The Kamao tumulus in Kumamoto city, Japan is a national historic site and is generally not open to the public because of potential deterioration of its decorated chamber walls. The deterioration is attributed to the flow of water on to the decorated walls owing to dew condensation and rainwater infiltration; however, the wetting mechanism of the walls has not been sufficiently examined. Therefore, the purpose of this study is to investigate this mechanism and to propose the most effective preservation method. The following examinations were done to achieve the same.
1. We analysed the temperature, humidity and wetting in the stone chamber using field surveys.
2. We developed a three-dimensional heat and moisture transfer model for the mound and surrounding ground. We then validated the model and examined the cause of wetting by comparing the results of the model to the measurements of the hydrothermal environment and wetting behaviour in the stone chamber.
3. We proposed an effective method for preventing dew condensation using a two-dimensional model that produces results similar to those of the three-dimensional model.
The main results of the field survey are as follows:
1. The decorated northern walls in the lower part in the burial chamber are dry in winter, whereas the entire surface is wet during summer.
2. There is moisture on the ceiling and upper part of the northern wall in the burial chamber throughout the year.
The main results of the case studies using numerical analysis model which was validated are as follows:
1. Wetting of the walls in summer is attributed to evaporation on the ceiling because of the high temperature and dew condensation on the lower cooler part of the northern wall; however the location of these effects is opposite in winter. Rainwater infiltration is another factor that occurs throughout the year, causing the wetting of the walls.
2. The main source of moisture responsible for the dew condensation in summer is the ventilation between the burial chamber and the entrance because of high absolute humidity and evaporation owing to the high outdoor temperature and solar radiation incident on the iron door.
3. The most effective methods for preventing condensation in the burial chamber are to improve the ventilation during the dry seasons of autumn and winter, protect the iron door from the sun and insulate the mound in addition to waterproofing the ceiling in the burial chamber.
4. The most effective methods other than improving the ventilation are shading the door and insulating the mound, as mentioned earlier; however, the dew condensation on the decorated chamber walls will still continue to occur in summer and can be suppressed either through cooling and dehumidification or only dehumidification of the stone chamber or through radiation heating of the stone surface.
