1. Soil Pile Group Interaction in FB-MultiPier
Dr. J. Brian Anderson, P.E.
Developed by: Florida Bridge Software Institute
Dr. Mike McVay, Dr. Marc Hoit, Dr. Mark Williams

2. Session Goals Soil-Pile Group Interaction
Discussion of Soil Strucuture Interaction Model
Lateral p-y multipliers
Axial efficiency factors
Example #2 Pile Group Analysis – Load Test at Roosevelt Bridge

3. Coupled Soil-Structure Interaction
Debris Impact
Scour
Plumb Piles/Shafts
Earthquake
Battered Piles
Live and Dead Loading
Ship Impact

4. Typical Deep Foundations:

5. Soil-Structure Interaction
Vertical Nonlinear Spring
Torsional Nonlinear Spring
Lateral Nonlinear Spring
Nonlinear Tip Spring

6. Single Pile Model P
(F/L) Y 
(F/L2) Z

7. Lateral Soil-Structure InteractionY
Passive State
Active State Y P

8. Soil-Pile Group Interaction
Lead Row
Smallest
Disturbance

9. Soil-Pile Group Interaction
P x Pm2
P-y curves P
P x Pm1
P-y curves
Group Interaction:
Modeled with Multipliers

10. Soil-Pile Group Interaction - Lateral
P-Multipliers
BROWN & REESE (1988) R R R I II
III
- Multipliers, Pm for P Values in P-y Curves
- Function of Row Position in Group
ROW Pm R I R II
Static R
Ship Load
III
Pm would be 0.3 for R or greater IV

11. Summing Effects of a Friction Pile Group (FHWA)
Soil-Pile Group Interaction - Axial
Axial Efficiency
Summing Effects of a Friction Pile Group (FHWA)

12. Block Failure Mode of Piles in Cohesive Soils (FHWA)
Soil-Pile Group Interaction - Axial
Axial Efficiency
Block Failure Mode of Piles in Cohesive Soils (FHWA)

13. Experiments Scale Cenrtifuge Models (UF) Full Scale
Plumb and battered pile groups
Embedded caps
Full Scale
Roosevelt Bridge Lateral Load Test (UF)
Axial Group Study (UH)

14. Centrifuge Modeling Field 1 ft Centrifuge 50 g 50 ft
Same Soil Stresses

15. Full Scale Load Test at Roosevelt Bridge

16. Roosevelt 4x4 Field Study

17. Prediction of Field Response1 2 3 4 5 6
200
400
600
800
1000
1200
LOAD-DEFLECTION CURVE
ROOSEVELT BRIDGE - TEST PILE GROUP
LOAD (KIPS)
TEST PILE GROUP (MEASURED)
FB-PIER PREDICTION
DEFLECTION (IN)

18. Single vs. Group Axial Behavior3D
10.75” pipe
FHWA: Houston
Study
25 ft
clay
18 ft
Sandy clay
Total Group
Individual Group Axial
Single Axial

19. Experimental Results: Plumb Piles
Efficiencies and multipliers are independent of soil density
Group Efficiencies:
At 5D Spacings - 95%
At 3D Spacings - 70% to 75%
Lateral Multipliers:
At 3D Spacing- 0.8, 0.4, 0.3, 0.2, 0.2,…,0.3
At 5D Spacing- 1.0 , 0.85, 0.7,…..,0.7

20. Experimental - Battered Piles
Efficiencies and multipliers are independent of soil density
Lateral Multipliers:
At 3D Spacing- 0.8, 0.4, 0.3, 0.2, 0.2,…,0.3
At 5D Spacing- 1.0 , 0.85, 0.7,…..,0.7
Data Available only for A frame design

21. Pinned Laterally Loaded Pile Group

22. Fixed Head Laterally Loaded Group

23. Design Summary
Pile Group response is strongly influenced by geometry, loading, connectivity, & material characterization
geometry: 3D vs. 5D, battered vs. plumb
connectivity: fixed vs. pinned pile heads
loading: lateral or combined lateral & axial
material: linear vs. nonlinear pile models

24. References
Zhang, L.M., McVay, M.C., Han, S.J., Lai, P. and Gardner, R., “Effects of Dead Loads on the Lateral Response of Battered Pile Groups,” Canadian Geotechnical Journal, Vol. 39, No. 6, June 2002, pg
McVay, M.C., Zhang, L., Molnit, T., Bollmann, H., and Lai, P., “Centrifuge Testing of Large Plumb Pile Groups (3x3 To 7x3) in Sands,” ASCE, Journal of Geotechnical Engineering, Oct. 1998, Vol. 124, No 10, pp
Zhang, L., McVay, M.C., and Lai, P., “Numerical Analysis of Fixed Head 3x3 to 7x3 Plumb Pile Groups in Sands,” ASCE, Journal of Geotechnical Engineering, Nov, 1999, Vol. 125, No. 11, pp
Brown, D, Morrison, C., and Reese, L. “Lateral Load Behavior of a Pile Group in Sand,” ASCE, Journal of Geotechnical Engineering, 1988, Vol 114, No. 11, pp
McVay, M.C., Zhang, L., Han, S., and Lai, P., “Experimental and Analytical Modeling of Laterally Loaded Pile Groups with Embedded Pile Caps in Sand,” Transportation Research Record, No. 1736, Dec. 2000, pp
Pinto, P. and McVay, M.C., Hoit, M., and Lai, P, “Centrifuge Testing of Plumb and Battered Pile Groups in Sand,” Transportation Research Record, No. 1569, Jan. 1997, pp
O'Neill, M. W., Brown, D. A., Anderson, D. G., El Naggar, M. H., Townsend, F. C., Mcvay, M. C. (1997). “Static and dynamic lateral loading of pile groups.” NCHRP 24-9, Highway Research Center, Harbert Engineering Center, Auburn University, Auburn, AL