Retaining Wall 101

Aaron Fisher | February 15, 2022

If you see a hill and think would be good to turn that into some level ground, a retaining wall may be in your future. There are many different types of retaining wall systems, and here we venture to educate you on the different options you have for retaining walls. This list is meant to be a quick primer, and not exhaustive. Want to learn more? Take a course.

Type	Use	Cost	Pros	Cons
Segmented Retaining Walls	T C R	$	Aesthetics/design flexibility; Durability; Ease of installation; Availability	Labor intensive
Natural Stone	R	$	Aesthetics	Labor intensive. Small walls only
Timber Walls	R	$	Economical	Quickly deteriorates; leaches chemicals
Gabion Walls	T C	$/SS	Limited excavation	Corrosion. Aesthetics. Small rocks may wash out
Precast Modular Blocks	T C	$$	May not require reinforcement, if <13 feet	Limited design flexibility; Site access limits use; Global stability is a concern
T-Walls	T	$$$	Limited excavation and backfill requirements	Not that popular anymore
Panel Walls	T	$$$	Wall can be used right after construction	Requires high quality backfill; Customized finishes add expenses
Cast in Place	T	$$$$	Well-established technology	Requires skilled labor; Concrete must be set before loading; Unseen differential settling can damage

Uses: T- Transportation, C- Commercial, R- Residential

Two quick things to keep in mind when designing your retaining wall:

Drainage. Water needs to be drained away from the wall to maintain the structural integrity of the wall
Terracing. When terracing walls, if the upper wall is not set far enough back (roughly twice the height), it should be treated as one large wall from a design perspective.

Segmented Retaining Walls (SRW)

Repeating dry cast unit
Variety of color and styles available
Have been in use for about 30 years and are widely available
Taller walls require geogrid reinforcement,
Reinforced backfill can be a wide variety of soil types
Durable
Easy-to-install

Natural Stone Walls

Uses natural stone
All rocks have to be installed to complement each other (or cut to fit)
Mostly landscaping walls

Timber Walls

Pressured treated wood is used
On a leveling gravel pad with a drainage pipe
For stability, deadmen (timbers perpendicular to the face) are added
Backfill and complete
Leach chemicals (preservatives used in lumber)
Wood deteriorates

(Source: Meyer Landscapes)

Gabion Walls

Gabions are gravity structures (weight).
Baskets are made of galvanized steel wire mesh.
Filled with rocks
Can be reinforced for taller walls
They have problems when small rocks are washed away.
Used in commercial and transportation projects

Precast Modular Blocks (PMB or Big Blocks)

They are precast concrete blocks
All finishes are available
Units are machine placed
Some units allow for walls up to 13 ft without reinforcement
Used in commercial and transportation projects

(Source: Plaisted Companies)

T-Walls

T-walls are prefabricated concrete units with reinforcement
Installed over a concrete leveling pad
Backfilled with gravel
Used to be popular in transportation projects

(Source: RECo)

Panel Mechanically Stabilized Earth Walls

Predominant for transportation
This system consists of
- Granular backfill (layers) – High quality gravel
- Steel reinforcement – bars or mats w/connectors
- A precast concrete panel – 4000 psi concrete (min.)
- Bearing pads and geotextiles for the joint
Installation method:
- Concrete leveling pad/Base panels
- Bearing pads/next courses/reinforcement
- Alternating with backfill

Mechanically Stabilized Earth (MSE) Retaining Walls

(Source: RECo)

Reinforced Concrete Walls (CIP)

This type of wall requires: ready-mix concrete, removable forms, steel reinforcement
Casting concrete in place involves a few distinct steps:
- Placing formwork
- Placing reinforcement (rebars)
- Pouring concrete
After the concrete is ready :
- Forms are removed
- Backfill is placed