Geoscience Reference
In-Depth Information
Figure 4.1
Standard penetration test.
Table 4.6
Standard penetration test in soils.
Symbol
Test
7, 11, 12 (eg)
Example of blows per 150 mm penetration.
N
23 (eg)
Penetration resistance (blows for 300 mm penetration following 150 mm
=
or N
SPT
seating drive, example of 11
+
12
=
23
=
N
SPT
(actual field value with
no correction factors).
N
>
60
Total hammer blows exceed 60.
7, 11, 25/20 mm (eg)
Partial penetration, example of blows for the measured penetration
(examine sample as either change in material here or fall in at top
of test).
N
Corrected N - value for silty sands below the water table.
N*
Inferred SPT value.
RW
Rod weight only causing penetration (N
I).
<
HW
Hammer and rod weight only causing full penetration (N
I).
<
HB
Hammer bouncing (typically N*
>
50).
(N
o
)
60
Penetration resistance normalized to an effective overburden of 100 kPa,
and an energy of 60% of theoretical free fall energy. (N
o
)
60
=
C
N
C
ER
N
SPT
.
C
N
C
ER
Correction factor for overburden (C
N
)
and energy ratio (C
ER
)
.
•
<
Typically (N
o
)
60
60 for soils. Above this value, the material is likely cemented
sand, coarse gravels, cobbles, boulders or rock. However these materials may still
be present for N - values less than 60.
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