1983
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Design of inverted T-shaped Cantilever Wall with a Relief Floor
Conception
d’un mur équerre avec dalle de délestage
P.P. Ganne & X. Raucroix
Engineering department, BESIX, Gemeenschappenlaan 100, 1200 Brussels, Belgium
ABSTRACT: Cantilever walls are widely used as ground retaining structures. The analytical approach of L-shaped and inverted T-
shaped cantilever walls results in reliable designs. This paper proposes and discusses an analytical approach for the geotechnical
design of inverted T-shaped cantilever walls with relief floor. This approach combines the analytical approaches of inverted T-shaped
walls and of relief floors. The resulting analytical approach is verified by numerical simulations of inverted T-shaped cantilever walls
with relief floor for 5m till 10m high retaining structures in unsaturated sandy soils, silty soils and alluvial clayey soils. Finally, rules
of thumbs for typical dimensions of the inverted T-shaped cantilever wall with relief floor are given, based on experience, analytical
calculations and numerical simulations.
RÉSUMÉ :
Les murs équerres sont communément répandus comme structure de soutènement. D’un point de vue de la conception
géotechnique, les méthodes analytiques sont éprouvées. Cet article propose et discute une approche analytique pour la conception
géotechnique des murs équerres avec dalle de délestage. Cette approche combine l’approche de dimensionnement analytique des m
urs
é
querres avec l’effet d’ombre des dalles de délestage. L’approche analytique
proposée est
justifiée à l’aide de
simulations numériques
modélisant des murs équerres avec dalle de délestage reprenant des différences de niveau allant de 5m à 10m et ce, dans des sols non-
saturés de nature sableuse, silteuse et alluvio-argileuse. En conclusion, des dimensions typiques de murs équerres avec dalle de
délestage sont données, basé
es sur l’expérience, d
es calculs analytiques et des simulations numériques.
KEYWORDS: inverted T-shaped cantilever wall, relief floor, soil retaining structure, finite element code
1 INTRODUCTION
In recent decades, the number of installations of permanent
ground retaining structures is drastically increasing. One of the
oldest ground retaining structures are the gravity walls. They
have a very easy way of realization and are particularly suitable
for retained heights of less than 3m. While they can be designed
for greater heights, other types of retaining walls such as L-
shaped cantilever walls are usually more economical as the
height increases.
L-shaped cantilever walls uses the soil upon the heel to
stabilize the horizontal soil pressures. One of the disadvantages
of the L-shaped cantilever walls is the high ratio between the
horizontal loads due to soil pressures and the vertical soil
weight, causing a disadvantageous eccentricity of the forces at
the base slab. Therefore, the length of the base slab can amount
up to 70% (sandy soils) and up to 120% (alluvial clay) of the
retaining height. In most projects, the realization of L-shape
structure is not possible due to the lack of required space to
excavate up to the rear edge of the base slab level with a
reasonable slope.
It is usually more economical to design the L-shaped
cantilever wall with a toe at its front side: the inverted T-shaped
cantilever wall. This increases the moment arm and reduces the
disadvantageous eccentricity of the forces in the base slab. The
distance between the front of the stem and the back of the heel
of the cantilever wall amounts to 50% (sandy soils) or to 60%
(alluvial clay) of the retaining height.
In some cases, it is more economical to further reduce the
required space between the front wall face and the temporary
slope at the back of the structure. In these cases, a relief floor
could be added : the inverted T-shaped cantilever wall with
relief floor. In this way, (1) the disadvantageous horizontal soil
forces are reduced and (2) the disadvantageous eccentricity of
the forces at the base slab could be reduced, generally down to a
negligible low value. The distance between the front of the stem
and the back of the heel of the cantilever wall amounts only
20% (sandy soils) or to 40% (alluvial clay) of the retaining
height.
The construction of the inverted T-shaped cantilever wall
with a relief floor itself is in most of the cases of lower
economical interest than the inverted T-shaped cantilever wall.
Nevertheless, reducing the space between the front of the stem
and the heel, increases the available space for the excavation,
necessary to reach the level of the base slab. The possible
economic benefit may be found in the less expensive temporary
excavation method.
The geometry of an inverted T-shaped cantilever wall with a
relief floor depends on the conditions of the specific project.
Therefore, each realization must be based on thorough
geotechnical evaluation of its design, a hydrogeological
evaluation, a detailed structural design, an analyses of the
construction methodology and a general risk evaluation.
This paper proposes a simplified analytical approach for the
geotechnical design of the inverted T-shaped cantilever wall
with a relief floor. This simplified analytical approach is
checked by numerical simulations for unsaturated sandy soils,
silty soils and alluvial clays. Finally, typical dimensions which
can be used for predesign estimations are given, based on
experience, analytical and numerical calculations.
Ganne P.P., Raucroix X.
