Research On Artificial Active Heating System And Frost Heave Prevention And Control Effect Of Railway Freeze-Damaged Subgrade

The railway subgrade in seasonal frozen soil area has different degree of freezing damage under the influence of alternating cold and warm environment.In order to control freeze-damage of subgrade,from the perspective of heat transfer,the effective way to control freeze-swelling of subgrade in cold areas is to actively supplement the heat dissipated by soil in freezing period,that is,to increase the heat storage of soil by conveying heat to subgrade,and thus prevent the development of freeze-damage of subgrade.Based on the Xinshuo Railway Science and Technology project of National Energy Group,"Research on Railway Subgrade Freezing Damage Prevention Technology Based on Active Heat Regulation"(SHXS-2020-05),this thesis put forward an active heat regulation technology for subgrade driven by geothermal energy based on the active heat regulation theory of heat budget balance.The heat supply effect is tested in the K44+980 ～ K45+000 test section of Junchi Railway.The main research contents and achievements of this thesis include:(1)By conducting conventional physical property tests and frost heave characteristic tests on field soil samples,the causes of frost damage to the subgrade of Zhunchi Railway are analyzed: the subgrade itself has strong frost heave sensitivity,the cold climate in Youyu County in winter and the groundwater level only 1.3m deep at the site.The development mechanism of freezing damage is as follows: the subgrade filling height is 0.6 m,1.9m away from the groundwater level,and the capillary water rising height is 0.7 m.When the freezing depth reaches 1.2 m,the subgrade development is caused by deep frost heaving caused by groundwater migration and recharge.(2)Based on the historical data of typical climate in the test area,the maximum heat load of the subgrade during the freezing period was calculated and predicted to be765 W/ yanm.The geothermal resources reserves at the subgrade were estimated according to the field survey data,and the feasibility of the active heating device was analyzed.Comsol finite element software was used to simulate the freezing damage control effect of heating subgrade in transverse and longitudinal sections under 45 working conditions,taking the transverse dip Angle of heating pipe(0°～8°)and longitudinal spacing(2.0 m～4.0 m)as control variables.The results showed that the spacing of heat exchange pipe and the planting Angle of heating pipe(4°)were the most reasonable layout scheme.And establish a 20 m long heating test section.(3)Based on the complete test data of a freezing period,the heat transfer effect of the heating device and the anti-frost heave control effect of the roadbed in the heating test section are analyzed.The results show that the heating temperature of the heat pump system can reach more than 50 ℃,the average daily heating temperature can reach 25 ℃,the heating coefficient is above 4.91,the heating grade is high and the heat supply is stable.The maximum freezing depth at the center of track,shoulder and foot of slope in the test section is 88 cm,75 cm and 58 cm,respectively,which is 60 cm,122 cm and 78 cm less than that of natural subgrade,and the freezing depth is controlled within the harmful critical value.The maximum frost heave of the natural track outside the heating test section was more than 9.4mm,while the deformation of the track inside the heating test section was controlled within ± 3mm,which did not exceed the line operation acceptance management value.