Hollow bar micropiles exhibit outstanding bond transfer values and have the ability to reinforce soft/loose soils thus improving the settlement behavior of foundations utilizing them. The behavior of hollow bar (fully bonded) micropiles in soil will be examined and a case history discussed where over 1000 hollow bar micropiles were used to reinforce soils beneath heavily loaded equipment pads at an aircraft manufacturing facility in soft coastal plain soils. A model of bonded anchors / micropiles in soil is developed for characterizing and describing micropile behavior. An extensive load testing program was implemented to optimize micropile lengths and finite element modeling was utilized to quantify the amount of improvement achieved by the micropiles.
Design-build contractor GeoStructures completed the foundation reinforcement of Pennsylvania’s historic Kinzua Bridge. Tension micropiles were required in order to add supplemental lateral load resistance for the remaining sections of the former railroad bridge that was partially destroyed by a tornado in 2003. The micropiles, which anchor the existing tower piers into rock, were installed through the existing sandstone tower pier foundations. GeoStructures installed a total of 48 primary tension micropiles with load capacities ranging from 54 to 84 kips to provide additional foundation uplift restance and 48 secondary anchors to reinforce the existing tower piers.
A case history on the project was presented at the International Society for Micropiles – International Workshop on Micropiles in Washington, DC. The case history presentation can be viewed HERE.