Four-Point Bending Test of Micropile Threaded Connections

A series of four-point bending tests on micropile specimens composed of a steel casing with a threaded joint and filled with grout had been performed. The objective of the testing program is to assess the predictability of failure loads and failure modes of the threaded joint when subjected to bending. This paper summarizes partial results on casings with outer diameter of 7'', 7-5/8'', and 9-5/8'' connected by threaded joints of variable length. It was found that casing diameter and threaded length play an important role on the overall connection behavior, controlling both failure mode and flexural strength. Moreover, the observed displacements suggest that the Euler-Bernoulli beam theory, often assumed on bending related problems, is not satisfied at the threaded joint, primarily due to the discontinuity introduced by the threads.