Results of Full Scale Testing of Micropile Casing-Video

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Video Summary

The presentation describes full-scale laboratory testing of Nucor Skyline 9⅝-inch, 80-ksi micropile casing to evaluate bending and tensile capacity, especially at its threaded box-and-pin joints. Eighteen bending specimens tested different configurations: ungrouted or grouted casing, with or without a center bar; three additional specimens underwent tension testing.<br /><br />All threaded-joint bending specimens failed consistently by tensile rupture through the box near its shoulder. The joint’s average bending capacity was about 40% of the full-thickness casing baseline. Grout provided no meaningful bending-capacity increase. A center bar had negligible effect on full casing but increased joint bending resistance by 22%; the presenters cautioned that this result needs further study. Tension specimens also ruptured through the box, with an average failure load of 456 kips.<br /><br />Overall, measured capacities could be reasonably estimated using standard mechanics and materials calculations. Findings apply specifically to the tested casing and thread type; other designs may behave differently.

Keywords

micropile casing

bending capacity

threaded box-and-pin joints

tensile rupture

laboratory testing