QUAKER program Topic B1 : inclined piles under seismic loads

Transcription

1 QUAKER program Topic B1 : inclined piles under seismic loads S. Escoffier, J.L. Chazelas, L. Thorel, J. Garnier, N. Chenaf A JOINT CFMS AND BGA MEETING - From Modelling to Practice in Geotechnical Engineering november 25, 25

2 Contents 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

3 Inclined piles in seismic area Codes 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 Drawbacks (G. (G. Gazetas technical report Quaker) 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

4 Quaker program topic B1 Behavior of deep foundations containing asymmetrically inclined pile under seismic loads Development and validation of experimentally simplified methods two simplified piles groups : two piles connected with a rigid beam fixed end conditions two site conditions : floating and end bearing piles 25 sand sand 25 sand sand Elastic layer Elastic layer v-piles group Floating piles i-piles group Floating piles v-piles group End bearing piles i-piles group End bearing piles

5 4 types of loadings: Quaker program topic B1 No seismic loads - Horizontal static and cyclic loading - shock and repeated shocks Seismic loads - sine - earthquake Sand 1 ms model scale Time Elastic layer Time Time Time

6 Set-up design Soil and elastic layer - Fontainebleau sand : I d =8% (γ d 16,9 kn.m -3 ) ; φ 4 ; E 23p c.5 (Gaudin, 22) - Elastic layer : E 48kPa Ø Piles design r o r i - Outer radius:36cm - Inner radius:3cm - EI: 197 MN.m² - Penetration pile from ground: 12m - Instrumented piles: 2 pairs of strain gages: bending moment profile - No instrumented piles

7 Design and geometry of the piles group Set-up design displacement sensor DH2 Horizontal static and cyclic load displacement sensor DH1 rubber Load sensor soil 12m 4 1m 2 pairs of strain gages One each.6m

8 Experimental program First Series: Devices and Installation Validation Elements Final Design Based on existing instrumented 12 m piles (strain gauges) Friction piles Static and cyclic horizontal loads Shocks and repeated shocks Second Series: Compared response to non seismic load 4 new instrumented piles Fast data acquisition system CAREMBA Repeatability of the pile group response Improvement of the experimental set-up Accelerometers in the sand Friction and end bearing piles group Static and cyclic horizontal loads Experimental data on the pile group behavior under non seimic loads Shocks and repeated shocks Third Series: Compared response to seismic load Shaker and laminar box Sine (and earthquakes) Experimental data on the pile group behavior under seismic loads

9 Unit Weight Box Design Loading (g.cm -3 ) Q Static+cyclic -96kN Improvements Q PB Static+cyclic -192kN Q5 Q Static+ cyclic -192kN Static+cyclic -192kN Pluviation_repositioning 2DS +1RS gages_axial force Q7 Q Static+ cyclic -192kN Static+cyclic -192kN Pluviation_thin cap +1RS Q1 Q Static+ cyclic -192kN Static+cyclic -192kN Pluviation_hanging in mid air

10 Friction piles - Group of two vertical piles Head displacement Bending moment profiles Applied force (kn) Q5-v Q6-v DH2 displacement (cm) Bending moment (kn.m) Depth (m) Q5-v_682kN Q5-v_1631kN Q5-v_cycle1 Q6-v_68kN Q6-v_168kN Q6-v_cycle1 DH2 displacement (cm) Test Fmax static 11 cycle Q5-v Q6-v Q/Qmin % %

11 Friction piles-group of vertical and inclined piles DH2 displacement Bending moment profiles Applied force (kn) Q2-i Q6-i Q5-i DH2 displacement (cm) Bending moment (kn.m) Depth (m) Q5-i_682kN Q5-i_1631kN Q5-i_cycle1 Q6-i_68kN Q6-i_168kN Q6-i_cycle1 Test Q5-i Q6-i DH2 displacement (cm) Fmax static 11 ème cycle Q/Qmin 52% 41% Maximum bending moment (KN/m) Fmax static 11 ème cycle % 3%

12 Improvements 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

13 Friction piles-group of vertical and inclined piles

14 Friction piles-group of vertical and inclined piles Applied stress (kn) DH2_displacement (cm) Q1-i Q11-i Bending moment (kn.m) Depth (m) Q1-i_688kN Q1-i_1638kN Q1-i-1863kN Q11-i_694kN Q11-i_1631kN Q11-i_1853kN Test Q1-i Q11-i DH2 displacement (cm) Fmax static 11 ème cycle Q/Qmin 29% 11% Maximum bending moment (KN/m) Fmax static 11 ème cycle % 7%

15 Fixed-end end moment piles group first results DH2_difference (%) Number of cycles Q5-Q6-i Q7-Q8-i Q1-Q11-i Maximum bending momentat Fmax_difference (%) Q5-Q6-i Q7-Q8-i Q1-Q11-i Number of cycles

16 New experimental devices 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 -Measurement of the normal force in the piles: feasability tests (no calibration) Additional pair of strain gages on the new pile Fast data acquisition system CAREMBA -32 synchronous channels -Sampling frequency 1.2MHz/channel > f > 5kHz -Digitization in the swinging basket 2 pairs of strain gages (AF+BM) 2 pairs of strain gages (AF+BM) 1D Shaker (1-8g) - Payload : 4kg (L=1m, w=.5m, h=.6m) 1 pairs of strain gages BM + = 1.1 m/s ; amax= 4g - Umax : 5mm ; Vmax 2 pairsresponse of strain:gages - Frequency 4 toaf 25 Hz 18 pairs of strain gages BM + 2 pairs of strain gages AF Laminar box (F. Derkx & S. Buttigieg, LCPC-SMI) F. Derkx

17 First comparison of piles group behaviour Bending moment kn.m Depth (m) Q5v_F=174kN Q6v_F=166kN Q1i_F=233kN Q11i_F=243kN Q5v_F=196kN Q6v_F=113kN Q1i_F=115kN Q11i_F=1143kN Q5v_cycle13 Q6v_cycle13 Q1i_cycle13 Q11i_cycle13 M ax im um bending m om ent (k N.m ) Q 5v Q 6v Q 1i Q 11i Num ber of c y c les DH2_displacement (cm) Q5-v Q6-v Q1-i Q11-i Number of cycles Bending moments are higher for the vertical 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)

18 Next experiments

19 Next experiments First Series: Devices and Installation Validation Elements Final Design Based on existing instrumented 12 m piles (strain gauges) Repeatability of the pile group response Friction piles Static and cyclic horizontal loads Improvement of the experimental set-up Shocks and repeated shocks Second Series: Compared response to non seismic load 4 new instrumented piles Fast data acquisition system CAREMBA Accelerometers in the sand Friction and end bearing piles group Static and cyclic horizontal loads Experimental data on the pile group behavior under non seimic loads Shocks and repeated shocks Third Series: Compared response to seismic load Shaker and laminar box Sine (and earthquakes) Experimental data on the pile group behavior under seismic loads