The use of sand layers for energy absorbing function in protection structures such as walls, embankments, and galleries is extensive in some countries. Full-scale experiments, prototype experiments, and numerical analyses by discrete element methods have been used to investigate the impact characteristics of the sand layers. This research utilized the finite element method (FEM) code LS-DYNA to investigate the dynamic behavior of a sand cushion subjected to impact loads. First, the sand analysis parameters were calibrated through a parametric study using sand tank data. The model was then validated using two previous sand tank and sand cell experiments. Two types of lateral boundary conditions were considered in the numerical model of the sand cell. A further investigation on the effect of the drop height on the impact phenomenon of the sand cell was performed. The simulated results indicated that the sand parameters had a large effect on the impact phenomenon. Comparisons between the simulated and experimental results for the sand tank and sand cell were in good agreement. The effects of the boundary conditions and drop height on the sand cell impact characteristics were analyzed. Above all, this research demonstrated that practical application of the FEM to the dynamic behavior of protection structures, including a sand-cushioning layer, is feasible and can aid in the development of protection technology against natural hazards.
A debris flow broke out at 16:40 on Aug. 18, 2004 in the Kitamatasawa, one of the right-bank tributaries of the Namekawa River in the Kiso River system. The flow volume (around 50,000 m3) was safely captured by the Namekawa No. 1 Sabo Dam, located at the downstream end of the tributary. Damage was successfully prevented, proving the dam´s effectiveness. A set of monitoring cameras installed around the site of the Namekawa No. 1 Sabo Dam and at various upstream points captured images of the debris flow. Here, we discuss the features of the debris flow based on analysis of these images.
The Tenryu River Upper Reaches River Office has carried out many investigations to reveal hydrological process and sediment discharge of Tenryu river upper reaches actually. We have placed the sediment transport observation facility in Yotagiri River that is a sediment discharge measurement device by the method to gather sediment discharge directly. It became clear that the tendency that quantity of sediment discharge increases after outbreak of debris flow temporarily and tapers after that, and sediment which flowed down at Bouzudaira consisted of about 50% silt, about 40% sand, and about 10% pebbles. It is necessary for us establishing of the ruled about repairing to slit type, and management of deposit of sabo dam based on the knowledge about sediment movement properties in the Yotagiri River.
On 30 September 2009, numerous landslides occurred in a mountain-ringed region of West Sumatra, Indonesia, triggered by an earthquake off the coast of Padang. The landslides blocked roads in the region, hindering efforts to determine the extent of the damage. Analyses of satellite images (coverage area 1,500 km2) of the most severely damaged districts, Padang Pariaman and Agam, revealed that 253 landslides had occurred. Severe landslides, involving more than 1 million m3 of collapsed sediment, were observed at 10 sites within the study area.