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RE: Lateral Resistance for Structured Pile Supported Foundation

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The lateral capacity of the pile depends on the pile diameter (capacity increases with pile diameter), pile depth and the type of soil. The allowable lateral load is also limited by the allowable lateral deflection at the ground level.

The allowable lateral load on a single pile could be smaller than the allowable load on a pile in a pile group.

Since the shear load comes from seismic considerations (direction reversal and direction migration) it will be unwise to rely on structural fill to mobilize lateral load capacity. The vibratory nature of ground shaking could loosen soil at the concrete/soil interface.

I would recommend a pile group analysis to design pile depth and diameter in order to obtain the required lateral load capacity.



From: Stuart, Matthew [mailto:mstuart(--nospam--at)]
Sent: Wednesday, May 30, 2007 4:33 AM
To: seaint(--nospam--at)
Subject: Lateral Resistance for Structured Pile Supported Foundation
I have conducted a peer review of a structured (one-way slab and grade beam) pile supported foundation design. The building is considered an emergency shelter under the IBC and is subject to a considerable seismic base shear. The total lateral load required per pile is 15 kips. The geotechnical engineer has indicated that the vertical piles are good for about 1 to 2 kips of lateral capacity. We have recommended that (since the foundation is already constructed) structural fill be placed next to the grade beams to provide enough passive resistance against the seismic base shear. The design engineer is of the opinion that as long as the piles remain adequately braced by the underlying soils during an earthquake that there is no need to provide lateral resistance for the base shear. I am not aware of any Code or design provisions that allow one to ignore the load path mechanism and not provide some form of lateral resistance (either via battered piles, passive soil resistance or vertical pile lateral resistance) against applied forces. Anyone interested in providing some input concerning this issue?
D. Matthew Stuart, P.E., S.E., F.ASCE, SECB
Senior Project Manager
Structural Department
Schoor DePalma Engineers and Consultants
200 State Highway Nine
Manalapan, NJ 07726
732-577-9000 (Ext. 1283)
908-309-8657 (Cell)
732-298-9441 (Fax)

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