Bishop's simplified method which is said to give satisfactrily approximate value of factor of Safety Fs, obtained by its rigorous method, is compared to the Fellenius method with the bouyant weight of submerged materiale which we name Tschebotarioff's method in this report.
　Three case records of failure in which soil properties are carefully investigated show that Fs obtained by Tschebotarioff's method are between 0.97 and 1.01 and obtained by Bishop's simplified method are larger from 6 to 27 percent than these values.
　Being varied the differences of Fs with the shapes of slopes and soil propertie, this trend appeared in all examples treated in this report both with no pore pressure and with hydrostatic pressure.
　In special case, Bishop's simplified method does not give Fs of positive.
　Lower limit of Fs by Bishop's simplified method is defined as (-tan αtan φ) max (>0),where α is central angle of slice and φ is strength parameter.
　In so called deep failure, that failure might occur in port and habour field, this lower limit of Fs may become remarkably large value.
　Therefore, Tschebotarioff's method seems to give more appropriate value of Fs in port and harbour field.
　Programming of both methods for electronics computer TOSBAC 3400 are reported as a supplement.