GEOTECH. ENG. IN OFFSHORE WIND
DERIVING CHARACTERISTIC SOIL
PARAMETERS
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
WHY ARE
WE HERE?
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
HOW DO
WE GET
THERE?
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
INTRODUCTION
Involved in:
AGENDA
• Interpretation of in-situ and
lab tests
• Establish design profiles
• Design of offshore structures
Characteristic values
Interpretation of in-situ and lab tests
Example: Design profile
Summary
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
CHARACTERISTIC VALUES
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
CHARACTERISTIC VALUES
Characteristic values
Interpretation of tests
Design profile
Summary
Measuring
Correcting
Correlating
Derived values
Considering
for use
Characteristic values
[www.femern.com]
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
CHARACTERISTIC VALUE
Characteristic values
Interpretation of tests
Design profile
Summary
ISO 19902
Value assigned to a basic variable associated with a prescribed
probability of not being violated by unfavourable values during
some reference period.
NOTE The characteristic value is the main representative
value. In some design situations a variable can have two
characteristic values, an upper and a lower value.
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
CHARACTERISTIC VALUE
Characteristic values
Interpretation of tests
Design profile
Summary
DNV-RP-C207
(…)The definition of a characteristic value is much governed by
the design problem in question and by the geometry. A
definition as the mean value of the property typically applies in
cases where local fluctuations of the soil property can be
assumed to average out over large soil volumes, such as in the
case of the axial capacity of long friction piles. A definition as a
lower-tail quantile in the distribution of the property typically
applies in cases where a local soil strength is governing, such as
in the case of the tip resistance of an end-bearing pile.
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
CHARACTERISTIC
Characteristic values
Interpretation of tests
Design profile
Summary
Minimised band  Optimised design
5%
95%
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
INTERPRETATION OF IN-SITU
AND LAB TESTS
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
DESIGN ASPECTS
Characteristic values
Interpretation of tests
Design profile
Summary
Deformation prop.  SLS
Strength prop.  ULS
(Focus of the presentation)
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
SAMPLE DISTURBANCE
Characteristic values
Interpretation of tests
Design profile
Summary
Sample Quality:
CuC/σ’vc
Based on change in void ratio and OCR
[Lunne, T., Berre, T. and Strandvik, S. (1997)]
OCR
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
CPT
Characteristic values
Interpretation of tests
Design profile
Summary
Depth Below Seabed [m]
Net Cone Resistance [MPa]
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
CONE RESISTANCE VS.
LAB STRENGTH
Characteristic values
Interpretation of tests
Design profile
Summary
[Kjekstad, O., Lunne, T. and Clausen., C.I.F. (1978)]:
• OC North Sea Clay
• 46 triaxial tests
• 37 CPTs
Coefficient of variation
COVmean, lab=0.25
COVmean, cone=0.09
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
CPT – RATE OF PENETRATION
Characteristic values
Interpretation of tests
Design profile
Summary
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
CONE FACTOR
Characteristic values
Interpretation of tests
Design profile
Summary
Number of occurences
BE
UB
LB
~5%
~95%
Nkt
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
Characteristic values
Interpretation of tests
Design profile
Summary
Depth [m]
HOW TO USE CONE FACTOR
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
EXAMPLE: DESIGN PROFILE
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
MEASURED VALUES
Characteristic values
Interpretation of tests
Design profile
Summary
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
INTERPRETED VALUES
Characteristic values
Interpretation of tests
Design profile
Summary
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
SUMMARY
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
SUMMARY
Characteristic values
Interpretation of tests
Design profile
Summary
Engineering judgement
• Use all available information
Uncertainties
• Correlations, sample disturbance
Foundation types
• Cautious mean/lower/upper
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01
GEOTECHNICAL ENGINEERING IN OFFSHORE WIND
2014/04/01