Retaining Wall Drainage And Waterproofing Systems

Retaining walls are rigid structures designed to support soil laterally so that it can be held at various heights on the two sides. The purpose of retaining walls is to hold soil to a slope that it would not naturally slide (typically a steep, near-vertical, or vertical slope). They are frequently utilized in terrain with unfavorable slopes or in regions where the environment needs to be drastically changed and constructed for more specialized purposes, including hillside farming or traffic overpasses. A seawall or bulkhead is a retaining wall that retains soil on the backside and water on the front.

It is crucial that every retaining wall has appropriate drainage. Retaining walls hold back large, erratic loads and must be constructed to support those dynamic or shifting loads. The dynamic load of water entering the system and applying pressure to the wall could cause the retaining wall to collapse if improperly managed during the construction of the wall. Therefore while constructing retaining walls, drainage needs to be considered.

Retaining Walls Drainage Systems

Building a quality retaining wall requires drainage for the wall. A drainage system is included in the wall’s construction to remove water that has been absorbed by the soil behind it. The retaining wall must be able to withstand the acting force of the ground, water pressure, and additional pressure that could cause shifting, bulging, or complete collapse. This makes it essential for there to be a drainage pathway and that the wall’s construction can securely support the anticipated load.

Materials And Drainage Systems

There are numerous ways to stop retaining walls from failing because of insufficient water drainage. While the advantages of each type of wall material, such as stone or block, are distinct, all retaining walls need some sort of drainage to maintain their structural integrity. Some of the drainage systems used during the construction of retaining walls include;

Geofabric Layer

Geofabric, a synthetic textile made of polyester fibers, is used in civil engineering for filtration and drainage. In this case, it is utilized to prevent soil and silt from getting into the backfill, which would prevent water from flowing freely through it. In order to avoid debris blocking holes in the drainage pipe and reducing its effectiveness for retaining wall drainage, a geotextile fabric is utilized.

Backfill Aggregate

A drainage pipe and a suitable backfill are both necessary for drainage behind a retaining wall. Backfill is composed of ¾′′ angular crushed clear stone that extends vertically up the wall and at least 12′′ behind the wall. It is a clear stone, which means that there are no fines in the washed aggregate. As a result, water entering the system can seep through the backfill and all the way to the retaining wall’s base.

The water must be collected and expelled from the system once it reaches the retaining wall’s base. Although some of the water may seep through the subsoil, thicker clay in your area may cause water to accumulate.

Drainage Pipe

To collect the water that accumulates at the base of retaining walls, pipe must be put behind them. This drainage pipe needs to be perforated so that water can enter and exit it as it leaves the system. The pipe should slope at least 1/8 inch per foot in the direction of the lowest point or the location where water will depart the system. Furthermore, an exit point through the wall’s face should be present every 50 feet of retaining walls.

This is achieved by forming a “T” in the drainage pipe and attaching a pipe or other object so that it extends past the face of the wall and allows water to drain away from it. To prevent water from flowing back towards the retaining wall and generating extra problems, the pavement or ground at the face of the wall also needs to slope away from the wall.

Flexible corrugated and perforated pipes would be the ideal drainage pipes for retaining walls. Due to its flexibility, the pipe can maneuver around retaining wall bends and withstand freeze-thaw cycles. These freeze-thaw cycles cause the water in the pipe to expand. Since the pipe is flexible, the water can expand along with the pipe. Conversely, a solid PVC pipe with a high crush grade is inflexible, and the expansion of the water will result in cracks appearing and eventually the pipe failing. The high crush rating of a PVC Schedule 40 pipe may be useful in places where there aren’t freeze-thaw cycles that cause water to expand and contract. The pipe ultimately needs to be perforated to enable the collection of water that enters the system through the backfill and travels all the way to the base of the retaining wall.

Types of Drainage Pipe Outlet

There are three types of drainage pipe outlets in use. They are;

Pipe Outlet Through The Face Of The Wall

This works best when the wall’s front ground level is flat.

Pipe Outlet Underneath The Wall

This method is employed when there is a toe slope in front of the wall. As a result, the pipe can be installed below the wall without having to cut the blocks.

Universal Wall Drain

This product is unique and not as well recognized as others. It attaches directly to the drain pipe’s perforated tee connector. With the universal wall drain, you can avoid the unsightly cut marks that are typical of pipe outlets. A built-in grate helps prevent rodents from entering your sewer and constructing a nest there. The labor required and the amount of materials required are both decreased by this outlet option.

When To Use a Drainage Pipe

Although it is a good idea to install drainage pipes on all walls, there are some instances where a perforated drain pipe is absolutely necessary. They include;

• Cinder Block or Cast Concrete Retaining Walls

Unlike segmental blocks and timber walls, these walls do not have natural joints for water to drain through. Regardless of wall height, these walls require a drainage system.

• Presence of Ground Water

  This may be a little more challenging to spot. Groundwater is likely present if the area is moist when you excavate for your wall or if you see water accumulating nearby even when it’s dry.

• The wall system must include drainage if there are poorly draining soils, such as clay, behind the wall.

• A drainage system is necessary for walls that contain subterranean water sources, such as irrigation pipes, water mains, or hose lines, within 50 feet of the wall’s location.

Retaining Walls Waterproofing Systems

Waterproofing is the process of making a building or an object watertight or water resistant. By using this technique, water cannot penetrate an insulated surface or structure. In order to prevent ground moisture from damaging retaining walls and to lower hydrostatic pressure buildup, waterproofing treatments are also necessary for retaining walls. A number of issues, such as steel support rods corroding and expanding and cracking the concrete, can be caused by water in the wall. Waterproofing also guards against water seeping into the wall from the drainage system.

Qualities of a Good Waterproofing Material

The material should possess the following qualities for effective waterproofing:

• The waterproofing material should be mineral based and should be able to meld with the supporting structure.

• A little substrate penetration is ideal for the waterproofing material. This prevents water pressure from pushing it off.

• To allow water vapor to penetrate the hardened coating, the material must be open to vapor diffusion.

• To protect the steel reinforcement, the material must be free of chlorides.

• The material should be resistant to high water pressure.

• The waterproofing material should be easy to install.

Some good waterproofing materials include;

• Cement Based Waterproofing Materials

• Liquid Waterproofing Membrane Materials

• Liquid Bituminous Membrane Waterproofing Materials

• Membrane Waterproofing Materials

• Polyurethane Liquid Membrane Waterproofing Materials

Types of Waterproofing Methods

Waterproofing of retaining walls is crucial because it creates an impenetrable barrier over foundations and wall surfaces, to protect them from water. The methods used most frequently for waterproofing retaining walls are listed below.

• Cementitious Waterproofing

Cementitious waterproofing is the easiest method of waterproofing in construction. The materials for cementitious waterproofing are readily available from suppliers of masonry products. And they are easy to mix and apply. They are applied on the wall surfaces of retaining walls to prevent the ingress of water into the structure.

• Liquid Membrane Waterproofing

Two topcoats and a primer coat make up the liquid membrane. The coatings can be applied with a sprayer, roller, or trowel. Compared to cementitious waterproofing, the liquid layer is thin and provides more flexibility. On the wall, the liquid hardens into a rubbery layer. The coat’s elongation abilities can increase by up to 280%. Depending on the type of polymer the manufacturer employed to create the liquid waterproofing, the waterproofing coating’s durability varies.

A liquid asphalt layer made of polymer-modified polymers can also be used as a liquid waterproofing membrane. Several manufacturers also offer polyurethane liquid membranes in distinct grades for trowel, roller, or spray applications.

• Bituminous Coating Waterproofing

Asphalt coating is formed of bitumen-based compounds, often known as bituminous coating. On the basis of its formulation and polymerization grade, it is a flexible protective coat. The grade of the polymer and the fiber reinforcement can have an impact on the flexibility and water resistance.

Areas below wet screed are where bituminous coatings are most frequently applied. It works wonders as a waterproofing and protective coating, especially on surfaces like concrete foundations.

Unless it is treated with a more flexible substance like polyurethane or acrylic-based polymers, it is not suited for exposure to sunlight.

• Bituminous Membrane Waterproofing

Due to their dependable performance, bituminous membrane waterproofing is a common technique for exposed surfaces of the retaining wall. The bituminous waterproofing membrane has a self-adhesive membrane and a torch on the layer.

Asphalt, polymers, and filler are the main ingredients in self-adhesive compounds. Some resins and oils can also be used to enhance adhesion properties. The self-adhesive variety has a short shelf life since the membrane’s bonding abilities weaken over time.

There are exposed and covered varieties of torch on membrane. To withstand weathering, the exposed layer frequently contains granular mineral aggregate. To stop the membrane from being punctured, the contractor must apply one protective screed to the other type of membrane.

• Polyurethane Liquid Waterproofing

This method of waterproofing is the most expensive and is often used for retaining walls that are constructed in areas of harsh weather conditions. This method requires the great care during installation and is offers high flexibility and durability.

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