Flexural Strength of Micropile Threaded Connections

Despite the widely recognized flexural weakness at threaded connections between steel casing segments of micropiles, relatively simple recommendations are often applied to address the reduced bending capacity at these locations and their degree of conservatism is not well-understood. A methodology to predict the bending capacity and governing mode of failure (jump-out or rupture) at the threaded connections is applied and compared with observations from several independent studies. The results suggest that the 50% reduction in wall thickness and bending capacity often adopted in practice is not always conservative and highly dependent on the thread connection details and geometry. It was illustrated that jump-out is the weak mode of failure. Thread details—including shape, thread angle, and thread length—are examined to illustrate the sensitivity of the failure mode to thread geometry.