C. N. Abadie , B. W. Byrne and S. Levy

Model pile response to multi-amplitude cyclic lateral loading in
cohesionless soils
C. N. Abadie
(1),
B. W. Byrne
(1)
and S. Levy-Paing
(2)
(1)
Department of Engineering Science, University of Oxford
(2) Département THEMIS, EDF R&D
1. BACKGROUND
›
Limited guidance on how to address effect of
cyclic loading over lifetime of foundation
Recent research shows that constant amplitude
cyclic loading causes significant increases in
pile displacement and rotation over time
OWT foundation are subjected to a range of
amplitudes of many different cycles
›
›
Load
type
ULS
SLS
FLS
Relevant
Cycle No.
1
100
107
›
›
›
Investigate pile response to multi-amplitude cyclic
lateral loading relevant to offshore wind turbines
› Considerations of scaling for model testing
› Analysis of 1-g small scale model test results
covering realistic multi-amplitude testing
› Interpretation of the results using a linear
superposition method
Load
Magnitude
74% MR
47% MR
27% MR
3. EXPERIMENTAL
EQUIPMENT
›
›
2. OBJECTIVES
Relevant design loads for a 2MW
turbine in terms of ultimate capacity
MR (Leblanc et al. (2010a))
4. SCALING METHODOLOGY
›
Dimensionless framework ensures small-scale laboratory tests capture field
conditions  Further consideration to bending stiffness and aspect ratio:
Motor frequency = 0.106Hz
Combined cyclic moment and
horizontal loading on pile at soil
surface
Displacement transducers (LVDTs)
and load cell
600 mm x 600 mm x 527 mm tank;
loose Yellow Leighton Buzzard sand
(Rd ≃ 4%)
Stiff copper pile
(D=77mm, L=360mm, h=430mm)
5. EXPERIMENTAL RESULTS
›
Multi-amplitude tests: (1) Aims at understanding the influence of increasing load events on continuous
cyclic FLS loading (2) Mimic the applications of 2 storms on a continuous FLS loading condition
Test 1
Test 2
6. LINEAR SUPERPOSITION
METHOD
›
›
Decomposition of load history into equivalent
set of uniform load reversals (rain-flow counting)
Prediction of the final pile rotation based on
linear accumulation of rotation from each
individual load sequences:
 a  (TbTc s ) a  ( N a )
N
eq
ab
  a 

 
 (TbTc s ) b 
0.31
0.31
 tot  (TbTc s ) b  ( N b  N )








max

,

b
tot
0
,
a
0
,
b

eq 0.31
ab
7. CONCLUSIONS
1) Series of laboratory floor model tests exploring pile response under multi
amplitude cyclic loading, representing storm loading on a monopile
2) Pile rotation appears to reach a limiting value following a series of maximum
storm type loads
Contact Details
Christelle ABADIE
[email protected]
3) Pile response to multi amplitude cyclic loading involves significant non-linearity,
particularly when large plastic deformations occur
4) A linear superposition method provides a reasonable but conservative
approximation to final pile rotation