Retaining Wall
There are different kinds
of retaining walls, follow me to see each type as well as design concept.
A retaining wall is a
structure that resists the lateral thrust of water or earth pressure which
could otherwise cause soil to move laterally or downward.
Retaining walls are a
crucial way to accommodate differences in ground level, including where sites
slope steeply; around gardens, buildings, parking areas or entrances leading
floors apart from each other because of elevation changes sited between them;
for maintaining soil stability because slopes tend toward erosion.
A retaining wall holds back
the earth, allowing for level places to be created on the mountainous terrain
even as it stops soil from eroding off and causing landslides.
In landscaping and civil
works, retaining walls are widely used, adding practicalities and beautify to
otherwise harsh terrain.
With proper design and construction,
they can prevent erosion and establish terraced landscapes while adding charm
to homeowners' property.
Kinds Of Retaining Walls
In all the following
examples we will deal with one and only type of retaining wall: 2 in x 8 in
pressure treated lumber (Which is the size most often used).
1. Gravity
Retaining Walls
They establish their own
stability by their weight; in effect each wall becomes both a dam for the soil
behind it and a dam across riverbeds or streams. Made out of solid concrete,
bricks or stones (wet-laid aggregate), these normally are not prone to sliding
except under unusual conditions such as hurry spent snapping or heaving because
soft ground has eroded away from beneath them.
Characteristics:
·
Simple to build
·
Useful for low retaining walls (typically stacked to 3-4 meters) which
require a large stable weight inside them in order to prevent slippage
·
May shift over time if not properly designed
2. Cantilever
Retaining Walls
Cantilever walls usually
have a stem and base slab. They turn the soil's pressure on them into an
opposing force which keeps them from overturning.
Characteristics:
·
More efficient than gravity walls
·
Suitable for taller walls (e.g. 4-7 m).
·
Require less material than gravity walls.
·
Counterfort Retaining Walls
3. Counterfort
walls
it comprise cantilever
walls with vertical reinforcements. At equal intervals on the rear side of the
wall there are column of reinforcements, counterforts as they are known. These
counterforts penetrate the ground to resist the pressure and stabilize the
wall.
Key Features:
·
Ideal for even taller walls (greater than 7 meters).
·
Provides extra strength without the need for a large amount of material.
·
In cases where gravity walls would be too heavy.
4. Sheet
Pile Retaining Walls
Sheet pile walls are
usually made of steel, vinyl, or wood and are driven into the ground to resist soil-side
forces. They are often used in waterfront applications where the worry is soil
erosion or water levels.
Key Features:
·
Suitable for use in narrow and waterfront locations.
·
Steel, wood and vinyl.
·
In applications where a tall wall is required but the required weight is
not so large.
5. Anchored
Retaining Walls
Anchored retaining walls
use tensioned anchors to secure the wall in place and give it added stability.
The anchors may be steel cables or rods, driven into the soil that is at the
back of a wall. This is particularly true for very tall structures or where the
available space is limited
Key Features:
·
Designed for use with higher walls, particularly in confined spaces.
·
Anchors give extra strength and reduce the need for large base
structures.
·
Used for projects with little or unusual soil conditions.
6. Segmental
Retaining Walls (SRWs)
Segmental retaining walls
(SRWs) are made up of pre-cast concrete blocks which are stacked to form the
structure. These blocks link together by means of an interlocking mechanism so
that they are easily assembled. Highly durable, they are widely used in landscaping
and garden features.
Characteristic:
·
Add up and fast installation is available in pieces.
·
Useful for residential landscaping as well as those smaller projects
that need an ad hoc touch.
·
Available in a variety of styles and finishes.
Design Example: Retaining Wall Design
When designing
a retaining wall, you need to consider factors like the wall's height, the type
of soil, and the loads acting on the wall (such as water or additional soil).
Here’s a simplified design example for a gravity retaining wall with a height
of 3 meters.
Assumptions:
- Soil behind the wall has a density of 18
kN/m³.
- The wall material has a density of 24 kN/m³.
- The wall is 3 meters high and 2 meters long.
- The angle of repose for the soil is 30°.
- The safety factor is 1.5.
Step 1:
Calculate the Lateral Pressure
The lateral
pressure from the soil can be calculated using the following formula:
Lateral
Pressure (P) = K × γ × h
Where:
- P = Lateral pressure (in kN/m²)
- K = Coefficient of lateral earth pressure
(assumed to be 0.33 for cohesionless soils)
- γ = Unit weight of the soil (in kN/m³)
- h = Height of the wall (in meters)
Using the
values: P = 0.33 × 18 × 3 = 17.8 kN/m²
Step 2:
Calculate the Base Width
The base width
of the wall should be wide enough to prevent it from overturning. Typically,
this is calculated using the formula:
Base Width (B)
= Height of the wall (H)/2
Where:
- B = Base width (in meters)
- H = Height of the wall (in meters)
Using the
values: B = 3/2 = 1.5 meters
Step 3:
Stability Check
·
The stability of the wall must be checked to ensure
it doesn’t overturn or slide.
·
This involves calculating the forces acting on the
wall, including the weight of the wall and the soil pressure.
·
To make sure the wall is stable, the resisting
forces should be greater than the driving forces, taking into account the
safety factor (1.5 in this case).
· the base width of the wall, and ensuring the wall’s stability under different forces.
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