quaker program topic b1 : inclined piles under seismic loads

QUAKER program QUAKER program Topic B1 : inclined piles under seismic Topic B1 : inclined piles under seismic

loadsloadsS. Escoffier, J.L. Chazelas,

L. Thorel, J. Garnier, N. Chenaf

A JOINT CFMS AND BGA MEETINGA JOINT CFMS AND BGA MEETING -- From Modelling to Practice in Geotechnical Engineering From Modelling to Practice in Geotechnical Engineering –– november november 25, 200525, 2005

ContentsContents

Introduction on inclined piles in seismic area

Quaker program Topic B1 : framework

Experimental program and set-up design

Validation tests and experimental improvements

First comparison of piles group behaviour

Next experiments

Inclined piles in seismic areaInclined piles in seismic area

PS92 : “The use of inclined deep foundations is prohibited”Eurocode 8 ch.5 : “If inclined piles are used, they should be designed to safely carry

axial loads as well as bending loads – note : it is recommended that no inclined piles be used for transmitting lateral loads ”

•••• Bending moments induced by the soil settlement•••• Large alternating forces acting at the pile/pile cap interface

•••• Large tensile forces which induced a decrease of the bending resistance of the inclined pile

•••• When inclination of the pile are not symmetric, permanent rotation may develop

CodesCodes

Drawbacks Drawbacks (G. (G. Gazetas Gazetas technical report Quaker)technical report Quaker)

Quaker program topic B1Quaker program topic B1

Behavior of deep foundations containing asymmetrically inclined pile under seismic loads

Development and validation of experimentally simplified methods

two site conditions : floating and end bearing piles

End bearing pilesv-piles group i-piles group

25°

sand sand

Floating piles End bearing pilesFloating piles

sand sand

Elastic layerElastic layer

two simplified piles groups : two piles connected with a rigid beam “fixed end conditions”

v-piles group i-piles group

25°

Sand

Elastic layer

- Horizontal static and cyclic loading

��

Time

- shock and repeated shocks

��

Time1 ms – model scale

Quaker program topic B1Quaker program topic B14 types of loadings:

• No seismic loads • Seismic loads

��

Time

��

Time

- sine

- earthquake

SetSet--up designup design

Soil and elastic layer

- Fontainebleau sand : Id=80% (γd≈16,09 kN.m-3) ; φ ≈40°; E ≈ 23pc0.5 (Gaudin, 2002)

- Elastic layer : E≈480kPa

Piles design

- Penetration pile from ground: 12m

- EI: 197 MN.m²

ri

ro- Outer radius:36cm- Inner radius:30cm

Ø

- Instrumented piles: 20 pairs of strain gages: bending moment profile

- No instrumented piles

SetSet--up designup designDesign and geometry of the piles group

4∅

soil

1m

12m

20 pairs of strain gages

One each 0.6m

Horizontal static and cyclic load

displacement sensor DH1

displacement sensor DH2

rubber

Load sensor

Experimental programExperimental programFirst Series: Devices and Installation Validation Elements Final DesignBased on existing instrumented 12 m piles (strain gauges) Friction piles Static and cyclic horizontal loads

Shocks and repeated shocks

Repeatability of the pile group response

Improvement of the experimental set-up

Second Series: Compared response to non seismic load•4 new instrumented piles

•Accelerometers in the sand

•Fast data acquisition system CAREMBA

•Friction and end bearing piles group

Static and cyclic horizontal loads


Experimental data on the pile group behavior under non

seimic loads

Third Series: Compared response to seismic load•Shaker and laminar box

Sine (and earthquakes)

Experimental data on the pile group behavior under seismic

loads

Box Design LoadingUnit Weight (g.cm-3)

Static+cyclic 0-960kNQ1

Q2

16.06

16.08 Static+cyclic 0-1920kN

Q5

Q6

16.09

16.11

Static+ cyclic 0-1920kN

Static+cyclic 0-1920kN

PB

Q7

Q8

16.1

16.08



Q10

Q11

16.2

16.2



Improvements

Pluviation_repositioning 2DS +1RS

gages_axial force

Pluviation_thin cap +1RS

Pluviation_hanging in mid air

Friction piles Friction piles -- Group of two vertical pilesGroup of two vertical piles•••• Head displacement •••• Bending moment profiles

TestDH2 displacement (cm)

Fmaxstatic 11 cycle

16.8

17.56

25.88

24.96Q5-v

Q6-v

∆∆∆∆Q/Qmin 4.5% 3.7%

-500

0

500

1000

1500

2000

0 10 20 30DH2 displacement (cm)

App

lied

forc

e (k

N)

Q5-vQ6-v

0

2

4

6

8

10

12

-500 500 1500 2500Bending moment (kN.m)

Dep

th (m

)

Q5-v_682kNQ5-v_1631kNQ5-v_cycle1Q6-v_680kNQ6-v_1608kNQ6-v_cycle1

•••• DH2 displacement

DH2 displacement (cm)Fmax

static 11èmecycle

9.08 14.4

14.56 20.28Q5-iQ6-i

Test

∆∆∆∆Q/Qmin 52% 41%

Maximum bending moment (KN/m)Fmax

static 11èmecycle

1252 1786

1867 2337

49% 30%

•••• Bending moment profiles

-500

0

500

1000

1500

2000

0 5 10 15 20 25DH2 displacement (cm)

App

lied

forc

e (k

N)

Q2-i Q5-iQ6-i

0

2

4

6

8

10

12

-500 500 1500Bending moment (kN.m)

Dep

th (m

)

Q5-i_682kNQ5-i_1631kNQ5-i_cycle1Q6-i_680kNQ6-i_1608kNQ6-i_cycle1

Friction pilesFriction piles--Group of vertical and inclined pilesGroup of vertical and inclined piles

Improvements of the device and procedureImprovements of the device and procedure

•••• Improvement of the pile group placement in the box

Rotation of the inclined pile

Replacement of the pile Modification of the soil structure

No control of the distance bottom of the pile cap / sand surface

Thin pile cap + cable

no repeatability Initially the pile group is push in the sand on 5 cm

Modification of the sand structure at the bottom of the pile

To suspend the piles group


0200400600800

100012001400160018002000

0 10 20 30DH2_displacement (cm)

App

lied

stre

ss (

kN)

Q10-iQ11-i

0

2

4

6

8

10

12

-500 0 500 1000 1500 2000 2500Bending moment (kN.m)

Dep

th (m

)

Q10-i_688kNQ10-i_1638kNQ10-i-1863kNQ11-i_694kNQ11-i_1631kNQ11-i_1853kN

DH2 displacement (cm)Fmax

static 11èmecycle

15.64 22.8

12.12 20.4Q10-iQ11-i

Test

∆∆∆∆Q/Qmin 29% 11%

Maximum bending moment (KN/m)Fmax

static 11èmecycle

1990 2578

1689 2403

18% 7%

FixedFixed--end moment piles group end moment piles group –– first results first results

0

20

40

60

80

0 5 10 15 20Number of cycles

DH

2_di

ffere

nce

(%) Q5-Q6-i

Q7-Q8-iQ10-Q11-i

0102030405060


Max

imum

ben

ding

m

omen

tat

Fmax

_diff

eren

ce

(%)

Q5-Q6-iQ7-Q8-iQ10-Q11-i

New experimental devicesNew experimental devices

•••• Fast data acquisition system CAREMBA-32 synchronous channels-Sampling frequency 1.2MHz/channel > f > 50kHz-Digitization in the swinging basket

•••• New piles-Determination of the moment at the pile/pile cap interface: a pair of gages above the soil surface

The fixed-end moment can be determined

Additional pair of strain gages on the new pile

-Measurement of the normal force in the piles: feasability tests (no calibration)

10 pairs of strain gages BM+

2 pairs of strain gages AF

2 pairs of strain gages (AF+BM) 2 pairs of strain gages (AF+BM)

18 pairs of strain gages BM+

2 pairs of strain gages AF

•••• 1D Shaker (10-80g) - Payload : 400kg (L=1m, w=0.5m, h=0.6m)- Umax : 5mm ; Vmax= 1.1 m/s ; amax= 40g- Frequency response : 40 to 250 Hz

•••• Laminar box (F. Derkx & S. Buttigieg, LCPC-SMI)

F. Derkx

First comparison First comparison of piles group of piles group behaviourbehaviour

0

500

1000

1500

2000

2500

3000

3500

0 2 4 6 8 10 12 14 16 18 20Num ber of c y c les

Max

imum

ben

ding

mom

ent (

kN.m

)

Q 5v

Q 6v

Q 10i

Q 11i

0

2

4

6

8

10

12

-300 200 700 1200 1700 2200 2700 3200Bending moment kN.m

Dep

th (m

) Q5v_F=174kNQ6v_F=166kNQ10i_F=233kNQ11i_F=243kNQ5v_F=1096kNQ6v_F=1103kNQ10i_F=1150kNQ11i_F=1143kNQ5v_cycle13Q6v_cycle13Q10i_cycle13Q11i_cycle13

0

5

10

15

20

25

30


DH

2_di

spla

cem

ent (

cm)

Q5-v

Q6-v

Q10-i

Q11-i

Bending moments are higher for thevertical pile group

Horizontal displacements are higher for the vertical pile group

More information are necessary to understand the stress distribution

(axial force in the piles)

Next experimentsNext experiments

Next experimentsNext experiments

Second Series: Compared response to non seismic load•4 new instrumented piles

•Accelerometers in the sand

•Fast data acquisition system CAREMBA

•Friction and end bearing piles group

Static and cyclic horizontal loads


Experimental data on the pile group behavior under non

seimic loads

Third Series: Compared response to seismic load•Shaker and laminar box

Sine (and earthquakes)

Experimental data on the pile group behavior under seismic

loads

First Series: Devices and Installation Validation Elements Final DesignBased on existing instrumented 12 m piles (strain gauges) Friction piles Static and cyclic horizontal loads


Repeatability of the pile group response

Improvement of the experimental set-up

quaker program topic b1 : inclined piles under seismic loads

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