Environmental Engineering Reference
In-Depth Information
0.6
37
25
29
Percent fines = 35
15
≤
5
0.5
10
0.4
20
CRR curves for 5, 15, and
35 percent fines, respectively
31
20
0.3
12
50+
17
27
18
50+
80
20
60
11
10
12
10
40
10
20
10
0.2
92
48
26
50
20
10
10
10
20
25
18
80
12
30
22
75
75
60
20
12
13
12
Fines content
≥
5%
27
67
30
50+
Modified Chinese code proposal (clay content = 5%)
No
liquefaction
10
10
13
20
30
0.1
10
Marginal
liquefaction
27
Liquefaction
31
Pan - American data
Japanese data
Chinese data
Adjustment
recommended
by workshop
0
0
10
20
Corrected blow count, (
N
1
)
60
30
40
50
FIGURE 11.35
Liquefaction resistance based on the SPT. (From Seed, H.B. et al.,
Proc. ASCE, J. Geotech. Eng. Div.,
111,
1425-1445, 1985. With permission.)
α
max
is the peak horizontal acceleration at the ground surface, g the acceleration due
to gravity,
where
'
vo
the effective vertical overburden stress on the stratum under consideration, and r
d
a stress
reduction factor (from Liao and Whitman, 1986).
For
z
σ
vo
the total vertical overburden stress on the stratum under consideration,
σ
1.174 - 0.0267
z
Using Equation 11.21 a value for CSR(1) is obtained. The value for (N1)
60
is entered on
the curve representing the percent fines to obtain a value for CSR(2).
The factor of safety against liquefaction
≤
9.15 m,
r
d
1.0 - 0.00765
z
and for 9.15 m
z
23 m,
r
d
CSR(2)/CSR(1). (The important factor of dura-
tion is not considered in the evaluation.)
CSR plotted vs. the corrected CPT tip resistance for
M
7.5 is given in
Figure 11.36.
Because data are limited compared with SPT data, the NCEER Workshop (Youd and Idriss,
1997) recommended that the CPT data be used with at least some correlative data. As the
information obtained with the CPT is more detailed than the SPT it is expected that as more
data become available in the future, the CPT correlations will find increased application.
