統計的手法を用いた事例解析による地すべり到達距離の検討
A study of landslide reaching distance in case analysis by statistical method
楠本岳志a)･中瀬有祐b)*･藤本 睦b)･中井真司b)
Takeshi KUSUMOTO, Yusuke NAKASE, Mutsumi FUJIMOTO and Shinji NAKAI |
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Abstract
It is very important for preventing the disaster by the landslide to estimate the landslide reaching distance. In this paper, it was tried to estimate the landslide reaching distance by analyzing past landslide cases. Before analyzing them, cases where the shape before and after the landslide movement was apparent were extracted from the literature and the report, etc., and they were objects of this study. As a result of patternizing the cases, mudstone and sandstone(including an alternation of sandstone and mudstone)amount to half the number of the population and Tertiary Period do to about 70 percent, therefore geological features of the landslide became clear. In multiple regression analysis, the extremely precise predicted expression was gained by assuming the prediction index to the slope gradient after the landslide movement:alpha , and doing the explanatory variable to between the slope gradient before it:theta and width of the landslide:W . Especially, the multiple correlation coefficient became R=0.923 on the mudstone in Tertiary Period. Moreover, significance and validity were confirmed by analysis of variance and residual analysis.
Key words:landslide reaching distance, patternizing, multiple regression analysis, variance analysis, residual analysis
和文要旨
地すべりの到達距離を予測することは，地すべりによる災害を防止する意味からも非常に重要である。本論文では，過去の地すべり事例を解析することによって，到達距離を予測することを試みた。解析にあたっては，文献・報告書等から，地すべり移動前後の形態が把握できる事例を抽出し，対象事例とした。対象事例を類型化した結果，母集団の半数が泥岩もしくは砂岩（砂岩・泥岩互層含む），約７割の地質時代が第三系で占められており，地すべりの地質的特徴が明らかとなった。重回帰分析では，予測指標を移動後の見通し角alpha ，説明変数を移動前の見通し角theta と地すべり土塊の幅W とすることにより，最も予測精度の高い予測式が得られた。特に，第三系泥岩では，重相関係数はＲ＝０．９２３となった。また，予測式に対して分散分析，残差分析を行い，その有意性・妥当性を確認した。
キーワード：地すべり到達距離，類型化，重回帰分析，分散分析，残差分析 |
降雨浸透に伴う地下水流の発達･減水過程と
斜面崩壊に及ぼす影響に関する考察
Simulation Analysis of Rainfall Induced Groundwater Flow in Association with Slope Failure
森脇 寛a)*･矢崎 忍a)･黄 文峰a)
Hiromu MORIWAKI, Shinobu YAZAKI and Wenfeng HUANG |
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Abstract
Groundwater flow due to rainfall was simulated using the Darcy's law both analytically and numerically to understand its effects on slope failure. Stationary solutions on the groundwater flow describing ground water table were obtained with implicit functions. In numerical calculations, effects of rainfall pattern, rainfall intensity and shape of slope layer on the development of groundwater flow were examined. The results were summarized as follows:1)Under a constant rainfall condition, the water level of groundwater flow increased gradually with distance near the upper part of the slope, and developed with time in parallel to the slope at the middle and lower parts of the slope;2)An approximate solution applicable to a steep slope provided the boundary above, development and retreat of the flow numerically;3)When rainfall ceased, groundwater totally moved downward, keeping the water table;4)Heavy rainfall raised the water level of the flow at the top of the slope;and continuous rainfall formed higher water level through the slope than intermittent rainfall in a condition of the same total amount of rainfall;5)Intermittent rainfall brought an increase in water level of the flow near the foot of the slope resulting in a small‐scale slide at the foot that consequently triggered a large‐scale landslide;6)When the slope was gentle toward its toe, the peak water level of the flow was found at the boundary and the peak water level continued to increase for a while after the rain ceased;and 7)The stability of a unit slope was estimated as a function of time using an approximate solution.
Key words:groundwater flow, slope failure, numerical simulation, approximate solution, safety factor
和文要旨
降雨浸透に伴い斜面土層内に発達する地下水流について,ﾀﾞﾙｼｰ則が適用できるものとして導いた物理方程式により定常流,非定常流について検討を行った｡定常流については斜面上の位置と水位の関係を陰関数の形で表した｡非定常流については近似解,数値解法により基本的な発達･減水過程を明らかにするとともに降雨特性や斜面勾配の変化が地下水流の形成ならびに斜面崩壊に及ぼす影響について考察した｡その結果を以下に要約する｡\外字(c222)定常降雨下では,地下水位は斜面下方に行くにつれて高くなるが,斜面上方では時間経過とともに徐々に一定値に近づき,斜面中･下方域では不透水層面にほぼ平行な水位を有する流れを示しながら,水位を上昇していく形態を示す｡\外字(c223)近似解によれば斜面上方域では斜面上端からの距離に比例した｢定常域｣,斜面中･下方域では時間に比例して水位が斜面に平行に増加･上昇する｢斜面平行増加域｣となり,両者の境界点は時間とともに下方へ移動する｡斜面中･下方域における地下水位の上昇速度は降雨強度に比例し,有効空隙率に反比例する｡\外字(c224)降雨が停止すれば,地下水面形はその形をほぼ維持したまま斜面下方へ流下する形をとる｡\外字(c225)降雨強度が大きいほど水位上昇速度は大きく,斜面上方まで水位が高くなる｡\外字(c226)同一総降雨量では断続的に降るよりも連続的に降るほうが斜面全層にわたって水位が高くなり,全層崩壊の危険性が高いが,断続的な降雨の場合,斜面下方の水位が特に高くなり,ﾊﾟｲﾋﾟﾝｸﾞ崩壊や洗堀崩壊の危険性が大きくなる｡\外字(c227)不透水層が遷緩点を有する斜面では,その付近で水位が特に高くなる｡また,降雨停止後もしばらくの間,さらに水位が上昇する｡一方,遷急点を有する斜面ではその付近で水位が低下する｡\外字(c228)近似解を用いて,地下水流の発達に伴う斜面土層の安全率の時間変化を表した｡
ｷｰﾜｰﾄﾞ:地下水流,斜面崩壊,数値解析,近似解,安全率
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活動中の地すべり地における中越地震発生時の移動および間隙水圧変動特性
Displacement and fluctuation in pore water pressure of active landslide
area by the Mid Niigata Prefecture Earthquake
岡本 隆a)*･松浦純生a)･浅野志穂a)･竹内美次a)
Takashi OKAMOTO, Sumio MATSUURA, Shiho ASANO and Yoshitsugu TAKEUCHI |
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Abstract
The authors analyzed the landslide displacement and fluctuation of pore water pressure at a reactivated landslide which moves more than one meter a year in Niigata Prefecture from the results of monitoring every ten minutes. The distribution of landslide displacement caused by the earthquake matched that caused by rainfall. Pore water pressure showed variations at each monitored point. Considering a relationship between the distribution of landslide deformation and of the pore pressure, the variation in pore water pressure is considered to be generated by local compression or extension in the landslide mass. Although the amount of landslide movement was large before the earthquake, it fell immediately after the earthquake, and remained low until the beginning of the next snow‐melt season.
Key words:Mid Niigata Prefecture Earthquake, Reactivated landslide, Automatic monitoring, Deformation, Pore water pressure
和文要旨
年間移動量が最大1m以上となる新潟県の再活動型地すべり地において,10分間隔の自動観測結果から新潟県中越地震発生時の地すべり変位と間隙水圧変動を明らかにした｡
地すべり地内の各観測点における変位量分布は,地震時と降雨時の間で調和的であった｡間隙水圧の変動は増減方向を含めて一様でなかった｡土塊の変形分布と間隙水圧分布との関係を考慮すれば,間隙水圧変動は地すべり土塊の局所的な圧縮および引張変形によって生じたと推察された｡
一方,地震前に活発であった地すべり移動が,地震発生後に急速に沈静化する現象が観測された｡沈静化現象は翌年の融雪期直前まで継続した｡
ｷｰﾜｰﾄﾞ:新潟県中越地震,再活動型地すべり,自動観測,変形,間隙水圧 |