FINITE ELEMENT ANALYSIS OF SEISMIC INDUCED DEFORMATION OF BREAKWATER The CRISP Consortium Ltd/South Bank University London 15th CRISP User Group Meeting Thursday 19 th September 2002. UNIVERSITYCOLLEGE LONDON DEPARTMENT OF CIVIL & ENVIRONMENTAL ENGINEERING In association with. - PowerPoint PPT Presentation
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FINITE ELEMENT ANALYSIS OF SEISMIC FINITE ELEMENT ANALYSIS OF SEISMIC INDUCED DEFORMATION OF BREAKWATER INDUCED DEFORMATION OF BREAKWATER The CRISP Consortium Ltd/South Bank University The CRISP Consortium Ltd/South Bank University London London 15th CRISP User Group Meeting 15th CRISP User Group Meeting Thursday 19 Thursday 19 th th September 2002 September 2002 UNIVERSITYCOLLEGE LONDON DEPARTMENT OF CIVIL & ENVIRONMENTAL ENGINEERING In association with
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FINITE ELEMENT ANALYSIS OF SEISMIC FINITE ELEMENT ANALYSIS OF SEISMIC INDUCED DEFORMATION OF BREAKWATERINDUCED DEFORMATION OF BREAKWATERThe CRISP Consortium Ltd/South Bank University LondonThe CRISP Consortium Ltd/South Bank University London
15th CRISP User Group Meeting15th CRISP User Group MeetingThursday 19Thursday 19thth September 2002 September 2002
UNIVERSITYCOLLEGE LONDONDEPARTMENT OF CIVIL & ENVIRONMENTAL ENGINEERING
In association with
This FE study was carried out for Mouchel This FE study was carried out for Mouchel Consulting Ltd by Amir Rahim and Andrew Consulting Ltd by Amir Rahim and Andrew Chan. Software used is CRISP and Chan. Software used is CRISP and SWANDYNE IISWANDYNE II
A breakwater is to be constructed in an area A breakwater is to be constructed in an area where earthquake is likely to occur.where earthquake is likely to occur.
The breakwater core consists of sand which is The breakwater core consists of sand which is dredged from seabeddredged from seabed
The breakwater lies above a layer of sand The breakwater lies above a layer of sand varying from few meters up to about 20m. The varying from few meters up to about 20m. The in-situ sand overlays bedrockin-situ sand overlays bedrock
Criteria for liquefactionCriteria for liquefaction
We check for liquefaction by checking We check for liquefaction by checking whether excess pore pressure has reached whether excess pore pressure has reached vertical effective stress for a period of time vertical effective stress for a period of time after the end of the earthquakeafter the end of the earthquake
Coast
Section 7-7
Section 9-9
Port side
Sea side
Round head
L2
U9
U12
U5
Plan of Breakwater
Earthquake Record usedEarthquake Record used
El-Centro earthquake (May 1940, Southern California). This was El-Centro earthquake (May 1940, Southern California). This was factored to a maximum acceleration or 0.3g.factored to a maximum acceleration or 0.3g.
Sand
Breakwater (rock)Accropode22 m
20 m
Bed rock
25 m
Section 9-9 at the roundhead
FE Mesh for BreakwaterFE Mesh for Breakwater
Material PropertiesMaterial Properties
Mg is slope of critical state line and is found by using PhiMg is slope of critical state line and is found by using Phi Mf, controls unloading modulus. We use the relationship Mf, controls unloading modulus. We use the relationship
which is based on the Relative Density. Mf=Mg x Drwhich is based on the Relative Density. Mf=Mg x Dr Other parameters are chosen for typical loose sand as detailed Other parameters are chosen for typical loose sand as detailed
in the book by Zienkiewicz, Chan, Pastor and Shiomiin the book by Zienkiewicz, Chan, Pastor and Shiomi
The armour materials were considered to be elastic with the The armour materials were considered to be elastic with the following propertiesfollowing properties
E=15000.0 KPaE=15000.0 KPa v=0.15v=0.15 The permeability coefficient for the breakwater core material The permeability coefficient for the breakwater core material
was initially taken as 5x10-5 m/s.was initially taken as 5x10-5 m/s.
Test 1Test 1FE results with following properties:FE results with following properties:Dr=35% for breakwater sandDr=35% for breakwater sandFor rock armour E=15000.0 KPaFor rock armour E=15000.0 KPa v=0.15v=0.15For breakwater sand k= 5x10For breakwater sand k= 5x10-5-5 m/s. m/s.
Excess pore pressure at various nodes
-400
-200
0
200
400
600
800
0 50 100 150 200 250 300 350 400 450
time (seconds)
Exc
ess
po
re p
ress
ure
(K
Pa)
XPP-23-crest of slope
XPP-25-top at centre
XPP-28-toe of slope
XPP-35-below breakw ater at centre
XPP-33-middle of breakw ater
XPP-61-middle of in-situ sand
Excess pore pressure at various nodes in section 9-9 for duration of quake of 53 seconds and further consolidation time up to 439 seconds. Excess pore pressures at nodes 23 and 25 are zero (free drainage)
Test 2 (effect of increasing sand permeability)Test 2 (effect of increasing sand permeability)FE results with following properties:FE results with following properties:Dr=35% for breakwater sandDr=35% for breakwater sandFor rock armour E=15000.0 KPaFor rock armour E=15000.0 KPa v=0.15v=0.15For breakwater sand k= 5x10For breakwater sand k= 5x10-3-3 m/s. m/s.
Excess pore pressure at various nodes in section 9-9 for duration of quake of 53 seconds and further consolidation time up to 439 seconds. Excess pore pressures at nodes 23 and 25 are zero (free drainage)
Excess pore pressure at various nodes
-300
-200
-100
0
100
200
300
400
500
0 50 100 150 200 250 300 350 400 450
time (seconds)
Exc
ess
po
re p
ress
ure
(K
Pa)
XPP-23-crest of slope
XPP-25-top at centre
XPP-28-toe of slope
XPP-35-below breakw ater at centre
XPP-33-middle of breakw ater
XPP-61-middle of in-situ sand
Test 3 Test 3 (effect of stiffness of surrounding rock armour)(effect of stiffness of surrounding rock armour)
FE results with following properties:FE results with following properties:Dr=35% for breakwater sandDr=35% for breakwater sandFor rock armour E=150.0 KPaFor rock armour E=150.0 KPa v=0.15v=0.15For breakwater sand k= 5x10For breakwater sand k= 5x10-5-5 m/s. m/s.
Here we reduced stiffness of rock armourHere we reduced stiffness of rock armour
Deformed mesh plot of section 9-9, with smaller stiffness for rock armour
Excess pore pressure at various nodes in section 9-9 for duration of quake of 53 seconds and further consolidation time up to 439 seconds. Excess pore pressures at nodes 23 and 25 are zero (free drainage)
Excess pore pressure at various nodes
-800
-600
-400
-200
0
200
400
600
800
1000
1200
0 50 100 150 200 250 300 350 400 450
time (seconds)
Exc
ess
po
re p
ress
ure
(K
Pa)
XPP-23-crest of slope
XPP-25-top at centre
XPP-28-toe of slope
XPP-35-below breakw ater at centre
XPP-33-middle of breakw ater
XPP-61-middle of in-situ sand
Test 4 Test 4 (effect of compaction of breakwater material)(effect of compaction of breakwater material)
FE results with following properties:FE results with following properties:Dr=70% for breakwater sandDr=70% for breakwater sandFor rock armour E=15000.0 KPaFor rock armour E=15000.0 KPa v=0.15v=0.15For breakwater sand k= 5x10For breakwater sand k= 5x10-5-5 m/s. m/s.
Here we have doubled the relative density of Here we have doubled the relative density of breakwater sandbreakwater sand
Excess pore pressure at various nodes in section 9-9 for duration of quake of 53 seconds and further consolidation time up to 439 seconds. Excess pore pressures at nodes 23 and 25 are zero (free drainage)
Excess pore pressure at various nodes
-300
-200
-100
0
100
200
300
400
500
600
0 50 100 150 200 250 300 350 400 450
time (seconds)
Exc
ess
po
re p
ress
ure
(K
Pa)
XPP-23-crest of slope
XPP-25-top at centre
XPP-28-toe of slope
XPP-35-below breakw ater at centre
XPP-33-middle of breakw ater
XPP-61-middle of in-situ sand
Test 5 Introducing rock filter at bottom of breakwaterTest 5 Introducing rock filter at bottom of breakwaterFE results with following properties:FE results with following properties:Dr=35% for breakwater sandDr=35% for breakwater sandFor rock armour E=15000.0 KPaFor rock armour E=15000.0 KPa v=0.15v=0.15For breakwater sand k= 5x10For breakwater sand k= 5x10-5-5 m/s. m/s.
3 meter layer rock filter is placed at bottom of breakwater. 3 meter layer rock filter is placed at bottom of breakwater. This has Dr=70% and k=1x10This has Dr=70% and k=1x10-3-3 m/s m/s
Excess pore pressure at various nodes in section 9-9 for duration of quake of 53 seconds and further consolidation time up to 439 seconds. Excess pore pressures at nodes 23 and 25 are zero (free drainage)
Excess pore pressure at various nodes
-400
-300
-200
-100
0
100
200
300
400
500
600
0 50 100 150 200 250 300 350 400 450
time (seconds)
Exc
ess
po
re p
ress
ure
(K
Pa)
XPP-20-crest of slope
XPP-22-top at centre
XPP-25-toe of slope
XPP-31-below breakw ater at centre
XPP-29-middle of breakw ater
XPP-46-middle of in-situ sand
ConclusionsConclusions
This Finite Element study concentrated on four factors linked to This Finite Element study concentrated on four factors linked to liquefaction. These are:liquefaction. These are:
Effect of using more permeable material for breakwater coreEffect of using more permeable material for breakwater core. . The permeability was increased from 5x10-5 to 5x10-3 ,as The permeability was increased from 5x10-5 to 5x10-3 ,as detailed in test 1 and 2. Although the results show some detailed in test 1 and 2. Although the results show some variation in deformation and excess pore pressure, overall variation in deformation and excess pore pressure, overall deformation remains the same. It can therefore be concluded deformation remains the same. It can therefore be concluded that changing the permeability will only allow excess pore that changing the permeability will only allow excess pore pressure to escape from the in-situ sand and move into the pressure to escape from the in-situ sand and move into the breakwater core material thus causing more liquefaction in this breakwater core material thus causing more liquefaction in this zone. Using more permeable material, therefore, may not zone. Using more permeable material, therefore, may not reduce the effect of liquefaction.reduce the effect of liquefaction.
ConclusionsConclusions
Effect of using stiffer material for rock Effect of using stiffer material for rock armourarmour. The rock armour stiffness was . The rock armour stiffness was changed to a small value as in test 3. The changed to a small value as in test 3. The results show considerable displacement and results show considerable displacement and the analysis had to be limited to a short period the analysis had to be limited to a short period of time (only 63 seconds) as severe of time (only 63 seconds) as severe deformation would cause numerical ill-deformation would cause numerical ill-conditioning.conditioning.
ConclusionsConclusions
Effect of compactionEffect of compaction. The relative density (Dr) . The relative density (Dr) specified for the breakwater core material below the specified for the breakwater core material below the water level is 35%. If this is to be increased to say water level is 35%. If this is to be increased to say twice as much, as in test 4, the settlement reduces by twice as much, as in test 4, the settlement reduces by nearly half as much. Therefore, compaction (increase nearly half as much. Therefore, compaction (increase in Dr) is likely to reduce the effect of liquefaction. in Dr) is likely to reduce the effect of liquefaction. The most critical material parameter for the The most critical material parameter for the densification model is the unloading parameter Mf densification model is the unloading parameter Mf which is linked to the relative density of the sand which is linked to the relative density of the sand (Dr).(Dr).
ConclusionsConclusions
Effect of using a rock filterEffect of using a rock filter. Adding a 3m rock . Adding a 3m rock filter at the bottom of the breakwater would filter at the bottom of the breakwater would have two main advantages which help reduce have two main advantages which help reduce liquefaction. These are higher density liquefaction. These are higher density associated with such rock material, and higher associated with such rock material, and higher permeability, allowing excess pore pressure to permeability, allowing excess pore pressure to dissipate more quickly.dissipate more quickly.
