Study on the penetration resistance of suction bucket foundation in

Study on the penetration resistance of suction bucket foundation in

Study on the penetration resistance
of suction bucket foundation in sand
PO. ID
007
Myounghak Oh1 / Osoon Kwon1 / Keunsoo Kim2 / Hyun Kang1
1Korea Institute of Ocean Science & Technology / 2 Naru EMS, Korea
Abstract
Results
Suction bucket foundations are likely to become one of reliable and cost-effective
options for offshore wind turbine foundations. Suction piles have numerous
advantages over conventional underwater foundation systems. The most significant
advantages are: easy installation, large bearing capacity, and retrievability.
The model tests of the suction bucket foundation are performed on the sand
ground. This study carried out a series of model tests to investigate the
penetration resistance of suction bucket foundation. And the mobilized soil
strength factor was reviewed through comparing the experimental results by two
installation ways (e.g., push-in-load and suction) and the results calculated by the
conventional equation.
 Penetration behavior of bucket foundation by push-in-load
Elapsed time (sec)
0
120
240
360
480
600
720
840
0
Introduction
Push-in-load
100
One of favorable foundation types for
offshore wind turbines.
Load (N)
Suction(pumping)
Outside pressure of caisson
PO.
XXXX
Inside pressure
of caisson
Frictional force
The suction bucket foundation is like a
large upturned bucket. On lowering
them to the seabed, they cut in a small
distance. The water trapped inside the
bucket is then pumped out, penetrating
the foundation to its final position.
Self weight
of caisson
Penetration force
= Self weight of caisson +
Differential pressure x Area
Resistance force
= Frictional force + Tip
resistance
Water Depth
40
300
60
400
80
500
100
0
Elapsed time (sec)
600
900
300
1200
1500
0
0,0
Tip resistance force
Differential pressure
0,5
Pressure (kPa)
Seepage
In Korea, a couple of off-shore
wind farms have being planned to
be built off the west coast of Korea.
They are West-South project with a
total capacity of 2.5 GW and
Jeonnam project. Meteorological
towers with tripod suction bucket
foundation were constructed.
20
Displacement
1,0
40
1,5
60
2,0
80
2,5
100
 Comparison of penetration resistance with penetration methods
Load (N)
Load (N)
0
0
50 100 150 200 250
100 200 300 400 500
HeMOSU-2
Ocean-mast 1
200
D = 150 mm
20
40
60
80
400
600
20
40
60
80
20
40
60
80
Push-in-load
Push-in-load
Push-in-load
Suction
Suction
Suction
100
100
800
D = 300 mm
Penetration depth (mm)
Penetration depth (mm)
Ocean-mast 1
Mokpo-Jindo OWF feasibility study
Private/Mokpo national Univ.
Shinan-gun
125-54-54.99 / 34-28-35.04
(DL-7.8m)
0
0
D = 100 mm
HeMOSU-2 Met-mast
South-Western sea 2.5GW OWF
KETEP/KEPCO/SPC(KOWF)
Gunsan-si
126-12-45.04 / 35-49-39.26
(DL-26.9m)
Load (N)
0
0
Penetration depth (mm)
Location
200
 Penetration behavior of bucket foundation by suction pressure
 Field Applications
Item
Estate Name
Organizer
20
Displacement
Penetration depth (mm)
 Suction Bucket Foundation
960 1080 1200
0
Penetration depth (mm)
In the design of the suction pile, the evaluation of the resisting force of the ground
against the pile penetration is crucial. In this study, the laboratory model tests that
are simulating the installation process of suction bucket foundation on the sand are
performed. The penetration resistance of suction bucket foundation was
investigated through a series of model tests.
100
 Penetration resistance derived by introducing the mobilized soil
strength factor(α)
Load (N)
10
20
30
40
50
0
Methods
 Test Chamber
Load cell
Pressure
transducer
LVDT
Guide rod
Water
(hw=35cm)
Water
(hw=35cm)
Soil
(hs=40cm)
Pumping
& balance
Guide rod
Chain
Test chamber
(cube of 80cm)
Penetration
by
push-in- load
Soil
(hs=40cm)
 Bucket models
100
1
0.05
6,361.7
1,492.3
150
0.67
0.033
15,393.8
2,277.7
300
0.33
0.017
66,052.0
4,633.8
0
80
60
80
D = 100 mm
20
120
150
0
F
F
(α=0.4)
Suction
40
60
80
100
30
D = 150 mm
20
F
F
(α=0.96)
Suction
40
60
80
100
D = 300 mm
Mounting frame
Mounting frame
LVDT
60
Load (N)
60
90
Conclusions
Hydraulic cylinder
Load cell
F
F
(α=0.1)
Suction
40
100
Hydraulic
cylinder
Diameter, D (mm)
Aspect ratio, L/D
t/D
Interior area, Ai (mm2)
Tip area, Ai (mm2)
20
40
0
Penetration depth (mm)
Penetration depth (mm)
0
20
Penetration depth (mm)
0
Load (N)
Penetration
by suction pressure after
initial penetration by pushin-load
Test chamber
(cube of
80cm)
When suction is applied in the suction bucket foundation, seepage developed from
outside into inside of bucket results in decreasing the effective stress of sand and
friction angle between sand and foundation. To consider the reduction of the shear
strength of the soil inside the bucket due to the applied suction, the mobilized
effective soil friction angle ratio can be applied. From the laboratory model tests,
mobilized soil strength factor on sand was ranged from 0.1 to 0.96. The
penetration resistance when the bucket pile is penetrated on sand by suction is
3.5~16.8 % of penetration resistance when the bucket pile is penetrated by pushin-load method.
Acknowledgement
The present work is a result of the project “Development of the design
technologies for a 10MW class wave and offshore wind hybrid power generation
system". All support is gratefully acknowledged.
EWEA Offshore 2015 – Copenhagen – 10-12 March 2015