quaker program topic b1 : inclined piles under seismic loads
TRANSCRIPT
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
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Time
- shock and repeated shocks
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Time1 ms – model scale
Quaker program topic B1Quaker program topic B14 types of loadings:
• No seismic loads • Seismic loads
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Time
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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
Shocks and repeated shocks
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
Static+ cyclic 0-1920kN
Static+cyclic 0-1920kN
Q10
Q11
16.2
16.2
Static+ cyclic 0-1920kN
Static+cyclic 0-1920kN
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
Friction pilesFriction piles--Group of vertical and inclined pilesGroup of vertical and inclined piles
Friction pilesFriction piles--Group of vertical and inclined pilesGroup of vertical and inclined piles
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
0 5 10 15 20Number of cycles
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
0 5 10 15 20Number of cycles
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
Shocks and repeated shocks
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
Shocks and repeated shocks
Repeatability of the pile group response
Improvement of the experimental set-up