“Pseudo Factor of Safety” was calculated by multi-planar sliding surface method using shear strength proposed by Okimura (1982) . Using pseudo factor of safety (
fp), following results are obtained in 6 sampled areas.
1) As obtained value of
fp is connected with thickness of failure potential layer (Figure 2), effect of the thickness on
fp needs to be taken off. Gamma, which is a function of thickness of the layer, is introduced to accomplish this purpose.
2) Discriminant function of slope failure, whose value can be called as critical pseudo factor of safety (
fpc), are regressed by using area of catchment (
S) and gamma explained above. If
fp is less than
fpc, slope failure will occur. The result obtained was that 73%-100% of slopes were properly discriminated in sampled areas.
3) The result of discrimination was obtained similarly to that of the previous analysis when 1.3 times as much as value of shear strength is used. If value of
fpc-
fp of a slope becomes plus, then its solpe will be failure. Average of the absolute value of differences between
fpc-
fp in previous cash and that in this case is 0.018-0.025.
4) A critical effective precipitation (
Pec) can be defined on each slope. If effective precipitation is more than
Pec of a slope, slope failure will occur in the slope.
Pec is linearly regressed by using logarithm of S,
fp, and gamma mentioned above. In one sampled area, relative error of decided
Pec is about 8%.
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