Investigation of seismic performances of unconnected pile foundations using dynamic centrifuge tests

Abstract

An unconnected pile foundation allows separation between the lower pile and the pile cap, and it has been proposed as an effective foundation type for reducing the seismic load during strong earthquakes. However, previous quantitative evaluations of unconnected piles with various foundation types and earthquake intensities are inadequate. In this study, the influence of base shaking level and the material of the interposed layer between pile and pile cap on the seismic behaviour of unconnected piles were evaluated using a centrifuge model test to reproduce the field stress conditions. A dynamic centrifuge model test was completed on an experimental model consisting of dry sandy soil, a foundation and a single degreeof-freedom structure. The acceleration of the structure and the settlement of the foundation system were measured during base shaking. For the unconnected pile system, the structural seismic load reduction effect due to rocking behaviour was confirmed, and the unconnected pile foundation with the interposed layer with large stiffness had less vertical settlement than the conventional shallow foundation. Finally, the rotational stiffness and damping ratio for the foundation system used in the centrifuge model tests were derived and discussed.

Seismic response of nuclear power station with disconnected pile-raft foundation using dynamic centrifuge tests

“…With the gravel cushion, the load-sharing relationship between shallow soils and piles becomes more reasonable than CPRF [20][21]. The settlement of the DPRF is smaller than a shallow foundation [22][23]. Evidence showed that the gravel cushion could also perform as an isolation layer because it can decrease the earthquake energy transferred to the superstructure [22,[24][25] and the inertial forces from the superstructure to the foundation.…”

Novel post‐tensioned rocking piles for enhancing the seismic resilience of bridges

“…Numerous ground improvement techniques for the rocking shallow foundation have been investigated, such as the integration of micropiles, 40 stone columns, 41 large rigid foundation slabs, 42,43 and unconnected piles—both short 44 and long 45,46 —to reduce or even eliminate the issues associated with soil settlements and permanent foundation rotations. Despite achieving this goal, the absence of energy dissipation—which would otherwise arise from the inelastic behavior of the bridge pier and the soil medium—results in larger inertial forces to the pier as well as larger deck displacements 47,48,14 .…”

Numerical model for the dynamic and seismic analysis of pile-supported structures with a meshless integral representation of the layered soil

“…The dynamic response of pile foundations and pile-supported structures has been an important subject of study during several decades (see e.g. Kaynia (1982); Kaynia and Kausel (1991); Miura et al (1994); Mylonakis and Gazetas (1999); Blaney and El Naggar (2000); Nikolaou et al (2001); Maeso et al (2005); Escoffier et al (2008); Rovithis et al (2013); Goit et al (2013); Dowling et al (2016); Li et al (2016); Carbonari et al (April 2019); Ha et al (2019) Chatterjee et al (2019); Correia and Pecker (2021)) due to the widespread use of deep foundations and the influence that the dynamic soil-pile-structure interaction (SSI) phenomena can exert on the dynamic and seismic response of the structures (see e.g. Veletsos and Meek (1974); Mylonakis and Nikolaou (1997); Gazetas and Mylonakis (1998); Mylonakis and Gazetas (2000); Stewart et al (1999aStewart et al ( , 1999b; Gerolymos et al (2008); Medina et al (2013); Di Laora and de Sanctis (2013); Pitilakis et al (2014); Medina et al (2015); de Sanctis et al (2015); Sun and Xie (2019)).…”