Effect Of Frost Heave Deformation Of Bridge Foundation On Running Safety Of High-speed Railway

With the development of high-speed railway network in China,harsh environment is involved,such as the alpine frozen soil area in the northeast,the strong wind area in the northwest,the plateau high earthquake area in the southwest,and the soft soil area in North China.The frost heave deformation of bridge foundation and its influence on the safety of high-speed driving cannot be neglected.Based on the background of the first high-speed railway,Harbin-Dalian high-speed railway,this thesis quantitatively studied the frost heave deformation of soil,the frost heave force of foundation structure,and the development mechanism of frost heave deformation under various freezing conditions,clarified the variation law of dynamic characteristics of vehicles with freezing conditions and different speeds,and put forward the safety threshold of frost heave deformation of bridge foundation.The main contents and conclusions are as follows:(1)Based on the frozen soil parameters,a multi-physics finite element model was established for the frozen soil,and used to study the influence of latent heat on frost heave index and the occurrence,development and evolution of frozen soil during low-temperature freezing.The results show that the latent heat is an important factor in the soil freezing process.The development of soil freezing can be divided into three stages during the freezing period: the stage of rapid temperature drop,the stage of gradual decrease of temperature,and the stage of stabilization.The duration of the first stage increases with the water content.(2)According to the soil type and freezing conditions along the Harbin-Dalian high-speed railway,the frost heave model of bridge foundation was established,considering the existence of unfrozen water in the freezing process.The soil moisture content and freezing temperature were selected as control variables to study the development law of frost heave deformation of soil and bridge foundation structure.Through a parametric study,the influence of water content and freezing temperature on frost heave deformation and frost heave force was clarified.The results show that the frost heave deformation of soil and bridge foundation structure is mainly vertical.The influence of low temperature load on soil is limited.The frost heave deformation occurs in the local area,which is shallow from the surface;the frost heave deformation of the soil near the foundation structure is less than that far from the end of the foundation due to the restriction of the bridge foundation;the temperature of frozen soil varies exponentially with the burial depth;the cap plate has a certain thermal insulation effect on the underlying soil,and the temperature of the underlying soil under the cap at the same depth is smaller than that at the end of the foundation structure.The normal frost heave stress of the base plate of the cap is symmetrical with respect to the midline of the cap,and the stress is W-shaped along the transverse direction of the cap.The normal frost heave stress at the edge of the cap and the hole of the central pile foundation is larger.Temperature and moisture content,as two important factors affecting the frost heave,have obvious effects on the frost heave process of the soil.Frost heave deformation of frozen depth,soil and bridge foundation structure increased with frozen temperature.The frozen depth decreased with water content.As the frozen depth exceeds the depth of the cap bottom,the frost heave deformation of foundation increases with the water content.The frost heave of foundation structure increases sharply when the frozen depth exceeds the depth of the cap bottom.(3)A high-speed train-bridge coupled finite element model was established.The dynamic response of the vehicle passing through the frost-heaving deformation area under different frost-heaving conditions of bridge foundation was analyzed.The variation of the dynamic characteristics of the vehicle with the frozen conditions(freezing temperature and moisture content)and the speed of the vehicle were studied.According to the limit of vehicle dynamic characteristic index(vertical acceleration of vehicle),the frost heaving threshold of bridge foundation structure was proposed.The results show that the vertical acceleration of train body is sensitive to the uplift deformation caused by frost heaving of bridge foundation;the response increases in the frost heaving area of bridge foundation,and the peak value appears in the "bending angle" deformation area of rail surface;the effect of the change of frozen temperature of soil on the vertical acceleration of train body caused by frost heaving of foundation is relatively definite;as the ground freezing temperature decreases,the vertical acceleration of the train body increases when the train passes through the frost heaving deformation area;when the frozen depth does not exceed the buried depth of the foundation,the higher the moisture content,the greater the vertical acceleration of the car body when the train passes through the deformation area,but the acceleration amplitude increases slightly with the moisture content of the frozen soil;when the freezing depth is large enough,the bridge foundation structure will appear large frost heave deformation under the normal frost heave force of the underlying frozen soil,which will cause the vertical acceleration of the vehicle body to increase sharply when passing the bridge;wheel load reduction rate and derailment coefficient are positively correlated with the change of pier uplift and vehicle speed.The lateral horizontal force of wheelset increases with the increase of vehicle speed,but the law of change with pier uplift is not obvious.Based on the limit value of vertical acceleration index of vehicle body,the frost heave deformation threshold of bridge foundation is determined as 14.4 mm.