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Table 1:
Factors affecting cyclic mobility or soil liquefaction characteristics
and penetration resistance (After Seed, 1979)
Factor
Effect on stress ratio
required to cause cyclic
mobility or liquefaction
Effect on penetration
resistance
Increased relative density
Increases stress ratio for
cyclic mobility or
liquefaction
Increases penetration
resistance
Increased stability of
structure
Increases stress ratio for
cyclic mobility or
liquefaction
Increases penetration
resistance
Increase in time under
pressure
Increases stress ratio for
cyclic mobility or
liquefaction
Probably increases
penetration resistance
Increase in K
0
Increases stress ratio for
cyclic mobility or
liquefaction
Increases penetration
resistance
Prior seismic strains
Increases stress ratio for
cyclic mobility or
liquefaction
Probably increases
penetration resistance
Table 2:
Recommended SPT procedure for use in liquefaction
correlations (Seed et al., 1984)
Borehole
4 to 5inch diameter rotary borehole with bentonite
drilling mud for borehole stability
Drill Bit
Upward deflection of drilling mud (tricone of
baffled drag bit)
Sampler
Outer Diameter = 2.00 inches
Inner Diameter = 1.38 inches – Constant (i.e. no
room for liners in barrel)
Drill Rods
A or AW for depths less than 50 feet
N or NW for greater depths
Energy Delivered to
Sampler
2520 in.lbs. (60 % of theoretical maximum)
Blowcount Rate
30 to 40 blows per minute
Penetration Resistance
Count
Measures over range of 68 inches of penetration
into the ground
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View Full DocumentTable 3:
Summary of the correction factors for SPT measurements
(After 1997 NCEER Workshop)
Factor
Term
Equipment Variable
Correction
Overburden Pressure
C
N

(P
a
/
σ′
v
)
0.5
C
N
≤
2
Energy Ratio
C
E
Safety Hammer
Donut Hammer
0.601.17
0.451.00
Borehole Diameter
C
B
65115 mm
150 mm
200 mm
1.00
1.05
1.15
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 Fall '06
 Cetin

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