Characterization of soil thermal, hydrological, and mechanical properties at Musashino fluvial terrace in Fuchu, Japan

The ground source heat pump (GSHP) system, based on heat exchange with the deep subsoil environment, generally operates with higher efficiency than the conventional air-source heat pump system. The GSHP system has received great interest in countries in North America and Western Europe because it can potentially reduce energy consumption and greenhouse gas emission. The GSHP releases heat energy to the subsoil during summer for cooling, while it pumps heat energy from the subsoil during winter for heating. To optimally design and operate GSHP systems, not only heat transport in the subsoil but also the influences of temperature changes on water flow, groundwater quality, and ground deformations need to be accurately simulated. The main objective of this study was to characterize soil thermal, hydrological, and mechanical properties of soils by monitoring subsoil temperature, groundwater level, and ground deformation at one of the potential GSHP installation sites in the Musashino fluvial terrace located in Fuchu-city, Japan. Monitoring instruments including resistance-temperature detectors and displacement transducers were installed inside a 50-m borehole excavated at the study site. Temperature observed at 5 m intervals in the borehole showed (i) that the soil temperature gradually decreased with depth, with the exception of temperature at the 5-m depth, and (ii) average temperatures increased as the average air temperature increased. Readings of the displacement transducers were found to be strongly affected by air temperature changes. Data observed at the borehole will be further evaluated and linked to soil physical properties measured from disturbed and undisturbed soil samples collected at the borehole.