(5)

Recompute the ultimate unit pile resistance using the formula

Su' = 3 Rd/As

where

Su' =

ultimate pile resistance per unit area for 20 BPI case, psi. This value

should not fall below 900 psi with concrete piles or 9,000 psi with

steel piles for subsequent computational purposes

(6)

Compute the minimum rated striking energy for the pile hammer for the particular

pile at 20 blows per inch. The formula used depends upon whether the pile is steel or

concrete.

Er 20BPI = Su' As/(30.72 e(-Su'/3333)) . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete Piles

Er 20BPI = As Su'1.68/13569 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steel Piles

where

Er 20BPI =

minimum hammer rated striking energy at 20 blows per inch of

resistance, foot-pound

(7)

The minimum rated striking energy for the hammer is the greater of Er 10BPI and Er

.

20BPI

(8)

Compute the minimum ram weight. Having computed the minimum rated striking

energy for the hammer, one or more hammers can be selected as possible candidates

for driving the pile. The equivalent stroke should be then computed by the equation

Seq = Er/Ws

where

Seq =

equivalent stroke, feet. This should not exceed 8 feet for subsequent

Er = rated striking energy of the hammer, foot-pounds

Ws = ram weight of the hammer, pound

(9)

The minimum ram weight for each hammer can be computed for concrete and

steel piles by the equation

Wsmin = 45.5 As/(Seq) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete Piles

Wsmin = 415 As/(Seq) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steel Piles

where

Wsmin = minimum ram weight, pounds

A hammer should be rejected if its ram weight is less than the minimum ram weight, and

other hammers should be considered until one has been selected with a sufficiently

large ram.

Figure 2-1b. (Concluded)

2-8

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