A Trusted Test Method Meets a Newer Pile: Usage of Dynamic Load Testing on Ductile Iron Pipe-PPT Presentation

PPT Presentation

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Alex Ryberg of GRL Engineers presented the use of dynamic load testing (DLT) on ductile iron pipe (DIP) piles. The presentation reviewed the development and basic theory of pile testing: strain gauges measure force, accelerometers measure motion, and analysis of the resulting data estimates pile resistance. DLT is well established for driven piles and can also be applied to other pile types.<br /><br />The case history involved 6.7-inch-diameter DIP piles installed in variable soils over shale. Initial testing during installation and subsequent restrike tests showed highly variable energy transfer, influenced by hammer settings and operator-controlled installation. Mobilized resistances of roughly 65–75 kips were below the project’s 120-kip target and were considered likely lower bounds, rather than ultimate capacities. Analysis also needed to account for the pile’s non-uniform composite section.<br /><br />Further testing with GRL’s APPLE drop hammer mobilized higher resistances, including greater shaft resistance and end bearing. The results demonstrated that hammer size can limit how much soil resistance is mobilized during installation; a larger, appropriately sized hammer may reveal additional capacity.<br /><br />The presentation concluded that DLT can be successfully performed on DIP piles during installation and afterward. Testing also supported the formation of the piles’ friction-welded joints during installation. Installation time alone is not a reliable indicator of capacity: correlations should account for delivered energy and crowd force, and equivalent blow count and energy may be more informative. DLT can complement or, in suitable cases, replace static load testing, while more reliable capacity correlations require high-quality testing.

Keywords

dynamic load testing

DIP piles

ductile iron pipe

pile resistance

strain gauges

accelerometers

hammer energy

restrike testing

shaft resistance

end bearing