slope tilted by tan^1 . The limit equilibrium analysis developed in Sarma
(1975) is frequently employed in this context as it is readily adapted to
include horizontal interslice forces. A simplified approach to earthquake
resistant design of embankment dams is presented in Sarma (1980).
The seismic risk to UK dams, including selection of design para-
meters, is addressed in Charles et al.(1991) and ICE (1998). Selection of
seismic design parameters has also been reviewed in ICOLD Bulletin 72
(ICOLD, 1989). Reference should be made to Seed (1981) and to Jansen
et al.(1988) for further detailed discussion of seismic analysis and in
particular of dynamic analysis and its application in design.
2.8 Settlement and deformation
2.8.1 SettlementThe primary consolidation settlements,
1 , which develop as excess
porewater pressures are dissipated, can be estimated in terms of mv, the
coefficient of compressibility (Section 2.3.3), the depth of compressible
soil, and the mean vertical effective stress increases, ∆. Subscripts ‘e’
and ‘f’ in the following equations refer to embankment and foundation
respectively:
1 fnmv∆ (2.29)(^) lemve H^2 /2, (2.30)
whereHis the embankment height, and
(^) ifmvfDf∆f (2.31)
whereDfis the depth of the compressible foundation. ∆fis given by the
relationship
∆fI (^) fze (2.32)
whereIis an influence factor determined by the foundation elasticity and
the width:depth ratio. Curves for Iunder the centre of a symmetrical
embankment are given in Mitchell (1983). For representative embank-
ment dam–foundation geometries with Df0.5H,I0.90–0.99.
The accuracy of settlement predictions is enhanced by subdividing
the embankment and/or foundation into a number of layers, and analysing
the incremental settlement in each in turn.
The secondary consolidation settlement,
2 , can be estimated from