Soil Pile Group Interaction in FB-MultiPier Dr. J. Brian Anderson, P.E. Developed by: Florida Bridge Software Institute
Soil Pile Group Interaction
in FB-MultiPier Dr. J. Brian Anderson, P.E.
Developed by: Florida Bridge Software Institute
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
Coupled Soil-Structure Interaction
Ship Impact
Debris Impact
Scour
Plumb Piles/Shafts
Earthquake Battered Piles
Scour
Live and Dead Loading
Soil-Structure Interaction
Vertical Nonlinear Spring
Lateral Nonlinear Spring
Torsional Nonlinear Spring
Nonlinear Tip Spring
Soil-Pile Group Interaction
Group Interaction:
Modeled with Multipliers
P-y curves
P x Pm1
P
P-y curves
P x Pm2
P
Static
Ship Load
R R R I II III
BROWN & REESE (1988)
- Multipliers, Pm for P Values in P-y Curves
- Function of Row Position in Group
ROW Pm
R 0.8
R 0.4
R 0.3
I
II
III
Pm would be 0.3 for R or greater IV
Soil-Pile Group Interaction - Lateral
P-Multipliers
• Axial Efficiency
Soil-Pile Group Interaction - Axial
Summing Effects of a Friction
Pile Group (FHWA)
• Axial Efficiency
Soil-Pile Group Interaction - Axial
Block Failure Mode of
Piles in Cohesive Soils
(FHWA)
Experiments
• Scale Cenrtifuge Models (UF)
– Plumb and battered pile groups
– Embedded caps
• Full Scale
– Roosevelt Bridge Lateral Load Test (UF)
– Axial Group Study (UH)
Prediction of Field Response
DEFLECTION (IN)
0 1 2 3 4 5 6 0
200
400
600
800
1000
1200
LOAD-DEFLECTION CURVE ROOSEVELT BRIDGE - TEST PILE GROUP
LO
AD
(K
IPS)
TEST PILE GROUP (MEASURED) FB-PIER PREDICTION
Single vs. Group Axial Behavior
3D
3D
10.75” pipe
25 ft
18 ft
clay
Sandy clay
FHWA: Houston
Study
Individual Group Axial Single Axial Total Group
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
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
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
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.
188-203.
• 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. 1016-1026.
• 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.
936-946.
• 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. 1261-1276
• 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. 12-18.
• 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. 8-16.
• 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