The lowest part of a structure is generally referred to as foundation.
To transfer load of the superstructure to the soil on which it is
A properly designed foundation is one that transfers the structural load
throughout the soil without overstressing of soil which can result in
either excessive settlement or shear failure,
both of which can damage the structure.
A shallow foundation is a type of foundation which transfers building
loads to the earth very near the surface, rather than to a subsurface
layer or a range of depths as does a deep foundation.
Shallow foundations include
• spread footing foundations,
• mat-slab foundations,
• slab-on-grade foundations,
• pad foundations,
• rubble trench foundations,
• earth bag foundations.
– Suitable soil bearing capacity
– Undisturbed soil or engineered fill
Basic types or configurations
– Column footings
– Wall or strip footings
Combined Rectangular Footing
Combined Trapezoidal Footing
Spread footing foundations, or simply footings, consists of strips or
pads of concrete (or other materials) which transfer the loads from
walls and columns to the soil or bedrock.
Embedment of spread footings is controlled by several factors,
including development of lateral capacity, penetration of soft nearsurface layers, and penetration through near-surface layers likely to
change volume due to frost heave or shrink-swell
These foundations are common in residential construction that includes
a basement, and in many commercial structures. But for high rise
building it is not sufficient.
Mat-slab foundations are used to distribute heavy column and wall
loads across the entire building area, to lower the contact pressure
compared to conventional spread footings.
Mat-slab foundations can be constructed near the ground surface,
or at the bottom of basements. In high-rise buildings, mat-slab
foundations can be several meters thick, with extensive
reinforcing to ensure relatively uniform load transfer.
• Slab-on-grade foundations are
commonly used in areas with
expansive clay soil, particularly in
California and Texas
• While elevated structural slabs
actually perform better on expansive
clays, it is generally accepted by the
engineering community that slab-ongrade foundations offer the greatest
cost-to-performance ratio for tract
• Elevated structural slabs are generally
only found on custom homes or homes
Rubble Trench foundation
• The rubble trench foundation, a
construction approach popularized by
architect Frank Lloyd Wright, is a type of
foundation that uses loose stone or rubble
to minimize the use of concrete and
• It is considered more environmentally
friendly than other types of foundation
because cement manufacturing requires
the use of enormous amounts of energy.
• However, some soil environments (such as
particularly expansive or poor load-bearing
(< 1 ton/so) soils) are not suitable for this
kind of foundation.
Earth bag foundation
• The basic construction method begins by digging a trench down to
undisturbed mineral subsoil.
• Rows of woven bags (or tubes) are filled with available material,
placed into this trench, compacted with a pounder to around 1/3
thickness of pre-pounded thickness, and form a foundation.
• Each successive layer will have one or more strands of barbed wire
placed on top.
• This digs into the bag's weave and prevents slippage of subsequent
layers, and also resists any tendency for the outward expansion of
• The next row of bags is offset by half a bag's width to form a
• These are either pre-filled with material and delivered, or filled in
place (often the case with Super adobe).
• The weight of this earth-filled bag pushes down on the barbed wire
strands, locking the bag in place on the row below.