A Study of Piles during Earthquakes: Issues of Design and Analysis

Abstract

The seismic response of pile foundations is a very complex process involving inertial interaction between structure and pile foundation, kinematic interaction between piles and soils, seismically induced pore-water pressures (PWP) and the non-linear response of soils to strong earthquake motions. In contrast, very simple pseudo-static methods are used in engineering practice to determine response parameters for design. These methods neglect several of the factors cited above that can strongly affect pile response. Also soil-pile interaction is modelled using either linear or non-linear springs in a Winkler computational model for pile response. The reliability of this constitutive model has been questioned. In the case of pile groups, the Winkler model for analysis of a single pile is adjusted in various ways by empirical factors to yield a computational model for group response. Can the results of such a simplified analysis be adequate for design in all situations?The lecture will present a critical evaluation of general engineering practice for estimating the response of pile foundations in liquefiable and non-liquefiable soils during earthquakes. The evaluation is part of a major research study on the seismic design of pile foundations sponsored by a Japanese construction company with interests in performance based design and the seismic response of piles in reclaimed land. The evaluation of practice is based on results from field tests, centrifuge tests on model piles and comprehensive non-linear dynamic analyses of pile foundations consisting of both single piles and pile groups.Studies of particular aspects of pile-soil interaction were made. Piles in layered liquefiable soils were analysed in detail as case histories show that these conditions increase the seismic demand on pile foundations. These studies demonstrate the importance of kinematic interaction, usually neglected in simple pseudo-static methods. Recent developments in designing piles to resist lateral spreading of the ground after liquefaction are presented. A comprehensive study of the evaluation of pile cap stiffness coefficients was undertaken and a reliable method of selecting the single value stiffnesses demanded by mainstream commercial structural software was developed. Some other important findings from the study are: the relative effects of inertial and kinematic interactions between foundation and soil on acceleration and displacement spectra of the super-structure; a method for estimating whether inertial interaction is likely to be important or not in a given situation and so when a structure may be treated as a fixed based structure for estimating inertial loads; the occurrence of large kinematic moments when a liquefied layer or naturally occurring soft layer is sandwiched between two hard layers; and the role of rotational stiffness in controlling pile head displacements, especially in liquefiable soils. The lecture concludes with some recommendations for 142 W. D. LIAM FINN practice that recognize that design, especially prelimi...

Evaluation of Soil–Structure Interaction in Structure Models via Shaking Table Test

“…The behavior of a pile foundation depends on the properties of the long, middle, and short piles [10,[24][25][26]. In this study, the pile analysis conditions used by Broms in 1964 were referred to (Table 2) [27].…”

Kinematic response analysis of piled foundations under seismic excitation

“…The accuracy of the VERSAT-P3D code has been checked against more rigorous solutions obtained by the boundary integral method for harmonic-type excitations (Fan et al 1991). Finn (2005) has reported a back-analysis of the dynamic response of a single-pile prototype in a centrifuge test. He found that the code was capable of reproducing the observed behaviour at a reasonable level.…”

System Identification of Mosques Resting on Soft Soil. The Case of the Suleiman Mosque in the Medieval City of Rhodes, Greece

“…Casolo et al [28] conducted comparative seismic vulnerability analysis on ten masonry towers to identify the factors that play a crucial role in their seismic vulnerability, while Hökelekli and Al-Helwani [40] investigated the effects of SSIs with infinite elements on the seismic damage behavior of stone masonry minarets with different soil types, considering the linear behavior of the soil domain. Several other studies also deal with the influence of soil-structure interactions on the fragility of buildings either on shallow or deep foundations [41][42][43][44].…”