Dealing with soil erosion or unstable slopes in the construction site could be a difficult problem to deal with, when it comes to construction work. But what if that’s all mitigated by a simple solution to hold everything in place? Enter the cantilever retaining wall. In this blog, we will learn how these walls work and how they have become a favorite wall type for soil and slope problems. Let’s jump right in!
What are Cantilever Retaining Walls?
The cantilever retaining wall is a wall that resists the local soil pressure by its weight and design and does not require the use of any external anchors or supports. Its design consists of a cantilever wall sitting on an extended base slab called the heel underneath the retained soil. The wall utilises gravity’s force to counter sliding and overturning. Hence, it is an effective choice to hold back soil on steep or elevated land.
The cantilever walls are generally made of reinforced concrete but on occasions, timber, stone, and steel may be used as well. Cantilever walls are predominant where there is a need for structural support exceeding that offered by a simple gravity wall, but doesn’t need the complexities of a counterfort wall.
Components of a Cantilever Retaining Wall
- Stem: It is the vertical portion of the wall that opposes pressure from the retained soil.
- Heel: It is a part of the base slab extending under the soil that aids in resisting soil pressure, making it an important contributor to stability.
- Toe: It is the part of the base slab extending outward to stabilize the wall and help prevent overturning.
- Key: It is a part of the base that extends into the earth to counteract sliding and give extra resistance.
- Drainage Pipes/Weep Holes: They are provided to avoid water buildup behind the wall, as high pressure from this water can cause failure.
These components act together against sliding, overturning, and the pressure exerted from the retained material.
Common Applications of Cantilever Retaining Wall
- Terracing and landscaping: They are often applied for aesthetic purposes in creating terracing in hill terrain.
- Roads and Highways: The use of cantilever walls determines slope stability either on roads, highways or embankments with steep grade.
- Bridge Abutments: These walls usually perform as foundation walls for bridges where soil is retained around bridge supports.
- Basements and Foundations: In residential or commercial construction, the purpose is to support basement walls or form a part of the foundation system.
- Flood Control: They are also used in flood protection projects to actually prevent soil erosion and once to control water flow.
Advantages of Cantilever Retaining Wall
- Efficient Use of Materials: These walls rely on their weight to counteract pressure, which is considerably more material-efficient compared to other retaining walls.
- Stabilization: By using cantilever geometry, walls can be made stable without the use of an additional supporting system such as tiebacks or anchors.
- Cost-Effective: Cantilever walls on the average tend to be less material-intensive, require fewer construction steps than other complex wall systems, and thus will eventually be much cheaper.
- Durability: Long-term stability is provided by proper drainage and reinforcement, and cantilever retaining walls can be expected to last for decades.
- Design Flexibility: A cantilever wall can be custom-suited to accommodate virtually any height and soil conditions that may be required for a given project.
Design Considerations for Cantilever Retaining Wall
Soil Type and Characteristics
The type of soil behind the retaining wall has an influence on the amount of pressure the wall has to withstand. Cohesive soils, like clay, cause greater lateral pressure than other sorts of more granular soils, like sand, and hence are considered in the design of such walls.
Index properties like shear strength and moisture content also determine the size and stability of a wall. High-pressure conditions that arise due to poor drainage also need preventative measures to avoid possible failure.
Wall Height
Taller retaining walls face an increased force due to the increase in weight of the retained soil. As the wall height increases, a thicker base, stronger reinforcement, and possibly counterforts will be a necessity. More caution has to be exercised for taller walls regarding sliding, overturning, and resisting pressure failure.
Water Table and Drainage
A high water table or poor drainage is conducive to water retention, thus inducing pressure on the wall and weakening it, becoming a resounding failure. Proper drainage using weep holes or pipes is therefore necessary to reduce and dissipate hydrostatic pressure and to prevent water build-up, keeping the wall in good standing.
Loading Applications
Considering loads, the cantilever wall not only have to withstand soil pressure, could possibly arise against the retaining walls from buildings, vehicular access, or fencing applications near to the wall. Such loads result in extra forces on the wall and should be considered in the design. The wall may need to be upgraded in size or reinforcing to offset these extra stresses so as to avert failure.
Safety Factors
Safety factors are those external loads that might be exerted on the wall, causing abnormal climatic loading or a rapid change in soil conditions. These factors ensure further safety input into the design, thus assuring no failure will occur during an event not normally considered behavior. Safety factors provide a degree of instability by design in favor of the wall resisting more pressures than expected.
Construction Process of a Cantilever Retaining Wall
Site Preparation
The first stage of construction for a cantilever retaining wall involves site preparation. Clear obstacles in the area, such as rocks or vegetation, and set soil levels as a level base. The soil test should be adequate to hold the wall.
Foundation and Base Slab
After the site is prepared, the next thing is excavation and pouring the foundation and base slab. The under soil is designed to bear the counter pressure from the soil retained by the base. Base usually comes along with steel bar reinforcement to have strength and stability.
Wall Construction
The vertical part (stem) of the wall is then constructed using reinforced concrete. They are designed to resist lateral soil pressures, using steel reinforcement (rebar) inside the concrete to enhance its strength.
Reinforcement and Drainage
Upon the construction of the stem, the wall is reinforced further with steel rebar for additional strength. At this stage, drainage systems like weepholes or pipes are also installed behind the wall to prevent water accumulation.
Backfilling
After the wall is installed in place, soil is carefully placed behind it, lifting the ground to form a backfill. Each layer is carefully compacted with an effort to avoid settling, which may cause the wall’s shift position. It allows a wall to remain firmly secured in place and provide proper support.
Conclusion
Cantilever retaining walls are a strong and economical option for soil retention in many construction projects. They are very efficient, stable, and flexible in design. When constructed properly, they provide ultimate support for areas such as gardens, roads, basements, and flood control. With some planning and construction involved, cantilever walls assist engineers to successfully and safely manage the pressures from soil and water.