Vibro compaction of granular soils 67
Table 3.6 Corrections to SPT values
Factor
Equipment variable
Term
Correction
Overburden pressure
C N
C N =
′
(
)
a
v0
0.5
p /σ
C N ≤ 2
Energy ratio
Donut hammer
C E
0.5–1.0
Safety hammer
0.7–1.2
Automatic-trip donut
type hammer
0.8–1.3
Borehole diameter (mm)
65–115
C B
1.0
150
1.05
200
1.15
Rod length (m)
3–4
C R
0.75
4–6
0.85
6–10
0.95
10–30
1.0
>30
>1
Sampling method
Standard sampler
C S
1.0
Sampler without liners
1.1–1.3
Source: NCEER, in Youd, T.L. and Idriss, I.M. (eds), Proceedings of the NCEER Workshop on Evaluation of
Liquefaction Resistance. Technical Report NCEER-97-0022, 1997.
100
150
2 00
250
50
0
0.3
0.2
0.1
0.5
0.4
0.6
0
Corrected CPT tip resistance q c,1N
No liquefaction
0.25 < D50 < 2 (mm)
fines content < 5%
Cyclic stress ratio (CSR)
300
M = 7.5
CRR-curve
Liquefaction
Figure 3.23 Curve for calculation of CRR from CPT data. (Redrawn from NCEER,
in Youd, T.L. and Idriss, I.M. (eds.), Proceedings of the NCEER Workshop on
Evaluation of Liquefaction Resistance, Technical Report NCEER-97-0022, 1997.)