地下流水音による崩壊発生位置の予測

Abstract

本研究では新たに地下水流の発する地下流水音によって地中水みちの位置を検知する手法を開発し，その有効性について述べた。また，本手法を多数の崩壊地に適用した結果，すべての崩壊発生地では地下流水音が周囲の崩壊非発生地に比較して大きいことが分かった。また，地形変化をモニターした結果，豪雨によっていくつかの崩壊が発生したが，崩壊発生部位は全て地下流水音が大きい部位であった。これらのことから，(1)崩壊は地下水の集中する部位で発生すること。(2)新たに開発した本手法によって崩壊発生位置を予測する可能性が示された。

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 answers 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 at the slope. In this study, a new method to detect the underground water path positions measuring sound of ground water flow by a sound sensor “hydrostat” was developed. As a first step, water flow through a single water pathway installed within an isotropic model soil layer was examined by this method. And as a second step, this method was applied to natural hillslopes and road cut slopes. Water springs from lower part of every slope were observed. As the results, underground sound pressure above the spring was biggest than other positions. Therefore, underground water path positions can be estimated by this new method. As a next step, this method was applied to the collapses in natural slope and road cut slopes. Measurement line was set up upper the scarp of collapse. And, underground sound pressure was measured at 2.0m intervals. Underground sound pressure in collapse position was bigger than other positions. Therefore, it was clear that the collapse position was decided by the water path position. The non-failure position that had big underground sound was monitored. This position was collapsed by the typhoon in 2004. As the result, there is a part which underground water daily concentrates in the slope. And, water path position was collapsed by the groundwater that was supplied to torrential rains.