Experimental Study On Optimization Of Subgrade Structure At The Transition Section Between Road And Bridge And Gravel In Permafrost Regions

Differential settlement in the transition section between road and bridge is one of the main diseases of railway construction,especially in permafrost regions,where the problem is more serious and complex.The road-bridge transition section is a key structure that combines the road and the bridge.The settlement difference between the roadbed and abutment seriously affects the safety of railway operations and the comfort of driving.Under the influence of external traffic loads,the differential settlement is more serious and prominent.The simplest and most effective treatment method for settlement diseases is to fill the ballast in the settlement depression behind the abutment and re-level it.However,this method can only solve the disease problem in a short time,and fails to start with the settlement mechanism to fundamentally solve the settlement difference.The long-term accumulation of ballast is not conducive to the stability of the frozen ground and may cause new diseases.Therefore,this article refers to the treatment measures for subgrade settlement in permafrost regions,starting with the "active cooling" foundation of a single particle size gravel material and short pile foundations to improve the overall rigidity of the subgrade,and proposes a new optimization of the road and bridge gravel transition section.Structural scheme.In order to explore the treatment effect of the single-size gravel material and short pile foundation structure in the optimized structure model,this paper sets up three test models:general road and bridge gravel transition section;single-size gravel road bridge transition section;road bridge Optimized structure of gravel transition section.According to the climatic conditions and external loads of the actual engineering section,the model’s temperature field,moisture field,and displacement field are compared and analyzed through indoor tests.The main research contents and conclusions are as follows:(1)In order to more truly reflect the characteristics of frozen soil in permafrost regions,before the cyclic temperature cycle,the active layer of frozen soil was simulated through the high and low temperature environment test box.It was found that the active layer formed well,and the soil of each layer formed a sinusoidal period As the soil deepens,the temperature change range gradually weakens,with a certain hysteresis.(2)Monitoring the temperature field of the three models found that the soil temperature of each layer of the single-size gravel structure is lower than that of the general gravel structure of the same depth,and the temperature fluctuation range at the bottom of the gravel layer is greater,indicating that the single-size gravel structure has a greater range of temperature fluctuations.The particle size gravel material can better realize the convective heat transfer,thereby achieving the purpose of active cooling and protecting the stability of the frozen soil foundation;the short pile foundation has a certain influence on the surrounding soil temperature field,but the influence range is limited,and the overall temperature is as single The structure of the particle size gravel has a small difference.(3)Monitoring the moisture field before and after the loading of the test model found that due to the influence of the temperature field,the moisture content of the foundation of the single-size gravel structure and the optimized structure is lower than that of the general gravel structure,and the impact of the short pile foundation makes the moisture content slightly There is an increase;under the influence of load and freeze-thaw cycles,the moisture content of the foundation changes to different degrees,and the moisture content of the optimized structure changes the least.(4)Before applying external load,a comparative analysis of the frost heave and thaw settlement laws of the roadbed and abutment found that due to the greatly reduced soil thickness,a single particle size gravel material can better protect the stability of the frozen soil foundation,And the short pile foundation has little influence on the temperature field of the foundation,so that the deformation caused by frost heave of the single-size gravel structure and the optimized structure are lower than the general road bridge gravel transition section.(5)After the external load is applied,the settlement law of the model structure is compared and analyzed,and it is found that the settlement difference between the single-size gravel structure and the optimized structure of the road and bridge is smaller than that of the general gravel transition section,and the settlement difference of the optimized structure model is the smallest.It shows that the single-size gravel material and the short pile foundation structure greatly enhance the overall rigidity of the transition section,have a good prevention effect on differential settlement diseases,and the short pile foundation effect is more significant.