Experimental study on interaction between soil and ground heat exchange pipe at low temperature

In the application of ground source heat pump (GSHP) in cold regions, soil-pipe interaction due to frost heave can lead to many problems influencing the system efficiency. The aim of this experimental study is to investigate the characteristics of soil-pipe interaction and test the feasibility of reducing the pipe deformation by increasing the grain size of soil in backfill. In this study, two types of soils with different grain sizes are used, the movement of freezing front, the pipe deformation and the freezing soil pressure on pipe are analysed. The results indicate that the U-pipe can result in an asymmetrical soil freezing area around it, the pipe's cross-section changes to be more and more elliptical, the soil pressure on pipe increases. An obvious reduction in the pipe deformation and the soil pressure on pipe can be shown in the soil with larger grain size, and the application of suitable large-grain soils in backfill is helpful to reduce the pipe deformation.