Research on a Geothermal Energy Conversion Subgrade and Field Tests on Its Frost Resistant Effect
Research purposes:In order to resolve the frost-heaving problem of railway subgrade in seasonally frozen soil regions,a novel energy conversion subgrade was proposed in this study.To this end,a special ground source heat pump system was installed to collect the low-grade geothermal energy of stability layer of the foundation near the subgrade,and convert it to a high-grade heat source.Then the generated heat was transferred to the frost-heaving layer of the subgrade to realize active heating and temperature control,thereby eliminating the frost-heaving problem.In order to analyze the performance of the proposed system,a 20 meters long geothermal energy conversion subgrade test section was constructed at a frost-heaving site of the Jungar-Shenchi Railway.The heating temperature of the heat pump,temperature field,freezing depth,and track frost-heaving deformation of energy conversion subgrade and natural subgrade during the winter of 2021～2022 were tested and analyzed.Research conclusions:(1)The maximum heating temperature of the heat pump and its average daily heating temperature during intermittent operation can reach 59.4℃and above 25.2℃,respectively.Accordingly,it is concluded that heat pumps can be effectively used as high-grade heat sources.(2)The freezing period of the natural subgrade lasted for 141 days,and the energy conversion subgrade was reduced by 20 days.Moreover,the maximum freezing depth at the track center,subgrade shoulder,and slope toe were 88 cm,75 cm,and 58 cm,respectively.These depths are within the critical value of harmful freezing depth and are 60 cm,122 cm,and 78 cm less than those of natural subgrade,respectively.(3)The peak frost-heaving deformation of the track under natural conditions reached 9.4 mm,which is beyond the acceptable criteria and may lead to harmful results.The obtained results show that the track deformation in the test section was less than±3 mm,which does not exceed the management value of regular maintenance.(4)The performed analyses demonstrate that the energy conversion subgrade is an effective method to prevent frost-heave of different parts,including embankment,cutting subgrade bed,turnout area,and culvert top.
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