Installation Instructions
23
RETAINING WALLS
GRAVITY WALL DESIGN ASSUMPTIONS
BASIC WALL INSTALLATION - GRAVITY WALLS
The design methodology for conventional gravity walls is based upon the following:
1. There is no slope behind the wall.
2. Surcharge loads applied at the top of the wall are limited to foot trac where the applied forces
will be between 0-50 PSF.
3. There is good surface and subsurface drainage to prevent hydrostatic pressures at the back of
the wall and the reinforced soil zone.
4. The site soil has adequate strength to support the wall and good draining soils will be used
behind the wall. In addition, the ground water table is assumed to be well below the reinforced
zone.
5. The cubic foot weight of the soil is the moist unit weight that includes the weight of water
occurring naturally in the soil.
6. Seismic loading is not considered.
7. The site can support the weight of the wall.
8. The foundation soil will not settle or deform to cause failure.
9. Keep in mind, conventional segmental retaining walls are generally eective as gravity
structures for most non-critical wall applications under 4 feet high, including the block below
grade. For walls exposed 3 feet or more, you must terrace the wall or use geogrid to reinforce
the soil. Consult a professional engineer for design assistance on taller walls. See Midwest
Manufacturing Engineering for more details.
Segmental Retaining Walls that rely on their own weight, core ll, friction between units and
setback are called gravity walls. Conventional segmental retaining walls are generally eective as
gravity structures for most non-critical wall applications. Don’t assume shorter walls never require
the services of a soils engineer. The heights listed by the manufacturer
are used as a rule of thumb when ideal wall conditions are present.
Walls that exceed the heights listed by the manufacturer require additional construction
techniques such as terracing or the use of geogrid reinforcement. These types of walls are known
as reinforced or engineered wall structures. They are also referred to as Mechanically Stabilized
Earth (MSE) walls.
The performance and construction of most retaining walls is highly dependent on the type
and condition of the on-site soils and the contractor’s placement and compaction of the soils
behind and under the walls. It is important to know the properties of various types of soils and
understand how they might aect your estimate. To get a better understanding about soils, a brief
review of soil types and properties is shown on page 24.