the horizontal. The latter is considered positive if upslope from the lowest
point on the failure arc. The Fellenius solution is, in practice, conservative
by comparison with more rigorous analyses, and may underestimate F
by 5–15%. This margin is generally unacceptable in terms of the cost
implications.
(b) Bishop semi-rigorous solution: circular arc surface
The Bishop semi-rigorous solution (Bishop, 1955) differs from the Felle-
nius solution in the assumptions made with regard to the interslice forces
required for static equilibrium:
86 EMBANKMENT DAM ENGINEERING
Fig. 2.14 Schematic of the variation of embankment stability parameters
during construction and operation (after Bishop and Bjerrum, 1960)
