The Cohesion and Angle of Internal Friction and the Change of These Values in the Landslide Face

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The clay layer in the landslide face is about 3mm thick. Accordingly, the constants of shearing strength are as follows; c'≈0.φ'>0 The reason is that the shearing conditions of sliding face are not consolidated-undrained but consolidateddrained. Therefore, the safety factor of landslide face can be expressed as; Fs=tanφ'∑ (W cos θ-uw) /∑W sin θ The pore water pressure Uw acting on the slide face, has direct effects upon the occurrence of the landslide which is caused by a heavey rain. When the sliding movement passes a certain value, the c' and φ' are changed by the negative dalatancy etc. So the safety factor Fs is given by the followng formula, Fs=c'L+tanφ'∑ (W cos θ-uw+u) /∑ W sin θ In the formula, U shows excess hydrostatic pressure. In the sliding, when the safety factor becomes fixed after reaching a certain value, it doesn't increase any more even if the pore water pressuer becomes higher.