| With the construction of transportation infrastructure in our country continues to extend to the midwest area,most railways need to be built on the frozen regions sensitive to temperature.The stability of frozen soil is an important factor affecting the stability of railway subgrade and the safety of train running.Pile-plate structure plays a significant role in solving subgrade settlement and deformation in melting soil area,so it is also applied in frozen soil area,but its frost heave characteristics and engineering applicability in frozen soil area need to be further studied.In this paper,the basic physical parameters of the soil used in the experiment were first tested through geotechnical tests,and then the one-dimensional freezing and freeze-thaw cycle model experiments of pile-plate structure subgrade under the condition of closed system were carried out by using the low-temperature environment model box independently designed by the research team.The temperature and moisture fields inside the pile-plate structure subgrade as well as the displacement changes at different positions of the pile-sheet structure subgrade were studied.Then the hydro-thermal coupling model was established and its reliability was verified.Finally,based on the geological data of Changchun test section of Shenyang-Harbin passenger dedicated line as the background,the predictive analysis of high-speed railway pile-plate structure subgrade was carried out by numerical simulation,and the prevention of frost heave of pile-plate structure subgrade was proposed by laying insulation materials.Through the numerical simulation analysis of pile-plate structure subgrade with insulation board of different thicknesses,the insulation effect and the influence of insulation boards of different thicknesses on the temperature and moisture distribution of pile-plate structure roadbed were explored,and a reasonable and economical laying scheme was given.The main conclusions are as follows:(1)Through the one-dimensional freezing test,it is found that the soil temperature in the subgrade varies greatly with time as the depth increases,and the temperature near the surface drops the fastest,while the soil temperature at the deeper distance from the surface changes more slowly.During the downward movement of the freezing front,the temperature gradient near the surface is the largest,so the temperature at the surface drops rapidly,resulting in drastic changes in water content.(2)With the increase of freezing duration,the displacement deformation at the concrete bearing plate increases at a faster rate with time,then the phenomenon of freezing contraction occurs,then the frost heave deformation increases,and finally tends to be stable.(3)Through the freeze-thaw cycle test,it is found that the temperature of soil at different depths changes periodically with the progress of freeze-thaw cycles.Due to the different degree of influence of cold source on soil mass at different depths,the temperature change of soil at different depths has a certain lag.With the periodic decrease and rise of temperature,the unfrozen water content of shallow soil decreases and increases first.(4)With the increase of the number of freeze-thaw cycles,the maximum freezing depth of soil on the natural surface,under the bearing plate and around the pile all increased,but compared with soil on the natural surface and under the bearing plate center,the maximum freezing depth of soil around the pile continued to increase with a small increase,while the maximum freezing depth of the other two places increased in a stepped shape.(5)With the periodic change of air temperature,the displacement at the joist(D3)and the center of the bearing plate(D4)changes little;the displacement D1 at the natural surface60 cm away from the edge of the bearing plate shows a periodic change,while the displacement at D2 shows a multi-peak form.(6)The reliability of the hydro-thermal coupling model was verified by using the data of one-dimensional freezing test,and the predictive analysis and anti-frost heave measures of the pile-plate subgrade of high-speed railway were carried out.It is found that when the natural surface reaches the maximum freezing depth,the inner side of pile foundation of pile-plate structure subgrade does not frost heave,but the edge of bearing plate is frozen.Laying insulation materials between the bearing plate and the surface can effectively prevent frost heave and ensure the smoothness of the track and the safety of transportation,but it will affect the moisture distribution of the soil under the subgrade. |
