Foundation and its types

FOUNDATION
S.MANIKANDAPRABHU @ SARAVANAN

DEFINITION
 Foundation is a structural part of a building
on which a building stands.
 The foundation of a building is that part of
walls, piers and columns in direct contact with
the ground and transmitting loads to the
ground.
 The lowest load-bearing part of a building,
typically below ground level.

FUNCTIONS
 Distribution of Load
 Reduction of Load Intensity
 Safety Against Undermining
 Lateral Stability
 Protection Against Soil Movements

FUNCTIONS
 Foundations distribute the non-uniform load of the
super structure evenly to the sub soil.
 Foundation distributes the loads of the super
structure, to a larger area so that the intensity of the
load at its base does not exceed the safe bearing
capacity of the soil.
 Foundation anchors the super structure to the ground,
thus imparting lateral stability to the super structure.

FUNCTIONS
 It provides the structural safety against undermining or
scouring due to burrowing animals and flood water.
 Special foundation measures, prevent or minimizes
the distress (or cracks) in the super structure, due to
expansion or contraction of the sub soil because of
moisture movement in some problematic soils.

CHARACTERISTIC
 The foundation, including the underlying soil and rock,
must be safe against a structural failure that could
result in Collapse
 During the life of the building, the foundation must not
settle in such way as to damage the structure or
impair its function
 The foundation must be feasible both technically and
economically and practical to build without adverse
effect to surrounding property

CHARACTERISTIC
 All foundations settle to some extent as the soil around and
beneath them adjusts itself to the loads of the building
 Foundations on bedrock settle a negligible amount
 Foundations on certain types of clay may settle to an
alarming degree, allowing buildings to subside by amounts
that are measured in feet or meters
 Foundation settlement in most buildings is measured in
millimeters or fractions of an inch
 Most foundation failures are attributable to excessive
differential settlement.

FACTORS AFFECTING DESIGN
 Soil types and ground water table conditions.
 Structural requirements and foundations.
 Construction requirements .
 Site condition and environmental factor.
 Economy etc.

TYPES OF FOUNDATION
 Shallow foundation
 Deep foundation

SHALLOW FOUNDATION
 The foundation provided immediately below the lowest
part of the structure near the ground level, transferring
load directly to the supporting soil, is known as
shallow foundation.
 Shallow foundation is provided when stable soil with
adequate bearing capacity occur near to the ground
level.
 Requirements:
 Suitable soil bearing capacity
 Undisturbed soil or engineered fill

SHALLOW FOUNDATION
 Strip footing/wall footing/continuous
footing.
 Spread or isolated footing.
 Combined footing
 Strap or cantilever footing.
 Mat or raft Foundation.
 Inverted arch footing

STRIP FOOTING
 This is also known as Wall Footing.
 This footing is provided throughout the length of
the wall and may be either stepped or single.
 These are used for light structures.
 E.g. Load bearing walls.

SPREAD OR ISOLATED FOOTING
 The spread / isolated / pad / column
footing is generally constructed to
support an individual column.
 The spread footing may be circular,
square or rectangular slab of
uniform thickness.
 Sometimes it may be designed as
stepped or launched to
spread/distribute the load over a
larger area.

COMBINED FOOTING
 The combined footing is designed to support two parallel
columns.
 It is principally used what the two columns are so close that
to one another that their individual footing would overlap.
 By combining it with that of an interior column, the load gets
evenly/uniformly distributed.

STRAP/CANTILEVER FOOTING
 A balanced footing which is also called as strap footings
consists of two separate footings connected by a strap beam.
 Balanced footing is required where the one of the footing has
limited space for bearing, or if there is any restriction over the
transfer of pressure from the footing to the ground.
 This case may arise where there is difference in soil bearing
capacity, or loose soil beneath one of the footing.
 The loads in a balanced footing is transferred from one footing
to the other by means of cantilever action.

MAT OR RAFT FOOTING
 A mat or raft foundation is a large slab supporting a number
of columns and walls under the entire structure or a large
part of the structure.
 A mat is required when the allowable soil pressure is low or
where the columns and walls are so close that individual
footings would overlap or nearly touch each other
 Mat foundations are useful in reducing the differential
settlements on non-homogeneous soils or where there is a
large variation in the loads on individual columns

INVERTED ARCH FOOTING
 It is constructed on soft soils.
 This type of foundation is suitable for bridges, reservoirs and
tanks.

GRILLAGE FOUNDATION
 A type of foundation often used at the base of a column. It consists of
one, two or more tiers of steel beams superimposed on a layer of
concrete, adjacent tiers being placed at right angles to each other, while
all tiers are encased in concrete.
 This is dependable foundation and is used in those place where the load
of the structure is pretty and bearing capacity of soil comparatively poor.
 The grillage foundation helps in distributing the load over a wider area of
subsoil.
 The grillage foundation helps in avoiding deep excavations as the

DEEP FOUNDATION
 A deep foundation is a type of foundation which transfers
building loads to the earth farther down from the surface than
a shallow foundation does, to a subsurface layer or a range
of depths.
 Deep foundations can be used to transfer the load to a
deeper strata at depth if unsuitable soils are present near the
surface.
 A pile is a vertical structural element of a deep foundation,
driven or drilled deep into the ground at the building site.

DEEP FOUNDATION
 Selection of pile foundation types and
length depends on following conditions:
 Soil conditions
 Loads from structures
 Nature of loads
 Number of piles to be used
 Cost of construction
 Installation Method

TYPES OF DEEP FOUNDATION
 Pile foundation
 Pier foundation
 Well foundation

PILE FOUNDATION
 Pile foundations are common type of deep foundation.
 These are relatively long, slender members that transmit
foundation loads through soil strata of low bearing capacity
to deeper soil or rock strata having a high bearing capacity.
 In addition to supporting structures, piles are also used to
anchor structures against uplift forces and to assist
structures in resisting lateral and overturning forces.

NEED FOR PILE FOUNDATION
 Top layers of soil are highly compressible
 Depth/Width >4
 Low Bearing Capacity of soil .
 Non availability of proper bearing stratum at shallow depths.
 Heavy loads from the super structure for which shallow
foundation may not be economical or feasible.
 Lateral forces are relatively prominent.
 In presence of expansive and collapsible soils at the site.
 Offshore structures
 Strong uplift forces on shallow foundations due to shallow
water table can be partly transmitted to Piles.

CLASSIFICATION OF PILE
FOUNDATION
 Based on material
 Concrete
 Steel
 Timber
 Based on Load transfer mechanism
 End bearing piles
 Friction/Floating piles
 Bearing cum Friction piles

CLASSIFICATION OF PILE
FOUNDATION
 Based on method of construction/installation.
 Driven /Displacement Pre cast Piles
 Driven/Displacement Cast in Situ Piles
 Bored/ Replacement Pre cast piles
 Bored/ Replacement Cast in situ piles.
 Based on inclination
 Vertical Piles
 Inclined/ raker Piles

TIMBER PILES
 Timber piles are mainly used to support light to
moderate loading structures.
 They are widely used for compaction of soils and
for the construction of temporary structures.
 They are also used in the protecting water- front
structure.
 The main advantages of timber piles are, they are
easy to handle, low initial cost, durable in non-
fluctuating weather conditions.

CONCRETE PILES
 Concrete piles are the widely used for heavily
loaded structures.
 Concrete piles can be pre-cast or cast in-situ piles.
 The precast piles may use ordinary reinforcing bars
or pre-stressed bars depending on the usage and
the loading conditions
 The main advantage is the higher loading capacity
and ease in construction.
 Disadvantages include high initial cost,
requirement of treatment when used in corrosive
areas, marine environment and splicing in case of

CONCRETE PILES
 Disadvantages include high initial cost, requirement
of treatment when used in corrosive areas, marine
environment and splicing in case of pre-stressed
piles.

STEEL PILES
 Steel piles of various cross sections such as Hollow
steel tubes, Box sections, H-sections, built -up
sections are available and have to be chosen carefully
according to the site conditions.
 Steel piles are easy to splice, handle and install where
deep penetrations are required.
 They can withstand high driving forces and any
damage to the pile head can be rectified by trimming
them and splicing with a newer section .
 Steel piles are best suited where ground heave and
lateral displacements are to be avoided.

PRE-CAST CONCRETE PILES
 These piles are manufactured in factory.
 The precast concrete piles are generally used for a
maximum design load of about 80 tons.
 They may be reinforced to withstand handling
stresses.
 It can be driven under water, if the subsoil water
contain sulphate the concrete for cast insitu piles
would not set.
 It is highly resistant to biological and chemical
reaction of subsoil.

BASED ON LOAD TRANSFER
MECHANISM
 End Bearing Pile
 If the pile transmits the load from the structure to a
considerable strong stratum mainly through the resistance
developed at the bottom or tip of the pile, then it is called
as end bearing pile.
 Friction Piles
 If the prominent load transfer is primarily by friction along
the surface of the piles, then they are termed as frictional
piles.
 Friction piles are generally used in low to medium dense
sand and where hard strata is not available at reasonable
depth.

BASED ON LOAD TRANSFER
MECHANISM

Based on Load transfer
mechanism
End bearing Friction Pile

BASED ON METHOD OF
CONSTRUCTION
 Driven pre-cast pile:
 The pile is casted in a yard brought to the site and driven
by some mechanism into the soil.
 Driven cast-in-situ pile:
 A casing plugged at bottom is driven into the ground and
then the pile is casted by removing or retaining the casing.
 Bored pre-cast pile:
 A bore is made and the soil inside is removed and then a
pile casted in some yard is put into the bore.
 Bored cast-in-situ pile:
 A bore is made the soil is removed and the pile is casted at
site in the bore.

BASED ON INSTALLATION TYPE -
REPLACEMENT PILES
 These piles are either bored and cast in-situ piles or drilled-
in tubular piles.
 In both the cases, the earth is removed where the pile has
to be installed and is then filled with reinforced concrete or
precast sections are erected.
 Steel liners, bentonite slurry may also be used according
the prevalent soil condition in the site.
 These replacement piles do not provide any additional
consolidation or displace the surrounding soil and hence
ground heaving is avoided.
 Due to no displacement during installation, there is no
heave in the ground.

 Cast in-situ piles may be cased or uncased (by
removing casing as concreting progresses).
 They may be provided with reinforcement if
economical with their reduced diameter.
 Enlarged bottom ends (three times pile diameter) may
be provided in cohesive soils leading to much larger
point bearing capacity.
 Example: Bored cast in situ or pre casts pile
REPLACEMENT PILES

BASED ON INSTALLATION TYPE
REPLACEMENT PILES

 Displacement piles are either solid sections or hollow sections
with a closed end driven into the soil, thus displacing the soil
around them.
 They are mainly used where there are no restrictions on ground
heaving and lateral displacement of soil.
 Displacement piles are mainly preferred in marine structures.
 Displacement piles are either solid sections or hollow sections
with a closed end driven into the soil, thus displacing the soil
around them.
 They are mainly used where there are no restrictions on ground
heaving and lateral displacement of soil.
DISPLACEMENT PILES

 In loose cohesionless soils
 Densifies the soil upto a distance of 3.5 times the pile
diameter (3.5D) which increases the soil’s resistance to
shearing
 The friction angle varies from the pile surface to the limit
of compacted soil
 In dense cohesionless soils
 The dilatancy effect decreases the friction angle within
the zone of influence of displacement pile (3.5D
approx.).
DISPLACEMENT PILES

 In cohesive soils
 Soil is remolded near the displacement piles (2.0 D
approx.) leading to a decreased value of shearing
resistance.
 Pore-pressure is generated during installation causing
lower effective stress and consequently lower shearing
resistance.
 Excess pore-pressure dissipates over the time and soil
regains its strength.
 Example: Driven concrete piles, Timber or Steel piles
DISPLACEMENT PILES

 Piles Larger than 600mm in diameter are called Large
Diameter Pile.
 Size 300 to 600mm are called normal or small
diameter pile.
 Pile 150 to 250mm are called mini piles.
 Pile less than 150 mm diameter are classified as micro
piles.
BASED ON SIZE

PIER FOUNDATION TYPE
 Pier foundations may be of the following types:
 Masonry or concrete pier
 Caissons.

PIER
 For homes and light
commercial building,
concrete piers or concrete
column that are formed by
pouring liquid concrete into
holes drilled into the ground.

TYPES OF CAISSON
 Box Caissons
 Excavated Caissons
 Floating Caissons
 Open Caissons
 Pneumatic Caissons
 Sheeted Caissons

BOX CAISSONS
 Box caissons are watertight boxes that are
constructed of heavy timbers and open at the top.
 They are generally floated to the appropriate location
and then sunk into place with a masonry pier within it.

EXCAVATED CAISSONS
 Excavated caissons are
just as the name suggests,
caissons that are placed
within an excavated site.
 These are usually
cylindrical in shape and
then back filled with
concrete.

FLOATING CAISSONS
 Floating caissons are also known as floating docks
and are prefabricated boxes that have cylindrical
cavities.

OPEN CAISSONS
 Open caissons are small cofferdams that are placed
and then pumped dry and filled with concrete.
 These are generally used in the formation of a pier.

PNEUMATIC CAISSONS
 Pneumatic caissons are large watertight boxes or
cylinders that are mainly used for under water
construction.

WELL FOUNDATION
 Well foundation is a type of deep foundation which is
generally provided below the water level for bridges
 They are quite appropriate for alluvial soil in rivers
and creeks where maximum depth of scour can be
quite large
 They are also known as caisson foundation or pier
foundation

WELL FOUNDATION
 Caisson is a cylinder or
hollow box that is sunk
into the ground to a
specified depth by
auguring a deep hole into
the strata.
 The cylinder or box is
then back filled with
concrete, thus creating

ADVANTAGES
 It is easily adaptable to varying site conditions. This means
that no matter where the structure is being constructed,
caissons can be easily put in place. The hardest part of
placing them is the drilling of the holes.
 High axial and lateral load capacity for these foundations. The
weight of the structure can be easily held by the piers and is
very sturdy.
 They are very economical. The cost to drill and install the
caissons is minimal when compared to the cost to any

 Piers minimize the need for pile caps. Because the piers are
filled with concrete, pile caps are really not necessary.
 The caisson foundation will reduce vibrations and has slightly
less noise. Since the foundation is based on piers, there are
less vibrations that will upset the structure.
ADVANTAGES

 There is a lack of expertise of these types of foundations.
Construction managers and crews are not as familiar with the
procedures and protocols related to caissons.
 Piers cannot be placed on contaminated sites. Due to the
amount of drilling required to place the caissons and pour the
concrete, they cannot be placed in an area where the soil has
been contaminated
 The construction procedures for placing caissons is very
sensitive. This is why there are not many construction
managers who are willing to work on a job requiring caissons to
be placed.
 There is a major lack of inspectors who are qualified to inspect
DISADVANTAGES

 Cutting edge
 Well curb
 Bottom plug
 Steining
 Top plug
 Well cap
SECTIONS OF WELL FOUNDATION

DIFFERENT SHAPES OF WELL FOUNDATION
 Circular
 Double D
 Double Octagonal
 Twin Circular
 Rectangular
 Double Rectangular
 The choice of a particular shape of well depends upon the
size of the pier, the care and cost of sinking, the
considerations of tilt and shift during sinking and the
vertical and horizontal forces to which well is subjected.

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