Static and dynamic lateral deflexion of piles in non-homogeneous soil stratum

Abstract

The Paper presents the results of a systematic parametric investigation of the static and dynamic response of single free-head piles embedded in a soil stratum, the modulus of which increases linearly with depth. The study is conducted by means of a dynamic finite-element formulation which accounts for the three-dimensionality of soil deformation while properly reproducing the radiation damping characteristics of the system. The soil is modelled as a linear hysteretic continuum and the excitation consists of a sinusoidally time-varying horizontal force or moment, applied at the pile head. Comprehensive plots of the results are presented in non-dimensional form, for a wide range of the most significant dimension-less groups of problem parameters. For the response of flexible piles, in particular, simple algebraic expressions are developed in terms of the ratio Ep/Es, of the pile and soil moduli. These expressions, being valid for several values of Poisson's ratios of the soil, compare favourably with results from previous studies and are expected to be useful in practical design calculations. Cet article donne les résultats de recherches paramétriques systématiques sur la réponse statique et dynamique des pieux libres en tête encastrés dans une couche de sol dont le module s'accroît linéairement avec la profondeur. L'étude est basée sur une formulation d'éléments finis dynamiques qui tient compte de la nature tridimensionelle de la déformation du sol, en même temps qu'elle reproduit de façon correcte les caractéristiques d'amortissement du systéme. Le sol est modehsé comme un continuum avec hystérśsise linéaire et l'excitation consiste en une force horizontale qui varie de façon sinusoidale dans le temps appliquée en tête du pieu. Les résultats sont tracés de maniére compréhensive sous une forme non-dimensionnelle pour une grande variété des groupes les plus importants des paramétres sans dimensions caractérisant le probléme. Plus particuliérement pour la réponse des pieux flexibles des expressions simples algébriques sont présentées en fonction du rapport Ep/Es des modules du pieu et du sol. Ces expressions, qui sont valables pour plusieurs valeurs du coefficient de Poisson pour le sol sont supérieures à celles fournies par les etudes précédentes, et on s'attend à ce qu'elles soient utiles pour els calculs pratiques des projects de fondations.

An experimental study on static and dynamic bending behaviour of piles in soft clay

“…It can also be concluded here that many piles, which exhibit a flexible (length-independent) static behaviour cannot be considered as flexible under dynamic loads at frequencies near resonance. Results of finite element studies carried out by Krishnan et al (1983) also leads to a similar conclusion that the active pile length increases significantly under dynamic load.…”

“…However, the field dynamic lateral load tests carried out at sites predominantly consists clay and sandy clay layers by various authors (Novak 1985;Blaney and O'Neill 1986;Nogami et al 1992;Puri and Prakash 1992;Dou and Byrne 1996;Anandarajah et al 2001;Pak et al 2003;Boominathan and Ayothiraman 2006) show large discrepancy between observed and estimated values due to nonlinear behaviour of soil and gapping at the pile-soil interface. Kuhlemeyer (1979), Angelides and Roesset (1981), Krishnan et al (1983) and Wu and Finn (1997) attempted to study the dynamic soil-pile interaction problem considering nonlinear behaviour of soil adopting finite element method (FEM). Though the FEM is a powerful method, a rigorous threedimensional finite element analysis of dynamic soil-pile interaction is computationally intensive and expensive too.…”

Earthquake-induced bending moment in fixed-head piles in soft clay

“…It does not account for non-linear soil behaviour and inertial loading effects arising from seismic soil-pile interaction that affect the bending moment response along the pile. Krishnan et al (1983) proposed an effective length for single free-head piles embedded in a soil stratum whose modulus increases linearly with depth. Their length criterion was based on the maximum pile head deflection and expressed as a function of only the relative pile-soil stiffness.…”

Dynamic pile‐soil‐pile interaction. Part II: Lateral and seismic response

“…They used a 3D FE formulation for the developing soil reactions against pile displacements. An alternative approximate 2D plane-strain model, presented by Gazetas and Dobry14 assumes that compression-extension waves propagate in the two quarter-planes along the direction of loading while shear waves are generated in the two quarter-planes perpendicular to the direction of loading [ Figure 4 (13) where ull is given by equation (11) and I)@, 19) is the attenuation function (still to be determined). It is sufficient to compute I)(r, 0) only for 0 = 0 and 0 = n/2 and then use the approximation $(r, e) z $(r, 0) cos2 e + I) I , -sin2 e to obtain a very good estimate for any arbitrary angle il.2*7, 28 The following approximate expressions for $(r, 0) and $(r, n/2) have been developed in Reference [S]:…”