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

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 Debris Impact Scour Plumb Piles/Shafts Earthquake Battered Piles Live and Dead Loading Ship Impact

Typical Deep Foundations:

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

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

Lateral Soil-Structure Interaction Y Passive State Active State Y P

Soil-Pile Group Interaction Lead Row Smallest Disturbance

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

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 0.8 I R 0.4 II Static R 0.3 Ship Load III Pm would be 0.3 for R or greater IV

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

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)

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)

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

Full Scale Load Test at Roosevelt Bridge

Roosevelt 4x4 Field Study

Prediction of Field Response 1 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)

Single vs. Group Axial Behavior 3D 10.75” pipe FHWA: Houston Study 25 ft clay 18 ft Sandy clay Total Group Individual Group Axial Single Axial

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

Pinned Laterally Loaded Pile Group

Fixed Head Laterally Loaded Group

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