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 Appendix A: Design Procedure for Riprap Armor
(4) Applications.
(a) The outer bank of straight channels downstream of bends should be
designed using velocities computed for the bend. The K1 side slope factor
is normally defined by the Carter et al. (1953) relationship
sin2
K1 '
1 &
(A.4)
2
sin
where
= angle of side slope with horizontal, and
= angle of repose of riprap material (normally 40 deg).
Results given in Maynord (1988) show that Equation (A.4) is conservative
and that the repose angle is not a constant 40 deg but varies with several
factors. The recommended relationship for K1 as a function of is given in
Figure A.7 along with Equation (A.4) using = 40 deg. Correction for the
vertical velocity distribution in bends is given in Figure A.8. Limited testing
has been conducted to determine the effects of blanket thickness greater
than 1D100(max) on the stability of riprap. Results are shown in Figure A.8
greater blanket thickness is used, it must be realized that some rock
movement will occur before the revetment becomes stable. While D30 is
considered to be the appropriate characteristic size, many designers prefer
to use D50. The required or computed D30 can be used to determine the
required D50 according to
1/3
D85
D50 '
D30
(A.5)
D15
(b) The basic procedure to determine riprap size using this method is as follows:
1.
Determine average channel velocity for the design condition using
computational methods, physical modeling or extrapolation of on-site
measurement
A-21
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