Research Projects on Micropile GroupsMicropile Groups Alexis RoseG t h i l E i i R h C tGeotechnical Engineering Research CentreCity University, London

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)

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

Apparatus used for laboratory tests

Pile cap: linear pile group Pile cap: rectangular pile group

Load-settlement response for 5x1 linear pile groupsad

, kN

3D pile spacing

Loa

Settlement mmSettlement, mm

Load-settlement response for square and rectangular pile groups, k

N

Groups of 8 piles

Load

Groups of 4 piles

Settlement, mm

Efficiency coefficient for linear groups – critical spacing approx. 3D

t, η

y co

effic

ient Trendline?

Effic

ienc

y

Relative spacing S/D

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

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

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

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

Piles

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

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

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)

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)

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

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…..