Research On The Effect Of Ventilated Duct On Temperature Distribution And Bearing Capacity Of Tower Foundation Of Transmission Power Line On Plateau Permafrost Region

Due to the global warming and the advancement of infrastructure construction in the plateau permafrost regions,the problem of degradation of frozen soil is serious,which poses a great threat to the stability of the tower foundation of transmission power line.In order to improve the bearing capacity of the tower foundation,it is recommended to replace the silty clay of the tower foundation with the coarse-grained soil which is an insensitive frost-heaving material,and design a tower foundation with ventilation duct which has active cooling measures.In this paper,the combination of test and numerical simulation is used to systematically study the bearing capacity of tower foundation in plateau permafrost regions,in order to provide scientific basis for key technical problems such as design and construction of tower foundation in plateau permafrost regions.The research contents are listed as follow:(1)The mechanical properties of silty clay in the high temperature range(-2 °C～2 °C)were studied.It was found that the mechanical properties of silty clay were seriously degraded in this temperature range.The frost heaving characteristics of coarse-grained soil affected by the compaction energy and fine particle content were studied.The particle grading and compaction conditions which were most insensitive for the frost heave of coarse-grained soil were obtained.Besides,the effect of temperature on the shear properties of coarse-grained soil was also studied.It was found that the shear strength of coarse-grained soil was significantly increased when the temperature under zero,but the regularity is not obvious.(2)The cooling measures of external(internal)ventilation duct were introduced into the treatment technology of tower foundation.Temperature of the tower foundation was simulated and analyzed in different seasons.It found that the ventilation ducts decline the temperature of foundation soil obviously in cold season(Temperature below 0℃),but the warm air run into the foundation soil in warm season.And the influence of factors such as diameter,spacing and buried depth of the ventilation duct on the cooling effect of the soil around the tower foundation was analyzed.The parameter combination which was beneficial to decrease the foundation soil around the tower was obtained.(3)In order to solve the problems of interference of the high temperature on the temperature field of soil around the ventilation duct during warm season(Temperature high 0℃),a comprehensive treatment technology of the tower foundation in the plateau permafrost region was put forward which combined with external ventilation duct and the adjustment switch.The ventilation duct kept open in the cold season and closed in the warm season.It was found that the combined measures can ensure the soil around the foundation in a negative temperature state during the warm season,which contributes to the stability of the tower foundation.(4)Combined with the change of performance parameters of shear strength of silty clay and coarse-grained soil with temperature and the cooling effect of ventilation duct on the soil around the tower foundation,the ultimate bearing capacity of the tower foundation was calculated and simulated.It was found that the silty clay replaced by the coarse-grained soil can significantly improve the ultimate bearing capacity of the tower foundation;the tower foundation of ventilation duct effectively improves the ultimate uplift bearing capacity and ultimate compressive bearing capacity of the tower foundation during the cold season,and so does the combination of the external ventilation duct and the regulating switch when is the warm season.