FOUNDATION 13-02-14 (1).ppt,TYPES,PROCESS

FOUNDATION

1. FOUNDATION
Foundation-Function, Different types of Foundations,
Excavation techniques. Drafting exercise on simple
shallow foundation footings using stone and brick,
stepped footing, Raft foundation

2. Foundation
Foundation is the lower most part of the building which transmits the load of the building
to the under lying earth.
A foundation is used to support a building or structure and transmits loads directly to the
underlying soil or rock.
 
The factor which decides the type of foundation is bearing capacity of the soil.
Foundations can be split into two main types:
1. Shallow foundation
2.Deep foundation (>3m)

3. Functions
1.Foundation transfers non-uniform load of the superstructure
evenly to the sub soil (due to periodic shrinkage and swelling of
subsoil)
2.It provides the stability against the undermining , souring flood
water and the burrowing animals.
3.Resist uplifting or overturning forces due to wind
4.Resist lateral forces due to soil movement (safety against sliding.)
5.It provides a level surface for the construction of the
superstructure.

4. Shallow foundation
Shallow foundations are constructed relatively close to the ground level. Shallow
foundations can only be used where the soil at that level is capable of adequately
supporting the load.
Shallow foundations are generally constructed using in-situ concrete but some
substructure elements can alternatively be constructed in precast concrete in part or
whole to improve speed of construction on site.
Shallow foundations can be sub-divided into the following main types
•
 
Strip foundations(footings) –
 a linear foundation which generally support walls.
 
• Pad foundations –
 a discrete square or rectangular foundation supporting columns or
piers.
•  Raft foundations –
 a large single foundation supporting a whole structure.

5. Strip footings
These are continuous foundation carrying continuous loads.
Strip footings are also called 'edge beams'.
A footing slab requires two separate concrete pours.
Advantages of footing slabs are that they:
•adapt to sloping sites
•require simple formwork (no edge rebates)
•require simple excavation that is exposed for minimal time
•do not require internal beams.

              
The fill material is usually restrained at the external walls.
Therefore these walls need to be strong enough to support the fill

6. Strip footings

7. Pad foundations
Pad foundations are used to support individual or multiple
columns, spreading the load to the ground below.
They are generally square or rectangular in plan, with the
plan area being determined by the permissible bearing
pressure of the soil.
The shape in plan will be dictated by the arrangement of
the columns and the load to be transferred into the soil.
The purpose of foundation is to transmit loads from the structure to the ground
making sure where there is a good uniform bearing stratum at a relatively shallow
depth.
The columns should be spaced sufficiently far apart for adjacent pads not to overlap.

8. Plan of Pad Foundation
1250mm
1250mm
300mm
300mm

9. Section of Pad Foundation
G.L
25mm Thick lean
concrete
300mm
750mm
Reinforced concrete
pad
Column stump

10. 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 and individual pad foundations
would interact.
A raft foundation normally consists of a concrete slab
which extends over the entire loaded area. It may be
stiffened by ribs or beams incorporated into the
foundation.
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 can
spread the loads over a larger area.
A raft is usually used when subsoil is weak, or columns are closely located and with
deviated loadings.
It also serves as a transfer slab to combine and tie up all the vertical loading
elements to the plate-form foundation. By doing so, differential settlement can be
avoided.

11. DEEP FOUNDATION
A deep foundation is used to transfer loads from a structure above ground through
upper weak strata of soil to a more competent one at depth, beyond which shallow
foundations become both impractical and uneconomic.
DEEP Foundation are those whose depth is very large when compared to its width.
DEEP Foundation are of following types
•Pile Foundation.
•Pier Foundation.
•Caisson or well Foundation.
Out of which Pile Foundation is more commonly used in building construction.

13. Classification of the pile based on its function
End bearing pile – used for transfer the load through the water or the soft soil to a hard
   
strata.
Friction pile- used to transfer the load by the skin friction
Compaction Pile – Used to compact the loose granular soil
Tension pile – to anchor down the structures subjected to the uplift pressure
Anchor pile – provide anchorage against the horizontal pull
Fender piles or dolphins -
 are used to protect the water front structures from the impact
from ships
Sheet piles – used to resist the seepage and uplift from the hydraulic structures

14. Classification of the pile based on material and composition
1. Concrete pile
 
      a) Pre cast
 
      b) cast-in situ
 
              i) driven : cased or uncased
 
              ii) bored :pressure piles, under reamed, bored piles
2. Timber piles
3. Steel piles
 
      a) H pile
 
      b) Pipe pile
 
      c) sheet pile
4. Composite pile
 
      a) concrete and timber
 
      b) concrete and Steel

15. Pre cast concrete pile
These are piles cast in yard, cured then driven into the ground. They are commonly of
square section. Other shapes are available , but the octagonal shape are better
appearance and reinforcement can be easly placed in it. Concrete mix generally used are
1:2:4 or 1:1.5:3. While driving these piles to the ground cast iron or mild steel shoes are
provided at the lower end. These piles can be driven under water also
Advantage
It can be examined and necessary repair works before use Positioning of the
reinforcement can be maintained
cast-in situ concrete pile
cast-in situ concrete pile are cast at the place where they have to function by driving a
casing into an excavated hole and filling up this with concrete. If the casing is kept in its
position after placing the concrete they are called cased cast-in situ concrete pile. If the
casing is withdrawn after placing the concrete then it is called uncased cast in situ pile.
Timber pile
A timber pile is made of a trunk of a tree. The building codes usually prohibit the use of
timber pile. These piles are driven with a light pile driving equipment. To protect the head
of the pile an iron ring is fixed at the top.

16. Steel pile
Steel pile may be a rolled section.Two or more sections of the steel pile may be connected
together in a box shape and are driven as a
single pile. Present practice is to use the steel pile in the following forms
 
      a) H pile
 
      b) Pipe pile
 
      c) sheet pile
composite pile
These are made of two portions of two different material. Driven one above the other.
Two common types of the composite pile are
 
      a) concrete and timber
 
      b) concrete and Steel
concrete and timber
The timber portion is used bellow the permanent and the lowest water level. While
concrete pile usually cast in situ is formed above it.
Due this combination the advantage of the both the pile is combined.
The total cost of the pile is reduced.
concrete and Steel
This type of the composite pile is used where the required length of the pile is greater
than that available for the cast in situ pile. The
consists of the steel pile attached to the lower end of the concrete pile.

17. Pier foundation:
Consists of a cylindrical column of larger diameter to support and transfer large
super imposed loads to the firm strata below.
It trnsfers the load through bearing.
Generally shallower in depth than pier foundations.
Preferred in location where the top strata consists of decomposed rock overlying
strata of hard rock.
Types:
1.Masonry or concrete piers.
2.Drilled caissons.

18. MASONRY PIER
CONCRETE IN STEEL PIPE
CONCRETE AND STEEL PIPE
IN STEEL SHELF
DRILLED CAISSON OF CONCRETE

19. Well foundations:
Are box like structures circular or rectangular .
Larger in diameter than pier and drilled caissons.
Uses:
1.Bridge piers and abutment in rivers and lakes.
2.Break waters and other structures for shore protections.
3.Large water front structures such as pump houses,...

21. EXCAVATION TECHNIQUES USED FOR CONSTRUCTION

22. Construction is a very complex activity and requires lot of work to
be done.
When you are getting started with a construction work, the very
first thing that needs to be done on the area is excavation
What is excavation?
Excavation is often used in digging holes for archaeological
purposes and also for studying the soil .
Excavation is also important in the field of building and house
constructions.
Excavation techniques are used to dig holes before starting a
construction. This hole can be used for drainage purposes or to
plainly renew the soil content

23. There is a lot of excavation techniques used in every
construction nowadays. Below are some of the widely used
excavation techniques today and why it is specifically used.
1.Horizontal
Excavation
•This is one of the
excavation
techniques used in
shallow sites where
there is light or no
commercial and
residential buildings
existing at all.
•This excavation is
done horizontally.

24. 2. Vertical Excavation
•Vertical excavation is the
widely used among the
excavation techniques.
•Contractors employ this
method in large areas and
urban sites where numerous
commercial and residential
buildings are existent.
•Every layer of the excavation
are is shown one part at a time.
• This exposes a rocky or soil
layer that is something like a
vertical shaft.

25. 3. Hybrid Excavation
•If you are looking for
excavation techniques that do
both vertical and horizontal
method then the hybrid
excavation is the one you
should employ because this is
already the combination of
the two.
•This technique is done only
when the area or site needs a
quite deep excavation.

26. 4. Cofferdams
Cofferdams are one of the
useful excavation
techniques that contractors
employ for waterlogged
areas.
Also, they use this method
when the excavated site
has a great probability of
collapsing.

27. 5. Step Trenching
•This method also involves
deep excavation.
•The difference of it from
the other excavation
techniques is that, steps are
made.
• As you dig deeper, the
steps get narrower.

28. •These excavation techniques serve their very own
purpose.
•But before contractors can deal with the excavation
of a particular site, they must thoroughly study the
soil in the area first and other factors as well.
• It would be better if you hire professional and
licensed excavators.
•But you can also do it on your own as long as you are
familiar with the different excavation techniques.

29. TYPES OF SOIL AND RECCOMENDED FOUNDATIONS:
LOOSE SOIL / CLAY – PILE FOUNDATION ( UP TO THE ROCK
AREA)
BLACK COTTON SOIL – PILE FOUNDATION / RAFT
FOUNDATION
GRAVEL REDDISH – ISOLATED FOOTING OF DIFFERENT
DEPTHS