Results of Full Scale Testing of Micropile Casing-PPT Presentation

PPT Presentation

Pdf Summary

GEI Consultants conducted full-scale bending and tension tests on 9.625-inch, 80-ksi micropile casing to evaluate threaded-joint capacity and compare test results with standard design methods. The program included 18 four-point bending specimens across plain, grouted, and central-bar configurations, plus three tension specimens.<br /><br />For intact casing, measured bending behavior was reasonably predicted by standard yield- and plastic-moment calculations. Threaded joints reached an average rupture moment of about 40% of the intact casing’s capacity. Failure occurred in tension near the box shoulder, passing through the threads; the pin remained undamaged, and there was no evidence of local buckling or thread shearing.<br /><br />Grout increased the maximum bending moment of intact casing by about 10%, but had negligible effect on threaded-joint strength or stiffness. A central bar had little effect on intact-casing bending resistance. Although joints with a central bar showed 22% greater bending resistance than grouted joints without one, the cause was unclear, so the increase should not be relied upon without further testing.<br /><br />In tension, specimens failed through the box at an average load of 456 kips. The results were close to the box’s net sectional area, excluding threads, multiplied by yield strength. The study concludes that conventional mechanics-of-materials methods reasonably estimate intact-casing bending capacity and that joint tension capacity can be estimated using the box area and yield strength.

Keywords

micropile casing

bending tests

tension tests

threaded joints

rupture moment

yield strength

plastic moment

grouted casing

central bar

mechanics of materials