The rocking behavior of a shallow foundation of a bridge pier has emerged as an effective mechanism for reducing the seismic load on the superstructure during a strong earthquake. However, a lack of understanding regarding the rocking behavior of shallow foundations has hindered the application of the rocking foundation design philosophy to construction. In this study, the soil-rounding effect on embedded foundations was evaluated to increase understanding of the rocking mechanism. A centrifuge apparatus was used to conduct horizontal slow cyclic tests on an embedded shallow foundation model for three different slenderness ratios (i.e., structure height divided by foundation length) at a centrifugal acceleration of 20 g. The soil-rounding phenomenon was examined according to variations in the soil pressure under the foundation during cyclic loading, and the shape of the rounded soil surface was evaluated as a function of the slenderness ratio. The ultimate moment capacity of the shallow foundation was observed to increase with the side soil pressure; this was verified by comparing the side soil earth pressure with the overturning moment. The rocking mechanism of the embedded shallow foundation was evaluated by focusing on soil rounding.

The response of the structure subjected to an earthquake load is greatly affected by the properties of the structure and soil so it is very important to accurately determine the characteristics of the structure and soil for analysis. However, studies on the effective profile depth where soil properties are determined, have been conducted in the presence of restricted conditions (i.e., surface foundation, linear soil properties), and without any considerations on damping. In case of the effective height of structure that affects its rocking behavior, it was only theoretically or empirically determined. In addition, most previously published studies on soil–structure interaction (SSI) focused on limited effects and parameters (e.g., rocking behavior, embedment effect, effective profile depth, spring constant, and damping coefficient) and not on comprehensive SSI parameters. Furthermore, no detailed validation procedure has been set in place which made it difficult to validate the SSI parameters. Since the effective height of structure and effective profile depth are the basis of all the input parameters of SSI analysis, it is important to validate and determine them. Therefore, in this study, the procedure used to optimize the two SSI parameters was established based on an analytical approach that considered all the possible SSI parameters that were investigated from conventional codes and studies and physical model tests. As a result of this study, the optimum values of the effective height of the structure and effective profile depth were respectively determined according to (a) the height from the bottom part of the foundation to the center of the mass of the superstructure, and according to (b) the depth at values equal to four times the radius of the foundation.