Journal of the Japan Society of Erosion Control Engineering, Vol.60,No.4,2007

Relation between collapse position and water path position in slopes

Yasuyuki Tada, Masaharu Fujita, Daizo Tsutsumi, Kan Koyama,Takayuki Kawai, Takenobu Okumura and Naomasa Honda


Abstract

In Japan, a lot of hillslope collapses triggered by heavy rainstorm almost every year. In spite of continuous effort to elucidate the mechanism of landslide occurrence, sufficient answer explaining why the particular position of the hillslope collapses have not been obtained. It has been pointed out that there is a close relationship between the landslide and underground water paths according to observations around the collapse site; i.e. outlet of soil pipes on the scarp, clouding, stopping or spouting of spring water just before or after the landslides. However, detail of these relationships has not been clearly understood yet, partly due to lack of an effective method to detect the water path within the slope. Recently, a new method to detect the underground water path positions measuring sound of ground water flow by a sound sensor "hydrostat" was developed.
In this study, water path position is detected by this new method. And estimated water position is compared with the collapse position in natural slopes and road cut slope. As the result, the hydrosonic in collapse position is higher than non collapse position. This result indicates that collapses is triggered at the position where the ground water gathers. In this investigation, there were the slopes that have the high hydrosonic position. Change of these slopes after heavy rainstorm ware monitored. As the result, the high hydrosonic position in slopes was collapsed, because of heavy rainstorms by the typhoon. These results clarified bellow. In the slope, there is the position which ground water concentrates on a daily basis, and this position was supplied bags of water by the heavy rainstorms. Therefor, the ground water concentrating position was collapsed. It is clear that supply condition of ground water is different in collapse position and another position.


Key wordsFcollapsed position, water path position, underground sound
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