Previous reports showed that the pipe flow and entrapped air have effects on the slope stability. Although a variety of studies indicated the role of the pipe flow on the rise of soil pore water pressure in hillslope, several effects, such as branch of soil pipe, entrapped air, has not been examined. In this paper, we conducted a bench-scale model experiment to clarify effects of branch of soil pipe and entrapped air on soil pore water pressure. We used the model which was composed of soil layer, artificial rainfall simulator, and artificial soil pipe in soil layer. We set up five conditions of model experiment, 1) no soil pipe, 2) only one pipe, 3) three pipes which joined into single pipe in middle of soil layer, 4) only one pipe with silica sand layer, 5) three pipes which joined into single pipe in middle of soil layer with silica sand layer. Silica sand layer was installed at the surface to prevent air escaping from soil layer. Under these conditions, we changed the water supplying level with time. The results showed that the spatial variation in drainage capacity of soil pipe, such as confluence of the soil pipe gave impact on soil pore water pressure distribution. So, the soil pore water pressure dramatically increased at the point where drainage capacity of soil pipe was smaller than that of upslope. Moreover, entrapped air enhanced the increase of soil pore water pressure at the point where drainage capacity of soil pipe was smaller than that of upslope.
Wooden Azekura dams sometimes require long members（approximately４m in length）as construction material, which are not readily available. Therefore, we devised a new arrangement of longitudinal members that reduces the use of long material and efficiently uses thinned wood in order to improve assembly workability. We performed experiments with full-scale models and verified differences in behavior between arrangements that used conventional long material and staggered arrangements that did not use the long material, by applying loads. No significant difference was observed in the displacement of the two structures during loading, and the effectiveness of structures that employed staggered arrangements was verified.
A questionnaire survey was conducted at the municipal disaster management sectors in northern Tohoku district, Japan, in order to understand the actual state of warning and evacuation systems for sediment disasters and the issues faced in their establishment. Though information on disaster-prone areas and disaster alerts has been properly disseminated, most municipalities suffer from insufficient knowledge on sediment-related disasters and have inadequate staff numbers to respond to such disasters. Moreover, disaster alerts have not been well utilized by the municipalities because of the low ratio of disaster occurrence. Areas prone to sediment disaster have not been understood well because of the difficulty in conducting disaster drills using the distributed maps that indicate disaster-prone areas. Information on the extent to which each area is susceptible to disasters is perceived as a requirement. Topographical and geological information on areas, which often indicate potential sediment hazards and are regarded as important by national and prefectural governments, were evaluated as sufficient. However, such regional information is of great importance in establishing collaborative warning and evacuation systems for municipalities and local communities and it is most effective when it is disseminated in an easily understandable manner.
In this study, we performed a load test and measured the horizontal load and horizontal displacement of a full size wooden structure built with experimental equipment. By steadily increasing the horizontal surcharge load, the maximum horizontal load (resistance) was observed at approximately 4 to 6 % of the height of the horizontal displacement. Using these results, we can set the control standard values of the horizontal displacement of the wooden structure to 5 % for the height.
An extremely heavy rainfall was observed in the northern part of Kyushu, Japan in July 2017. For example, the highest daily rainfall was 803 mm on July 5, 2017 at Kurokawa, Asakura-City of Fukuoka Prefecture. The heavy rainfall caused many slope failures, debris-flows, sediment-flows and floods, which killed 37 people at the current stage. Phenomena such as surface slope failures and sediment-flows were concentrated around the eastern part of Asakura-City. They flowed down as floods and damaged many residential areas. The bedrock where the phenomena occurred was not only weathered granite but also weathered schist included in Sangun metamorphic rocks. It is a very important feature that enormous driftwood has discharged by sediment-flows, floods and so on. Some large failures also occurred out of Asakura-City. In Hita-City of Oita Prefecture, a large failure with a width of ca. 200 m, a length of ca. 350 m and a depth of ca. 15 m occurred and blockaded Ono-river. Because this disaster caused serious damage to surrounding areas, the comprehensive countermeasures such as construction of sabo-facilities and setting warning-evacuation system must be needed.