Slope disasters inducing stony-type flow are occurring more frequently due to ongoing global climate changes, but the mechanisms of granular flow have not been thoroughly explained. The mechanism of dry granular flow was examined in micro and macro views. First, flow behaviors of dry granular materials on a slope were examined using PIV image analysis and a discrete element method in two dimensions. The simulation results replicated the tendencies shown in the test model results. Relationships exist between macro and micro behaviors during phenomena such as velocity distributions in depth stratification and uplifts of large particles that change flow gradings. Similarly, stress chains which are transmission paths of contact forces, are focused. The distribution of the averaged coordination number was found to correspond to the distribution of velocity, indicating three layers of structure. This stratification could be explained by the state parameter, a relative variable dependent on void ratio, mean normal stress, and critical state. Moreover, the stress chains formed from the riverbed concentrated the larger particles and pushed them upwards towards the flow surface.
In planning for the arrangement of countermeasures in such a basin where has a large amount of sediment discharge, a series of grid check dam structures will be constructed. In this case, decision making of the space between steel pipes in consideration of change of characteristic of sediment rocks is substantial because characteristic of sediment rocks is used for design of grid check dam structures, and it change when it pass through the grid .This paper discusses an evaluation method of effect of grid shape on the probability of rocks capturing, and then an evaluation of effect of a series of grid check dam structures on the probability of rocks capturing. First, it is assumed that the capturing events are based on a probability process, i.e., a geometric distribution in a Bernoulli sequence. Second, the probability of what a rectangular space is stuffed by some rocks following log-normal distribution diameter is estimated using MonteCarlo simulation. Third, in cases where same dam models were arranged at upstream and downstream, the number of rocks captured by the dam at downstream is less than 20% of number of rocks that pass through the dam at upstream. Fourth, in cases where the dam at downstream is designed to account for characteristic of rocks that pass through the dam at upstream, the number of rocks captured by the dam at downstream is about 50%.
There are many areas in Iwate prefecture that are at risk of landslides and other sediment-related disasters. Moreover, the percentage of landslide prone areas with preventative works in place is quite low ; 10% lower than the national average. As a result of the 2002 Kamaishi landslide, Iwate Prefecture set forth some new projects in 2004, one of which was a project to promote the removal of housing from landslide risk areas. In this project, Iwate Prefecture independently adds funds to an existing national system to promote the active relocation of housing from landslide risk areas. There are few reports about the housing relocation from areas subject to disaster. Residents who used the system, and administrators in charge of this system, were interviewed to inquire into the present condition and issues facing the system.
Check dam is the most effective structural measure to protect inhabitants, properties, communities from sediment related disasters in river around mountainous and hilly areas. Check dam has a variety of functions. Among those, sediment control function is one of the most important functions of check dam. By this function, runoff sediment from upstream during large flood is saved temporarily, and this sediment is transported to downstream by medium or small floods which occur during several years or over decade after that large flood. Through this function runoff sediment is smoothed in the standpoint of time and damages by flood or sediment are reduced. The idea of this function was proposed about 70 years ago and was discussed based on qualitative recognition at first, but it had become to be discussed as a function of individual check dam quantitatively. Furthermore, the concept of this idea was gradually generalized after establishment of sediment control master plan. The process of discussions of sediment control function of check dam showed above is clarified in this paper by the review of previous papers and documents. This paper is useful for future study on sediment control effect functioned by check dam in mountain stream basins.