Hydrostatic Pressure for Retaining Walls. 

Hydrostatic pressure is a critical factor when installing steel garden edging. It's especially critical  if your system also functions as a retaining wall. Without proper drainage, this pressure can cause damage to your edging, surrounding landscape, or even create a safety hazard. This blog will discuss how hydrostatic pressure affects our four edging systems—Groundline, Contour, Anco, and Contain.  It provides practical solutions for effective drainage.

Understanding Hydrostatic Pressure

Hydrostatic pressure is the force exerted by standing water against any structure in contact with it. In the context of steel garden edging and retaining walls, it occurs when water builds up behind the edging, saturating the soil. Without a way to relieve this pressure, your edging could bow, corrode, or even fail

Groundline (50-150mm high edging)

Groundline, our lowest-profile edging system, typically experiences minimal hydrostatic pressure since it’s used more for defining borders or edges rather than holding back significant amounts of soil. However, in areas with high rainfall or poorly draining soil, even this small edging can encounter issues if water accumulates around the base.

Drainage Solution for Groundline:

- Install a shallow trench filled with gravel under the edging to promote natural water movement.

- Use perforated drainpipes in water-prone areas to channel excess water away from the edge.

- Ensure soil grading directs water flow away from the edging.

Contour (200-600mm high edging)

Contour is designed for more significant edging projects, possibly holding back light to moderate amounts of soil. Because it handles more material, the hydrostatic pressure becomes more pronounced, particularly in wet conditions.

Drainage Solution for Contour:

- A gravel trench or French drain behind the edging will help relieve hydrostatic water pressure.

- Consider using a geotextile membrane to separate soil from gravel, ensuring proper water filtration without clogging.

-  When using Corten or Stainless steel you can drill small weep holes at the base of the edging.  This allows trapped water to escape and prevent buildup.

Anco (300-1200mm high edging)

Anco is where the risk of hydrostatic pressure truly comes into play, as its height and function often serve as a retaining wall. This means it's crucial to address drainage properly.

Drainage Solution for Anco:

- A robust drainage system, like a French drain or perforated pipe, should be installed behind the wall.

- Use coarse backfill material such as gravel behind the edging to allow for better water movement.

Contain (Large Premade Plant Pots)

Although Contain serves a different purpose, proper drainage is still essential. Each Contain planter comes with pre-drilled drainage holes. However, we recommend adding a liner to prevent soil from washing out with the water. Keep in mind, placing the planter on a non-porous surface can obstruct drainage, so ensure it sits on a well-draining area.

General Tips for Managing Hydrostatic Pressure in Steel Edging

1. Proper Backfilling: Use well-draining materials like gravel or crushed stone behind your edging systems to allow water to pass through easily.
2. Sloped Grading: Make sure the ground behind the edging slopes slightly away from the structure to naturally divert water.
3. Inspection and Maintenance: Regularly check for blockages in your drainage systems or signs of stress or wear in your steel edging to avoid long-term issues.

Hydrostatic pressure can pose a significant challenge, but with the right drainage techniques, your steel edging—whether it’s Groundline, Contour, Anco, or Contain—can stand the test of time. By addressing water flow from the start, you'll ensure that your edging system not only looks great but also performs reliably through any weather condition.

Other retaining wall materials: 

Different materials respond differently to hydrostatic pressure, and the potential for water drainage is a critical factor in the wall’s longevity and stability. Let’s explore how this pressure impacts gabion baskets, steel edging, block walls, and timber walls.

1. Gabion Baskets

Gabion baskets are wire mesh containers filled with rocks or stones.  Because of this, they have a significant advantage when it comes to hydrostatic pressure. The permeable nature of gabions allows water to flow through the gaps between the rocks, which prevents water buildup behind the wall. This means that gabion walls experience little to no hydrostatic pressure compared to solid walls.

Because the water is allowed to drain freely, the risk of lateral pressure accumulation is minimized. The structure remains stable even in areas with high water exposure, such as near riverbanks or in areas with high rainfall. However, the effectiveness of a gabion wall depends on the quality and durability of the wire mesh over time, especially in environments with corrosive water or salt content. Proper material selection and periodic maintenance are necessary to ensure the long-term performance of the wire mesh.

2. Steel Edging

Steel edging, often used for low retaining walls or raised beds, can be susceptible to hydrostatic pressure if not properly designed with drainage in mind. Because steel itself does not allow water to pass through, if water builds up behind a steel wall, it can create significant pressure, potentially leading to deformation or failure over time.

To mitigate this, incorporating drainage solutions such as weep holes, gravel backfill, or perforated pipes behind the steel edging is essential. This ensures that water is directed away from the wall, reducing hydrostatic pressure. For higher steel walls, proper drainage is even more critical, as the force exerted by water increases with the height of the wall.

3. Block Walls

Block retaining walls, often made from concrete, can be highly susceptible to hydrostatic pressure if drainage is not carefully managed. These walls are solid and impermeable, meaning that water cannot pass through them. Without sufficient drainage, water accumulates behind the wall, exerting pressure that can lead to cracking or even failure.

Proper drainage systems are essential for block walls. Common solutions include installing weep holes at the base of the wall, using drainage pipes to channel water away from the structure. Backfilling with free-draining materials such as gravel to help water flow down and out rather than accumulating behind the wall. Additionally, waterproofing membranes can be applied to the back of the wall to prevent water infiltration.

4. Timber Walls

Timber retaining walls are also prone to hydrostatic pressure, and their longevity depends largely on how well drainage is managed. Because timber is organic, constant exposure to water can cause the material to degrade or rot over time. If hydrostatic pressure is allowed to build up behind a timber wall, it not only stresses the structure but also increases the likelihood of water damage to the timber itself.

Like with block and steel walls, installing proper drainage systems is vital for timber retaining walls. Backfilling with gravel and using drainage pipes helps prevent water from building up and reduces the stress caused by hydrostatic pressure. Additionally, treating timber with water-resistant coatings or using rot-resistant wood species can extend the lifespan of the structure.

Conclusion

In all cases, proper drainage is the key to managing hydrostatic pressure and ensuring the longevity of retaining walls. Gabion baskets naturally handle water well due to their permeable nature. While steel, block, and timber walls require additional drainage solutions to prevent water buildup. Without these measures, hydrostatic pressure can cause significant damage to retaining walls, leading to costly repairs or failure over time.