Engineering and Construction

A retaining wall is defined as a structure whose primary purpose is to provide lateral support for soil or rock.

In some cases, the retaining wall may also support vertical loads. Examples include basement walls and certain types of bridge abutments.

Some of the more common types of retaining walls are gravity walls, counterfort walls, cantilevered walls, and crib walls. Gravity retaining walls are routinely built of plane concrete or stone and the wall depends primarily on its massive weight to resist failure from overturning and sliding.

Counterfort walls consist of a footing, a wall stem, and intermittent vertical ribs (called counterforts) that tie the footing and wall stem together. Crib walls consist of interlocking concrete members that form cells, which are then filled with compacted soil. Common types of retaining walls are shown in Fig. 11.1.

Although mechanically stabilized earth retaining walls have become more popular in the past decade, cantilever retaining walls are still probably the most common type of retaining structure.

There are many different types of cantilevered walls, with the common features being a footing that supports the vertical wall stem. Typical cantilevered walls are T-shaped, L-shaped, or reverse L-shaped (Cernica, 1995a, 1995b).

Clean granular material (no silt or clay) is the standard recommendation for backfill material.

There are several reasons for this recommendation:

1. Predictable behavior. Import granular backfill generally has a more predictable behavior in terms of earth pressure exerted on the wall. Also, expansive soil related forces would not be generated by clean granular soil. If clay backfill should be used, the seepage of water into the clay backfill could cause horizontal swelling pressures well in excess of at-rest values. For example, Fourie (1989) measured the swell pressure of compacted clay for zero lateral strain to be 8800 psf (420 kPa). Besides the swelling pressure induced by the expansive soil, there can also be groundwater or perched water pressure on the retaining or basement wall because of the poor drainage of clayey soils.

2. Drainage system. To prevent the buildup of hydrostatic water pressure on the retaining wall, a
drainage system is often constructed at the heel of the wall. The drainage system will be more
effective if highly permeable soil, such as clean granular soil, is used as backfill.

3. Frost action. In cold climates, frost action has caused many retaining walls to move so much that they have become unusable. If freezing temperatures prevail, the backfill soil can be susceptible to frost action, where ice lenses will form parallel to the wall and cause horizontal movements of up to 2 to 3 ft (0.6 to 0.9 m) in a single season (Sowers and Sowers, 1970). Backfill soil consisting of clean granular soil and the installation of a drainage system at the heel of the wall will help to protect the wall from frost action.

Movement of retaining walls (i.e., active condition) involves the shear failure of the wall backfill and the analysis will naturally include the shear strength of the backfill soil. Similar to the analysis of strip footings and slope stability, for most field situations involving retaining structures, the backfill soil is in a plane strain condition (i.e., the soil is confined along the long axis of the wall). As previously mentioned, the friction angle f is about 10 percent higher in the plane strain condition as compared to the friction angle f measured in the triaxial apparatus. In practice, plane strain shear strength tests are not performed, which often results in an additional factor of safety for retaining wall analyses.


Previously will discuss the basic retaining wall equations for a simple retaining wall without and with wall friction. The following sections will then discuss in more detail the design and construction of retaining walls, restrained retaining walls, mechanically stabilized earth retaining walls , sheet pile walls, and temporary retaining walls, which are often needed to support foundation excavations. The final is devoted to moisture migration through retaining walls. Geotechnical earthquake engineering analyses for retaining walls will be covered later.