TYPES OF Foundations ( Shallow Foundation)

1. TYPES OF
Foundations
Shallow Foundation

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What Is Foundation?
The foundation is the lowest portion of
a structure which transfers the load into
the supporting soil. The main purpose of
the foundation is to distribute the total
weight of the superstructure over a large
area of soil. Various types of foundations
are described below which are used in
construction.
Purpose Of Foundation
Foundations are mainly provided for the following purposes:
• To distribute the load of the structure on a bigger area
so that the intensity of the load does not exceed the
safe bearing capacity of the underneath soil.
• To distribute the load underneath soil uniformly and
thus prevent unequal settlement of the foundation.
• To provide a leveled and hard surface for the super-
structure to be built over it.
• To increase the stability of the structure against sliding,
overturning, or any other forces like wind, rain, etc.
• To prevent lateral movement of the supporting material
to ensure the safety of the structure is not at risk.

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Foundations can be classified into two general categories:
Types Of Foundation
Shallow Foundation Deep Foundation
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Wall or column
level
More
than 3m
Deep foundation
Shallow foundation
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Shallow Foundation
When the depth of the foundation is
equal to or less than its width, it is
called a shallow foundation. In this type
of foundation, the foundation part is
situated instantly below the lowest part
of a structure.
The total load of the structure is
distributed over a horizontal area at a
shallow depth below the ground level. In
simple words, if a foundation is constructed
at a reasonable depth then it is a shallow
foundation.
There are about five types of
shallow foundations.
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Classification Of
Shallow Foundation
• Mat (Raft) Foundation
• Spread Footing
• Basement Foundation
• Crawl Space Foundation
• Concrete Slab Foundation
Mat (Raft) Foundation Spread Footing
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Crawl Space Foundation
Basement Foundation
Concrete Slab Foundation
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Mat (Raft) Foundation
Consisting of a single large continuous
rectangular or circular slab under a
building, the mat (or raft) foundation
carries and distributes an entire load of a
structure. Raft foundations can support a
number of columns and walls at once and
spread the load out under the entire
footprint of the building.
When the soil layer beneath a building
has low stability or bearing capacity,
mat foundations can reduce differential
settlement. Mat foundations are
common in commercial building projects
and in areas where basements are
popular.
• What it looks like: Large continuous rectangular or
circular concrete slab
• Often used for: Basements or commercial buildings
column
Foundation
soil
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Spread Footing
Footings are the bottom part
of a foundation that actually
touches the ground. They help
transfer the weight of the
building directly to the soil,
as well as prevent moisture
from seeping into the
structure, which can cause
mold and mildew problems.
Different types of foundations
use different types of
footings: concrete footings are
common, but stone, brick,
and wood footings also exist.
1
A type of shallow foundation known as spread footing (or pad footing)
has a wider base than the top. This design helps spread the weight of
the structure to a larger area, creating greater stability. Spread footing
comes in various sizes and shapes, including square, round, and
rectangular.
2
Common uses of spread footings in
construction include supporting
individual columns of a building or
piers of a bridge. Residential home
foundations also frequently employ
spread footings as a cost-effective
way to increase stability.
3
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Depending on the type of construction
project at hand, you may see the following
types of spread footing:
Isolated footings: With an isolated foundation (or
“isolated column footing”), each column has a
separate foundation in order to distribute its load
uniformly over the soil.
Combined footings: In this type of
footing, a single base supports two or
more columns together.
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Continuous footings: With this
type of footing, more than two
columns in a row share a base.
You may use continuous footing
when you have soil with low load-
bearing capacity and/or columns
spaced too close together for
individual footings.
column
Iron plate
Steel beams
Concrete
Grillage footing: Grillage
foundations provide stability
when excessive column weight—
such as in high-rise buildings—
and weak soil prevent the
construction of a deep
foundation.
Grillage footing
Continuous footings
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Raft footing: Raft footing provides
common footing to multiple columns,
ensuring uniform weight distribution
when the column load is excessive or the
load-bearing capacity of the soil is low.
Strip footing: Strip footing runs
beneath load-bearing walls to help
maintain the stability of a structure.
Raft footing
Strip footing
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Basement Foundation
Basement foundations serve the same purpose
as regular foundations: to distribute a building’s
weight evenly and protect it from moisture and
water. Unlike typical foundations, however,
basement foundation walls are fully submerged
in the soil to create working or storage space
below the ground level.
Because basements are typically completely
below ground level, they can take longer to
build than standard foundations. They often
require heavy-duty equipment like excavators,
cranes, and graders to dig and move soil.
Despite the difference in depth, basement
foundations are constructed in the same way
as regular foundations, using poured concrete,
concrete blocks, or precast concrete slabs.
• What it looks like Concrete walls consisting of
footings
• Often used for Residential buildings
Basement Foundation
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Crawl Space Foundation
Typically elevated a few feet off the ground, crawl
space foundations are deeper than standard
foundations but more shallow than basement
foundations. These foundations leave a small
protected space of about three to four feet high
under the house, providing access to drainage pipes,
plumbing, and other elements running beneath the
house, but not enough room for most people to
stand.
In addition to making it easier to reach plumbing and
piping, crawl spaces keep houses cooler in warmer
climates by allowing air to move freely underneath
the structure. Although crawl space foundations tend
to cost less to build than other basement
foundations, you will also need to consider insulation
and moisture control. Moisture control may mean
installing a vapor barrier, a sump pump, or both.
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Concrete Slab Foundation
The most common type of foundation, slab
foundations consist of a 6- to 8-inch concrete pad
underneath a structure. The load your foundation
needs to bear determines the thickness of the slab.
Although less suited to extremely cold climates that
get a lot of freezing temperatures and snow and
earthquake-prone areas, slab foundations tend to be
relatively cheap, easy to build, low maintenance, and
energy efficient.
Constructing a simple slab foundation
involves pouring concrete directly onto
soil prepared with sand or gravel to
assist with drainage. Other slab
foundations have additional components
like supporting concrete feet or
insulating foam.
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