Load Transfer in Rammed Aggregate Piers

Predicting the load–settlement and load–transfer behaviors of rammed aggregate piers are important aspects of design. Use of advanced engineering models, however, can be complex involving uncertainty in selection of nonlinear constitutive model parameters for the aggregate and surrounding matrix soils and in selection of in situ stress fields. For purposes of simpler design calculations, this paper uses the closed-form approximate solution and the boundary-element method using both elastic (i.e., neglecting interface slip) and elastic–plastic soil–pier interface (i.e., considering interface slip) to predict load–settlement and load–transfer for rammed aggregate piers. Unlike previous studies that evaluate load–settlement and load–transfer for stiff, slender piles (e.g., concrete and steel piles) or fully penetrating granular piles, this paper focuses on floating rammed aggregate piers having slenderness ratios $(L∕D)$ of 3–10 and pier–soil stiffness ratios $(E_p∕E_s)$ of 5–80. Predictions of load–settlement and load–transfer as a function of depth are compared to three full-scale instrumented load tests. Based on the calibrated models, equations for predicting load–settlement response and load–transfer as functions of $E_p∕E_s$ , and $L∕D$ are presented with example calculations.