がけ崩れの観測手法 Monitoring method for slope failure がけ崩れの特徴 Characteristics of (rapid, surface soil) slope failure • 崩落速度が速く、移動時間 が非常に短い The speed of failure is fast, and very short duration movement. • 前兆現象を認識しにくい Difficult to recognize the warning sign がけ崩れの発生 Occurrence of slope failure 降雨、融雪等による水の供給 Supply of water by rainfall and snow melt ・斜面の土壌水分量の増加→強度低下 Increase of water contents in slope soil → decrease of soil strength 間隙水圧の上昇 Increase of pore pressure パイピングによる局部破壊とその進行 Local progressing collapse due to piping in the slope がけ崩れ Slope failure ・ ・ がけ崩れの観測手法 Monitoring method for slope failure • 降雨観測 Rainfall monitoring →現象(発生条件)の解明、警戒避難 To make clear the phenomena(condition of occurrence), warning and evacuation 雨量計、レーダー雨量計 Rain gauge, Radar rain gauge • 発生や前兆現象の検知 Detection of occurrence and warning sign →警戒避難 Warning and evacuation 非常に困難 Very difficult ・ がけ崩れの観測手法 Monitoring method for slope failure • 崩壊過程の観測 Monitoring of failure process →現象の解明To make clear the phenomena ・崩壊状況の撮影(監視カメラで のビデオ撮影) Picture of failure using video camera ・変動の観測(伸縮計等) Monitoring of movement (Extensometer etc.) 観 測データが絶対的に不足 Lack of data of the slope failure process • 崩壊、堆積状況等に関する調査、測量 Investigation and survey about occurrence of failure and sedimentation →現象の解明 To make clear the phenomena 降雨観測の目的 Purpose of rainfall monitoring 現象の解明 To make clear the phenomena • 降雨及びがけ崩れ発生実態のデータ蓄積 Accumulation of data of rainfall and occurrence of slope failure • がけ崩れが発生する降雨条件の解明 To make clear the condition of slope failure occurrence 発生予測及び警戒避難 Prediction of occurrence, warning and evacuation • 降雨観測値（＋予測雨量）からのがけ崩れ発生予測 Prediction of slope failure occurrence from the observed rainfall (+predicted rainfall) • 警戒避難の実施 Warning and evacuation がけ崩れ発生危険基準線の設定 Set up of critical line between safe area and dangerous area against slope failure occurrence Slope failure occurrence rainfall Slope failure non-occurrence rainfall Dangerous area safe area Critical line 降雨からのがけ崩れ発生予測の課題 Problems about prediction of slope failure occurrence from the rainfall • 雨量観測値及び予測値の精度向上（空間分布等） Improvement of the accuracy of rainfall observation and prediction →雨量観測点の高密度化、レーダー雨量計の活用、予測手法 の向上 High density of the distribution of rain gauge stations, application of the radar rain gauge, improvement of prediction method • 発生前の長期的な降雨によって土中に貯留される水量の評価 Evaluation of water content accumulated in the slope soil by long-term rainfall before the occurrence of debris flow 連続雨量→タンクモデル、実効雨量 Continuous rainfall → tank model, effective rainfall タンクモデル及び実効雨量の問題点 Problems of tank model and effective rainfall • 入力（降雨観測値）と出力（土石流の発生・非発生）のみが与えら れ、途中の過程がブラックボックスの状態での解析によって係数 や半減期を設定The tank factors and the reduction factors of effective rainfall are set up by analysis in which only input (observed rainfall) and output (occurrence and non-occurrence of debris flow) are given, and the process is ‘black box’. • 設定された係数や半減期が本当にその地区の土壌水分変化を 精度よく表現できているとは限らない The factors do not always represent the change of water content of slope soil accurately. • 予測のばらつきの一因 It is one of the cause of an error of prediction タンクモデル及び実効雨量の問題点 Problems of tank model and effective rainfall 改善策 Improvement method • 降雨時の土壌水分変化の実態に合わせたタンクモデ ルの係数設定、実効雨量の半減期設定 Set up of the tank factor and reduction factor of effective rainfall fitting with the change of water content of slope soil • 土壌水分量あるいは斜面からの流出量そのものの観 測値を指標とした警戒避難基準の設定 Set up of warning and evacuation standard using water content value or water flow out volume itself － 土壌水分変化のデータが絶対的に不足 － Lack of data of the change of water content 斜面の土壌水分変化及び崩壊過程に関する 観測データの不足 Lack of data about the change of water content in the slope and the process of slope failure • 全斜面に観測機器を設置することは不可能 It is impossible to install monitoring instrument in all slopes. • 選定した観測斜面が崩壊に至らない Selected monitoring site do not easily result in the failure occurrence. • 斜面に人工降雨を与えて崩壊実験？ Slope failure experiment by the artificial rainfall supplied in the slope? がけ崩れの発生・前兆の検知のための新技術 New technique for detection of warning sign or occurrence of slope failure • 光ファイバーセンサーによる監視（道路斜面での事例） Monitoring using optical fiber sensor (Example of the roadside slope monitoring) ・道 路斜面に沿って配置 → 地表面変位の監視 → 前兆現象等の 検 知 → 通行規制 Installation in Optical fiber the slope along the roadside sensor → Monitoring of surface movement → Detection of warning sign or other unusual sign → Closing of traffic Real-time monitoring
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