Environmental Engineering Reference
In-Depth Information
Table 6.3.
Skempton (1986) method for estimating relative
density (D
R
) from (N
1
)
60
value.
Relative Density (%)
Condition
(N
1
)
60
0
0
Very loose
15
3
Loose
35
8
Medium dense
65
25
Dense
85
42
Very dense
100
58
where C
N
factor to correct N
60
to 100 kPa effective overburden stress
200
100
for fine, normally consolidateddsand
(6.25)
′
vo
300
200
(6.26)
for coarse, normally consolida
ted sand
′
vo
170
(6.27)
for overconsolidated sand
70
′
vo
effective overburden stress at the level of the SPT test (in kN/m
2
)
Skempton (1986) then uses the (N
1
)
60
value to estimate relative density from Table 6.3.
For D
R
where
vo
35%, this can be approximated by
(N )
/D
2
60
(6.28)
160
R
This method applies to naturally occurring sands, of other than very recent deposition.
Skempton (1986) also considers the effect of the age of the deposit on the SPT values.
Discussing this, Jamiolkowski et al. (1988) produced
Figure 6.34
which indicates that
(N
1
)
60
/D
2
is dependent on the age of the deposit and will be less for recently deposited soil
than for the more common aged soil.
This also means that for recently dredged fills, or deposits of mine tailings, a (N
1
)
60
value of say 10, will imply a relative density of
50%, compared to 40% for an aged nat-
ural deposit.
6.1.9.1.2 Cone Penetration (CPT) and Piezocone (CPTU) Tests
The effective friction angle
can be determined directly from the CPT and CPTU using
charts which have been developed by several authors e.g. Robertson and Campanella
(1983a,b), Marchetti (1985, Kulhawy and Mayne (1988), Jamiolkowski et al. (1985),and
Olsen and Fan (1986). Lunne et al. (1997) reviewed the methods and concluded that the
