Retaining Walls - Design of Reinforced Concrete - page 392

13

Retaining Walls

13.1 INTRODUCTION

A retaining wall is a structure built for the purpose of holding back or retaining or provid-
ing one-sided lateral confinement of soil or other loose material. The loose material being
retained pushes against the wall, tending to overturn and slide it. Retaining walls are used
in many design situations where there are abrupt changes in the ground slope. Perhaps the
most obvious examples to the reader occur along highway or railroad cuts and fills. Often,
retaining walls are used in these locations to reduce the quantities of cut and fill as well as
to reduce the right-of-way width required if the soils were allowed to assume their natural
slopes. Retaining walls are used in many other locations as well, such as for bridge abut-
ments, basement walls, and culverts.
Several different types of retaining walls are discussed in the next section, but
whichever type is used, there will be three forces involved that must be brought into equi-
librium: (1) the gravity loads of the concrete wall and any soil on top of the footing (the
so-called developed weight ), (2) the lateral pressure from the soil, and (3) the bearing re-
sistance of the soil. In addition, the stresses within the structure have to be within permis-
sible values, and the loads must be supported in a manner such that undue settlements do
not occur.

13.2 TYPES OF RETAINING WALLS

Retaining walls are generally classed as being gravity or cantilever types, with several
variations possible. These are described in the paragraphs to follow, with reference being
made to Figure 13.1.
The gravity retaining wall , Figure 13.1(a), is used for walls of up to about 10 to 12 ft
in height. It is usually constructed with plain concrete and depends completely on its own
weight for stability against sliding and overturning. It is usually so massive that it is unre-
inforc ed . Tensile stresses calculated by the working-stress method are usually kept below
Gravity walls may also be constructed with stone or block masonry.
Semigravity retaining walls , Figure 13.1(b), fall between the gravity and cantilever
types (to be discussed in the next paragraph). They depend on their own weights plus the
weight of some soil behind the wall to provide stability. Semigravity walls are used for
approximately the same range of heights as the gravity walls and usually have some light
reinforcement.

c . 1.6 f

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