Geosynthetics for Retaining Wall Drainage

Geosynthetics for Retaining Wall Drainage

Rainwater and groundwater erode soil on slopes and can trigger large landslides. Retaining walls hold the ground in place. For taller walls, conventional concrete gravity walls are often more expensive than reinforced soil walls built with geosynthetics, which is why reinforced soil is now widely used for highway and slope stabilization/erosion control work. Ocean Geosynthetics manufactures geogrids and drainage geosynthetics for these walls in India.

What is a retaining wall?

A retaining wall holds soil at a slope steeper than it would stand on its own. Retaining walls are built where the ground has an unwanted slope or where the landscape has to be shaped for a road, building or yard, and they stop the retained soil eroding or sliding.

The wall resists lateral pressure from the soil behind it, whether earth fill, sand or other granular material, and from water. In landscaping they are used for terraced yards, planting beds and as ornamental walls in flat yards.

They range from low stone walls around a home garden to large soil-retaining walls on highway projects. Their main job is to prevent soil movement and erosion, and a well-built wall with good drainage needs little maintenance.

Types of Retaining Walls

The main types of retaining walls are:

• Gravity walls
• Crib walls
• Gabion walls
• Cantilever walls
• Counter-fort/buttressed walls
• Anchored walls
• Piled walls
• Mechanically stabilized earth walls
• Hybrid systems

Factors to consider in retaining walls

Whatever the wall type, check the location, the soil, the design and the retaining wall drainage before building one for commercial or residential use.

Points to settle before construction starts:

• The site survey, and whether the wall sits on a slope that needs extra fill
• Where excess soil from cutting the hillside will be stored or taken
• Natural drainage paths across the site
• Surcharge loads above the wall, such as fencing, parking areas and guardrails

Benefits of Retaining Walls

Retaining walls:

• Prevent soil erosion
• Help with flood control
• Add an attractive element to the landscape
• Mark property boundaries
• Create terraced planting areas and raised flower beds, or divide a property into sections, all of which add usable space

The importance of retaining wall drainage

Poor drainage is one of the most common causes of retaining wall failure. When water cannot escape, it builds up behind the wall and adds hydrostatic pressure on top of the soil pressure the wall was designed for. A drainage system behind the wall relieves that pressure. Geosynthetics do this in different ways: a drainage geocomposite or dimple drain board against the back of the wall carries water down to a perforated pipe at the base; a nonwoven geotextile filter keeps backfill fines out of the drain; and geogrids reinforce the backfill itself, which should be free-draining granular soil.

Where the backfill is also reinforced with geogrid, our guide to designing a geogrid and geotextile retaining wall explains what each layer does, how the reinforced block is sized and why fill and drainage decide most failures.

Advantages of using Geosynthetics in retaining walls

Polymer geosynthetics do not corrode, are flexible and economical, work with other materials, last a long time in the ground, resist weather, need less heavy equipment and specialist labour than concrete walls, and help the wall drain.

In a reinforced soil wall, the geogrids are connected to the facing panels or blocks, and lengths of geogrid can be joined with a bodkin joint (a bar threaded through overlapped apertures). In a geocell-faced wall, the honeycomb cells let water drain out while holding the infill in place.

Ocean Geosynthetics supplies products for civil, landscaping and architectural retaining walls. Our products are lightweight, easy to install and treated to resist weathering.