Distribution Regularity And Disposal Measures Of Seasonal Frozen Soil Of Sichuan-Tibet Transportation Corridor In West Sichuan Plateau

This paper initially describe the distribution regularity and disposal measures of seasonal frozen soil of SiChuan-Tibet transportation corridor in the West Sichuan Plateau by the methods of field survey and consulting relevant documents.The finite element software ABAQUS is used to build respectively the embankment temperature field finite element model taking into account local climate conditions and three-dimensional semi-filling and semi-excavating subgrade model which geocells are applicated.By analyzing the results of numerical simulations to make some suggestions for future engineering constructions.In this paper, main conclusions are as follows:(1) Permafrost,seasonal frozen soil and temporay freezing soil are founded at the transporation corridor of Sichuan to Tibet in West Sichuan Plateau.Only near the snowline on mountains can develop mountainous permafrost, and the majority of area is stable seasonally frozen soil. The lower limit of seasonal frozen soil is approximately from3000m to3300m. The time of freezing is roughly from mid-November to mid-December.The maximum frozen depth arrival time is around mid-January, and at the end of February seasonal freezing layer disappears.As altitude increases, the ground freezing time in advance, the saving time of frozen layer would be extended.Most areas are developed both media-shallow seasonal frozen soil and seasonally frozen, and it distributes shallow seasonal frozen soil and petempory freezing soil in southern. In the past years maximum frozen depth is around in the north of32°north latitude, and it can reach1.0～2.5m, belonging to media-shallow seasonal frozen soil.And then in places farther southward,the frozen death would less than1.0m. The freezing depth of about0.4m～0.8m, to an altitude of3500～4100m deep freeze when the season increased to0.8～1.6m。 When at an altitude of3000m～3000m, the freezing depth is about0.4m to0.8m,and at the altitude3500～4100m the frozen depth increases to0.8～1.6m.But since snow cover, precipitation,soil and direction slope are different, the seasonal frozen depth would change a lot.(2) Through the analysis of the temperature field numerical simulation,it’s known that E-W direction subgrades are more easily affected by the problem of shady slope and sunny slope than the S-N direction one’s. And on the contrary the melting time of sunny slope is earlier than shady slope’s. Freezing and thawing in time differences may lead to uneven settlement of subgrade.The maximum freezing depth of sunny slope is less than shady slope’s, so in practical engineering design should take shady slope as contral point.(3) From the perspective of the numerical simulation of semi filling and semi diggingembankment,the application of geocell layer can acquire a good effect of engineering control by improving the bearing capacity of subgrade, effectively reducing the roadbed settlement, uneven settlement, lateral displacement of embankment slope and stress of the basement, enhancing the subgrade and the stability of slope.By simulating different locations and modulus of geocell layer in the subgrade, it can be concluded that the effect of reinforcement of geocell layer is not obvious for high strength soil, but for low strength soil,it has a good engineering economy. Thegreater the modulus,the better effect of engineering it is.However,is not proportional,for example, with the increase of geocell elastic modulus, the subgrade settlement decreased continuously, but the magnitude of reducing is becoming smaller and smaller.(4) In seasonal frozen regions, it is necessary to increase the shear resistance and friction of foundation material in order to improve the bearing capacity of foundation. If this material can’t be obtained, or transportation nearby is not convenient, the cost of purchased materials would be accounted for a significant proportion of the total cost of the whole project. So the using of geocell can utilize the general soil nearby, thus it will greatly reduce the engineering cost.