USE OF CPT/CPTU FOR SULUTION OF

PRACTICAL PROBLEMS

CPT/SPT CORRELATIONS

DIRECT APPLICATIONS OF CPT/CPTU

RESULTS

Depends on several factors:

Indirect design method:

Interprete CPT/CPTU results to arrive at soil
design parameters
Classical foundation analysis
Direct design method:
Use CPT/CPTU results directly without
intermediate step of soil parameters

CPT/SPT CORRELATIONS

Correlations to SPT (standard penetration tests)

Axial capacity of piles
Bearing capacity and settlement of shallow
foundations
Ground improvement - quality control
Liquefaction potential evaluation

CPT/SPT CORRELATIONS

Energy level delivered to SPT - use N60

Grain size distribution (D50)
Fines content (FC)
Overburden stress + other factors

Comment:
Single most important factor influencing N value is energy
delivered to SPT sampler, expressed as rod energy ratio.
Energy ratio of 60% is generally accepted to represent
average SPT energy. Results should be corrected to N60.

CPT/SPT CORRELATIONS
Effects of fines content

Depends on several factors:

Energy level delivered to SPT - use N60

Grain size distribution (D50)
Fines content (FC)
Overburden stress + other factors

Correlations most used:

Robertson et al. 1983
Kulhawy and Mayne, 1990

Robertson and Campanella (1983)

Mayne and Kulhavy (1990)

Pa = reference stress = 1 atm = 100 kPa

If no grain size data available- use Soil

behaviour classification chart

6
4
OC
R

St

10

6
5

4
1

e
St

2
0.1
-0.2

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0.1
0

Pore press ure parame ter, Bq

Soil Be ha viour Type :

Se nsitive fine grained
Organic mate ria l
Cla y
Silty clay to cla y

5.
6.
7.
8.

Cla yey silt to silty clay

Sa ndy silt to claye y silt
Silty sa nd to sa ndy silt
Sa nd to silty sa nd

9.
10.
11.
12.

100

Zone refers to Soil

Behaviour type diagram

Sa nd
Gra velly sand to sand
Very stiff fine grained*
Sa nd to clayey sa nd*

10

qt

uo

u2
u -u
Bq = q 2- o

vo

5
4
1

OC
R

St

0.1
-0.2

* Overconsolidated or cemented.

0.2

0.4

100
6

Qt

10
5

12

0.8

1.0

1.2

Sensitive fine graine d

Orga nic ma terial
Clay
Silty clay to cla y

5.
6.
7.
8.

qt
u

Qt

10

Increasing
OCR , age

3
1

1
2

2
1

10

-0.4

0.4

0.8

1.2

10

6
5

4
1

e
St

1
0.1
0

Zone
1.
2.
3.

Friction ratio (%)

Soil Be ha viour Type:

1.
2.
3.
4.

vo

Increasing
sensitivity

0.1

P ore pre ssure pa ra me ter, Bq

Zone :

7 uo
100

11

2
1.4

8
9

1
0.6

Increasing
OCR, age
cementation

1
10

vo
9

Soil Behaviour Chart

(Robertson et al, 1986)

100
10

9,
10,
11
or 12

Dr.

Zone :

Friction ra tio (%)

1000
7

d
ate
olid
ns
co

5
1

1000

O
CR

u -u
Bq= q 2- o
t vo

Cone resistance, q t (MPa)

u2

11

OC
R

10

Cone res istance, qt (MPa)

uo
7

12
9

Normalized soil behaviour classification chart

(q c/pa)/N 60
2
1
1
1.5
2
2.5
3
4
5
6
1
2

y
all
rm
No

qt

Soil behavior type

Sensitive fine grained
Organic material
clay
Silty clay to clay
clayey silt to silty clay
Sandy silt to clayey silt
Silty sand to sandy silt
Sand to silty sand
sand
Gravely sand to sand
Very stiff fine grained
Sand to clayey sand

Cone resistance, qt (MPa)

10

vo
8

1.
2.
3.
4.

Zone
1
2
3
4
5
6
7
8
9
10
11
12

100
10

9,
10,
11
or 12

Dr.

Cone re sis tance, q t (MPa)

100

SOIL CLASSIFICATIONS AND RATIOS

Claye y silt to silty clay

Sa ndy silt to c laye y silt
Silty sa nd to s andy silt
Sa nd to silty s and

9.
10.
11.
12.

Soil behaviour type

Sensitive, fine grained
Organic soils-peats
Clays-clay to silty clay

Zone Soil behaviour type

4. Silt mixtures clayey silt to silty clay
5. Sand mixtures; silty sand to sand silty
6. Sands; clean sands to silty sands

Zone
7.
8.
9.

Soil behaviour type

Gravelly sand to sand
Very stiff sand to clayey sand
Very stiff fine grained

Sand
Gra velly sa nd to sa nd
Very stiff fine grained*
Sand to cla yey sand*

* Overconsol idated or cemented.

Robertson et al.,1986

CPT/SPT CORRELATIONS
In lack of soil grain size data, use Robertson (1990) soil
classification chart to define soil behaviour type index:

I c = (3.47 logQt ) + (log Fr +1.22)

Qt =

qt

v0

v0

'

, Fr =

fs
v0

'

Soil behaviour type

Index Ic
Ic < 1.31
1.31 < Ic < 1.205
2.05 < Ic < 2.60
2.60 < Ic < 2.95
2.95 < Ic < 3.60
Ic < 3.06
100 0
7

Incr ea sing
OCR, age
ce mentat ion

Gravilly sand
Sands clean sand to silty sand
Sand mixturees silty sands to sandy silts
Silt mixtures clayey silts to silty clay
Clays
Organic soils - peat

7 uo
9

Westport
Warehose
facility outside
Kuala Lumpur

Soil
investigation
by Soils and
Foundations
Sdn.Bhd

qt
u

d
ate
lid
nso

Qt

10

Incr ea sing
OCR, age

3
1

Incre as ing
se nsi tivity

1
0 .1

vo

100

co

10

pa = atm. Press. = 100 kPa

N60: SPT value corresponding to energy ratio of 60%

Soil behaviour type

7
6
5
4
3
2
100 0

10 0

Qt

Zone

ly

p a ) N 60 = 8 . 5 (1 I c 4 . 6 )

Example CPT/SPT Correlations

BOUNDARIES OF SOIL BEHAVIOUR

TYPE

mal
Nor

(q c

2 0.5

Robertson,1990

Soil Behav iour Chart

(Roberts on et al, 1986)

1
2

2
1

Zo ne Soi l behavi our type

1 . Sensitive, fi ne grai ned
2 . Organic soil s-peats
3 . Cla ys-cl ay to silty cl ay

10

-0.4

Zon e Soil be havio ur type

4. Si lt mixtures claye y sil t to si lty cla y
5. Sa nd mixtures; sil ty sand to sa nd silty
6. Sa nds; cl ean sands to silty san ds

0.4

0.8

1.2

Zon e Soil be havio ur type

7 . G ravel ly sa nd to san d
8 . Very sti ff san d to cla yey san d
9 . Very sti ff fine graine d

Ic = (3.47logQt ) +(logFr +1.22)

2

2 0.5

A lot of old
investigations with
SPT

CPT/SPT correlations

PILE BEARING CAPACITY

Qult = fpAs + qpAp (side friction plus tip resistance)

If grain size distribution data are

available
Use (qc/pa)/N60 from Robertson et al.,1983 (Fig.6.1)(D50)
and/or (qc/pa)/N from Fig. 6.3 ( Fines content)

If grain size distribution data are not

available

Several studies
Robertson et al., 1988; 8 cases
Briaud, 1988; 78 pile load tests
Tand and Funegrd, 1989; 13 cases
Sharp et al.,1988; 28 cases
NGI, 1998

Use soil behaviour index , IC ( = f(Qt,Fr )

(qc/pa)/N60 =8.5(1 - IC/4.6)

All show CPT methods better than other

methods

BEARING CAPACITY FACTORS, kc

(BUSTAMANTE AND GIANESELLI, 1982)
Nature of soil
Soft clay and mud
Moderately compact clay
Silt and loose sand
Compact to stiff clay and
compact silt
Soft chalc
Moderately compact sand and
gravel
Weathered to fragmented
chalk
Compact to very compact sand
and gravel

qc
(Mpa)
<1
1 to 5
5
>5

Factors kc
Group
Group
I
II
0.4
0.5
0.35
0.45
0.4
0.5
0.45
0.55

5
5 to 12

0.2
0.4

0.3
0.5

>5

0.2

0.4

> 12

0.3

0.4

AXIAL PILE CAPACITY

Computation of qc for tip resistance

Bustamante and Gianeselli (1982)

fp = qc/
qp = kc qca
and kc empirical constants for different pile and soil types
Based on a very large number of case histories (197) in France
tables have been made with and kc factors according to soil
type and to type of pile

FRICTION COEFFICIENT,
(BUSTAMANTE AND GIANESELLI, 1982)

qp = kc qca

Group I: plain bored piles; mud bored piles; micro piles (grouted under
low pressure); cased bored piles; hollow auger bored piles; piers;
barrettes.
Group II: cast screwed piles; driven precast piles; prestressed tubular
piles; driven cast piles; jacked metal piles; micropiles (small
diameter piles grouted under high pressure with diameter < 250
med mer); driven grouted piles (low pressure grouting); driven
metal piles; driven rammed piles; jacket concrete piles; high
pressure grouted piles of large diameter.

Pile end bearing

is dependant on
soil above and
below pile tip.
Need to evaluate
average qc to
represent this
influence area.

Nature of soil

qc (Mpa)

Soft clay and mud

Moderately compact clay
Silt and loose sand
Compact to stiff clay and compact clay
Soft chalk
Moderately compact sand and gravel
Weathered to fragmented chalk
Compact to very compact sand and gravel

<1
1 to 5
5
>5
5
5 to 12
>5
< 12

fp = qc/
Bustamante and Gianesseli(1982)

I
A
30
40
60
60
100
100
60
150

Category
Coefficients,
II
B
A
90
90
80
40
150
60
120
60
120
100
200
100
80
60
300
150

B
30
80
120
120
120
200
80
200

FRICTION COEFFICIENT,

FRICTION COEFFICIENT,

(BUSTAMANTE AND GIANESCELLI, 1982) Ctd.

(BUSTAMANTE AND GIANESELLI, 1982) Ctd.

Nature of soil
Soft clay and mud
Moderately compact
clay
Silt and loose sand
Compact to stiff clay
and compact clay
Soft chalk
Moderately compact
sand and gravel

qc (Mpa)
<1
1 to 5
5
>5
5
5 to 12

I
A
0.015
0.035
(0.08)
0.035
0.035
(0.08)
0.035
0.08
(0.12)

Category
Maximum limit of fp (Mpa)
II
III
B
A
B
A
B
0.015 0.015 0.015 0.035
0.35
0.035 0.035 0.08 0.12
(0.08) (0.08)
0.035 0.035 0.035 0.08
0.035 0.035 0.035 0.08 0.20
(0.08) (0.08)
0.035 0.035 0.035 0.08
0.035 0.035 0.08 0.12 0.20
(0.08) (0.12)

Weathered to fragment
chalk
Compact to very compact
sand and gravel

>5
> 12

I
A
0.12
(0.15)
0.12
(0.15)

Category
Maximum limit of fp (Mpa)
II
III
B
A
B
A
0.08
0.12
0.12 0.15
(0.12) (0.15)
0.08
0.12
0.12 0.15
(0.12) (0.15)

Pile Capacity from CPT

B
0.20

Example from
Westport, Kuala
Lumpur

0.20

Cone resistance
in sand for pile
bearing capacity
calculation

Pile bearing capacity from

CPTU data

Pile Capacity from CPTU

Pile tip
resistance in
sand by CPT
method

qc (Mpa)

Category: IA: plain bored piles; hollow auger bored piles; micropiles
(grouted under low pressure); cast screwed piles; piers; barrettes.
IB: cased bored piles; driven cast piles. IIA: driven precast piles;
prestressed tubular piles; jacket concrete piles. IIB: driven metal
piles; jacked metal piles. IIIA: driven grouted piles; driven rammed
piles. IIIB: high pressure grouted piles of large diameter > 250 mm;
micropiles (grouted under high pressure).
Note: Maximum limit unit skin friction, fp: bracket values apply careful
execution and minimum disturbance of soil due to construction.

fp = qc/

Example from
Westport Kuala
Lumpur

Nature of soil

It is recommended to use several

methods and to adopt the lowest value
for evaluation of pile bearing capacity

Bustamante and Gianeselly(1982) ( French method)

de Ruiter and Beeringen (1979) (European method)
Imperial College Method (1996)( mainly sand)
Almeida et al (1996) (clay only--- uses q t)

If local experience exist, may use only method that

has shown to give the best prediction

Ground improvement quality control

Purpose of deep compaction is often to fulfill one
of the following:
Increase bearing capacity ( i.e. shear strength)
Reduce settlements ( i.e.increase modulus)

Increase resistance to liquefaction (i.e. density)

Cone resistance in cohesionless soils is governed by

factors including soil density, in situ stresses, stress
history and soil compressiblity
Changes in cone resistance can therefore be used to
document effectiveness of compaction

Deep compaction

Suitability of soil for vibrocompaction

vibrocompaction
vibro-replacement
dynamic compaction
compaction piles
deep blasting

Compaction
control
Range of cone
penetration test
values before and
after compaction
and surface
compaction with
vibrating plate

CPT is found to be best method to monitor and document effect

of deep compaction
Important to consider time effect
Massarsch(1994)

Compaction by blasting

Compaction control

Lindberg and Massarsch(1991)

Influence of time on penetration

resistance after dynamic compaction

Effect of time

Example of
comparative
before and after
CPT logs with a
near-surface
clay layer
From Mitchell and Solymar(1984)

From Woeller et al. (1995)

The aging effects

of sands

Days after dynamic compaction

10 m silty sand (Schmertmann, 1991)
6 drops

Effect of vibrocompaction at
Chek Lap Kok airport in
Hong Kong.

4 drops

2 drops

Ground improvement quality control

For large projects:
Develop experience with increase in cone
resistance with time after compaction took place.
Use this experience to make criteria for
acceptance or rejection based on CPT/CPTUs
carried out just after compaction took place

Where resistance to liquefaction is major issue,

measurement of shear wave velocity will provide
additional data

CPTU data can be used to evaluate if compaction will be

efficient or not ( ref. soil behaviour chart)

Time in days
From Ng, Berner and Covil (1996)

Liquefaction resistance
Major concern for structures constructed
with or on sand and sandy silt.
Cyclic loads from : earthquakes, wave
loading, machine foundations and other
To evaluate potential for soil liquefaction
important to determine soil stratigraphy and
in situ soil state

CPT/CPTU ideal because of its repeatablity,

reliability, continuous data and cost effectiveness

Diagram developed for correcting cone resistance measured just

after compaction large project in Florida

Evaluation of liquefaction potential

CPT/CPTU provide valuable data
detect even thin sand layers that could liquefy
pore pressure data tells us about groundwater
conditions and additional information to estimate
grain size and fines content ( together w/sleeve
friction)
cone resistance gives input to in situ state of
sandy soils

SCPTU can give valuable additional data

soil type
state of soil in situ

Liquefaction control from CPT/CPTU

Different approaches :
1. a) Estimate Dr from
qc, vo,Dr relationship
b) Perform cyclic triaxial
and/or direct simple
shear tests in laboratory
on samples reconstituted
to estimated Dr and relevant
cyclic stress level ( cy / vo)
2. Estimate directly from CPT/CPTU results using
empirical methods developed in North America and
Japan

Liquefaction potential directly

from CPT/CPTU results

Liquefaction potential directly

from CPT/CPTU results

1. Correct qc for overburden stress effect

Qc = C*qc
2. Estimate average cyclic stress ratio
(due to wave loading or earthquake or
other source) cy/ vo
3. Establish D50 by grain size analysis on
obtained sample -or estimate from
CPT/CPTU results using soil classification
charts

Correction factor for

cone resistance to
predict liquefaction
potential of sand
(from Shibata and
Teparaksa, 1988)

Liquefaction potential directly

from CPT/CPTU results

Liquefaction
potential from
cone resistance
(after Shibata and
Teparaksa, 1988)

4. Check liquefaction by cy / vo, Qc , D50

diagram

Liquefaction potential directly

from CPT/CPTU results

Comparison of qc
with estimated (qc)cr
value in 1983
Nihonkaichuba
earthquake (from
Shibata and
Teparaksa, 1988)

Vibratory cone for liquefaction

evaluation

Evalaution of
liquefaction
potential in
Japanese
soil

Effect of compaction on fs

PERCEIVED APPLICABILITY OF THE

CPT/CPTU FOR VARIOUS DIRECT DESIGN
PROBLEMS
Pile design
Sand
Clay
Intermediate
soils

1-2
1-2
1-2

Bearing
capacity
1-2
1-2
2-3

Settlement
2-3
3-4
3-4

Compaction
control
1-2
3-4
2-3

Reserve overheads

Liquefaction

Massarsch and Fellenius (2002) present a method for estimating the change in K0 of a hydraulic
fill before and after compaction. This simple method uses the sleeve friction measured during
CPTUs and estimates of the respective internal friction angles with the following formula:

1-2

K01 / K00

(fs1 tan 0) / (f s0 tan 1)

K00
K01
0
1
fs0
fs1

=
=
=
=
=
=

coefficient of earth pressure at rest before compaction

coefficient of earth pressure at rest after compaction
internal angle of friction before compaction
internal angle of friction after compaction
sleeve friction on cone before compaction
sleeve friction on cone after compaction

Eq. 4.1

Where

Reliability rating:
1=High
2=High to moderate
3=Moderate
4=Moderate to low
5=Low

Figure 4.4 Cone resistance and sleeve friction before

and after compaction

Figure 4.5 K0 before and after compaction using friction

angles of 30 and 36 degrees respectively

C one Resistance qc, kPa

0

2000

4000

6000

8000

10000

12000

0.0

1.0
0.4

2.0

Coefficient of Earth Pressure K0

0. 5
0.6
0.7
0.8

0.0

1.0

3.0
m
,
e
c
a
rfu
s
w
o
le
b
h
tp
e
D

2.0

4.0
3.0
m
, 4.0
e
c
a
rfu
s
w 5.0
o
le
b
h
tp
e 6.0
D

5.0

6.0

7.0
7.0

8.0

8.0

9.0

9.0

10.0

10.0
0

10

20
30
40
sleeve friction fs, kPa

qc0
qc1
fs0
fs1

50

60

K 00
K 01

0.9

Summary of Imperial College

Method in Sands

Compaction by blasting

Pile Design method

(after de Ruiter European CPT and Beringen, 1979)
Clay :

Shaft Capacity : Qs = D fdz

Local shear : f = rf tan f
rf = rc + rd
Local radial effective stress = f( qc, vo, h/r)
Dilatant increase in local radial effective stress
during pile loading : rd = f (qc , vo)

Effect of time

Unit skin friction,fp, minimum of:

-fp = *su
.where = 1 for NC clays ; 0.5 for OC clays

Unit tip resistance, qp, minimum of :

-qp = Nc*su where Nc = 9 and su = qc/N
Nk = 15 -20

D2/4

Base capacity : Qb = qb
Pile base resistance qb = f(qc, D/DCPT)
D = pile diameter ; DCPT = 0.036 m

Computation of qc for pile tip

resistance : European method

From Mitchell and Solymar(1984)

Pile Design method

(after de Ruiter European CPT and Beringen, 1979)

AXIAL PILE CAPACITY IN CLAY

CPTU METHOD

SAND:
Unit skin friction,fp, minimum of :
-f1 = 0.12 Mpa

Qu = Qs + Q p = f p As + q p Ap

-f2 = CPT sleeve friction, fs

-f3 = qc/300 ( compression piles)
-f4 = qc/400 (tension piles)

fp =

f
N
qt v 0 qnet
, k1 = k t ; = p
=
su

k1
k1

qp =

qnet
N
, k 2 = kt ; N c = 9
k 2
Nc

Unit end bearing,qp, minimum of :

-qp from fig. 6.6

De Ruiter and Beeringen(1979)

(From Almeida et al. 1996)

CPTU method pile capacity

Limited values of pile tip resistance

CPT/SPT CORRELATIONS

fp= qnet / K1
qnet = qt - vo

De Ruiter and Beeringen (1979)

From Almeida et al.(1996)

Bearing capacity of shallow

foundations on sand

Mayne and Kulhavy (1990)

Bearing ratio/Footing width

(from Tan et al., 1995)

Bearing capacity shallow footing on

sand

Meyerhof (1956) : qult = qc,av (B/C)(1+D/B)

B = footing width (ft); D = Embedment depth (ft)
qc,av = average over depth = B

Tand et al.(1995) : qult = Rk*qc +v0

Rk = 0.1 - 0.2 ( see chart)

Eslamizaad and Robertson(1996) : qult = K*qc,av

(see chart)
Eslaamizad and Robertson(1996)

Settlement of shallow
foundations on sand

Settlements of footings on sand,

approximate range

Settlements of shallow
foundations on sand
Schmertmann (1970,1978)

Meyerhof (1974) : settlement = p*B/2 qc

s = C1*C2*p*(Iz/Es) z

p = net foundation stress

B = width of footing

C1 = correction for depth of embedment

Burland et al (1977) : settlement = f(B, p )

C2 = creep ( time) correction

p = net extra foundation stress

see chart

Iz = strain influence factor

Schmertmann(1970,1978)

Es = Equivalent Youngs modulus = *qc

E = *qc (Youngs modulus)

= 2.5 square footing ; = 3.5 long footing

Use of strain influnece chart

Burland et al.(1977)

Strain influence method for footings

on sand

Schmertmann(1970)

Strain influence method for

footings on sand ( Schmertmann,1970)

z = thickness of sublayer