2621
Analysis of Displacements of GPA in Normally Consolidated Soft Soil
L'analyse des déplacements des GPA dans le sol mou Normalement consolidé
Vidyaranya B.
Research Scholar, Osmania University, Hyderabad, India
Madhav M.R.
Professor Emeritus, JNT University, & I.I.T., Hyderabad, India
ABSTRACT: Granular piles (GP) offer most effective and economical solution for ground improvement due to their drainage,
densification and reinforcement actions, GPs mitigate liquefaction induced damages. An anchor placed at the base of the granular pile
and attached to the footing by a cable or rod transfers the applied pullout force to the bottom of the GP termed as Granular Pile
Anchor (GPA). The effective stresses in a normally consolidated saturated soil increase linearly with depth. Consequently, the
undrained strength and the deformation modulus of the soil increase linearly with depth. Analysis of the displacements of granular
pile anchor is presented considering the influence of the linearly increasing undrained modulus of soil and of the GPA with depth on
the load – displacement response of the GPA. A parametric study quantifies effects of the length to diameter ratio of GPA, and the
relative stiffness of the GP with respect to that of in situ soil at ground level, on the variations of tip and top displacements of GPA
with applied load, variation of shear stresses and pullout load with depth, etc.
RÉSUMÉ : Pieux granulaires (GP) offrent une solution plus efficace et économique pour amélioration des sols en raison de leur
drainage, la densification et des actions de renforcement, les médecins généralistes atténuer les dommages induits par liquéfaction. Un
point d'ancrage placé à la base du pieu granulaire et fixée à la semelle par un câble ou une tige transfère la force de traction appliquée
sur le fond de la GP qualifié de mouillage pieu granulaire (GPA). Les contraintes effectives dans un sol normalement consolidé saturé
augmente linéairement avec la profondeur. Par conséquent, la résistance non drainée et le module de déformation du sol augmente
linéairement avec la profondeur. L'analyse des déplacements de l'ancre empilement granulaire est présentée compte tenu de l'influence
de plus en plus le module linéaire non drainée du sol et de l'GPA avec la profondeur de la réponse force - déplacement du GPA. Une
étude paramétrique de quantifier les effets de la longueur par rapport au diamètre de l'GPA, et la rigidité relative du GP par rapport à
celle du sol in situ au niveau du sol, sur les variations de pointe et des déplacements supérieurs de GPA avec la charge appliquée, la
variation de cisaillement contraintes et la charge de retrait avec la profondeur, etc
KEYWORDS: Granular pile anchor, modulus of deformation, homogenous ground, displacements, load transfer.
1 INTRODUCTION.
Granular piles (GP) offer most effective and economical
solutions in soft marine clays to counter-act low undrained
shear strength and stiffness of the deposits. GPs improve the
performance of ground by reinforcement, densification,
increasing bearing capacity and resistance to liquefaction by
increasing strength and stiffness of ground. GPs are ideally
suited as they form elements of low compressibility and high
shear strength. The effective stresses in a normally consolidated
saturated soil increase linearly with depth. As a result the
undrained shear strength and deformation modulus of the soil
also increase linearly with depth. The increase in modulus of
soil and granular material with depth result in reduced load-
displacements response and increased confinement pressure.
The functional utility of the GP in compression is extended
by placing an anchor at its base to transfer the pullout load or
uplift forces to the base and the assembly is termed as Granular
Pile Anchor (GPA). Granular pile treated expansive soil adjusts
itself to changes in moisture better than an untreated-soil (Phani
Kumar
et al.,
2004). White
et al.
(2001) studied the application
of reinforced geopiers for resisting tensile loads and settlement
control. Lillis
et al.
(2004) reported results from in situ tests on
pullout response of GPA. Kumar
et al.
(2004) present results
from laboratory and field tests on pullout response of GPA in
cohesive and cohesionless soils. A linear analysis of
displacements of GPA is presented by Madhav
et al.
(2008).
2 PROBLEM DEFINITION
A granular pile of length, L, and diameter, d, with the soil and
pile material characterized by moduli of deformation E
s
and E
gp
,
and unit weights of γ
s
and γ
gp
, respectively is considered (Fig.1).
A force, P
o
, applied at the base of GPA is resisted by the shear
stress,
, acting along the periphery of the pile. The force and
the stresses acting on the GPA are depicted in Figure 2a. The
stresses transferred to the in situ soil are shown in Figure. 2b.
The non-homogeneities of deformation moduli of soil, E
s
and
granular material, E
gp
(Fig. 3 & 4)are defined by the parameters,
s
&
gp
, to quantify the rate of increase of deformation moduli
of in-situ soil and granular material with depth. The Poisson’s
ratio of the soil is ν
s
. In order to evaluate the upward
displacements of the elements of the soil adjacent to the GPA
Fig. 1 GPA under Pullout
(a) (b)
Fig. 2 Forces and Stresses acting
on GPA and Soil.
due to the boundary stresses, τ, the GPA surface is divided in to
‘n’ elements of length,
L (=L/n). The stress acting on a typical
