INTRODUCTION TO CPT

 Course content
 What is CPT and what is CPTU
 Typical test results
 Equipment for deployment
 Data processing
 Measured and derived parameters
 Available standards and guidelines
 Need for quality control CPT course Kaula Lumpur 9 April 2019
 PROGRAMME CPT course
8:30am - 8:50am Registration
outline
8:50am - 9:00am Opening Address

9:00am - 9:40am Session 1: Introduction, CPT data processing, corrections and accuracy, available Standards and
data quality by Tom Lunne

9:40am - 10:20am Session 2: CPT interpretations on soil layering, soil identification with examples by Dr. John Powell

10:20am - 10:30am Q & A Session

10:30am - 11:00am Coffee/Tea Break

11:00am - 11:45am Session 3: CPT interpretations on clay by Dr. John Powell

11:45am - 12:30pm Session 4: CPT interpretations on sands and other soils by Tom Lunne

12:30pm - 12:45pm Q & A Session

12:45pm - 2:00pm Lunch

2:00pm - 3:00pm Session 5: Case Study from onshore applications by Ir. Liew Shaw Shong

3:00pm - 3:40pm Session 6: Case study from offshore applications by Joehan Rohani
fs
3.40pm - 4:00pm Coffee/Tea Break

4.00pm - 4.35pm Session 7: Direct application of CPT for design and practical examples by Tom Lunne u2
4.35pm - 5.10pm Session 8: Other add-on sensors by Dr. John Powell
60o
5.10pm - 5.30pm Session 9: Demonstration of equipment by William Bond qc
5.30pm - 6.00pm Q & A Session

6.00pm Closure
 Principle of testing with CPT

A cone penetration test

(CPT) is a 36 mm diameter
instrumented steel probe
that is pushed into the soil
while measuring resistance
as function of depth

36 mm diameter
probe (10 cm2)
TERMINOLOGY FOR CPTU AND WHAT DO WE MEASURE

U means we also
measure pore
pressure

Pore pressure filter,

standard position

In addition frequently measure inclination, i

 Range of cone penetrometers available

qt (MPa) fs (kPa) u2 (kPa) DEM, e

0 10 20 0 300 600 -100 200 500 0.5 1
0 0 0 0

5 5 5 5 DEM

10 10 10 10
Depth BGS (m)

15 15 15 15

20 20 20 20
fs
25 25 25 25
u2
30 30 30 30
60o
35 35 35 35 qc

Typical CPTU result

Example CPTU profile
Cone resistance, Sleeve friction, Pore pressure,
qc, MPa fs, kPa u2, kPa

CPTU is the best geotechncial

profiling tool available today:
 Continuous measurements
 Three parameters
supplementing each other
 Cost efficient performance
 A large number of correlations
to soil parameters reported in
geotechnical literature
Now we have very effient CPT rigs tailor made for
many different purposes

Special rig for

Australian conditions Geomil standard
truck Remotely operated rig for
Pagani light large water depths
weight rig
CPT Operation in Bangladesh 2016
CPT/CPTU on land

Improvised testing in Armenia 2016 by

UK company In Situ
Pagani small trackmounted CPT rig

Increased reaction force by earth screws

Example CPT equipment used in Malaysia
For transport over longer distances
Rig types – more examples
Geomil GEORIG 504 rig can be
equipped for most geotechnical
investigation methods such as
soil rock drilling, swedish weight
sounding, dynamic
sounding/SPT, CPT and more.

Track mounted rig

In situ testing in nearshore/offshore geotechnical investigations

Deployment platforms
Jack up rigs
Barges
Survey ships
Special soil drilling vessels
Operation nearshore from jack up platform

Rig is firmly founded on sea

bottom; ie no movement of
working platform. CPTs can
be carried out thorugh a
casing fixed on seafloor
using on land equipment
Lightweight jackup rig used by Australian
company IGS
In situ testing in offshore geotechnical investigations
from floating vessels

Basically two modes of operation:

• Seafloor mode
• Down-hole mode
 Seafloor mode
Roller wheel principle

qc Truly continuous test

sand
fs u • Increased quality
clay
• Increased efficiency

sand

clay
Now most common
sand
 Fugro’s wheeldrive CPT system

Heavy duty rig 20 t,

profiling to 45-50 m
penetration possible

Special soil
investigation vessel

From brochure
ROSON 100 seafloor rig manufactured by
APvandenBerg, Netherlands

Roller wheels
Geomil Manta system

Belt system – less wear on

the rods

Roller wheels
Example of light mini-rig with coiled rod for use in deep
waters

Neptun 2 rated for 15 m

penetration, can use 10 cm2 or 5 Courtesy of Gardline
cm2 cone Geosciences
 Seafloor mode

Down – hole
mode

Sampling
CPT
Drillin
Drilling
sand sand
stroke
g
clay clay
CPT strokes typically 3
m
sand sand

q
clay c clay

sand fs u sand
Down-hole in situ testing

Principle with drilling unit on ship,

usually:

Operation with umbilical, hydraulic cylinder

pushes tool below bottom of borehole. Data
aquisition through cable and real time display
of test results. Depth limitation about 700 m.

From Fugro brochure

In situ testing in offshore geotechnical investigations

Orca-125 down
hole system
For deep water investigations use remote operated rig

Benthic,
Australia
CPT/CPTU MEASUREMENT
SYSTEMS
 Depth measurement
 Cone resistance/sleeve friction strain gauge
load cells
 Pore pressure - pressure sensors
 Data acquisition
EXAMPLE OF DEPTH REGISTRATION SYSTEM
EXAMPLE OF DEPTH REGISTRATION SYSTEM

Courtesy of APvandenBerg
DESIGN OF CONE PENETROMETERS.
SUBTRACTION TYPE CONE
PENETROMETER.

Measure:
qc – cone resistance
fs + qc – cone resistance + sleeve friction
DESIGN OF CONE PENETROMETERS.
Separate load cells for cone resistance and sleeve friction
 Measurement of
Friction sleeve pore pressure

Strain
gauges

Importance of good
Pressure transducer
saturation – ref later in
presentation

Porous filter u2 position

CPT/CPTU MEASUREMENT SYSTEMS
Depth measurement
Cone resistance/sleeve friction strain gauge
load cells

Pore pressure - pressure sensors

Data acquisition
• Transmission via cable
• Cableless transmission
• Storing data in memory mode
CPT/CPTU MEASUREMENT SYSTEM

Traditional approach using cable

GEOTECH’S SYSTEM WITH ACOUSTIC TRANSMISSION
OF SIGNALS

Data from the probe is transmitted

through the steel of the rod to the
pushing microphone and combined
with the depth encoder information
in the interface that communicates
with the logging software in your
computer.

Other manufacturers also

make cordless systems
GEOTECH’S
FLEXIBLE
SYSTEMS

May use
combination of
acoustic transition
and memory
Depth measured on rig is
synchronised with memory
measurements of qc, fs and u2,
based on measurements vs
time.
Main purpose of standards is to ensure high quality data

Two basic components:

How to get good CPT (CPTu) data?
─ Consultants - Specifications (Standards)
─ Contractors - Equipment & procedures

How to evaluate the data you have?

─ What to do with what you have?
─ Evaluate, correct and process data and report
 How to get good CPT (CPTU) data?

In general, CPT is very reliable, since it’s essentially

operator independent?
However, there are some issues to consider ensure
good data
To follow recognized international standard is essential
CPT/CPTU DATA etc
Standards and guidelines (what they cover)
Equipment
Procedures
Corrections
Accuracy and precision - Classes
Calibration requirements
Checks
Reporting
What we SHALL do and adhere to
CPT/CPTU Available standards

─ ASTM D:5778-12, 2012 – includes the CPTU

─ ISO Standard for CPT and CPTU (ISO 22476-1: 2012)
─ Other National standards and codes
─ Offshore: ISO 19901-8: 2014 some special
adaptions/modifications
Main elements of ISO standard
Equipment:
Cone apex angle : 60 deg.
Diameter : 36 mm ( opens up for range : 25 to 50 mm)
Area friction sleeve 150 sq. cm
Prefered filter location for CPTU behind cone
Procedures:
Corrections:
Other aspects:
Pore Pressure measurement

Over the years pore pressures

have been measured at
different locations

u2 is now preferred position

 Main elements of ISO/CEN standard

Equipment:
Procedures:
Penetration speed (rate) : 20 mm/sec (± 5 mm)
Log at least one set of readings every sec (2.0 cm)
Requirements to saturation of pore pressure
measurement system
Dissipation tests: stop penetration and log u vs. time
Saturation of piezocones
There are no major differences in field test operations between standard
CPT and CPTU soundings, except those required for the saturation of the
piezocone.
To have good pore pressure response during a piezocone test it is necessary
to have a very rigid pore pressure measuring system and a fully saturated
system.
Friction sleeve
To achieve this the following elements shall be completely saturated:
the filter
the channel or tubing between the filter and the transducer Strain
gauges
the transducer housing cavity

Pressure
Housing transducer
Filter
Channel
Field saturation of Pagani piezocone

Onsøy, Norway 2001

Importance of saturation on measured pore pressure response

What you
should get
Poor Better
Filter saturation

Misleading results will be obtained if the filter and its measuring system
are not fully saturated.

Errors will then also occur in the calculation of qt (later).

Watch out for cavitation

Fluids?

Pre boring?
 Dissipation test
During a pause in the penetration any excess pore pressures generated
around the cone will start to dissipate. The rate of dissipation depends upon
the coefficient of consolidation, which, in turn, depends on the
compressibility and permeability of the soil.

sometimes a fixed period of dissipation for all soil layers is used

sometimes dissipation is continued to a predetermined percentage of
degree of dissipation (U),
it is frequently specified to continue the dissipation to at least U= 50% (!).
Example of dissipation test

Required logging frequency according

to ISO 22476-1
-1st minute at least: 1 Hz
-Thereafter may halved every log
(time) cycle

Record all data

Example of a dissipation test (normalised!)
Main elements of ISO

Equipment:
Procedures:
Corrections:
Pore pressure effects on cone resistance +
Effect of inclination
Other aspects:
Pore water pressure effects on qc and fs (clay)

The corrected total cone resistance (qt) is given by the equation:

qt= qc+ (1-a) u2

qc= measured cone resistance

a = area ratio ( 0.3- 0.85)
u2= measured pore pressure
behind cone
Simple chamber for calibration of a and b factors

NOT geometry – calibrate

Offshore can check calibration
Effect of pore pressure on cone resistance

Cones with area ratio a = 0.59 to 0.9

Corrections required to CPTU results according to ISO

Pore pressure effect on cone resistance +

Inclination correction to measured penetration
length
Effect of verticality on
measured depth
Penetration length and
penetration depth
Correction of penetration depth according to ISO

1
Z=  Ch  de
0
z = penetration depth, in m;
l = penetration length, in m;Ch = correction factor for the effect of the inclination of the
cone penetrometer relative to the vertical axis

For single axis inclinometer : Ch=cos

 is the measured angle relative to vertical axis

For bi-axial inclinometer: Ch= (1 + tan2  + tan2  )-1/2

 and  are the angles relative to vertical axis and perpendicular to each other
For Accuracy Classes 1, 2 and 3
 0 0 0
slope
slope EW
10 10 10 slope NS

Example
20 20 20
of depth
30 30 30
correction
Depth (m)

Depth (m)
Depth (m)
40 40 40

50 50 50

60 60 60

70 70 70

0 10 20 30 40 50 0 10 20 30 40 50 0 5 10 15 20 25
Cone resistance MPa Soil Profiles Cone resistance MPa Slope (degr)
with and without
No Correction for Slope correction With Correction for Slope Netherlands
 Non-vertical CPT

CPT Cone
CPT Truck
Main elements of new ISO/CEN

Equipment:
Procedures:
Corrections:
Other aspects:
Maintenance, calibration, requirements to
accuracy, pore pressure response, wear,
tolerances in dimensions, need for
documentation when deviating from
requirements, etc
REPORTING of RESULTS
The information that should be presented falls
naturally into the following 3 categories:

─ Measured parameters
─ Corrected and derived parameters
─ Additional information
CPT/CPTU ISO - presentation of results

Measured Parameters
 Cone resistance vs. depth qc - z
 Sleeve friction vs. depth fs - z
 Penetration pore pressure vs. depth u2 - z

 Pore pressure dissipation vs. time u - t

 Inclination -z

Standards give recommendations on scales to use

Example: Measured parameters – Nearshore UK
 CPT/CPTU ISO - presentation
Derived parameters

─ Corrected cone resistance qt = qc + (1 - a)u2

─ Friction ratio Rf = (fs/qt) . 100%
─ Pore pressure ratio Bq = (u2 - u0)/(qt - vo)
─ Excess pore pressure u = ut - u0
─ Normalised excess pore pressure U = (ut - uo)/(ui - uo)
Example: Derived parameters – Nearshore UK
Why do we need to check CPTU data?

In most cases the results are reliable and

representative for ground conditions
However, in some cases results are not
representative

Interpretation in terms of layering, soil type

and soil parameters should always consist
of:
─ Evaluate data in terms of reliability, apply
corrections or discard results if relevant
─ Use sound interpretation principles
Summary
CPT/CPTU technology has developed over > 80 years and is now mature
Equipment exist for testing over a large range of soil conditions and
different environments – both onshore and offshore
Important to follow sound practice according to international standards

With high quality CPTU data it is possible to define layering across site
and to interpret results in terms of a number of soil parameters – as will
be covered in the following presentations
Thank you for your attention!
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