BUILDING
COMPONENTS
1.Sub
structure
2.Super
structure
Weathering Course
Parapet
Roof Slab
Brick Masonry
Lintel
Door
Damp Proof Course
Floor Finish
Floor Concrete
Plinth
Step
Ground Level
Basement
Sand Filling
Foundation
Foundation concrete
COMPONENTS OF A BUILDING
FOUNDATION
 Foundation
is the part of the
structure which is in direct
contact with the ground to
which loads are transmitted.
A weak foundation destroys the work which is built
upon it.
Functions of foundation

Even distribution of load

Reduction of load intensity

Reduction of differential settlement

Safety against sliding and overturning

Safety against undermining

Provide firm and level surface

Protection against soil movement
Requirements of a good
foundation

Constructed to sustain dead load and
imposed load and transmit them to
underlying soil

Rigid-to avoid differential settlement

Taken to sufficient depth

Performance should not be affected due to
any unexpected future influence
Factors for the design
1.
Bearing capacity
of the soil
2.
Settlement of
foundations
Ultimate bearing
capacity
 Safe bearing
capacity
 Allowable bearing
capacity

Uniform
settlement
 Differential
settlement

BEARING CAPACITY
• Supporting power of soil without any failure
• Depends on :
1. Properties of soil
2. Position of water table
3. Physical features of foundation like type, size & shape
•
Ultimate Bearing Capacity : minimum gross pressure intensity at the
base of foundation that the soil fails in shear
• Net Ultimate Bearing Capacity : minimum net pressure intensity at
which the soil fails in shear
• Net safe bearing capacity : obtained by dividing the net ultimate bearing
capacity of the soil with a suitable factor of safety
• Safe bearing capacity : Maximum pressure the soil can carry safely
without the risk of shear failure
SETTLEMENT OF FOUNDATIONS
Settlement of foundations
No settlement
Total settlement
Differential settlement
Uniform
settlement
is
usually
of
little
consequence in a building, but differential
settlement can cause severe structural damage.
Settlement of foundation means the sinking of foundation
as a consequence of compression or deformation of the
soil under the foundation
Equal Settlement :
• The structures settles by uniform amount at each and
every portion of the structure
Unequal Settlement:
• The amount of settlement is different at different parts of
the building
Causes of settlement:
• Due to weight of the structure transmitted to the soil
• Due to increased load on the surrounding soil
• Due to excavation near the foundation
• Lowering of water table
• Vibrations from moving machineries
• Deterioration of concrete by the chemical action of soil, seawater etc…
• Due to mining and tunnelling operations
Causes of differential settlement:
• Non uniform load distribution on foundations
• Non uniformity of soil types
• Percolation of water
• Overlap and concentration of stresses due to presence of adjacent foun
dations
Causes of foundation failure
Unequal settlement of subsoil under the
foundation
 Unequal settlement of the masonry
 Lateral movement of earth
 Shrinkage of soil bed due to seasonal variation of
moisture content
 The penetration of the roots of trees
 Atmospheric action
 Lateral escape of the soil beneath the foundation
 Horizontal movement of the soil adjacent to the
structure

Types of Foundations

Shallow Foundations D<=B

Deep Foundations
D>B
D - Depth of foundation
B – Width of foundation
Shallow foundations
Types of shallow foundations
Isolated or column footing
Wall or strip footing
Combined footing
Continuous footing
Cantilever footing
Raft or mat foundation
Isolated or column footing
When the load on the column is less, a
spread is given under the column
Wall or strip footing

The foundation which is provided through
out the length of a continuous structure is
called strip footing.
Combined footing
When a foundation or footing is constructed
for two or more columns is called
as combined footing
 Two individual footings overlap
 When bearing capacity is less
 when footings are constructed
near boundaries of the plot
 Trapezoidal footing – when column
loads vary considerably

Continuous footing
A single continuous reinforced concrete
slab is provided as foundation for three or
more
columns
in
a
row.
Continuous
footing is more suitable to prevent the
differential settlement in the structure and
for the safety against earthquake.
Continuous footing
Cantilever Footing (Strap)
Consists of an eccentric footing for the
exterior column and a concentric footing
for the interior column.
 A strap or a cantilever beam connects
them.

Strap footing
Raft or mat foundation

A raft foundation is a combined footing
which covers the entire area beneath a
structure and supports all the walls and
columns
Raft or mat foundation
Mat foundation
Raft or Mat Foundation

Raft foundations are suitable when
1.The
building loads are heavy
2.The
allowable soil pressure is small
3.Individual
footings would require more
than half the building area
4.In
highly compressible soil
5.Weak
spots and loose pockets in soil mass
are suspected
Deep Foundation

The foundations having very large depth
compared to width are called deep
foundations
E.g. Pile foundations
Well foundations
Pile Foundation

Piles are long slender members driven
into ground or cast at the site. Pile
foundations are common where the soil
conditions are unfavorable for the use of
shallow foundations
Suitability of pile foundations





Loose foundation soil but hard strata is
available at a depth of 10-15 m
Heavy dead and live loads
Near seashore or riverbed where scouring
action of water occurs
Position of water table is likely to fluctuate
appreciably
Canals or deep drainage lines near by
Classification of Piles
Method of load transfer
2. Function or action
3. Composition and material
4. Installation
1.
Classification based up on
method of load transfer
End bearing Piles
2. Friction Piles
1.
End bearing piles

End bearing piles-Used to transfer load
to a suitable bearing stratum
Friction piles

Friction Piles- used to transfer the loads
to a depth by friction along the surface
area of the piles.
Classification based up on
function or use
1.
2.
3.
4.
5.
Compaction Piles
Tension or uplift piles
Anchor Piles
Fender Piles
Sheet Piles
Compaction Piles

Used to anchor structures subjected to
hydrostatic pressure (against pilling or
pushing forces)
Anchor Piles and Tension piles

To protect water front structures like
docks, harbours etc… against impact from
ships
Fender Piles

Used to retain the sides of excavation, to
prevent seepage below dams, to construct
retaining walls etc.
Sheet Piles
Classification based up on
material and composition
Timber Piles
2. Steel Piles
3. Concrete Piles
4. Composite Piles
1.

Timber Piles perform well both in dry
condition and in submerged condition
Timber Piles

Used to resist lateral or horizontal forces.
More durable.
Steel Piles
Concrete Piles

Used when part of the pile is submerged
under water. Made up of concrete and
steel
Composite Piles
Classification based upon
installation
Precast Piles
2. Cast In Situ Piles
1.
Precast Piles
CAST IN SITU PILES
• CASED CAST IN SITU PILES
• UNCASED CAST INSITU PILES
Well Foundations
A well foundation is a well type structure,
which built at the ground level and sunk
into the soil at the required level.
 The bridge pier will be resting on the top
of the well foundation.
 The bottom of the well is plugged with
concrete.
 The top is covered with a well cap which is
a thick concrete slab


1.
2.
3.
4.
5.
6.
The bottom edge of the well foundation
consists of a cutting edge. The different
c/s adopted for well foundations are
Circular
Twin circular
Double D
Dumb bell
Twin hexagonal
Rectangular
Components of well foundation






Well curb
Cutting edge
Steining
Bottom plug
Top plug
Well cap
WELL CAP
TOP PLUG
STEINING
SAND OR
SOIL FILLING
WELL CURB
BOTTOM PLUG
CUTTING
EDGE

Well curb
 Support the wt of the well

Cutting edge
 Sharp angle for cutting the soil without making it too weak

Steining
 Walls of the well

Bottom plug
 Concrete plug provided to balance the soil pressure

Top plug
 Concrete plug provided above the sand/soil filling

Well cap
 Serves as platform for the supporting members of the
superstructure
Well sinking operations
Laying the well curb
 Construction of masonry in wall
steining
 Well sinking
 Completion of well

Soil excavation
Construction of well cap
Machine foundation

To support the dynamic forces produced by
the operation of the machine

To avoid large settlements at resonance,
natural frequency of foundation should be
different operating frequency of the machine
Types of machines
 Impact type
Presses, forge hammers

Reciprocating type
Compressors, engines

Centrifugal type
Motors, turbines

Miscellaneous types
Machine foundation
BLOCK TYPE
BOX TYPE
WALL TYPE
FRAMED TYPE
DETERMINATION OF
BEARING CAPACITY
Plate load test
Plate load test
PLATE LOAD TEST







It is a field test used to determine the ultimate
bearing capacity of soil
A pit is dug up to the foundation level
A square plate of 300mm x 300mm & 25 mm is
placed at the centre of the pit
A dial gauge is connected to the test plate
Now weights in the form of sand bags are placed on
the platforms in equal increments.
The test is continued till the failure occurs or the
plates settled by 25 mm whichever occurs earlier
The load settlement curve is then recorded.
Load v/s settlement graph
Standard Penetration Test
STANDARD PENETRATION
TEST






Test is conducted in a bore hole 50 to 150 mm
in diameter
Split spoon sampler (pipe-like weight) is driven
into the ground by a weight of 65 kg
weight is repeatedly raised and dropped a
distance of 750 mm to drive in sampler
number of blows required to drive the sampler
for a penetration of 300mm is recorded
The number of blows is known as penetration
number (N Value)
There are empirical charts from which the
bearing capacity can be calculated based up on
the N Value
Methods for improving Bearing
Capacity






Compaction
Drainage
Vibratory methods
Chemical stabilisation
Grouting
Geotextiles