Design of embankment dams to withstand earthquakes - Geotechnical Engineering of Dams - page 509

Figure 12.23. Grain-characteristic correction factor K c for determination of clean-sand equivalent CPT

resistance (Youd et al., 2001; reproduced from Robertson and Wride, 1998, reproduced
with permission of ASCE).

where fs CPT sleeve resistance (kPa); vo total vertical stress at test level (kPa)

and q c is as defined above.
(b) Calculate I c from Equation 12.20.

I [(3.47 logQ)

2

(1.22 logF )]

2 0.5

(12.20)

c

(c) If I c 2.6, the soil is classified as clayey, so is unlikely to liquefy. Check this using the

criteria detailed in Section 12.4.2;
(d) If I c

2.6, the soil is likely to be granular, so recalculate c Q , Q, and I c using n 0.5;

If the recalculated I c 2.6, the soil is nonplastic and granular. This I c is used to calcu-

late liquefaction resistance.
If the recalculated I c

2.6, the soil is likely to be silty, possible plastic, so q c1N and
I c should be recalculated using n

0.7, and this value of I c used to calculate liquefac-
tion resistance. Check if the soil is liquefiable as described in Section 12.4.2.

The correction to an equivalent clean sand value (q c1N ) cs is done by:

(q ) K q

(12.21)

c1N cs c c1N

where K c is the correction factor for grain characteristics, is defined by the following
equations (Robertson and Wride, 1998):

for I 1.64 K 1.0

(12.22a)

c c

4 3

2

(12.22b)

for I 1.64 K 0.403 I 5.581 I 21.63 I 33.75 I 17.88

c c c c

2.6, the
curve is shown as a dashed line, indicating that soils in this range of I c are most likely too
clay-rich or plastic to liquefy.
With an appropriate I c and K c , calculate (q cIN ) cs from Equation 12.21 and Figure 12.22
can then be used to calculate CRR 7.5 .

The K c curve defined by Equation 12.22b is plotted in Figure 12.23. For I c