Volume 6 – Geotechnical Manual, Site Investigation and Engineering ...

Chapter 7 RETAINING WALL
7 RETAINING WALL
7.1 GENERAL
Generally the main application of retaining wall is to hold back earth and maintain a difference in
the elevation of the ground surface. The retaining wall is designed to withstand the forces exerted
by the retained ground or “backfill” and other externally applied loads without excessive
deformation or movement, and to transmit these forces safely to a foundation and to a portion of
the restraining elements, if any, located beyond the failure surface. Figure 7.1 illustrated the forces
acting on a retaining wall and some of the related terminology commonly used in retaining wall
design.
Special considerations are often necessary for retaining walls to be constructed close to land
boundaries, particularly in urban areas. Land take requirement for construction often place
limitations on the use of certain forms of earth retention. The cost of constructing a retaining wall is
usually high compared with the cost of forming a new slope. Therefore, the need for a retaining
wall should be assessed carefully during design.
Figure 7.1 Forces Acting On Retaining Wall And Common Terminology
7.2 TYPE OF RETAINING WALLS
The rigidity or flexibility of a wall system is fundamental to the understanding of the development of
earth pressures and the analysis of the wall stability. In simple terms, a wall is considered to be rigid
if it moves as a unit in rigid body rotation and/or translation and does not experience bending
deformation. Most gravity walls can be considered rigid walls. Flexible walls are those that undergo
bending deformations in addition to rigid body motion. Such deformations result in a redistribution of
lateral pressures from the more flexible to the stiffer portions of the system. Virtually all wall
systems, except gravity walls, may be considered to be flexible.
March 2009 7-1