Japan has many unexcavated tumuli, most of which were buried along with artifacts of precious cultural heritage. For such a tumulus, it is essential to understand how changes in its exterior environment affect its interior environment, and how those interior changes affect the deterioration of the relics buried in the stone chamber. In this study, an underground space was constructed in the forest of the Katsura Campus of Kyoto University to simulate the environment of an unexcavated tumulus, and long-term monitoring was implemented in the simulated stone chamber, including the temperature, humidity, water potential, wetness, and oxygen and carbon dioxide concentrations, along with metal corrosion tests. This article is focused on environmental monitoring, and the results demonstrate that the simulated tumulus has the general characteristics of the hygrothermal environments of an unexcavated tumulus that has small temperature fluctuation and near-saturation humidity. The ceiling of the simulated chamber condensed significantly from October to April, which is related to the variations of the ceiling and floor temperatures. Also, the wetness of the walls in the simulated chamber was affected by rainfall. The oxygen concentration in the simulated stone chamber varied in the range of 13%–19% in 2015, and the variation of carbon dioxide concentration in the simulated stone chamber was contrary to the oxygen concentration and varied in the range of 3%–9% in 2016. The oxygen concentration in the stone chamber was similar to that in the surrounding soil that decreased at times of rainfall, contrary to the fluctuations in the soil water content.

In this paper, we develop a numerical analysis model to calculate the heat and moister behavior at Motomachi Sekibutsu and clarify the effect of suppressing salt damage by renovation of the shelter. Using this model, we divide the renovation as three component, thermal insulation, airtightness, solar transmission, and verify the effectiveness of them. Our results show that all the renovation contribute to decreasing the evaporation from the statue and suppressing the salt phase change. Thus, we consider that the renovation of the shelter suppresses salt damage

This paper presents environmental measurement and numerically quantifying influences of the heat and moisture behavior in the stone Buddha carved into a cliff in Motomachi, Oita City. The simulation results show as follows. The water content is always high deep inside the Buddha statue but is low at and near the surface, which will result in more salt precipitation and thenardite-mirabilite cycles near the surface than deep inside the stone. The surrounding environmental and geological condition lead to more salt precipitation in autumn to winter and dissolution of thenardite often occurs in winter to spring, particularly at the knee.