Investigation of rocking mechanism of shallow foundations on sand via PIV technique

Abstract

Adoption of the rocking isolation concept in foundation design is considered as an effective method in reducing seismic loads of structures. Despite much research conducted on the rocking behavior of foundations, concerns regarding the practical application of the rocking foundation design concept still prevail. The concerns primary stem from the lack of accurate understanding and knowledge associated with the soil‐foundation deformation mechanisms during rocking motions. Determination of deformation mechanisms and soil mass failure modes during foundation rocking helps to gain insight into the rocking behavior, recognize influential factors on foundation settlement or uplift, and propose appropriate improvement strategies to control foundation deformations. The primary objective of this study is to investigate the deformation behavior and failure modes of the soil mass beneath a rocking foundation with various initial static vertical factors of safety (F.S.v) and embedment depths. To this end, a series of reduced‐scale slow‐cyclic tests under 1g condition have been conducted using a single degree of freedom (SDOF) model. To determine soil deformation mechanisms, soil displacement fields have been measured using Particle Image Velocimetry (PIV) technique. Soil deformation mechanisms during loading and unloading paths, as well as causes leading to the foundation settlement or uplift have been evaluated and discussed. Additionally, changes in the effective soil‐foundation contact area in different loading cycles have been examined based on the PIV results. Based on the results, soil deformation mechanisms in the loading portions include soil densification, wedge deformation and scoop deformation. As the footing embedment depth increases, wedge deformation mechanism becomes limited, while scoop deformation mechanism becomes stronger. Additionally, as the foundation F.S.v increases, the depth of influenced zone of the rocking foundation decreases and the soil displacement occurs to a more limited depth.

Modeling Techniques, Seismic Performance, and the Application of Rocking Shallow Foundations: A Review

“…Consequently, to account for the impact of uplift on the rocking response, other researchers made substantial efforts. Particle image velocimetry was used by Moradi et al (2023) [49] to investigate the deformation mechanisms beneath shaking foundations. They found that during loading cycles, foundations with larger FSv have less contact area with the earth, which causes visible rise on the unloaded side (heel side).…”

“…Kawashima and Hosoiri (2003) [52] conducted a study on the inelastic rocking response of large, rigid foundations. Their findings revealed that rigid foundations do not undergo overturning, even when exposed to ground motions with accelera- Particle image velocimetry was used by Moradi et al ( 2023) [49] to investigate the deformation mechanisms beneath shaking foundations. They found that during loading cycles, foundations with larger FS v have less contact area with the earth, which causes visible rise on the unloaded side (heel side).…”

“…Their findings revealed that rigid foundations do not undergo overturning, even when exposed to ground motions with accelera-Densification Rotation Rotation Settlement Settlement 6. The mechanism of soil particle displacement for foundations with large (a) and small (b) vertical factors of safety throughout the loading quarter cycles [49]. Psycharis and Jennings (1983) [50] explored the dynamic behavior of a rocking, rigid block allowed to uplift.…”

Effect of Footing Shape on the Rocking Behavior of Shallow Foundations

“…These shape differences arise from variations in the soil-foundation contact area and the degree of toe (loaded side) penetration into the subgrade during rocking. Moradi et al [52] studied the deformation mechanisms beneath rocking foundations using the PIV technique. They found that foundations with large FSv have a smaller contact area with the soil during loading cycles, resulting in a notable uplift on the heel side (unloaded side).…”