Considerations in Retaining Wall Design

Association of Construction and Development
August 16, 2012 — 1,861 views  

Retaining walls, created to restrain soil between two different elevations or unnatural slopes, are unique in their design. As a fairly different architectural structure, these walls may appear to be simple to develop and construct. However, there are certain factors that contractors, city planners or do-it-yourself homeowners should consider before going through with their retaining wall design.

The pressure of earth

Perhaps the most important consideration to keep in mind when undergoing such a project is that designing any retaining wall requires substantial knowledge of lateral earth pressure, defined as the pressure caused by the backfill. According to Concrete Network, the force generated by the lateral earth pressure comprises a majority of the load that the wall will be erected to combat against. When first assessing the pressure at a particular segment, there are several basic soil parameters to be mindful of. Soil unit weight, angle of internal friction, cohesion and plasticity indices and the water table location are all contributing factors to the overall lateral earth pressure behind the wall.

Regulations to follow

According to The California Department of Transportation, retaining walls should be designed for a service-life based upon the potentially-deleterious effects of the material components of the wall. More permanent walls are designed for a minimum service-life of 50 years, while temporary retaining walls carry a minimum of 5 years of service.

Another legal consideration to keep in mind is the restrictions of state laws and local building codes. According to Concrete Network, all retaining wall designs taller than four feet must be designed or approved by a qualified, licensed professional engineer. Since these walls are primarily viewed as load-bearing tools instead of aesthetic landscapes, local building codes must be strictly followed.

Do-it-yourself tips

There is a host of do-it-yourself tips for the successful and stress-free construction of a restraining wall, as recommended by The DIY Network. One important tip is to make sure that you have created a good, sound base. Virgin soil is more supportive of restraining wall structures than soil that has previously been used in landscaping projects before. Manufactured blocks provide a myriad of options for colors, shapes and styles, and are among the easiest materials to lay. Installing gravel directly behind the wall allows you to direct water to wherever you want it to go. Finally, backfilling as you go can create structural advantages for a safer and more effective wall.

Association of Construction and Development