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

Pile Groups

Bridges

Bridges

Soil-Structure Interaction

Vertical Nonlinear Spring

Lateral Nonlinear Spring

Torsional Nonlinear Spring

Nonlinear Tip Spring

Single Pile Model

P

(F/L)

Y

Y

P

(F/L)

Y

P

(F/L)

(F/L2)

Z

(F/L2)

Z

(F/L2)

Z

Y

Z

Lateral Soil-Structure Interaction

Passive State Active State

2

0

r dr)L/F(P

Y

P

Y

Soil-Pile Group Interaction

Lead Row

Smallest

Disturbance

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)

Centrifuge Modeling

50 ft

1 ft

50 g

Same Soil Stresses

Field Centrifuge

Full Scale Load Test at Roosevelt Bridge

Roosevelt 4x4 Field Study

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

Pinned Laterally Loaded Pile Group

No Vertical

Movement

Moment Shear Axial

Fixed Head Laterally Loaded Group

Axial ForcesMoment Shear

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

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