Modulus Load Test Results for Rammed Aggregate Piers^TM in Granular Soils

In the past five years, over 25 structures in the states of California, Oregon, and Washington, have been supported by Rammed Aggregate Piers constructed in granular soils. The piers are installed by drilling 60 to 90 cm diameter holes and ramming thin lifts of highway base course stone within the drilled cavities. The elements are used to support conventional shallow footings. The system is unique and innovative because it incorporates features associated with the design and construction of shallow and deep foundation systems. Accordingly, the design procedures include concepts derived from conventional shallow foundation design, historical stone column soil improvement system design, and cast-in-drilled-hole concrete shaft design. Unlike design values for drilled deep foundation systems, which are well-documented in the literature, parameter values for rammed aggregate piers are established from the results of modulus tests conducted at each project site. This paper presents results of 19 rammed aggregate pier modulus tests performed at sites underlain by granular soils. Test results are correlated to matrix soil characteristics and length of the piers. This paper is of particular significance because it presents a database of in-situ modulus values used in the design of a cost-effective and increasingly popular drilled foundation system.