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Research Projects on Micropile GroupsMicropile Groups Alexis RoseG t h i l E i i R h C tGeotechnical Engineering Research CentreCity University, London
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Recent and current research projects on micropiles
Leonora Begaj Qerimi:
“Foundation Improvement using Micropile Groups” (PhD)p g p p ( )
Hitesh Halai:
“Laboratory Experiments on Micropile Groups” (MEng)
Alexis Rose:Alexis Rose:
“High Capacity Foundations using Micropile Groups” (PhD)
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Hitesh Halai: “Laboratory Experiments on Micropile Groups”
Simple laboratory tests using model piles in dry sandSimple laboratory tests using model piles in dry sand
Investigation of linear and rectangular groups
Main findings relate to confirmation of critical pile spacing
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Apparatus used for laboratory tests
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Pile cap: linear pile group Pile cap: rectangular pile group
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Load-settlement response for 5x1 linear pile groupsad
, kN
3D pile spacing
Loa
Settlement mmSettlement, mm
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Load-settlement response for square and rectangular pile groups, k
N
Groups of 8 piles
Load
Groups of 4 piles
Settlement, mm
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Efficiency coefficient for linear groups – critical spacing approx. 3D
t, η
y co
effic
ient Trendline?
Effic
ienc
y
Relative spacing S/D
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Alexis Rose: “High Capacity Foundations using Micropile Groups”
Aim: to explore the strength and stiffness characteristics of ‘rings’ of micropiles
Actions:Centrifuge model tests (City)Numerical analysis (GCG)Testing and monitoring prototype (Foggo)
City UniversityProf. Neil Taylor
Foggo AssociatesJim Fraser / Tony Taylor
Geotechnical Consulting GroupProf. Hugh St John
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Cannon Place, London
Micropile summary
- 11 micropile groups with 16 to 24 piles in each300mm diameter 30m long 500mm c/c
Monitoring
- Precise levelling- Extensometers- 300mm diameter, 30m long, 500mm c/c - Extensometers
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Existing knowledge in area of research
FOREVER – French National Project on jMicropiles (R. Frank)
Foundation Improvement using Micropile Groups (L. Begaj-Qerimi)G oups ( egaj Qe )
FlemingVesicDe MelloO’Neill
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Centrifuge model tests
Established at City U i it i 1989University in 1989
Acceleration field up to 200 times Earth’s gravity
A l ti lAcceleration scale = geometric scale
Study various geotechnical events
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Piles
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Apparatus
100+ components will be made to allow variety of pile groups to be tested
T t 30 il d ilTest 30+ pile groups and pile arrangements over 12 months
Current situation:
Strong box and main frame constructed
Pile caps and installation system being made
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Pile spacingGroup geometryGroup diameter
Testing plan
Group diameterLoad distributionComparison tests
Pile Spacing (D)
1.25
1 5
Group arrangement
No. ofpiles
circle 6
circle 8
Group arrangement
No. of Piles Load cell location
line 5 single pile cap
line 5 load cell on central pile1.5
1.75
2
2 25
circle 8
circle 10
circle 12
circle 14
line 5 load cell on central pile
line 5 load cell on end pile
line 5 load cell on 2nd/4th pile
2.25
2.5
2.75
3
circle 14
square 8
square 10
square 123 square 12
square 14
square 16
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Proposed pile group variations (1)
8 piles 12 piles
circular group
area = 329mm2
p
circular group
2area = 329mm2
(at 2dia. c/c)area = 866mm2
(at 2dia. c/c)
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Proposed pile group variations (2)
12 piles12 piles
square group
area = 625mm2
circular group
area = 866mm2 area 625mm(at 2dia. c/c)(at 2dia. c/c)
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Results…?Circular group (prototype)
3000
3500
Diameter = 300mmLength = 15m
2000
2500
a (k
N)
Pile spacing = 2dia. c/cSoil = Kaolin clay
500
1000
1500Qa
0
500
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
number of pilesnumber of piles
sum of individual piles caisson single large pile
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What next?
Begin centrifuge tests in June 2009
Report on interim results at the Physical Modelling inReport on interim results at the Physical Modelling in Geotechnics Conference (June 2010)
Final report expected end of 2011Final report expected end of 2011…..