Retaining Walls for Slopes


What is a Retaining Wall and Why Do You Need One?

Retaining Wall Basics

A retaining wall is a sturdy structure designed to hold back or retain soil on a slope. By resisting the lateral pressure exerted by the earth behind it, a well-built retaining wall prevents the loose soil on a slope from sliding, slumping, or eroding. Retaining walls stabilize slopes and embankments, provide erosion control, and create usable flat areas for gardens, patios, and other outdoor spaces on hilly or elevated terrain.

Benefits of Building a Retaining Wall

Retaining walls create usable flat space on slopes, prevent erosion, stabilize slopes prone to landslides, enable multi-tiered landscaping, support infrastructure on embankments, and protect properties from damage caused by sliding soil.

Factors to Consider Before Building a Retaining Wall

Key factors in building a retaining wall include: assessing slope, height and load needs to determine design; evaluating soil composition, drainage, weight load and earth pressure through tests and analysis; considering frost line depth, climate, and freeze-thaw cycles for proper footing and drainage; researching applicable zoning laws, codes, regulations and permits; and contemplating aesthetics, site lines and landscape integration for cohesion.

Choosing the Right Retaining Wall Design

Common retaining wall types are gravity walls using mass and weight for stability, piling walls with columns anchored in bedrock, cantilever walls with flared bases extending underground, and counterfort walls with vertical buttresses. The optimal design depends on site conditions, wall size, and soil characteristics. Engineer involvement is required for high, multi-tiered, or complex walls.

Retaining Wall Materials

Common DIY retaining wall materials are concrete blocks, natural stone, timber, gabion baskets, and reinforced concrete. Concrete blocks are inexpensive, modular, and decorative. Natural stone is attractive but requires expertise. Timber is easy to work with but rots over time. Gabion baskets with stone provide flexible construction. Reinforced concrete needs drainage but offers strength. Experienced contractors can recommend suitable materials.

How to Build a Retaining Wall on a Slope

Preparing the Slope and Laying the Foundation

The first step in any retaining wall project is proper site preparation. The area must be cleared of vegetation, leveled, and graded. For walls higher than a few feet, it’s necessary to excavate a footer trench below the frost line to prevent frost upheaval. The trench should be filled with packed gravel to create a stable base. Compact the soil thoroughly before laying the first course of blocks, stones, or other materials on the prepared foundation.

Installing the First Row

Use a level and string line to double check that the first row of blocks or stones is perfectly straight and level. Drainage aggregate like crushed gravel should fill the gaps between blocks to encourage water drainage. Compact and flatten the soil behind the first row before moving upward. Check that each block is stable and aligned with the string line as you go.

Building Additional Tiers

Continue stacking rows of blocks, stones, or timbers to the desired height, overlapping each row and offsetting the seams from the row below. Adhesive or construction glue helps secure each tier atop the one below. Insert reinforcing tie-backs or geogrid periodically to strengthen the wall structure. Backfill behind the wall with free-draining aggregate like crushed stone.

Proper Drainage for a Slope Retaining Wall

Proper drainage is crucial to prevent buildup of hydrostatic pressure behind the wall. Install perforated drainage pipes at the base of the backfill to direct moisture away from the slope. The backfill material behind the wall should be free-draining gravel, never compacted soil. Ensure the grade slopes away from the base of the wall to facilitate runoff.

Backfilling and Finishing Touches

Backfill behind the completed wall in thin layers, compacting the soil after each layer to prevent settling. Cap the top of the wall with coping blocks or a concrete curb to provide an attractive finished edge. Hydroseed bare soil areas to promote vegetation coverage and prevent erosion. Avoid planting woody plants like trees and shrubs directly on the wall structure.

Tips for Landscaping a Slope with a Retaining Wall

Creating Terraced Gardens with Retaining Walls

A series of retaining walls creates terraced flat zones ideal for planting gardens on a slope. Tailor terraces to fit garden beds, paths, and stairs. Multi-level gardens can combine flowers, ground covers, shrubs, vegetables, trees, and other plantings.

Adding Water Features to Enhance the Landscape

Small ponds, streams, and waterfalls built into retaining wall terraces add visual interest and sound to the landscape. Recirculating pumps allow water features to operate properly on a slope. Line ponds with plastic liners or poured concrete.

Design Ideas for Patios on Slopes

Gently curving walls with plantings help patios blend into the natural topography. Staggered, stacked retaining walls create usable flat spaces for multi-level patios connected by steps and paths. Incorporate ramps for accessibility.

Preventing Soil Erosion with Proper Landscaping

Strategically placed trees, shrubs, and groundcovers help retain soil on a slope and prevent erosion. Hardy, low-maintenance plants like succulents, sedum, ivy, and wildflowers are good choices.

Vegetable Gardens on Steep Slopes

Creating terraced garden beds allows vegetables to be grown successfully on steep terrain. Build terraces wide enough for pathways between beds. Improving soil quality, drainage, and irrigation ensures optimal growing conditions.

Common Problems with Retaining Walls on Slopes

Dealing with Drainage Issues

Prevent water buildup by grading soil away from the wall, using porous backfill material, and installing subsurface drainage pipes and gravel. Drain spouts through the wall also help.

Preventing Structural Failure

Adhere to maximum height limits for the wall design and construction method. Use proper reinforcement, anchoring, compaction, and allow materials to settle completely before backfilling to prevent bulging or collapse.

Addressing Soil Erosion and Its Impact

Control stormwater runoff with gutters, drains, and plants above the wall. Avoid disturbing soil at the base of the slope. Plants and groundcover help stabilize the soil on the face of the slope.

Choosing the Right Wall Height

Taller walls require additional reinforcement and engineering considerations. Very steep slopes are best served by a series of terraced retaining walls of moderate height rather than a single tall wall.

Maintenance and Repairs

Inspect retaining walls periodically, especially after heavy rains. Clear any debris from drainage pipes and weep holes. Repair cracks, bulges, and misaligned sections promptly. Remove invasive roots or woody growth on the wall.

Professional Help for Slope Retaining Walls

When to Consult a Landscape Architect

For large, multi-tiered, or high retaining walls, consult a professional landscape architect for the design and planning. They can create a beautiful, functional design tailored to your property and project requirements. Landscape architects are also very helpful if you need permitting or engineering approvals.

How to Choose the Right Retaining Wall Contractor

Look for a contractor thoroughly experienced in building retaining walls on slopes and hills. Check references to evaluate quality of past work. Choose a company that is licensed, insured, and up to date on local building codes and regulations. Make sure they will pull all required permits. Ask about warranty on materials and workmanship.

Building Codes and Permits

Most jurisdictions require permits for retaining walls over 4 feet in height. Research local requirements regarding zoning setbacks and other regulations. Larger retaining walls often require approval from a structural engineer as part of the permitting process. The contractor usually handles permits and engineering approvals.

Designing a Wall that Complements the Landscape

Choose colors, textures, and style of wall materials that integrate with the aesthetics of your yard. Incorporate additional decorative features like lighting, plantings, or rock accents. Position and contour the wall to complement the curves and elevation changes of your landscape.

Latest Trends in Retaining Wall Construction

Some current trends include multi-textured patterned wall faces, gabion walls filled with colorful rocks, living walls integrated with plants, and curved walls with serpentine shapes. Discuss options with your landscape designer to pick the right retaining wall look and features for your yard.

Q: What are retaining walls for slopes?

A: Retaining walls for slopes are structures built to hold and support soil on steep slopes. They are designed to prevent soil erosion and control water runoff.

Q: How do retaining walls help with hillside landscaping?

A: Retaining walls are an essential component of hillside landscaping. They help create level areas for gardens, patios, and other outdoor living spaces on steep slopes.

Q: What is the purpose of a stone retaining wall?

A: A stone retaining wall serves both a functional and aesthetic purpose. It helps to prevent soil erosion and slope instability while adding beauty and character to the landscape design.

Q: How can I prevent erosion on a steep slope?

A: Building a retaining wall on a steep slope is an effective way to prevent erosion. The wall holds the soil in place, preventing it from washing away during heavy rains.

Q: Can I use pavers to build a retaining wall?

A: Yes, pavers can be used to build a retaining wall. They offer a versatile and attractive option for creating a durable and functional hillside retaining wall.

Q: What is the recommended base material for a retaining wall?

A: The recommended base material for a retaining wall is gravel backfill. It provides proper drainage and stability for the wall, ensuring its long-term effectiveness.

Q: How can I address poor drainage behind a retaining wall?

A: Installing a perforated drainpipe behind the retaining wall can help address poor drainage. It allows excess water to escape, preventing hydrostatic pressure build-up.

Q: Can a retaining wall be used to create a fire pit?

A: Yes, a retaining wall can be incorporated into a fire pit design. It can provide the necessary structure and stability for the fire pit while enhancing its overall aesthetic appeal.

Q: What should I do if my retaining wall leans or starts to fail?

A: If your retaining wall leans or shows signs of failure, it is important to seek professional assistance. A failing retaining wall can pose safety risks and may require proper remediation.

Q: Do I need a permit to build a retaining wall?

A: The need for a permit to build a retaining wall depends on local regulations. It is recommended to check with your local building department to determine the specific requirements for your area.