Rockfall protection-walls and -fences were constructed along the roadsides with steep cliff to ensure the safety of people's lives and transportation networks. Generally, the walls were of gravity-type made of plain concrete and the base of the steel posts of the fences were embedded into the box-release space in the top of the walls. However, the anchoring depth of the posts has been designed by not considering dynamic effects due to rocks impacting but considering only static loads following the specifications of the design guideline. It may be important to establish a rational design method for the anchoring depth of the posts for upgrading those impact resistant capacity together with the energy absorption and capturing capacities of the fences against falling rocks. To accomplish this, static and drop-weight impact loading tests of H-section steel post embedded in the plain-concrete block were conducted varying the anchoring depth of the post under the condition coupling between bending and shearing actions. The results obtained from this study were as follows : (1) the plastic hinge was formed in H-section post near the base of foundation under not only static but also impact loading ; (2) the concrete block failed in punching shear failure mode when the adequate anchoring depth of the post was not secured ; (3) the adequate anchoring depth obtained from the impact load testing tends to be decreased comparing with that from the static load testing ; and (4) the required anchoring depth obtained following the design specifications approximately corresponds to that obtained from the experiments.

In Japan, sediment disasters occur frequently due to national land and weather conditions, and many precious lives and property have been lost. Non-structural and structural measures need to be further strengthened to mitigate damage. However, there are still some issues with the measures. Kagoshima City issued an evacuation advisory throughout the city during heavy rains from the end of June 2019. Therefore, this study conducted a resident questionnaire on evacuation behavior and disaster prevention awareness in the city. The study also objectively analyzed evacuation behavior and recognition of residential risk by relationship of inside and outside the sediment disaster warning area, and relationship of natural phenomenon that could cause sediment disasters. The main result was that the percentage of evacuees living inside the warning area was higher than outside the warning area. In addition, the more accurately they were aware of the residential risk related to the warning area, etc., the higher the ratio of taking appropriate evacuation behavior. From this, it is considered important to narrow down the areas subject to announcements such as evacuation advisories and to correctly recognize the residential risk.

The training dike of large-sized sandbags stacking are often used for emergency remedial works in the steep mountainous area following debris flow disasters. According to the existing reference standard for the construction of temporary coffering design, it is applied under the condition that the flow velocity is under 2.0 m/s and only water flows down. However, those sandbags in the steep mountainous area are exposed both to water and sediment loads with flow velocity generally exceeding 2.0 m/s. To evaluate the stability of those sandbag-based structures under different flow conditions, we firstly employed a flume experiment to examine the destruction types of the structure, by changing channel gradient and angle of dike for flow. The movement of those sandbags exposed to sediment-laden flow from the upper flume was monitored with installed cameras and laser sensor. Secondly, we conducted safety factor calculations based on experimental results and limit equilibrium method. As a result of the flume experiment, the movement of the stacked sandbags are categorized into two patterns : outflow of individual sandbags at the lower end and the slide of all staked sandbag. From the result of the safety factor calculation, it could not be evaluated that the safety factor in the limit equilibrium state is 1.00. However, when the safety factor decrease, sandbags stacking slide and the lower end sandbags outflow. Our findings suggest that the stability of those structures should be carefully considered when applied for emergency remedial works in steep channels.

At Sakurajima Volcano, debris flows frequently occur under the changes of volcanic ash fall thickness by continuous eruptions. To clarify effect of the volcanic ash fall on debris flow occurrence, we investigate relations with slope erosion and sedimentation rates, the amount of rainfall, ash fall and debris flow occurrence. The slope erosion and sedimentation rates were estimated from the difference value of Lidar data in the upper Arimura River basin of Sakurajima from 2010 to 2018. As a result of investigation, the erosion and sedimentation mainly occurred in the uppermost basin (basin 1 to 4). In basin 1 where relatively old pyroclastic materials had dissected, sediment runoff occurred due to the expansion of developed gully on slope and the erosion of riverbed sediments, regardless of the amount of ash fall. In basins 2-4 where latest pyroclastic materials deposited, erosion rate on the slope increased with the development of gully on the slope after the amount of ash fall decreased. The scale of debris flow was estimated from the height of broken wire sensor in lower Arimura River. Although the scale of debris flows tended to be large in the period when the riverbed erosion occurred, it tended to be small in the period when the gully develop on the slopes where latest pyroclastic materials deposited. This result suggests that characteristics of sediment runoff with continuous volcanic eruptions depends not only on the amount of ash fall, but also on the type of erosion in the basin, the materials of eroded sediments, and the volume of deposits in the basin.

Information of pore fluid in a debris flow is unclear, despite its contribution to the fluidity of the debris flow. To observe sediment concentrations of the pore fluids in debris flows, we established a novel monitoring system in Arimura River Catchment, Sakurajima Island, southern Japan. A culvert, 1.0 m in width, 1.5 m in height and 2.0 m in length, was placed along the stream bank. An intake of 0.8×0.8 m, which is covered by steel grating, was equipped on the side of the culvert so that only pore fluid of debris flows was led inside of the culvert. Measurements of dielectric constants, as well as pressure heads, were conducted within the culvert and used for the calculation of sediment concentrations of the fluid. The sediment concentrations of the pore fluid were successfully measured for natural debris flows. The preliminary observation revealed that the volumetric sediment concentration of pore fluid varied from approximately 22 to 69%. Successive occurrences of debris flow caused decreases in the sediment concentration of the pore fluids with each surge.

In elementary schools, the government curriculum guidelines were revised. Education on “acquiring knowledge about natural disasters”, “protecting oneself from disasters” and “behaving to protect people from disasters” is required. Such the education is expected to be fully implemented in 2020. In Wakayama prefecture, many human losses were caused by typhoon TALAS in 2011 and large-scale sediment disasters occurred in the southern part of the prefecture. In this study, a new approach for the education of sediment disaster prevention is proposed in which an RPG (role-playing game) is used. The RPG was developed for the upper grade of elementary school in collaboration with NITW (National Institute of Technology, Wakayama College) and IWSRE (Wakayama Sabo Research and Education Institute). The education using the RPG was carried out at some schools, and its effectiveness was investigated by the questionnaire survey to the students and teachers.

Around Mt. Fuji area, People have been afraid of spring's sediment disaster caused by a highly fluid avalanche “Yukishiro” since the 16th century. In the beginning of 21st century, the Mt. Fuji Sabo Office, which is in charge of the sabo works of Mt. Fuji, has begun to use the term “slash avalanche” for debris flows containing snowmelt water with the aim of facilitating the evacuation of residents. In this report, we position the slash avalanche disaster of Mt. Fuji as a large-scale sediment disaster scenario and describe that we conducted exercises with related organizations.