Load Test Comparisons for Rammed Aggregate Piers and Pier Groups

Abstract

Design methods used to estimate the settlement below Geopier Rammed Aggregate Pier — supported footings rely on the performance and interpretation of a modulus test conducted on a single Rammed Aggregate Pier element. The test is used to determine the spring stiffness of a single element. However, actual footings are generally supported by multiple elements and the interaction effects between groups of elements are not simulated in the modulus tests. This paper presents the results of research performed to investigate the interaction effects between groups of Rammed Aggregate Piers installed at test facilities at the University of Utah and Iowa State University. The full-scale field test programs include load tests for individual elements, footings supported by groups of elements, and footings not supported by reinforcing elements. The results of the research demonstrate the increase in bearing capacity that is afforded by the installations of the piers. The results also indicate that a group interaction factor of 1.0 is appropriate for design. This paper is of particular significance because it is used to verify design procedures for a soil reinforcement method widely used in the United States.