Plywood cushion blocks for driving precast concrete piling
Call DFP Sales for your prestressed concrete driving cushions! 201-337-5748Precast concrete piles are a good choice for certain applications.  They are ideal when they can be driven to tip elevation and do not have to be cut.  However, cutting the piles is a fairly simple task.  Extreme care must be taken while handling and cutting the waste sections.



This cushion was fabricated using 10 layers of 3/4" plywood (actually 23/32")
Note the cropped corners at about 3°-5° to avoid binding in the cap
Fabricated cushionOne item that is important, is to use adequate cushioning material between the driving head and the concrete pile.  This is not to be confused with hammer cushion material.  Plywood cushioning material of 4" (100 mm) thick may be adequate for piles of 50' (15m) or less with moderate tip resistance.  Plywood cushioning of 7 or 8" (175 mm to 200 mm) thick may be required when driving longer piles and plywood up to 20" thickness has been used when piles are driven in soft soils.

Manitowoc 4100 on barge, piles in the foreground with falsework

Manitowoc 4100 on barge, piles in the foreground with falseworkWhen the wood shows signs of being highly compressed, delaminated or burned it should be replaced.  It may be necessary to change the plywood cushion if it starts to fail.  This should be done before the pile reaches final tip elevation or blow count.  A new cushion should be used on every pile.  The cushion may look usable, but it is compressed and likely has an impression from the previous pile that will not exactly fit to the next pile.  This could cause pile breakage.

16" x 16" prestressed piles ready for cutoff
16" x 16" prestressed piles ready for cutoffRemember that the cost of the wood cushion is small compared to the cost of the pile and a possible redesign, delay and added labor.

The job photos show that with proper methods the precast concrete piles can be handled and driven efficiently and without problems occurring.

These piles were driven at a Brooklyn, New York pier by Contractor Spearin Preston & Burrows from a barge using a Manitowoc 4100 crane and an ICE 42S 42,000 ft/lb. hammer.  The piles are 65-70' 16" X 16" square prestressed.  The pier is being constructed for the NYC Economic Development Corporation.

Used cushions may look useable, but don't be tempted to reuse

Used cushions may look useable, but don't be tempted to reuseThe plywood cushions were fabricated by DFP Foundation Products, LLC., Franklin Lakes, NJ 201-337-5748.  FAX 201-337-9022.

For more information on this subject contact the Prestressed Concrete Institute and ask about the PCI Committee on Prestressed Concrete Piling report titled: "Recommended Practice for Design, Manufacture and Installation of Prestressed Concrete Piling."  This report was published in the Mar/April 1993 PCI Journal.

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