Thursday, November 22, 2012

Verification of Design Structural Integrity of Driven Piles.

Piles can be bent or sheared during installation and can cause a reduction  in pile capacity.  Piles can also undergo excessive tensile stresses during driving, specifically when soil layers have variable density or strength or when there is no significant end bearing  resistance.  Field test procedures such as standard penetration  tests, pile driving analysis (PDA) with the wave equation, restrikes, and pile load tests can determine the ability of the pile to carry design loads.  Refer later, for guidance on load tests.  Typically 2 to 5 percent of the production piles should be driven as indicator piles, at the start of construction at locations specified by the design engineer or at suspicious locations to confirm the capability of the driven piles to support the structure.  PDA should also be performed during the driving of indicator piles and some static load tests performed  to calibrate wave equation analyses.  Table 6-1 illustrates  an example procedure for verifying pile design. Analyses by wave equation and pile driving are presented.

a.  Wave equation analysis.  The penetration resistance in blows/feet (or blows/inch) measured when the pile tip has been driven to the required depth can be used to calculate the ultimate bearing capacity and verify design.  Wave equation analyses can relate  penetration resistance to the static ultimate bearing capacity....

b.  Pile driving analysis.  Improvements in electronic instruments  permit the measurement of data  for evaluating hammer and driving system performance, pile driving stresses structural integrity, and ultimate pile capacity.  The required dat may be measured and pile performance evaluated in fractions o a second after each hammer blow using pile driving analyze equipments.  PDA is also useful when restriking piles after som time following pile installation to determine the effects of freez or relaxation on pile performance....

Table 6-1 Procedure for verifying Design and Structural Integrity of Driven Piles.

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