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

PPT Presentation

Pdf Summary

The presentation examines the use of concrete plugs in open-ended steel pipe piles to promote plugging and increase toe resistance, particularly where piles need greater lateral resistance or scour protection. Plugs create a major impedance contrast that changes high-strain dynamic testing (HSDT) signals. Their effects are difficult to model because plug properties, steel–concrete bonding, length, and location may be uncertain; previous signal-matching results varied substantially.<br /><br />In a British Columbia case study, 914 mm diameter piles were initially driven open-ended to depths of 45–50 m without meeting termination criteria. Concrete plugs were then installed, in some cases far above the pile toe because of equipment limits. On redriving, penetration resistance rose from about 20 blows per 250 mm to refusal.<br /><br />The authors compared HSDT upwave signals collected before and after plugging. This “signal stacking” showed consistent signals between blows and clearly illustrated the plug’s effect, including changes in the response of the pile section below it. Rather than independently fitting every parameter, they used shaft-resistance values established from the unplugged pile tests and adjusted pile properties along the plug and toe resistance for the plugged-pile analysis. The estimated total resistance increased from 5.2 MN to 6.6 MN, with the toe component rising from 2.6 MN to 3.9 MN.<br /><br />The authors recommend designing plugs to resist driving forces and avoid debonding, keeping them short but generally at least five pile diameters long. A preliminary sizing equation is provided: plug length ≈ toe pressure × pile inside diameter / 2000, using the stated bond-resistance assumption and a factor of safety of 2. Plugs should be placed close to the toe, accurately measured, and considered in drivability simulations. Testing before and after installation—or testing an adjacent unplugged pile—can reduce uncertainty. Signal stacking is strongly recommended, and static or rapid loading tests may help validate assumptions.

Keywords

concrete plugs

open-ended steel pipe piles

toe resistance

high-strain dynamic testing

signal stacking

plugging

pile drivability

shaft resistance

debonding

British Columbia case study