Retaining walls are custom designed and constructed to level uneven areas, effectively maximizing space for development. Sometimes, these wall structures are built solely for their aesthetic value. It can function as a landscaping feature that separates areas in the garden. In addition, these walls can also help create focal points in the outdoor space.
But more frequently, they are built to prevent soil erosion and provide structural support to infrastructure running along naturally sloping or hilly terrains.
Types of Retaining Walls
Retaining walls can be constructed from simple sheet piling to using advanced engineering techniques. There are four typical retaining wall designs used in construction. The designs of the walls depend on their purpose.
True to its name, a gravity wall uses its weight to counter the lateral earth pressure. It relies on gravity to pull down the heavy concrete blocks, bricks, or masonry from toppling over and overturning the wall.
It utilizes incremental setbacks between layers of retaining materials to increase the vertical force exerted against the lateral force due to soil pressure. The use of gravity to hold up a wall is an old technique that dates back to ancient times.
Cantilever walls are built from reinforced concrete with an L- or inverted T-shaped foundation. This design allows the transfer of the wall’s vertical stress to the foundation, which increases the wall’s capacity to withstand lateral earth pressure.
Embedded retaining walls are used in underground structures like basements, car parks, and metro stations. Some of these walls can be very deep, with the height of the wall reaching 40 meters like the Westminster underground station wall next to the House of Parliament in London.
Failing embedded walls can cost lives and severe property damage. Hence, the construction of embedded walls should be done by professionals, and best if not done as a DIY project.
Mechanically stabilized earth (MSE) or reinforced soil Walls
MSE or reinforced walls use alternating backfill and reinforcements like sheet pile walls or geogrids, which are connected mechanically to the facings of the retaining wall. The facings are usually thin because their primary function is to stop the spilling or erosion of the soil.
The strength and stability of the wall come from the interaction of the composite materials in the geogrids. By its design, MSE walls are generally more flexible and can withstand a variety of heavy lateral loads.
How to Choose the Right Retaining Wall Design
Many factors come into play when deciding what retaining wall design best suits a specific project. Here are five of the most important ones.
Is the retaining wall intended to stand out or are the walls required to blend in its environment? Will it serve as a focal point in the outdoor space or as a discreet structure hidden under the flower beds? Are there any adjacent structures that need consideration?
These and other questions related to how the retaining wall will look when completed are crucial questions needing answers before the onset of the construction. When addressed accordingly, it can serve as a guide on the overall scope of the project and its most cost-effective design.
How long are the wall blocks supposed to last? Will they be permanent fixtures that will not be disturbed or dismantled for decades? Are they temporary landscaping features bound to be altered every few years?
For a permanent retaining wall, does its design include provisions for easy maintenance and inspection throughout its asset life? How about those that are supposed to be temporary walls? Were they designed with the dismantling and disposal process and cost considered?
Will the wall be exposed to graffiti and other forms of vandalism? Are there provisions for easy repairs when damage occurs, or are repairs not expected?
Designing the retaining walls with these questions in mind can help determine the required durability of the individual components used to construct them. It also paves the way for innovative designs that will help minimize maintenance and disposal costs.
Space constraints often dictate the design of any structure, retaining walls included. Is it more practical to minimize the footprint of the retaining wall? Is the cost of using a vertical wall proportional to the value of the real estate added to the property by avoiding a sloping retaining wall design?
Space constraints during construction also need to be considered. How will the materials be transported? Is there enough space for the heavy equipment required to construct specific wall designs? Is there an existing access road wide enough to easily haul the materials? Or is the access road to the site just enough for small or hand-held equipment?
A retaining wall retains soil, so it is evident that the geotechnical features of the terrain where it will be constructed are also carefully examined. Exposure to water for extended periods is the crux for most structures, especially retaining walls. Will groundwater be an issue? If it is, the design must include proper drainage elements that will deal with the groundwater.
Another vital factor to consider is the load that the retaining wall has to hold up — on top of the weight of the compacted backfill materials pushing against it. Will a portion of the retained soil have foot traffic, or will it only hold vegetation? Will the wall be stand-alone, or will it be connected to other structures or buildings?
Geotechnical analysis requires some level of expertise in the field; this is why the construction of retaining walls that resolve geotechnical concerns is best left in the hands of professionals.
As with any construction project, the final design is a delicate balance between scope and budget. For example, a space-saving vertical wall is generally more expensive than a steep-sloped one. But it can also withstand more lateral forces per unit square area. Moreover, an aesthetically pleasing retaining wall can improve the appearance of the overall outdoor space, but it will also be more costly to construct given that it uses more expensive materials like natural stones.
L&L Specialties is a landscaping company based in Waco, TX. If you have any questions about our services, or if you want to get your free comprehensive quote today, call us right away at (254) 744-9119.