1943
Anchored sheet pile wall design in expansive soils
Conception d’un mur de palplanches ancré dans les sols expansifs
Bilgin Ö., Mansour E.
University of Dayton, Dayton, Ohio, U.S.A.
ABSTRACT: Expansive soils cause damage to civil engineering structures in various parts of the world, because they swell when
absorb water and shrink when dry out. Due to swelling pressures, retaining walls can be subjected to additional lateral pressures
causing increased wall deformations and bending moments. Anchor forces can also increase, if the walls are anchored. When
expansive soils are present behind retaining walls, swell pressures should also be considered during design in addition to the
traditional lateral earth pressures. This study proposes a method to predict potential swell pressures acting on retaining walls for use in
design of these walls. A parametric study using the limit equilibrium approach was performed to investigate the effect of swell
pressures on the design of anchored sheet pile walls in expansive soils. The results of the study show that the presence of expansive
soils can significantly affect earth retaining structures and swell pressures should be considered in the design of retaining walls when
the expansive soils are present at the site.
RÉSUMÉ : Les sols expansifs causent des dommages à des structures de génie civil dans diverses parties du monde, ils gonflent
quand ils absorbent de l'eau et se contractent quand ils se dessèchent. En raison des pressions de gonflement, les murs de soutènement
peuvent être soumis à des pressions latérales supplémentaires augmentant les déformations et les moments fléchissant. Les forces
d'ancrage peuvent également augmenter, si les murs sont ancrés. Lorsque les sols expansifs sont présents derrière les murs de
soutènement, les pressions de gonflement devraient également être envisagées, en plus des pressions latérales des terres
traditionnelles. Dans cette étude, une méthode a été proposée pour prédire d'éventuelles pressions de gonflement agissant sur les murs
de soutènement, à utiliser dans la conception de murs de soutènement. Une étude paramétrique en utilisant l'approche d'équilibre
limite a été réalisée pour étudier l'effet des pressions de gonflement sur la conception de rideaux de palplanches ancrées dans les sols
expansifs. Les résultats de l'étude montrent que la présence de sols expansifs, peut influencer considérablement la conception de
structures de soutènement et doit être pris en compte dans la conception des murs lorsque les sols expansifs sont présents sur le site.
KEYWORDS: Retaining wall, anchored sheet pile wall, expansive soil, swell pressure, wall design.
1 INTRODUCTION AND OVERVIEW
The sidewalls of structures and retaining walls may experience
additional lateral pressures when they are located within
expansive soils. When the expansive soils absorb water the
moisture content increases and the soil tends to expand. If the
free swelling or expansion of the clay is restricted, then swell
pressures develop and this cause an increase in the lateral
pressures acting on the structures. The design of retaining walls
usually specifies cohesionless soils as a backfill material behind
the wall mainly to avoid hydrostatic pressures by providing easy
drainage. These cohesionless materials also help to prevent
swell pressures that may develop if cohesive soils are used.
Due to economical reasons, local soils which may be
expansive are sometimes used as a backfill material (Thomas et
al. 2009). However, use of these soils as backfill may result in
wall failures (Marsh and Walsh 1996) not only because of the
hydrostatic pressures but also due to the additional lateral earth
pressures caused by the swelling of expansive soils.
The selection of soils behind the wall is not even optional for
in-situ retaining walls, such as cantilever and anchored sheet
pile walls, slurry walls, secant and tangent pile walls. These
walls are installed in existing soils and front of the wall is
usually excavated. When these walls are installed at locations
where expansive soils are present, the walls would experience
not only the traditional lateral earth pressures but also the swell
pressures when soil’s moisture content increases.
The objective of this study is to investigate the behavior of
anchored sheet pile walls when they are installed in expansive
soils and exposed to additional stresses due to the swelling of
these soils.
1.1
Expansive soils
The best way to deal with the shrinkage and swelling of
expansive soils is to maintain constant soil moisture. If the soil
moisture content does not change, there can be no shrinkage or
swelling. However, it is usually not possible to maintain
constant soil moisture. Moisture content fluctuates due to
several factors, such as precipitation and evaporation. The
seasonal variation of soil moisture is much higher at shallower
depths and it decreases as the depth below the ground surface
increases (Figure 1).
Figure 1. Moisture content fluctuations with depth.
