Uplift Testing of Rammed Aggregate Pier® Systems

Abstract

Recent changes and consolidation in building codes across the U.S. have put a larger emphasis on the need for cost-effective foundation support of both bearing and uplift foundation loads resulting from wind and seismic forces. The Rammed Aggregate Pier (RAP) system is a commonly-accepted soil reinforcement method that results in highly-densified aggregate columns for liquefaction mitigation, bearing capacity enhancement, and uniform settlement control for conventional shallow foundations. The RAP system provides a cost beneficial alternative to deep foundations such as pre-cast driven piles, auger-cast piles, or concrete piers and to mass excavation and replacement for shallow foundations. In high seismic and wind areas, uplift loads created by overturning forces on foundations are resisted with uplift RAPs that are equipped with a structurally designed steel anchor assembly. Typical uplift capacities in California range from 178 to 445 kN (40 to 100 kips) for 762 to 838 mm (30 to 33 inch), 3.6 to 7.0 m (12 to 23 feet) meter long RAP elements using ASD (allowable stress design) and incorporating a minimum factor of safety of 2. Full scale load tests on uplift RAPs show repeatable tangent stiffness after multiple overstress load cycles. This paper presents the first published results of psuedo-cyclic uplift load tests on uplift RAPs installed on projects in California.