Reduction of Seismic Loading on Structures Induced by Piles in Inhomogeneous Soil

Abstract

Abstract. The kinematic response of flexible piles in inhomogeneous soil

The Beneficial Role of Piles on the Seismic Loading of Structures

“…First, the similarity of FE-based curves of I u indicates that the dimensionless frequency a eff,La effectively describes the combined effect of the excitation frequency, the diameter and Young's modulus of the pile, the density and Poisson's ratio of the soil, and the soil stiffness and its distribution with depth on kinematic pile response. Thus a eff,La may be considered the single dimensionless parameter that controls the kinematic response of a pile embedded in a soil with continuous variation of stiffness with depth by incorporating eight physical quantities, in agreement with the Winkler-based results reported in Rovithis et al (2017).…”

“…The behavior of Equation 7 is shown in Figure 2a-2d, where the amplitude of I u against a eff,La is compared with the rigorous FE model response for the homogeneous, linear, parabolic, and proportional profile of soil stiffness, respectively. The comparison is performed for a wider frequency range over an earlier Winkler-based analysis of the authors (Rovithis et al 2017). In each plot four soil-pile configurations are analyzed, combining average shear wave velocity V S,30 at 100 and 200 m/s and pile diameter d at 1 and 1.5 m. The following points are worthy of note.…”

“…Thus the dimensionless parameter a eff requires, as all the Winkler-based solutions, the selection of a coefficient δ relating the spring stiffness to the soil Young's modulus (Roesset 1980, Dobry et al 1982, Gazetas and Dobry 1984. To overcome this limitation and since μ and L a reflect the same physical mechanism, following the expression μ ¼ 2.5∕L a (Di Laora and Rovithis 2015), an alternative frequency parameter may be defined as (Rovithis et al 2017):…”

“…Fan et al (1991) came practically to the same conclusion for a group of piles connected rigidly by a free-to-rotate cap. Rovithis et al (2017) studied the kinematic response of fixed-head piles embedded in a viscoelastic soil with stiffness varying continuously with depth according to a generalized power law function. The study was performed by means of a Beam-on-Dynamic Winkler Foundation model and led to an analytical expression of the horizontal kinematic interaction factor I u ð¼ a p ∕a s Þ as a function of a single dimensionless parameter that incorporates the excitation frequency, the diameter and Young's modulus of the pile, the density and Poisson's ratio of the soil, and an average soil stiffness and its distribution with depth.…”

“…(2) explore the effectiveness of a unique frequency parameter to describe the modification of free-field motion induced by piles for a wider range of frequencies over earlier Winklerbased studies of the authors (Rovithis et al 2017); (3) propose a simplified expression for I u that may be reliably employed for practical time-domain applications; (4) present a novel physical interpretation of the kinematic interaction factor by introducing the concept of soil motion being averaged by pile stiffness over an effective pile length; and (5) propose a set of simplified formulae for a preliminary assessment of the importance of the filtering effect of piles in terms of spectral acceleration. An application of the proposed formulae is performed to normally consolidated clays for both surface and embedded pile caps, and selection criteria are derived for the pile diameter associated to maximum filtering action.…”