Micropile response to combined loading

The familiarity and acceptance of micropiles by engineers, contractors, and owners has greatly expanded in recent years such that they are routinely considered on many projects. However, research regarding the behavior of micropiles has lagged behind. The goal of this research project was to address some of the fundamental gaps that were not addressed in engineering practice and require further study and testing. Specifically, this research studied the behavior of micropile foundations subjected to simultaneous axial and lateral (combined) loading, including an assessment of the impact of axial load on lateral behavior of micropiles. This research project consisted of three experimental tasks to evaluate the effect of combined loading on micropiles. Task 1 consisted of laboratory testing of scale model micropiles installed in prepared sand. Task 2 consisted of installation and testing of six (6) full-scale micropiles at a clay site to assess the impact of combined loading on the lateral capacity of micropiles. Task 3 consisted of instrumentation of production micropiles used to support a bridge in the Smoky Mountains in eastern Tennessee. The results indicated that, for micropiles in clay, the presence of an axial load resulted in small decreases in both lateral deflection and bending moment compared to the lateral load tests. For micropiles in sand, the lateral deflection was not significantly affected by introduction of a constant axial load, but bending moments in the micropiles were significantly increased for combined load conditions. In addition, p-y analysis accurately predicted load-deflection behavior of micropiles in clay, but over-predicted the maximum bending moments --Abstract, page iii