Up to five sizes of quarry run riprap can be specified and will be used in the
calculations instead of the default if they appear in the data set. This capability is
not available in SAMwin at this time. However, the quarry run riprap data can
be input on the RQ record with an editor; see Appendix C. That data set can then
be run with the "Run" option of the SAMwin main menu. No plots are available
from these calculations.
The safety factor, Sf , accounts for variability and uncertainty in calculated
hydrodynamic and non-hydrodynamic imposed forces and/or for uncontrollable
physical conditions. The minimum safety factor recommended in EM 1110-2-
1601 (USACE 1991, 1994) is 1.1. This is the default value used in SAM.
However, a larger value may be specified on the riprap input screen. A
discussion of appropriate values for the safety factor is presented in EM 1110-2-
1601 (USACE 1991, 1994).
The thickness coefficient, CT , accounts for the increase in stability that occurs
when riprap is placed thicker than the minimum thickness. Minimum thickness
is the greater of d100 MAX and 1.5 d50 MAX. If minimum thickness is desired, then
CT = 1.0. EM 1110-2-1601 (USACE 1991, 1994) provides three curves for
determining CT as a function of the ratio d85/d15 and the ratio of design thickness
to minimum thickness -- TR/TMIN. Currently, SAM uses the curve that results in
the least reduction in design riprap size:
T R + 0.14 T R
1≤ TR ≤ 2
CT = 1.44 - 0.58
T MIN
T MIN
T MIN
where:
TR = riprap thickness
TMIN = d100 MAX or 1.5 d50 MAX, whichever is greater.
= 1.7, which corresponds to the gradations recommended in EM 1110-2-1601
(USACE 1991, 1994). Larger gradation uniformity coefficients would result in a
smaller value for CT. In SAM, the default value for TR/TMIN is 1.0. A different
ratio may be prescribed as variable RSEC on the RS record or a variable RT(i) of
the RT record. TR/TMIN ratios usually range between 1.0 and 1.5.
NOTE: THIS DESCRIPTION AND CODING FOR CT REFLECTS 1991
GUIDANCE.
The stability coefficient for incipient failure, CS , has been determined to be
0.030 for angular rock, and 0.0375 for rounded stone. These values have been
for the angular rock. The rounded stone coefficient may be used by specifying a
negative thickness ratio, TR/TMIN , for the variable RSEC on the RS record or for
variable RT(L) on the RT record. The stability coefficient for incipient failure
may also be changed by changing the variable CIFRRS on the RR record and
101
Chapter 6
Input Requirements and Program Output for SAM.hyd
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