Residual strength and stability of natural slopes in Shimajiri mudstone (Department of Agricultural Engineering)

泥岩斜面地すべりについての安定解析から以下のような2,3の結果がえられた。(1)ピーク強度定数を用いて安定解析を行なった場合Fs=7∿11となり, 実際と矛盾する。(2)飽和時にすべりが発生する時, 如何程のセン断強度であればよいかを求めるために作成したc'-tanφ'図に, 実験からえられたφ^^^-'=15°∿20°を適用した場合c^^^-'=0∿0.130kg/cm^2をえる。(3)高良地内地すべりの安定解析は, 新鮮泥岩の強度定数c_=1.20kg/cm^2,φ_=20°, c_=0,φdr=17°を適用し, すべり面に作用する平均セン断強度を求めた。すなわちすべり後の現地形でR=0.94,c^^^-'=0.072kg/cm^2,φ^^^-'=17.2°, 現地形の初期すべりでR=0.91,c^^^-'=0.113kg/cm^2,φ^^^-'=17.3°となる。このようにすべり面に働く平均セン断強度はピーク値よりも残留値に近いことがわかる。したがって既存面すべりばかりでなく, 初期すべりにおいても進行性破壊^や完全軟化土の概念と残留強度を導入して安定解析を行なう必要がある。The results obtained are as follows : 1. When the slips are analysed using the peak strength parameters, the calculated factor of safety is F_S=7∿11. 2. The estimated value of effective cohesion is c'^^^-=0∿0.130kg/(cm)^2. This value is obtained from the c'-tanφ' diagrams made by the stability analysis of five landslides, using φ'^^^-=15∿20°obtained from the present shear test. 3. According to the stability analysis of the slope after sliding and that of the original slope, results obtained from the Takara landslide show as follows : The factor of safety is 10.9 for the slope after sliding and 7.8 for the original slope when the peak strength is applied to the stability analysis. On the other hand the factor of safety is 0.6 for the slope after sliding and 0.29 for the original slope when the residual strength is applied. Since the correct factor of safety is 1.0 at the failure, the residual factor R=0.94 corresponding to the factor (of safety) gives c'^^^-=0.072kg/(cm)^2 and φ'^^^-=17.2°for the slope after sliding. The value R=0.91 for the original slope gives c'^^^-=0.113kg/(cm)^2 and φ'^^^-=17.3°. As mentioned above, the analysis of the forces acting on the slip surface shows that average shear strength is rather close to the residual and fully-softened strength than the peak strength. Therefore, it is necessary to analyse the stability of natural slopes in softened Shimajiri mudstone by using the mechanism of progressive failure, and residual and fully-softened strength