Environmental Engineering Reference
In-Depth Information
To avoid bias in the analysis from short duration, high frequency acceleration estimated
from near-field small magnitude earthquakes, the peak horizontal acceleration should be
based on the influence of earthquakes Magnitude 5 or greater.
12.4.3.4
Evaluation of Cyclic Resistance Ratio from the Standard PenetrationTests
The CRR for M7.5 earthquakes can be estimated from the curves in Figure 12.19. It is rec-
ommended that the SPT Clean Sand Base Curve be used, with correction for fines content
as detailed below.
In this figure, (N
1
)
60
is the SPT blow count normalised to an effective overburden pres-
sure of 100 kPa, a hammer energy of 60%, borehole diameter, rod length and sampling
method. (N
1
)
60
is given by:
(N )
N C CCCC
(12.12)
160
m
N EBRS
where N
m
measured standard penetration resistance; C
N
factor to normalize N
m
to
a common reference effective overburden stress; C
E
correction for hammer energy ratio
Figure 12.19.
SPT Clean-sand base Cyclic Resistance Ratio curve for magnitude 7.5 earthquakes with
data from liquefaction case histories (Youd et al., 2001; modified from Seed et al., 1985b,
reproduced with permission of ASCE).
