A series of numerical analyses has been performed on the characteristics of heat transfer in a closed-loop vertical ground heat exchanger (U-loop). A 2-D finite element analysis was conducted to evaluate the temperature distribution over the cross section of the U-loop system involving high-density polyethylene (HDPE) pipe/grout/soil to compare the sectional efficiency between the conventional U-loop and a new latticed HDPE pipe system, which is equipped with a thermally insulating lattice in order to reduce thermal interference between the inlet and outlet pipes. In addition, a 3-D finite volume analysis (FLUENT) was adopted to simulate the operation of the closed-loop vertical ground heat exchanger with the consideration of the effect of a distance between the inlet and outlet pipes, grout's thermal properties, the effectiveness of the latticed HDPE pipe system, and the rate of circulation pump. It was observed that the thermal interference between the two strands of U-loop is of importance in enhancing efficiency of the ground heat exchanger. Consequently, it is recommended to modify the configuration of the conventional U-loop system by equipping the thermally insulating lattice between the two pipe strands. ground heat exchanger, HDPE pipe, latticed pipe, sectional efficiency Citation: Lee C, Gil H, Choi H, et al. Numerical characterization of heat transfer in closed-loop vertical ground heat exchanger.

This paper introduces the improvement of connection method for segment in tunnel lining system using prestressed steel cable and presents the results of real-scale tests. It conducted a study about the applicability and mechanical behaviour analysis of the new method that connects segment tunnel lining using prestressed steel cable by real-scale test. Through the research, it was found that the new method has stronger connection than conventional assembling methods. Also, the new method can be expected to have integrated behavior and stability increase of shield tunnel lining.It is considered that the new method is much more effective than conventional assembling methods.