Geotechnical Engineering

DHARM

608 GEOTECHNICAL ENGINEERING

D (depth)f

b

(width)

D b Shallow foundation

D > b Deep foundation

f

f

£

Fig. 15.1 Foundation-shallow or deep (Terzaghi)

Further classification of shallow foundations and deep foundations is as follows:

Shallow Foundations

Footings Rafts (Mats)

Spread

footing

Strap

(Cantilever)

footings

Combined

footings

Continuous

(strip or wall)

footings

Isolated

(individual)

footings

Rectangular Trapezoidal

Square Circular Rectangular

Deep Foundations

Deep footings

(continuous or isolated)

Piles Piers Caissons
(Wells)
The ‘floating foundation’, a special category, is not actually a different type, but it repre-
sents a special application of a soil mechanics principle to a combination of raft-caisson foun-
dation, explained later.

A short description of these with pictorial representation will now be given.

Spread footings

Spread footing foundation is basically a pad used to ‘‘spread out’’ loads from walls or columns
over a sufficiently large area of foundation soil. These are constructed as close to the ground
surface as possible consistent with the design requirements, and with factors such as frost
penetration depth and possibility of soil erosion. Footings for permanent structures are rarely
located directly on the ground surface. A spread footing need not necessarily be at small depths;
it may be located deep in the ground if the soil conditions or design criteria require.

Spread footing required to support a wall is known as a continuous, wall, or strip foot-
ing, while that required to support a column is known as an individual or an isolated footing.