| With the gradual improvement of the national expressway network,high-grade wide highways are gradually developing in the permafrost regions of the Qinghai-Tibet Plateau.However,under the influence of the heat absorption of asphalt pavement and the global climate rise,the permafrost temperature at the bottom of the subgrade will rise.So,the subgrade will appear a series of diseases such as thermal thaw subsidence,which brings more difficulties to the stability of the broad permafrost embankment.As a kind of active cooling measure,ventilated embankment,widely used in the Qinghai-Tibet Railway,can reduce the permafrost temperature and raise the artificial permafrost table of subgrades.The traditional ventilated embankment is not suitable for the construction of the QinghaiTibet Expressway,which is about five times larger than the railway width and has high heat absorption capacity due to its disadvantages.Given above reasons,a new ventilation device proposed by the research team can get rid of many restrictions of the traditional ventilated embankment and is an active cooling measure to protect the warm permafrost.Based on the geological data of Beiluhe in Qinghai-Tibet Plateau,we established a 3-D model of new ventilated embankment and studied the temperature field variation law of the subgrade during the 30-year service period.It mainly includes the following aspects:(1)Given the shortcomings of the traditional ventilated embankment,a new active ventilation device is proposed to solve the problems of the traditional ventilated embankment easy to be blocked and low cooling efficiency.Meanwhile,we verified the feasibility of the device through indoor air extraction tests and studied how the new active ventilation device can be applied to the engineering technology of the Qinghai-Tibet Expressway.Finally,we compiled the design parameters and the assembly construction instructions of the new ventilated embankment.(2)Based on the results of numerical calculations,by comparing the ground temperature,the permafrost table,the working state of ventilation pipes,and the change law of subgrade settlement.The result proves that the ventilation modes of the existing ventilated embankment are insufficient and do not make full use of wind energy.The cold season ventilated embankment avoids the warm airflow entering the ventilation pipe,but the high negative temperature airflow entering the ventilation pipe at the end of the cold season will heat the soil.However,when the new ventilated embankment is in intelligent temperature control mode.The airflow temperature in the pipe is always lower than the subgrade soil temperature,which can extend the freezing time of the subgrade and reduce the settlement deformation of the subgrade.(3)The pipe design parameters of the new ventilated embankment were further optimized.We found that the pipe diameter is 0.4m,the pipe spacing is 2.4m,and the pipe is buried in the natural ground 0.0m in the subgrade with a better cooling effect and is convenient for construction.Meanwhile,due to the significant heat absorption of the subgrade slope,insulation boards should be laid on the embankment slope to reduce the thaw depth of slopes and the sunny-shade slope effect.(4)We established the functional relationship between the longest use distance of the new ventilated embankment and the subgrade site factors.We studied the temperature and settlement changes of the subgrade under the longest use distance,which can provide a theoretical basis for applying new ventilation devices in the Qinghai-Tibet Expressway. |
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