RECENT HIGH-STRAIN DYNAMIC TESTING EXPERIENCE WITH STEEL PILE PILES WITH CONCRETE PLUGS-Paper

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The paper examines high-strain dynamic testing (HSDT) of open-toe steel pipe piles fitted with partial concrete plugs to increase toe resistance. Such plugs may help piles reach termination criteria in dense granular soils or where cobbles and boulders impede driving, but they create a major impedance contrast that complicates interpretation of force and velocity signals and signal matching.<br /><br />Numerical simulations and case histories show that a plug can dominate a pile’s dynamic response, making resistance estimates uncertain when plug behavior, properties, and location are not well known. In a recent project, piles tested before and after plug installation showed a marked change in the stacked upwave signals. Comparing the tests allowed the team to retain the shaft-resistance estimate from the unplugged pile and vary only plug impedance and toe resistance in the plugged-pile analysis. IMPACT and AllWave-DLT produced similar results; the analysis indicated an approximately 1.3 MN increase in mobilized toe resistance. The plug also increased driving resistance to refusal.<br /><br />The authors recommend stacking signals to assess data quality and compare pile behavior across blows and before and after plug placement. Where possible, piles should be tested both before and after installation of the plug, or an adjacent unplugged pile should be tested. Plug construction details should be carefully documented, particularly to assess possible debonding.<br /><br />Plugs should be as short as practicable—generally no less than about five pile diameters—and placed close to the toe where feasible. Drivability simulations should explicitly account for the plug. The proposed design guidance is preliminary: further testing, including static or rapid load tests, is needed to validate resistance estimates and determine whether plugs are necessary.

Keywords

high-strain dynamic testing

open-toe steel pipe piles

partial concrete plugs

toe resistance

pile driving

signal matching

impedance contrast

stacked upwave signals

drivability simulations

static load tests