointed out that the most adverse status of the stability of slope embankmentappears in warm season in September or October, but not in November which themaximum thawing depth appears at the same time. That is determined by the outsidetemperature change conditions of local area.5. By the theoretical analysis on the monitoring curve of key cross section in sitewhich has the different amount of ice, it is considered that the nether deformationboundary of slope embankment in permafrost regions is the nether temperature limitsof the plastic permafrost. Although its shear strength is greater than which is in thefreezing and thawing interface, as well as more than the full financial soil shear strength, but under the long term loads, the accumulation of creep deformation generated by the plastic permafrost can cause the upper rock and soil in slope embankmentto slide down, and in the stability analyzing it must be taken into account. For example, on site monitoring results show that on the high ice content K1139+070 section,0.3℃isotherms is the nether deformation boundary of the slope embankment. However, as the nether deformation boundary of the slope embankment in permafrostare controlled by many factors, in order to simplify the calculation, it is recommendedthat the artifical table should be treated as the nether deformation boundary in theprocess of actual calculation, while in the eventual analysis and evaluation the calculation results can be reduced according to actual situation of frozen soil composition,moisture content, and ground temperature etc.6. Combined with the actual situation in permafrost regions and existing engineering specifications, the stability evaluation criteria in permafrost regions of theQinghai Tibet railway slope embankment can be proposed. The principle is simpleand clear, it is suitable for the design of on site repair or reinforcement for slope embankment, and it can provide strong technical support to ensure the safety of Qinghai Tibet Railway in operational period.