Model Test Research On The Influence Of Groundwater To The Differential Settlement Of Embankment–bridge Transition Section

Qinghai-Tibet Railway is an existing railway, and along the railway line most of environment is located in permafrost region. So its differential subsidence problem of bridge transitional section is more serious and complex than the general area. After the investigation of some the Qinghai Tibet railway lines, it is known that the differential settlement of the bridge transition section is very common, and it has the characteristics of large settlement. At present, the main method to control that disease is ballast landfill method. Through the late monitoring of bridge transitional section which use this method, it is found that this method is effective for a short period of time, but the railway transition section still have substantial settlement after train run a long time.In addition, with the frozen soil temperature rise, climate environment change and frequent human activities, the original geohydrologic environment of permafrost region gradually changed and the influence of ground water to the differential settlement of bridge transition section is gradually increased. Due to the domestic research on settlement of bridge transition section which in the frozen soil area with ground water are scarce, and the field test is influenced by the geological environment and other factors, led to the current research of bridge transition section is basically based on theoretical analysis and finite element simulation analysis. The existing indoor model tests are carried out under constant low temperature environment, it causes the frozen soil model can't form the active layer, which is not in accordance with the actual conditions. Based on these problems, this paper combined with the characteristics of frozen soil water to carry out the indoor model test. This experiment mainly have two purposes; active layer of frozen soil is formed in alternating temperature environment; The influence of slope water and groundwater on differential subsidence of bridge transition section is observed by burying simulation equipment, this equipment can simulate the ground heat effect and seepage effect of groundwater.(1) In the process of active layer of frozen soil from the initial to basic stability, soil layer is close to the outside atmosphere, the change trend of soil temperature showed a more regular sine wave. With the farther away from external atmosphere, the change of soil temperature will gradually reduce to a constant value.(2) With the gradual increase of the outside temperature, the melting depth of the active layer increased gradually, it reach the maximum value in September and October, and the freezing phenomenon occurred in November. The freezing process of the active layer will appear a bidirectional freezing phenomenon, the active layer is frozen from the surface layer and permafrost table.to Interior. In the freeze-thaw cycles, time of freezing period is less than thawing period.(3) The settlement of transition section under alternate temperature is signifycantly increased than that under constant temperature. In the case of constant low temperature, the settlement of the transition section will only appear a larger settlement. In the case of alternating temperature, the transition period will appear two significant settlement phenomenon.(4) In general, Influence of seepage effect on settlement of transitional section is greater than the Influence of heat effect. In this experiment, the heat effect and seepage effect of the slope water make settlement of the transition section respectively increased 0.8mm and 0.9mm. the heat effect and seepage effect of water below frozen soil stratum make settlement of the transition section respectively increased 0.7mm and 1.2mm.