Types of Retaining Walls – All You Need to Know
- May 20, 2020
Retaining walls often around us, but we fail to notice its importance in our life. When we are going to do landscaping or outdoor construction, we need to know all about retaining walls. World of Stones USA is going to furnish required knowledge about retaining wall and design ideas you need for inspiration.
What Is a Retaining Wall?
A retaining wall, according to Wikipedia, designs to restrain soil (Also water) to a slope that it would not naturally keep to. A retaining wall binds soils between two different elevations, often in a landscape that needs to be shaped for specific purposes.
However, different types of retaining walls are serving different purposes. Before knowing the goals of retaining walls, let’s understand the fundamentals of retaining walls and its different models from the perspective of a landscape designer, and often a civil engineer/architect.
Basics of Retaining Walls:
Let’s learn common terminology and key structural elements of retaining walls.
The Base of Retaining Wall:
- The retaining wall must have a suitable base prepared from appropriate base materials. The compact soil, sand, & gravels/stone aggregates are standard components of any structure in the construction industry.
- The depth of the base of the retaining wall depends on the height, weight, and the live/dead load it is bearing temporarily or permanently.
- The base must prepare according to types of ground soil. Sandy soil is stable, while clay soil is tentative. Most contractors and landscape designers know the local soil type and have solutions accordingly.
The Face of Retaining Wall:
Most retaining walls have two different soil elevations. Lower elevation exposes the face or front part of the retaining wall, which is visually visible.
Backfill or Earth Fill of Retaining Wall:
- The higher elevation part of soil usually hides the rear portion of the retaining wall.
- The attached soil part of the retaining wall needs to fill up with soil carefully to ensure proper rainwater or groundwater drainage.
- Twelve inches or one-foot granular materials like gravel or stone aggregates must install directly behind the wall. It assures proper drains of water.
- The next vertical column of the backfill must have compacted soil to provide stability.
- The top layer should have native soil to encourage the growth of vegetation.
Vertical Stem of Retaining Wall:
Retaining walls with some heights always have a thicker base, which is called the stem of the retaining wall. Stem resists horizontal pressure from the backfill of the retaining wall, and simultaneously pass the vertical load of the retaining wall to the footing/base/ground.
Toe & Heel of Retaining Wall:
In concrete retaining walls, mostly gravity type or cantilever type walls, the footing slab is extending horizontally at the front as well as backsides. Just like the human leg, the frontal extension of the foundation/footing slab is referring as the toe slab of the retaining wall while the backward footing slab is called the heel slab of the retaining wall.
Drainage of Retaining Wall:
Be it is stones, bricks, or concrete materials used in the construction of retaining wall, waterlogging at the backfill side is harmful. The accumulation of rainwater or groundwater leads to the growth of molds. It also causes deposits of deteriorating chemicals within the mass of the wall as well as on the surfaces.
Thus, a proper drainage plan is essential. In due course, the adjoining vertical layer of backfill always remains porous to leech water below. Near the footing area, a porous drainage pipe fitted in a pit-like structure made of big-size gravels, which has proper water outlets at the ends.
The Footing of Retaining Wall:
Footing or foundation is a supportive and essential structure in any retaining wall, be it made of RCC or natural stones. The footing is running perpendicular to the vertical stem of the retaining wall.
Weep Hole of Retaining Wall:
Weep holes usually found above the footing/foundation areas in the retaining wall to allow excessive drainage of water at the backfill side. It cut the burden of water drainage during heavy rains or groundwater seepage.
Drainage Stones or Compacted Backfill of Retaining Wall:
Drainage stones also refer to compacted backfill. It usually is made of gravels, pebbles, or stone aggregates to allow water drainage.
Filter Fabric of Retaining Wall:
A layer of filtering material made of synthetic or natural material covers the drainage stones next to a vertical retaining wall structure. It allows the seepage of water but prohibits soil particles from checking the drainage system made of drainage stones.
A Batter of Retaining Wall:
In the layout design of retaining walls, the face is remaining sloppy while back straight to create gradual slenderness in height from wider/extended bottom to narrow top. Batter offers the horizontal load-bearing capacity to the vertical wall emerging from the backfill side. A one-inch regression at every one-foot height is a norm in vertical wall construction, be it dry-stoning or mortar filled.
Shear Key of Retaining Wall:
To provide stability against various failure modes, including load bearing failure, sliding, and overturning, the structure of retaining walls often gets additional strength from the shear key. The shear key (additional reinforcement) takes place either on the top or bottom of the foundation/footing slab. So, it is absent in walls made of stones or other non-RCC materials.
Cap of Retaining Wall:
It gives the top of the retaining wall a finished look. It also facilitates the installation of additional safety structure or decorative structure.
Retaining Wall Materials
The following construction material commonly found in the contemporary retaining wall designs:
- Cement-concrete blocks
- Poured concrete with reinforced structural-materials like steel bars
- Natural stones
- Clay bricks
- Steel/metal sheets
Gravity Wall Brick
Gravity Wall Natural Stones
Gravity Wall Concrete
Today, RCC structure is universal and affordable, while natural stones are a pricy yet highly advantageous option for the construction of retaining walls. So, our prime focus would be on the natural stone retaining walls. Of course, a natural stone veneer offers a great combination of RCC & stones.
Basic Types of Retaining Walls:
We learned the fundamental terminology used in the designing of different retaining walls. Let’s explore the different types of retaining walls with basic knowledge.
|However, according to Wikipedia, four common types of retaining wall concept are prevailing in the construction industry.
||I have chosen dimensions of retaining wall components, i.e., heights of a wall as a parameter to categorize retaining walls.
In my opinion, the dimension-based classification almost covers all types of retaining walls. Let’s elaborate on it.
Curb/Kerb Retaining Walls
By definition, the curb is an edge structure to define space. It delineated the edge of payment in your landscape design. The typical height of the curb is 4 to 6 inches.
So, a single lined of crafted stones can define your walkways and driveways in almost non-intrusive ways. It could be a straight/leaning stone or an L-shaped stone.
Curb stones can serve multiple purposes. Here, it aids in the construction of a Gutter for drainage system besides defining an edge of a road and providing a separation line between two spaces in the landscape.
Short Retaining Walls
Up to 3m or 10 feet height of retaining walls, we can consider short retaining walls. The short retaining wall used to pass the vertical and lateral loads to the ground using gravity principles without additional structural support. All stone walls are of gravity types walls.
Reinforced concrete walls have sturdy footing with toes and heels like supports at the foundation level. Cantilevered retaining walls engineered with upper/lower shear keys to sustaining in various bending movement conditions.
Tall Retaining Walls
When the height of a retaining wall goes beyond 3m, we consider it as a tall retaining wall. In ancient eras, natural stones were the best material to create tall gravity types of retaining walls. With the pace of increased technical advancements, today, most of the tall retaining walls are made of reinforced concrete structures.
In the case of Buttressed retaining walls & Counterfort retaining walls, additional support structures are created either at the front face side or within the backfill side at regular intervals.
The Anchored retaining walls have extra support by steel/metal anchors with bulging structure at the backfill side.
The latest Sheet Piling technology allows the construction of a sturdy Piling retaining wall without consuming much space like in the above cases.
Mechanically Stabilized Earth (MSE) retaining walls are economical solutions in the construction of over bridges and dense vehicle passages. It contains a mix of panels, concrete blocks/slabs, and stones. Metallic or plastic meshes can hold together the compacted/granular soils.
Crib Retaining Wall contains boxes made of woods or metals, which are filled with crushed stones or stone gravels to make it a gravity type of retaining wall.
Gabion retaining wall is made of rectangular wire mesh boxes or steel bars and filled with stone pieces to give it desired stability.
What Are the Purposes of Retaining Wall?
Let’s see some primary purposes of retaining walls in our landscapes.
Creating & augmenting an aesthetic appeal in your landscape design.
Act as Delineator by marking boundaries around a property
Defines spaces internally.
Furnish usable land in your odd terrains.
Provides additional flat area.
Helps in designing decorative landscaping elements.
Offers extra utilities in your outdoor spaces.
Cuts soil erosion substantially.
Gain safety with Retaining Walls
What Is Retaining Wall Failure?
Your retaining walls may on risks due to failure. According to expert opinion, there are three most common signs indicating the retaining wall failure, and those are Leaning, Cracking, & Bulging.
Mechanism of Retaining Wall Failure:
There are three possible mechanisms for retaining wall failure.
|Sliding of retaining wall, which is a linear horizontal movement of the entire structure.|
|Overturning of retaining wall, which is a vertical movement due to excessive pressure on the top portion of the retaining wall.|
|Soil bearing failure of retaining wall, which is due to the inadequate load-bearing capacity of ground soil beneath the footing or foundation of the retaining wall.|
- Sliding of retaining wall, which a linear horizontal movement of the entire structure.
- Overturning of retaining wall, which is a vertical movement due to excessive pressure on the top portion of the retaining wall.
- Soil bearing failure of retaining wall, which is due to the inadequate load-bearing capacity of ground soil beneath the footing or foundation of the retaining wall.
Different Pressures behind Retaining Wall Failure:
Technically, three different types of pressures play vital roles in the mechanism of retaining wall failures.
We have seen the possible mechanism of retaining wall failure. So, three kinds of pressures, Bearing Pressure, Sliding Pressure, and Overturning Pressure, can cause retaining-wall failure.
Causes of Retaining Wall Failure
The leading cause of retaining wall failure are:
- Shallow footing or depth of foundation.
- Poor drainage to minimize hydrostatic pressure, particularly in the rainy season.
- Excessive (uncountable) load on the top backfill side of the retaining wall.
- Low-standard construction material or faulty construction.
- Slop failure due to changing dynamics of the slope the wall is holding back.
Most of civil engineers and architects know and desired expertise to design your retaining wall considering such causes of failures. They can help you in avert the possible retaining wall failures, as well as repair it once any occurs.
The Lifespan of Retaining Walls
The lifespan of a retaining wall mostly depends on the following factors:
- Use of wall material. Natural stone is an excellent choice when you think of durability, longevity, aesthetics, and property value. Natural stone retaining walls in your property can improve the overall curb appeal of your property besides adding natural beauty in it.
- Climatic conditions of the location of your property where you have constructed retaining walls. Various weathering factors cause fast wear & tears such as harsh Sunlight, adverse heat & cold seasons, excessive rains and snowfalls, as well as natural disasters like earthquakes and heavy wind storms.
- Technically correct building of retaining wall design can avert wall failure earlier than anticipations. Balanced live & dead loads can extend the lifespan of retaining walls.
It has seen that careful planning and design of a natural stone retaining wall can yield long-lasting structures. Half to full century is commonly found lifespan of natural stone retaining walls in the history.
DIY Retaining Walls
Do you think to go for DIY (Do It Yourself) way to build your stone retaining walls? World of Stones USA always encourages the enthusiastic and capable homeowners and landscaping champions by providing proper guidance and material for it. We have a range of natural stone products to offer you for the construction of natural stone retaining walls. Explore our online product catalog and find the best choice for you to make your next order.