Yukiyoshi Teramoto

Site Investigation and In Situ Testing on Shallow Landslide Scars of Natural Slopes Covered by Volcanic Ash and Pumice Fall

The slopes composed of Shirasu and other volcanic product often fail due to heavy rain in the rainy season. In order to prevent shallow landslides, six field test sites, where past occurrence of landslides due to heavy rainfall were identified, have been determined in the Takakuma experimental forest of Kagoshima University. In this study, site investigation and in situ testing on shallow landslide scars of natural slopes covered by volcanic ash and pumice fall are conducted to investigate the stability of the slopes and the effect of revegetation and soil development of forest topsoils from the viewpoint of forest ecology and geotechnical engineering. In the site investigation, the growth condition of forest trees, the measurement of dry density of topsoil and investigation using soil augers are carried out. Furthermore, simple dynamic cone penetration test and the investigation of slope topsoil using a soil strength probe are performed in situ. Finally, a judgment regarding the stability of slopes and the effect of revegetation and soil development could be made.

Factors controlling sediment production from a yarding road and its temporal pattern in an abandoned clear-cut plantation forest in the Shirasu (pyroclastic flow deposits) area, Kagoshima Prefecture, Japan

To understand the temporal pattern in sediment production from a yarding road, we investigated sediment yield and grain size composition, and examined the relevant physical factors in an abandoned clear-cut plantation forest, based on the 3-year onsite monitoring in Shirasu area, Kagoshima Prefecture, Japan. Under a given amount and intensity of rainfall, although sediment yield and grain size of the sediment increased with increasing rainfall, they remarkably decreased each year; that is, the annual sediment yield from the yarding road in the first, second and third years were 6.1, 2.7, and 1.4 mm, respectively. With the elapsed year, the proportion of gravel and coarse sand gradually decreased, whereas the proportion of fine sand and silt-clay gradually increased. Dry density of surface layers decreased with increasing vegetation coverage at the survey site each year. Additionally, surface grain size at the rill and inter-rill points gradually increased with the elapsed year. The results indicated that the annual decrease in both sediment yield and its grain size are associated with an increase in soil porosity (i.e., increase in infiltration capacity) due to root development and increased intensity of ground resistance to overland flows and sediment transport following both vegetation growth and surface armouring.

Recovery and Disaster Prevention Capability of Coastal Japanese Black Pine (Pinus thunbergii) Forests on the Fukiage Sand Dunes of Southern Kyushu, Japan

In this study, we investigated the Fukiage sand dunes of southern Kyushu, Japan. We surveyed the status of recovery of coastal Japanese black pine forests damaged by pine wilt disease and their disaster prevention capability. We placed two transects: Transect 1, in an area that was severely damaged (80-90% damage rate) by pine wilt disease, and Transect 2, in an area that was mostly undamaged (