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A boulder retaining wall can bring structure and definition to your landscape design. Boulder retaining walls utilize large, naturally shaped rocks to hold back soil and create decorative hardscaping features. These sturdy walls prevent soil erosion on slopes and can transform steep inclines into useful yard space. Boulder retaining walls bring an organic, rustic look to landscapes with their asymmetric stacked stone design. With this given information, you will be able to decide if this rugged wall form is a good option for your home landscaping.
What is a Boulder Retaining Wall?
A boulder retaining wall is a construction designed to keep soil back and prevent it from eroding or sliding. It’s generally used in landscaping and structure systems to produce position regions on the ground.
The wall is erected of big jewels that are precisely placed and mounded together. The size and weight of the monuments give the necessary strength to hold the soil behind the wall. The holes between the monuments give for drainage, precluding water buildup that may undermine the wall.
Do boulders make good retaining walls?
Yes, boulders do make good retaining walls in numerous cases. They’re solid, resistant to corrosion from rainfall, and can repel a lot of pressure, which makes them an excellent structure material for retaining walls.Still, it’s important to note that while boulders are generally a good choice, their effectiveness can depend on colorful factors, such as the design of the wall, the specific conditions of the point, and the quality of the construction. For example, if the wall is not erected correctly, it could potentially fail.
How long do boulder retaining walls last?
Boulder retaining walls that are well-built are known for their longevity. They can last upwards of 100 years or more, making them one of the most lasting types of retaining walls. However, this lifespan can greatly depend on several factors, including the quality of construction, materials used, soil conditions, and groundwater levels.
It’s important to note that improperly built boulder retaining walls might not last long. Many retaining walls fail because they’re not built correctly. Therefore, it’s critical to ensure that the wall is properly installed to maximize its lifespan.
Pros of a Boulder Retaining Wall:
- Rustic, natural appearance complements gardens and wooded areas
- can be built to curve and meander
- Provides seating areas when built with wide capstones
- Long-lasting and low-maintenance without mortar
- A permeable design won’t cause drainage issues
- Can incorporate planting pockets between boulders
Cons of a Boulder Retaining Wall:
- Requires heavy equipment to move large boulders
- Professional installation is mostly recommended for structural walls
- Loose rocks may shift over time if not stacked properly
- Not recommended for steep slopes without geogrid reinforcement
- Irregular shapes make walls thicker, block-retaining walls
Construction Methods for Boulder Retaining Walls
There are three main techniques for building boulder retaining walls:
Dry Stack (Gravity Wall) Method:
The Dry Stack (Gravity Wall) Method is a technique used in constructing retaining walls where stones or blocks are stacked on top of each other. The dry stack method relies on the sheer mass of the boulders to keep the wall in place. The boulders interlock tightly, and gravity holds them together. This type works for walls up to 4 feet tall.
Wet-Laid (Mortared) Method:
Mortar is use to stabilize boulders in the wet-laid method. The Wet-Laid (Mortared) Method is a construction technique used for building retaining walls where stones are held together. Mortared boulder walls have thinner profiles than dry-stacked walls. Mortar adds strength but reduces permeability and drainage. The mortared method is best for walls over 4 feet tall.
Some walls use both dry stacking and mortared construction. Large boulders are dry-stacked, while smaller filler rocks are mortared between the main rocks. Weep holes are added for drainage. This combines the look of dry-stacked walls with the strength of mortared walls.
What are the benefits of boulder walls?
Boulder walls, also known as retaining walls or rock walls, offer several benefits in various applications. Here’s a brief explanation of their advantages:
- Erosion control: Boulder walls effectively prevent soil erosion by holding back and stabilizing soil on slopes. They can be particularly useful in areas prone to landslides or where erosion is a concern.
- Structural support: These walls provide structural support to prevent the collapse or movement of soil, rocks, or other materials. They can used to create terraces or level areas on slopes, allowing for safer construction or landscaping.
- Aesthetics: Boulder walls can enhance the visual appeal of outdoor spaces. They add a natural and rugged charm, blending well with the surrounding landscape. These walls can designed in various shapes and sizes to complement the overall aesthetics of the environment.
- Increased usable space: By creating terraces or leveling steep slopes, boulder walls can help maximize usable space in hilly or sloping areas. This can be advantageous for gardening, landscaping, or creating functional outdoor areas.
- Low maintenance: Once constructed, boulder walls generally require minimal maintenance. Unlike some other types of walls, they do not typically need regular painting or sealing. The natural materials used in boulder walls make them low-maintenance structures.
Choosing Rocks for Boulder Retaining Walls
Boulder retaining walls work best with rugged, irregularly shaped rocks at least 8–12 inches thick. The boulders should vary in size, from small filler rocks to larger rocks over 3 feet wide. Stones with flat bottoms and tops allow for sturdy stacking. Granite, limestone, and sandstone are common boulder materials. Avoid thin or rounded stones that won’t stack well.
Tips for Boulder Retaining Walls:
- Excavate a footer trench and fill it with compacted gravel for drainage
- Stack boulders tightly without wiggle room for stability
- Place capstones for an even-finished edge
- Include drainage pipes, gravel backfill, and weep holes
- Add soil separators and geogrid if needed for reinforcement
- Retaining wall blocks can be incorporated into curves
Boulder Retaining Wall Cost:
Boulder retaining walls cost $25–$50 per square foot, on average. Shorter gravity walls under 3 feet tall range from $15 to $30 per square foot. Taller structural walls cost $30–$60 per square foot. Factors affecting the cost include:
- Wall height and length
- Boulder size and type
- Dry stack versus mortared construction
- Use of heavy equipment for installation
- Whether a stonemason is required
- Excavation challenges
- Addition of drainage materials or geogrid
Creative Boulder Retaining Wall Ideas
- Dry Stacked Flat Boulders: Use flat sandstone or limestone boulders tightly stacked side-by-side.
- Mortared Stone Wall: Mortar smaller filler stones between large boulders for a structural wall.
- Seating Wall: Build the wall 25–30″ tall and top it with wide capstones for built-in seating.
- Mixed Retaining Wall: Combine boulders with wall blocks to make curves, corners, and steps.
- Boulder Planters: Leave gaps between boulders for planting flowers, grasses, or succulents.
Boulder retaining walls bring natural style to landscapes with their bold, asymmetric rock designs. When properly constructed, they make rugged and long-lasting retaining walls. Consider a boulder wall with drainage and geogrid reinforcements for your landscape.
Choosing Boulder Sizes and Shapes
- Use a variety of rock sizes for structural integrity. Larger boulders (2–3 feet) are mixed with smaller filler rocks.
- Angular, blocky boulders stack better than round stones. Look for rectangular or square-shaped rocks.
- Flat-ish boulders with relatively smooth tops and bottoms create a stable base.
- Very jagged, knobby boulders take more effort to stack neatly.
Boulder Sourcing and Transportation
- Quarries offer boulders, or rocks can be gathered locally. Delivery fees may apply.
- Special equipment like conveyors, cranes, or boom trucks may be needed to move and place large boulders.
- Some boulder suppliers have stone yards where you can hand-select rocks.
Wall Batter (Lean)
- Dry-stacked walls should be built with a slight inward slope or batter.
- The wall can lean 2–5 degrees towards the soil it is retaining. This helps counteract forces from the soil.
- Mortared walls can be built more vertically but still benefit from a slight backward batter.
Boulder Retaining Wall Foundation
- Excavate a footing trench the width of the wall and 6–12 inches deep.
- Fill the trench with compacted gravel, then level it with a layer of compacted sand.
- This provides a stable base and helps prevent settling and shifting.
- Perforated drainage pipes at the base and backfill with gravel allow water flow.
- Weep holes also allow drainage and should be placed every 3-6 feet.
- Proper drainage prevents the buildup of hydrostatic pressure behind the wall.
Boulder retaining walls are an aesthetically pleasing and robust result for landscaping requirements, especially in areas with rocky terrain. They give strength, life, and beauty to your geography as they’re made from 100 natural gravestones with no complements, enhancing the look of out-of-door spaces. The process of erecting a boulder retaining wall involves sourcing the boulders, which can generally be set up at the original chases. There are also professional services like Stonewall Inc., trusted for their high-quality boulder retaining walls and creative natural gravestone outcroppings.