The basement retaining wall prevents soil erosion, keeps moisture out, and protects the foundation from cracking by acting as an external brace against the surrounding soil that supports the basement.
Concrete retaining walls are designed and constructed to ensure the structural integrity and long-term safety of the foundation. This article will guide you through everything you need to know about basement retaining walls.
What is the Basement Retaining Wall?
A basement retaining wall is a structural wall designed to hold back the surrounding soil and prevent it from collapsing into the basement foundation area, which is typically below ground level. Its primary function is to resist lateral earth pressure and maintain soil stability around the basement.
In addition to supporting the soil, the wall also helps manage hydrostatic pressure and groundwater by directing water away from the foundation, thereby reducing the risk of water intrusion and flooding. These walls are typically constructed from durable materials such as reinforced cement concrete, stone, or masonry, as they must withstand significant loads from both soil and water pressure.
Benefits of Basement Retaining Wall
A basement retaining wall is a key supportive structure that is meant to guard and take the load of the basement against soil pressure, water penetration, and ground moving.
- Soil Retention: Prevents the soil from shifting into the basement and maintains the ground’s stability, ensuring the foundation remains intact.
- Water Management: This allows for the management of both groundwater and surface water, directing the water to the other side of the basement and preventing flooding and moisture problems.
- Prevents Erosion: This means that underground water is less likely to lead to soil erosion around the basement, especially in areas with high rainfall or steep terrain.
- Structural Stability: The wall enhances the basement’s structural integrity in general by providing extra support against soil pressure and external forces.
- Foundation Protection: The wall serves as a barrier not only for the basement but also for the foundation against external causes, such as water and soil pressure.
- Increases Property Value: A well-built retaining wall reflects safety and strength throughout the whole building, and therefore, it increases the value of the property.
Types of Basement Retaining Walls
The following are the various types of basement retaining walls, each with designs tailored to specific soil and environmental conditions.
1. Gravity Walls
Gravity retaining walls depend on their massive weight to counteract the pressure exerted by the earth on them. They are made of concrete, stone, or masonry and are thick and heavy, ensuring stability through gravity that prevents the soil from shifting. They are perfectly suited for smaller- or medium-sized retaining jobs where soil pressure is moderate.
2. Cantilever Walls
Cantilever retaining walls consist of a thin upright section and a base slab that extends mainly to provide extra support. Such walls are steel-reinforced, and both the weight of the wall and the leverage of the base slab act as resisting elements against the ground pressure. Generally, they are best suited for higher walls due to their structural efficiency and the material’s strength.
3. Anchored Walls
Derived from the necessity of cables or other anchoring systems in the earth to bridge the gap between the wall and the soil, anchored retaining walls are a viable solution that utilises the additional support provided by the earth. On the whole, they are suitable for situations where space is limited for constructing a large and heavy structure. These are employed generally in the mitigation of high earth pressure or problematic soil conditions.
4. Soil Nailing
Soil nailing is a method where long, steel rods (nails) are inserted into the soil to reinforce it and create a stable retaining wall. This technique is especially useful for steep slopes and unstable ground conditions. The nails, combined with shotcrete or a facing system, hold the soil in place, preventing erosion and soil movement. Soil nailing is cost-effective and ideal for projects with limited space or where traditional wall structures may not be feasible.
Design Considerations of Basement Retaining Walls
The main considerations in the construction of a basement retaining wall are as follows,
- Soil Conditions: Analyze and determine soil type, soil stability, and soil load-bearing capacity. These factors have a direct effect on wall strength and stability.
- Water Management: Incorporate the use of waterproofing materials and drainage systems (e.g., French drains and weep holes) into the water control design to prevent water accumulation and damage.
- Material Selection: Choose materials such as concrete, masonry, or reinforced concrete that can withstand soil pressure, moisture, and environmental conditions.
- Wall Height: The higher the walls, the more reinforcement forces they will require. Additionally, it is advisable to lift or anchor the wall to increase stability.
- Reinforcement: Steel bars (rebar) or anchoring systems can be applied to increase the strength and resistance of the load.
- Environmental Factors: Select the seismic action, frost heave potential, and groundwater level based on the climatic and geological conditions of the area.
- Construction Method: Decide the extent of excavation, what type of form should be used, and installation techniques according to the materials you have chosen.
- Aesthetic Considerations: When the retaining wall is visible, include designs that can harmonize it with the landscape.
Construction Process of Basement Retaining Walls
1. Site Preparation and Excavation
The site is first deprived of all the garbage, vegetation, and some other buildings. After that, the land is excavated to the required depth and width, ensuring sufficient space for the wall to be constructed and laid with its foundation.
2. Foundation and Footing
The base of the excavation is poured with a concrete footing. This will validate that the weight of the wall is spread equally. Rebar is placed in the footing to provide additional reinforcement to the wall, preventing it from sliding or settling.
3. Wall Construction
Consider that you are constructing a gravity retaining wall. It is built using heavy materials such as concrete blocks, stone, or precast units. Their primary resistance to soil pressure comes from their own weight. Blocks or stones are stacked, often using mortar, and may be reinforced depending on the design. The wall height and thickness are then determined to resist the lateral pressure of the surrounding soil.
4. Waterproofing
A significant role in eliminating water infiltration from the basement walls is played by a waterproofing membrane or coating, which is usually applied on the outside. To move the water away from the wall and to stop the water pressure build-up, the French drain or weephole drainage system is placed, and the drainage system is installed inside the wall (the other solutions mentioned are less suitable than this one).
5. Backfilling
When the wall has been finished with proper construction and waterproofing, the space around the wall is filled up with soil, which is then properly compacted to guarantee no settling or movement will occur.
6. Final Inspection
The final step is to conduct a thorough inspection of the wall to ensure its condition, the effectiveness of water protection, and the capacity of the drainage system. If necessary, corrective measures and adjustments are implemented before we can declare the project closed.
Waterproofing and Drainage of Basement Retaining Walls
Waterproofing and drainage are the first line of defence in shielding basement retaining walls against moisture damage. Correctly installed waterproofing prevents water from entering, and an efficient drainage system regulates water pressure at the back of the wall.
- Waterproofing Process
Surface Cleaning: The wall surface should be carefully cleaned to remove dirt and old paint coatings, as this significantly contributes to good bonding with the substrate.
Applying Waterproof Membrane: The process is completed by covering the wall with bituminous coatings or rubberized membranes that offer effective basement waterproofing.
Sealing Cracks: Sealing visible cracks with flexible sealants or epoxy is another critical step to keep out water.
- Drainage Process
French Drains: Create a trench around the base of the wall, insert a pipe with holes, and then cover the pipe with gravel to help the collected water drain without compromising the basement’s foundation.
Weep Holes: These tiny openings provide an easy escape route for the water that becomes confined in the wall, preventing it from causing a thrust on the wall.
Backfilling with Gravel: Using crushed stones and openly spaced gravel within a trench during backfilling encourages water to flow directly into the drainage system.
Sump Pumps: In areas with a high water table, sump pumps are used to pump water out of the basement actively.
Together, waterproofing and drainage ensure the durability of the retaining wall and prevent water damage.
How do you check the Basement Wall Stability?
First of all, you should carry out a visual check to confirm the wall’s stability. Check for cracks that are easily visible, especially if they are diagonal; this may indicate that the wall is leaning or settling. Ensure the walls are perpendicular and not curved; if they are bending or leaning, a structural problem is obvious. Also, do the inspection for water damage, like moistness, mold, and efflorescence (white powdery deposits) on the walls.
Then, use a level to verify that the walls are not leaning one way or another and that they stand very straight. You can also decide to measure visible cracks to ensure they are not increasing or worsening over time. Additionally, the draft created around an opening, whether it is a window or a door, or the junction of the wall and the floor, may be a hint to a wall-shifting problem.
If you find severe signs, including large cracks, leaning, or indications of a water problem, do not hesitate to seek the help of a structural engineer who can conduct a detailed inspection and do all the necessary repairs.
Conclusion
Without a doubt, it is paramount to ensure your home’s walls are strong and free from defects, as this not only equates but also outweighs the safety factors. Regular checks for signs of cracks, water damage, and movement are paramount to identifying the issues on time.
For reliable help, research beyond specialists, and get in touch with Brick & Bolt. The team of that company will find and then implement the most suitable solutions for your basement that will keep the space dry and the foundation standing.
Apoorva H P Achar