68 Ground improvement by deep vibratory methods
In Figure 3.24, a soil behavior type chart is shown as developed by
Robertson (1990) identifying different soil types as a function of their cone
resistance and their friction ratio. The CPT friction ratio (sleeve resistance
f s divided by cone tip resistance q c ) increases with increasing fines content
and plasticity of the soil. The boundaries between the different soil types
of the graph can be approximated by concentric circles of the radius I c ,
referred to as the soil behavior type index:
I
Q
F
c
2
2
(
log ) (1.22 log )
=
−
+
+
3 47
.
(3.11)
with Q and F representing the normalized cone resistance and the normalized friction ratio as follows:
Q
q
p
p
n
=
−
′
⋅
(
)
c
v
a
a
v
σ
σ
0
0
(3.12)
1
100
1000
φ′
I n c r e a s i n g
O
C R
a n d
a g e
I
n
c
r
e
a
s
i
n
g
I
C
I n c r e a s i n g
s e n s i t i v i t y
I n c r e a s i n g
O C R , a g e , a n d
c e m e n t a t i o n
N o r m a l l y c o n s o l i d a t e d
Normalized cone resistance Q
10
1
0.1
10
1
2
3
9
8
6
7
5
4
I C
= 2 .6
Normalized friction ratio F =
⋅ 100%
f S
q c − σ vo
Figure 3.24 CPT-based soil behavior type chart after Robertson 1990. 1 = sensitive,
fine-grained, 2 = organic soils—peat, 3 = clays—silty clay to clay, 4 = silt
mixtures—clayey silt to silty clay, 5 = sand mixtures—silty sand to sandy silt,
6 = sands—clean sand to silty sand, 7 = gravelly sand to dense sand, 8 = very
stiff sand to clayey sand*, 9 = very stiff, fine-grained* (*heavily overconsolidated or cemented). (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.)
In Figure 3.24, a soil behavior type chart is shown as developed by
Robertson (1990) identifying different soil types as a function of their cone
resistance and their friction ratio. The CPT friction ratio (sleeve resistance
f s divided by cone tip resistance q c ) increases with increasing fines content
and plasticity of the soil. The boundaries between the different soil types
of the graph can be approximated by concentric circles of the radius I c ,
referred to as the soil behavior type index:
I
Q
F
c
2
2
(
log ) (1.22 log )
=
−
+
+
3 47
.
(3.11)
with Q and F representing the normalized cone resistance and the normalized friction ratio as follows:
Q
q
p
p
n
=
−
′
⋅
(
)
c
v
a
a
v
σ
σ
0
0
(3.12)
1
100
1000
φ′
I n c r e a s i n g
O
C R
a n d
a g e
I
n
c
r
e
a
s
i
n
g
I
C
I n c r e a s i n g
s e n s i t i v i t y
I n c r e a s i n g
O C R , a g e , a n d
c e m e n t a t i o n
N o r m a l l y c o n s o l i d a t e d
Normalized cone resistance Q
10
1
0.1
10
1
2
3
9
8
6
7
5
4
I C
= 2 .6
Normalized friction ratio F =
⋅ 100%
f S
q c − σ vo
Figure 3.24 CPT-based soil behavior type chart after Robertson 1990. 1 = sensitive,
fine-grained, 2 = organic soils—peat, 3 = clays—silty clay to clay, 4 = silt
mixtures—clayey silt to silty clay, 5 = sand mixtures—silty sand to sandy silt,
6 = sands—clean sand to silty sand, 7 = gravelly sand to dense sand, 8 = very
stiff sand to clayey sand*, 9 = very stiff, fine-grained* (*heavily overconsolidated or cemented). (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.)