When designing and having a retaining wall installation, there are a variety of factors to consider, regardless of whether it’s intended for commercial or residential use. The same standard of care should be applied to walls as a bridge since they’re both structures. Depending on the installation and your experience, you may wonder what style of the wall will work best for the location, how deep the footing needs to be buried if the wall needs to be reinforced, or what material is best to use for the location.
Before you begin designing your wall and choosing the aesthetics, you need to understand the location and environmental factors that can make your wall fail. Having a retaining wall installation takes advanced planning and careful layout to avoid it getting a hazard or collapsing. Below are some factors that need to be considered during the design phase with guidance on choosing the best type of retaining wall for your retaining wall installation project.
The purpose of installing retaining walls is to hold all of the soil behind them. Still, the specific requirements will vary depending on the installation project. Walls can range from small landscape stone walls to surround your garden to large soil-retaining installation projects along a highway. Others can help control erosion from heavy rains or install a terraced yard to reduce maintenance. When you begin the original planning, several considerations will affect the material and type of wall you will install.
When choosing the location for your wall, make sure you have a detailed understanding of property lines both above and below ground utilities including stormwater management systems and irrigation.
The soil that creates the foundation, or base, needs to be examined to make sure it meets the strength needed to support the wall. You should determine the type, bearing capacity (the capacity of soil to support a load), stress parameters, and friction angle ( resistance to movement) of the soil used for the foundation and reinforced zone along with the retained soil zone.
In general, the base soil needs to be firm, solid, and strong, and it shouldn’t be moist. Wet soils similar to clay soil are also not recommended for infilling. They’re already saturated with water, so additional moisture on the soil can not make its way through to the drainage channels. Also, in areas where there’s freezing, wet soil can expand and contract which will damage the wall. On the other hand, sandy soils allow for good drainage. Consult the geotechnical report which describes the on-site soils, poor chemical parcels, groundwater conditions, and more.
To begin the design, you must calculate the corresponding wall heights, footprint sizes, slopes, and the setback angle which are dependent on the site elevation and grade. You must also consider that gravity will cause the retained material to naturally move downslope. This should be counteracted within the design to minimize the size of earth pressure behind the wall, which, at maximum value, can eventually capsize the wall. Your wall height is dependent on soil and slope, setback, and size of the block.
- Wall Reinforcement: If gravity alone won’t support your wall, there are reinforcement styles available that depend on the wall type, height, design, friction, angle, soil material, and more. Mechanically stabilized earth (MSE) is soil with some means of artificial reinforcement similar to swords or geosynthetics (such as geogrids). Geogrid is often made of a high-tensile fabric woven into a grid pattern. It’s placed in between the layers of retaining wall blocks and rolled back into the earth. Other types of reinforcement include soil nailing, earth anchors, among others.
Considering that the most common reason that retaining walls fail is water, it is very important to make sure your retaining wall has good drainage and that there will be no buildup of water behind the wall. Identify potential surface water sources and make sure drainage adjacent to the wall has been accounted for. It’s important to grade the location for drainage patterns and construct a drainage system behind the wall to minimize the amount of hydrostatic pressure the groundwater could produce. An example drainage system could include backfilling with gravel, using drain pipes, and using “ weep” holes to allow water to pass through the wall. Larger retaining wall installation systems, similar to those for transportation, should have a hydrology analysis done.