Foundation ppt

Presented By:
Prof Dr Kanya Lal Khatri
CONSTRUCTION
ENGINEERING

3
FOUNDATION:
The lowest artificially built part of structure
which transmits the load of structure to the
ground is called foundation.
FUNCTIONS/PURPOSE OF FOUNDATION:
(1) To transmit and distribute the total load of
structure to a larger area of under lying
support.
(2) To prevent differential settlement of
structure.
(3) To provide the stability to the structure
against wind, rain, earth quake.

4
FUNCTIONS/PURPOSE OF Continued…
FOUNDATION:
(4) To prevent the lateral movement of the
building materials.
(5) To secure a level and firm bed.
(6) To increase the stability of the structure
as a whole.

5
Foundation Loads:
•Dead Load
•Live Load
•Wind Load
•Horizontal Pressure below grade
•Structural member forces
•Uplift
•Earthquake

Primary Factors Affecting
Foundation Choice:
-Sub-surface soil
-Ground water conditions
-Structural requirements

Secondary Factors Affecting
Foundation Choice:
-Construction access, methods
and site conditions
-Environmental factors
-Building codes and Regulations
-Impact on surrounding structures
-Construction schedule
-Construction risks

TYPES OF FOUNDATIONS:
Foundation systems are often
classified as Shallow or Deep
foundations depending on the depth
of the load-transfer member below
the super-structure and the type of
transfer load mechanism. The
required foundation system depends
on the strength and compressibility
of the site soils, the proposed
loading conditions. Continued---

10
TYPES OF FOUNDATION:
In construction sites where
settlement is not a problem, shallow
foundations provide the most
economical foundation systems.
Shallow foundation construction is
typically utilized for most residential
and light commercial raised floor
building sites.
Continued--

11
TYPES OF FOUNDATION
Where poor soil conditions are found,
deep foundations may be needed to
provide the required bearing capacity and to
limit settlement. Additionally, structures in
coastal high-hazard areas are required to be
elevated above the base flood level
(BFE), commonly on piles. Examples of
deep foundation systems include driven
piles(e.g. pressure treated timber piles,
concrete, or steel piles), drilled shafts.
Continued-----

12
TYPES OF FOUNDATION
- Shallow foundations (Some times also
called spread footings) include pads
(isolated footings), strip footings and raft
footings.
- Deep foundations include piles, pile walls,
and caissons.

13
SHALLOW FOUNDATION:
Requirements:
-Suitable soil bearing capacity
-Undisturbed soil or engineered fill
Basic types or configurations
-Column footings
-Wall or strip footings

14
1- Pad Foundations:
-Pad foundations are used to support
an individual point load such as the load of a
structural column. They may be
circular, square or rectangular.
-They usually consist of a block or
slab of uniform thickness, but they
may be stepped if they are
required to spread the load from a
heavy column.
-Pad foundations are usually shallow, but
deep pad foundations can also be used.

16
2-Strip Foundations:
-Strip foundations are used to support a
line of loads, either due to a load
bearing wall or if a line of columns need
supporting where column positions are
so close that individual pad foundations
would be inappropriate.

18
3-Raft Foundations:
-Raft foundations are used to spread the
load from a structure over a large area,
normally the entire area of the structure.
They are used when column loads or other
structural loads are close together.
-A raft foundation normally consists of a
concrete slab which extends over the entire
loaded area. It may be stiffened by steel
bars.
Continued----

Raft Foundations
-Raft foundations have the
advantage of reducing differential
settlements as the concrete slab
resists differential movements
between loading positions. They
are often needed on soft or loose
soils with low bearing capacity as
they spread the loads over a larger
area.
19

Raft Foundations (Construction)
-The whole area is digged up to required depth
and 30 cm more wider than the covered area.
-The bed is compacted properly. A layer of lean
concrete is laid to a suitable thickness.
-After this the reinforcement is laid as vertical
members and horizontally too.
-Then the concrete of 1:2:4 is laid and is cured
properly and the walls can be erected.
-This foundation is constructed when the
ground conditions are poor and the soil is also
poor to bear the loads.
21

22
4- Stepped Foundations:
-When the ground is in slope, the
foundation trenches of walls are made
stepped to prevent wastage of labour and
material.
-This also results in keeping the depth of
walls as nearly uniform as possible.
-Care should be taken to extend the lower
layer of concrete under the upper one for a
distance equal to thickness of concrete.

24
Stepped Foundations (Construction)
-This type of foundation is constructed by
excavating the ground in steps having short
length and uniform height.
-Then the concrete is laid according to
specific thickness and then the masonry is
done on the horizontal bed of concrete
already prepared.

25
DEEP FOUNDATION:
-The foundation constructed sufficiently
below ground level with the same
artificial arrangements such as piles,
walls, etc, at their base is called deep
foundation.
-These are further classified as under:
(a)Pile
(b)Cofferdams
(c)Caissons (iron sheets used)

26
PILE FOUNDATION:
-A foundation (spread footing or
grillage) supported on piles is called pile
foundation.
-A pile foundation usually consists of a
base of spread footing or grillage
supported by piles at their bottom.
-- piles distribute the load of structure of
the soil in contact either by friction
alone or by friction combined with
bearing at their ends.

28
PILE FOUNDATION:
-Piles are relatively long and slender
members used to transmit foundation
loads through soil strata of low bearing
capacity to deeper soil or rock having a
higher bearing capacity.
-Pile resistance is comprised of:
-End bearing
-Shaft friction
-For many piles only one of these
components is important. This is the basis of
a simple classification.

Prepared by:G.S.Solangi
Pile Foundations
-Piles are gradually classified into two categories:
-According to function
-According to the composition of material of
construction

30
Pile Foundations
According to the function
(1) Bearing Piles:
The piles which rest on hard strata
and act as column to bear the load
of structure are called bearing
piles.
These piles are used to bear the
vertical loads. They take and
transfer the load to the hard strata
lying underneath.

32
Pile Foundations
(2) Friction Piles:
The piles which do not rest on hard
strata and bear the loads on account
of the frictional resistance between
the outer surface and the soil in
contact are called friction piles.
These piles are used to when the soil
is soft and there is no hard strata
available at a considerable depth.
They are generally lying in depth.

34
Pile Foundations
(3) Friction cum bearing Piles:
The piles which rest on hard strata and
resist the loads partly by bearing and
partly by their skin friction are known as
friction cum bearing piles.
(4) Batter Piles:
The piles driven at an inclination to resist
inclined loads are called batter piles.
These are generally used to resist the
lateral forces in case of retaining wall
abutments.

37
Pile Foundations
(5) Guide Piles:
These are gradually used in foundation of
cofferdams which are temporarily
constructed to provide foundation under
water.

Pile Foundations
(6) Sheet Piles:
The piles which consists of thin steel
sheets to enclose an area are known
as sheet piles. These piles are used to
enclose soil so as to prevent the
leakage of water and to enclose soft
material. These are not required to
carry any load but should be strong
enough to carry/ take the lateral
pressure of earth filling/water etc,

Pile Foundations
(7) Anchor Piles:
When piles are used to provide anchorage
against horizontal pull from sheet piling
walls or other pulling forces, they are
termed as anchor piles.
(8) Compaction Piles:
When piles are driven in granular soil with the
aim of increasing the bearing capacity of
the soil, the piles are termed as
compaction piles.

42
Pile Foundations
According to the material used for their manufacturing
(1) Timber/Wooden Piles:
-The piles made of wood are called timber
or wooden piles.
-The timber piles used for this construction
should be free from defects, decay etc
and those should be well seasoned.
-Transmission of load through timber piles
takes place by the frictional resistance
of the ground and the pile surface.
Continued----

Pile Foundations
According to the material used for their
manufacturing
(1) Timber/Wooden Piles:
-Timber piles proves economical, for
supporting light structures to be located
in compressive soils constantly saturated
with water.
-Timber piles may be circular or square in
cross-section.

44
Advantages of Timber/Wooden Piles:
- Timber piles are economical
- They can be driven rapidly and as such
there is great saving in time.
- On account of their elasticity, timber
piles can be recommended for sites
where piles are likely to the subject to
unusual lateral forces.
- They do not need heavy machinery and
elaborate technical supervision.

Disadvantages of Timber/Wooden
Piles:
- Timber piles must be cut off below the
permanent ground water level.
- Timber piles can not be driven in filled up
ground without injury and as such they
can not be recommended for such sites.
- They are liable to decay or deteriorate by
salt water.
- On account of their restricted length, they
can not be used for jobs where long piles
are needed.

46
Pile Foundations
According to the material used for their manufacturing
(2) Concrete Piles:
The piles made of cement
concrete are called concrete
piles. These piles are strong
and durable and can bear
more load than timber piles.
Concrete piles may be further
classified as:

(a) Pre cast Piles:
-These are RCC piles which are usually
square, circular in cross section. After
constructing or pouring and curing they
are handled, driven like wooden piles. In
these piles some additional reinforcement
is provided both at top and bottom. They
vary in length from 2 to 30 m.

(b) Cast in-situ Piles:
This type of pile is constructed in its
location and is located in a bore hole
prepared for this purpose.

49
Advantages of Concrete Piles:
- Durability of concrete piles is
independent of the ground.
- On account of their large size and
greater bearing power, the number of
piles required for supporting the
structure is much less.
- They can be cast to any length, size
and shape.
- They can be used for marine works
without any treatment.

Disadvantages of Concrete Piles:
- Their cost is much more than timber
piles.
- They can not be driven rapidly.
- Concrete piles require elaborate technical
supervision and heavy driving machines.
- They must be reinforced to withstand
handling stresses.

Advantages of Cast-in-situ Piles:
- These piles are cast in exact length
and as such there is no wastage of
time, money and material, as is
common in pre-cast piles.
- They are not subjected to the
vibrations due to hammering, hence
they are sound in construction.
- Cost of transportation is nil.
- They can be made to bear heavy
loads by adopting simple method.

52
Disadvantages of Cast-in-situ Piles:
- They can not be used under water.
- If the piles to be reinforced, there is every
possibility of the reinforcements getting
displaced.
- As concrete has got to be dumped from great
height, the quality of work is not appreciably
good.
- The ramming of the concrete mass cannot be
inspected and as such there is every possibility
of the voids being left, rendering the construction
unsound.
- In unsound piles, green concrete is liable to
loose its water by coming in contact with the dry
soil and hence it may result in making the pile
structurally weak.

(3) Steel Piles:
The piles which consist of steel section
are called steel piles. These are useful
where driving conditions are difficult
and other types of piles are not suitable.
They are generally used for building and
bridge foundation.
These are available in following forms:
(a)Steel pin Piles
(b)Sheet Piles
(c) Disc Piles
(d)Screw Piles

Driven Piles
The basic types of Piles
- End bearing pile-point loading
- Friction pile-load transferred by frictional
resistance between the pile and the earth.

Pile material
- Steel, H-piles, Steel pipe
- Concrete, Site cast or Precast
- Wood, Timber
- Composite
55

56
Loads applied to Piles:
- For the majority of foundations the loads
applied to the piles are primarily vertical.
- Combinations of vertical, horizontal and
moment loading may be applied at the soil
surface from the overlying structure.
- For piles in jetties, foundations for bridge
piers, tall chimneys and offshore piled
foundations the lateral resistance is an
important consideration.
- The analysis of piles subjected to lateral
and moment loading is more complex than
simple vertical loading because of the soil
structure interaction.

58
TYPES OF SOIL AND CHARACTERSISTICS:
The soil is made up of rocks and organic matter.
The rocks are changed into soils by weathering or by
disintegration. Weathering may be chemical or physical.
The action of sun, wind, water, plants and chemicals cause
the rocks changed into different sizes of soils.
Continued-----

TYPES OF SOIL AND CHARACTERSISTICS
Rocks: Broken into regular and irregular sizes by
joints.
Boulder: (too large to be lifted by hands),
Cobble:(Particle that can be lifted by a single hand).
Gravel:(Course grained particle larger than 6.4 mm).
Sand:(frictional, size varies from 6.4 to 0.06 mm).
Silts :(frictional, size varies from 0.06 mm to 0.002
mm), and
Clays :(cohesive-fine grained, size smaller than
0.002 mm).
Peat :(Soils not suitable for foundations).
For any type of foundation clay is poor but boulder,
gravel, sand and silt are best soils for foundation.
59

PILE DRIVING
Piles are driven in ground by three methods.
- By Drop Hammer
- By Steam Hammer
- By Boring

(1) By Drop Hammers:
- It is a method of pile driving, in which
hammer is raised by a rope or steel cable
and then allowed to drop on the pile cap.
- This method takes lot of time and thus it
is being replaced by steam hammer
these days.
- The weight of drop hammer varies from
350 to 1800 kgs.
- The exact weight of the drop hammer to
be used to be governed by the shape and
length of the pile as well as the nature of
ground to be penetrated.

(2) By Steam Hammers:
- In this type of pile driving method
hammer is raised and then dropped from
a short distance by means of a steam
cylinder and piston.
- The frame work supporting the hammer
also has pile lifting device.
- Due to uniform steam pressure, the rate
of hammer blows on the pile is also
uniform.
TYPES
- Single Acting
- Double Acting

PILE DRIVING
(2.a) Single Acting:
- The hammer is operated by steam
from one direction.
- The force of each stroke depends
upon the weight of the hammer and
the height of fall.
- Number of blows are dependable
on steam pressure.

PILE DRIVING
(2.b) Double Acting:
- Hammer usually weighs 2000 to 4000
kgs.
- Steam plays its part from both
directions.
- The number of blows are usually 100
to 200 per minute.
- These rapid blows result in quick
driving of the pile.
66

(3) Pile driving by Boring method:
-If the pile is required to penetrate beds of
hard soil, or soft rock to reach its required
depth, driving of the pile by boring is an
economical solution.
- In dry soil boring may be done through
an auger.
- In soft clay, rotary well drills may be used.
- The bore is made up to required depth of
the pile.
- Pre-cast piles are then put in the bore hole.

Length and Safe Bearing capacity of
Pre-cast Piles :
The load bearing capacity of Pre-cast pile
depends upon the following factors:
- Nature of surface to be penetrated.
- Depth of penetration.
- The area of cross-section of the pile and
its centre to centre distance in a group.
- The manner in which the pile supports
the load.

Selection of Type of Pile
It depends upon:
- Nature of the ground primarily governs the
selection of the pile type.
- Other important factors which must be
considered in this regard are:
* The nature of structure
* Loading conditions
* Elevation of ground water level
w.respect to the pile cap
* Probable length of pile required
* Availability of materials and equipments
* Probable cost of pile.

COFFER DAMS:
* Cofferdams are temporary barriers
commonly made of wood, steel, or
concrete sheet piling.
* Cofferdams are often used in temporary
works to enclose the construction area
within a continuous sheet pile wall around
and protect it from water entering from
out side.

Types of Cofferdams:
Considering the material used in their
construction, cofferdams can be divided
into following types:
• Earthen Cofferdam
• Rock-Fill Cofferdam
• Single-Walled Cofferdam
• Double-Walled Cofferdam
• Cellular Cofferdam

Earthen Cofferdams:
•Essentially consist of an earthen
embankment built around the area to be
enclosed.
•Not much depth of water (1.5 to 1.8 m).
•If velocity of current is low.
•The earthen embankment is constructed
from mixture of clay and sand or clay and
gravel.
•To prevent embankment from scouring due
to the action of water, side slopes of the bank
on water side should be pitched with
boulders.

Rock-Fill Cofferdams:
•If the depth of water is to be retained by the
embankment , stone or boulders are used
for the embankment.
•The stones are assembled in the required
shape of the embankment and the voids are
partially filled with earth and stone-chips.
•The side slope on the water side should be
protected by pitching.

Single Walled Cofferdams:
•This type of cofferdam is constructed where
the small area is to be enclosed.
•Depth of water around 4.5 to 6 m.
•Timber piles known as guide piles are first
driven deep into firm ground below the river
bed.
• Depending upon the velocity of the current,
centre to centre spacing of the piles may vary
between 1.8 to 4 m.

Double Walled Cofferdams:
* This type of structure is constructed where
the larger area is to be enclosed.
* There single walled structure becomes un-
economical.
* Construction procedures almost the same,
except the provision of single is changed with
double wall.
78

Cellular Cofferdams:
•This type of structure is used for de-
watering large areas in places where
the depth of water may be around 18 to
21 m.
• Mostly used during the construction of
marine structures like dam.
• They are arranged in a shape of
series of inter-connected cells.
• The cells are constructed in various
shapes and styles to suit the
requirements of site. Continued79

Cellular Cofferdams: Continued----
• Finally the cells are filled with clay, sand or
gravel to make them stable against the
various forces to which they are likely to be
subjected to.
• The common shapes of cellular cofferdams
are:
- Circular type cellular cofferdams
- Diaphragm type cellular cofferdams
80

CAISSON:
* A watertight structure made up of wood,
steel or reinforced concrete.
* It is constructed in connection with
excavation for foundations of bridges, piers,
abutments in rivers, lakes, docks, etc.
* The caisson remains in its position and
ultimately becomes an integral part of the
permanent structure.
* Mostly used for deep foundations under
water where the foundations must extended
up to or below the river bed from stability
considerations.
82

CAISSON Installation Sequence:
* Hole drilled with large drill rig
* Casing installed (typically)
* Bell or tip enlargement (optional)
* Bottom inspected and tested
* Concrete replacement (& casing removal)
84

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