Retaining Wall Drainage: A Complete Guide

by craftyclub

When there is a significant change in elevation, a retaining wall is used to hold back the soil. Retaining walls are frequently used to terrace yards with a steep slope. Retaining walls can also be used to provide usable outdoor area and manage erosion. Lower retaining walls are often used as gardening beds, and they can give life to a flat yard.

Retaining Wall Drainage: A Complete Guide
Retaining Wall Drainage: A Complete Guide (from Pinterest)

How Important is Retaining Wall Drainage?

Many commercial and residential constructions use retaining walls as a design feature. They not only increase the overall visual appeal and beauty of your property but also provide support for huge planter beds. While they may appear to be simple, the engineering that goes into ensuring that they can endure pressure is intricate. To be safe and sturdy, all retaining walls must have proper drainage systems. Understanding retaining wall drainage will help you assess the efficiency of your retaining wall and identify potential problems before they occur.

What is Drainage?

Water runs down the walls when it rains. So when it finishes raining, your landscape should have a little amount of surface water. That’s how drainage works.

The importance of retaining wall drainage cannot be overstated. It prevents water from accumulating behind the wall. A good drainage system gathers up all the rainwater and changes its direction so that it’s away from the wall. It reduces erosion and settlement of water by decreasing pressure on the soil around the foundation and within the wall.

The weight of the ground or gravel at the back of the retaining wall is a force that the retaining wall must bear in order to keep standing. Any amount of water that has been gathered up behind the wall creates compounding pressure that can cause sliding, bulging, or catastrophic collapse. As a result, it’s critical that there’s a drainage channel and that the wall’s construction can safely sustain the anticipated load.

A Retaining Wall Drainage must consist of:

If you’re thinking about hiring someone to create a retaining wall on your property, you should know what goes into effective retaining wall design. This way, you can be guaranteed to have a high-quality wall that will last longer and hold water effectively. A poorly constructed retaining wall may swell, split, or tilt, causing you an unpleasant eyesore and a headache.

  • A Strong Base
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To begin, a retaining wall must be constructed on a sufficient base. The significance of beginning with a sound foundation is stressed by both block producers and experienced contractors and engineers. A retaining wall’s base should be situated below ground level. The higher a wall is, the lower it should be set below ground level. A good base of compressed soil and a layer that is six inches at most is essential for sustaining the rest of the wall.

  • A backfill

Secondly, the backfill of a retaining wall must be appropriately compacted. The gravel behind the wall is referred to as a backfill. 12 inches granular at most of the backfill should be placed directly behind the wall to allow optimum drainage. The rest of the space behind the wall can be backfilled with compressed native soil. Native soil, which is more than 6 inches, should also be laid over the gravel fill if you plan to conduct landscaping at the back of the wall.

  • Drainage

Thirdly, because most retaining walls are impenetrable, meaning water cannot move through the walls, proper drainage is essential. Hydrostatic pressure will build up behind the wall if drainage is not handled, causing damage such as bursting or splitting. There are several options for ensuring proper water drainage behind a retaining wall. The first step is to ensure that your landscaping operator backfills a foot space with gravel at the back of the wall. The second option is to put a perforated pipe along the inside bottom of the wall. Finally, determine whether leak holes are required to allow water to drain through the wall.

  • Height

Lastly, remember that the height of a retaining wall dictates the load it can support and how much further reinforcing is required. The average height of a residential retaining wall is 3 to 4 feet. Without the need for anchors, cantilever brakes, or any supplementary reinforcements, this height gives outstanding strength. If your property necessitates a higher wall, you have two options: hire an engineer to build the wall or use a series of 3 or 4 foot walls to give a terraced look.

Materials for Retaining Wall Drainage

You may protect yourself from retaining wall failure caused by poor water drainage in a variety of ways. While materials such as blockwork and maybe stone have their own characteristics and advantages, all types of retaining walls require some type of drainage to keep their structural strength.

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Geofabric:

Geofabric is a polyester-based synthetic textile usually used in civil engineering applications for drainage and filtration. For drainage purposes, it’s being utilized here to keep soil and sediments out of the backfill, which would prevent water from freely flowing through it. To prevent dirt or debris from being clogged up in holes and restricting its efficiency for retaining wall drainage, a geotextile sock should be applied around the drainage pipe.

Aggregate for backfill

A substantial layer of dry drainage material should be placed behind any retaining wall to keep it apart from the soil. Gravel, rocks, or crumbled stone, often known as aggregate, can be used as a backfill. This aggregate will let water to freely flow to a drainage pipe or out through weeping holes and away from the wall, relieving pressure.

Pipe for drainage

From the base of the wall, perforated draining pipes or agriculture draining pipes should be used to flow the water away from the back of the wall and through the weeping holes. The pipe should run the length of the retaining wall and be vented at regular intervals to enhance retaining wall drainage.

Holes

Weep holes are openings in the wall that route water out to alleviate hydrostatic pressure. Weep holes are frequently only required at the base of shorter walls, but larger walls require a grid-like structure with several smaller weep holes protruding from the wall. To avoid stains from the water from the weep holes, we propose applying a protective varnish to the wall.

Soil Compaction

To minimize the capacity of the soil behind the backfill to absorb the water, it should be compressed during the construction procedure. By ensuring effective on-site drainage and temporarily grading the soil, the chance of water lying behind the retaining wall accumulating early is reduced.

How to check for drainage

Check if there is water flowing from weep holes after rain to verify if your retaining wall is draining water properly. If the retaining wall is straining, irregular, or crumbling, water is most likely not draining properly. Because mortar, bugs, and other debris can impede the weep holes, it’s necessary to examine and clean them as frequently as possible.

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What happens if there is no retaining wall drainage?

Water will jeopardize the safety and stability of your retaining wall if there is no drainage. If drainage measures were not taken, it is critical that the wall be fixed or rebuilt. This can result in significant property damage, as well as the cost of repairs and the installation of a new wall. Early warning indications of retaining wall failure are easy to identify, yet poor water drainage isn’t always the culprit.

How does drainage affect the life of a retaining wall? 

Your retaining wall’s life will be cut short due to poor drainage. When water cannot flow away from the back of the wall, pressure builds, causing the footing (and occasionally the wall) to fail.

Drainage is also crucial since it determines how frequently the wall will need to be repaired. It’s much less probable that you’ll need to drill through the wall to address a crack or other issue if you have a well-placed drainage system.

Concluding Tips

  • Backfill, or the 12 inches of area at the back of a retaining wall, should be included. Shredded gravel or rock should be used to fill it.
  • Even if a draining pipe is not needed, drainage stone should be necessary to be included in all retaining walls.
  • Place the filter fabric below the dirt and above the drainage stone. Fine particles and organic waste are prevented from getting clogged in the drainage stone in this manner.
  • Your drainage pipe has several output possibilities. Regardless of which option you choose, make sure there are outlets every 30 or 50 feet across the wall.
  •  If you require a drainage pipe for your retaining wall, make sure it has openings on all of the sides rather than one. A drainage pipe would be necessary to acquire if:
  • If the retaining wall is 4 feet tall or high at most.
  • If there are poor draining soils used at the back of the wall like clay.
  • If within 50 feet of the area of the retaining wall, there are sources of water that are buried.

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