2695
P-Y curves from the prebored pressuremeter test for laterally loaded single piles
Courbes P-Y à partir de l’essai pressiométrique préforé pour les pieux isolés sous charge latérale
Bouafia A.
University of Blida Department of civil engineering P. O. Box 270 R. P Blida 09000 Algeria
ABSTRACT: The paper aims at presenting a practical method of constructing the P-Y curves for the analysis of the lateral load-
deflection behaviour of single piles on the basis of the prebored pressuremeter test data. This method was derived from the
interpretation of several full-scale lateral loading tests on fully instrumented piles in a variety of soils. After presenting the
methodology of construction of the P-Y curve, the paper focuses on the validation of the proposed method, the comparison with the
existing approaches and on the discussion of the concept of the critical deflection and the effect of the lateral pile/soil stiffness ratio
on the P-Y curve parameters.
RÉSUMÉ : La communication a pour objectifs de présenter une méthode pratique de construction des courbes P-Y pour l’analyse du
comportement en déflection des pieux isolés à la base des données de l’essai pressiométrique préforé. Cette méthode a été développée
suite à l’interprétation de plusieurs essais de chargement latéral en vraie grandeur de pieux instrumentés dans une variété de sols.
Après une présentation de la méthodologie de construction des courbes P-Y, la communication focalise sur la validation de la
méthode proposée, la comparaison avec les méthodes existantes, ainsi que sur l’interprétation du concept du déplacement latéral
critique et de l’effet de la rigidité latérale relative pieu/sol sur les paramètres de la courbe P-Y.
KEYWORDS: P-Y curve, Pile, Lateral load, Deflection, Pressuremeter test, Loading test, Full-scale.
1 INTRODUCTION.
During more than half a century the design methods of piles
under lateral loads based on the P-Y curves concept
demonstrated their capability to accurately predict the lateral
pile response. The simple physical model of a spring at the
pile/soil interface allows taking into consideration the non
linearity of the pile/soil interaction as well as the non
homogeneity of the soil properties along the pile.
As shown in figure 1, the P-Y curve is characterised by an
initial slope denoted E
ti
called the lateral reaction modulus, and
a horizontal asymptote P
u
corresponding to the lateral soil
resistance.
The pressuremeter test PMT provides an experimental stress-
strain curve describing the lateral expansion of the soil borehole
under horizontal axisymmetric loads. Some methods of
construction of P-Y curves assume some similarity in terms of
stress and displacement fields between the lateral response of
the pile and that of the PMT borehole (Baguelin et al, 1978),
and relate the P-Y curve parameters E
ti
and P
u
to the ones of the
PMT test, namely E
M
and P
l
which are respectively the Ménard
deformation modulus and the PMT limit pressure, according to
the following general equation at a given depth:
f(P
l
*, E
M
, E
p
I
p
, D, B, P
u
, E
ti
) = 0
(1)
P
l
*, E
p
I
p
, D and B are respectively the net PMT limit pressure,
the pile flexural stiffness, the pile embedded length and the pile
diameter (or the dimension perpendicular to the lateral load
direction).
Dimensional analysis of this equation according to the
Buckingham’s theorem leads to the dimensionless equation:
(2)
Figure 1. Schematic shape of the P-Y curve
The first ratio is noted K
E
and called the modulus number
such as:
E
ti
=K
E
.E
M
(3)
The second ratio is noted K
p
and called the lateral resistance
factor:
P
u
=K
p
.P
l
*.B (4)
The third ratio is the pile slenderness ratio and the last one is
noted K
R
and called the lateral pile/soil stiffness ratio. Equation
2 shows that K
E
and K
p
are both functions of K
R
and D/B.
Because of the three-dimensional aspect of the lateral
pile/soil interaction and the multitude of the key parameters
involved in such an interaction, a rigorous determination of K
E
and K
p
is rather complex. Alternatively, full-scale lateral
loading tests on instrumented piles were carried out for more
than half a century to investigate this topic. P-Y curves are
0 )
, ,
,
(
4
*
DE
IE
B
D
BP
P
E
Eg
M
p p
l
u
M
ti
