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project of foundation (footing)

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complete project of foundation and type of foundation for civil technologies.

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                      Session : 2011




 PROJECT : FOUNDATION AND ITS DIFFERENT TYPES




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Chapter   Contents                         Page No
No
1         Foundation                       7-8



2         Types of foundation & shallow    9-13
          foundation


3         Deep foundation& types of deep   14-20
          foundation




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                   List of figures
S .No   Figures                          Page No
1       Foundation .fig.1                7
2       Shallow foundation. fig.2        9
3       Spread footing. fig.3            10
4       Grillage footing. fig.4          11
5       Raft footing .fig.5              12
6       Inverted arc foundation.fig.6    13
7       Deep foundation. fig.7           14
8       Pile foundation .fig.8           15
9       Bearing & fraction pile .fig.9   16
10      Well foundation .fig.10          17
11      Open caisson fig.11              18
12      Box caisson fig.12               19
13      Monolithic caisson fig.13        20




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Chapter -1

Foundation
Intoroduction:
A foundation (also called a groundsill) is a structure that transfers loads to the earth.
Foundation is the base of any structure. Without a firm foundation, the structure cannot stand. That is
the reason why we have to be very cautious with the design of foundations because our entire structure
rests on the foundation. Foundation of a structure is like the roots of a tree without which the tree
cannot stand.
Almost all building, regardless of their size, shape, intededpurpose, type of construction or geographic
locationm share a common problem. They rest on the ground. Thus the design of adequate foundations
is a gereral problem in building design. Since each building site is essentially unique in terms of specific
geological conditions, each foundaiton presents unique desing problems. The foundation designer must
understand the basic principles of behavior of building structures and of soil stress-and-strain
mechanisms in order to apply them to a wide range of possible interractions between buildings and the
ground. Although the main purpose of this book is to present practical design information, there is also
an effort to geeralize the problems to permit readers to develop their own solutions to their own unique
problems.




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Fig.1: foundation.




In professional design firms structural coputations are most commonly done with computers,
particularly when the work is complex or repetitive. Anyone aspiring to participation in
professional design work is advised to acquire to the application of experience necessary to the
application of computer-aided techniques. Footings are designed to have an adequate load
capacity with limited settlement by a geotechnical engineer, and the footing itself is designed
structurally by a structural engineer.
The primary design concerns are settlement and bearing capacity. When considering
settlement, total settlement and differential settlement is normally considered. Differential
settlement is when one part of a foundation settles more than another part. This can cause
problems to the structure the foundation is supporting. It is necessary that a foundation not be
loaded beyond its bearing capacity or the foundation will "fail"

Before designing the foundation, the type of soil is determined. Depending on whether the soil
is hard soil or soft soil, a specific type of foundation is adopted.
Foundations are made in various materials… They could be reinforced cement concrete
foundations or brick foundations or stone rubble masonry foundations etc. The choice of
material to be used in the construction of foundations also depends on the weight of the
structure on the ground.Foundations are broadly classified into shallow foundations and deep
foundations. The depth of the foundation means the difference of level between the ground
surface and the base of the foundation. If the depth of the foundation is greater than its width
the foundation is classified as a deep foundation.

Selection of foundation type.
The first formal part of the foundation design is the determination of the foundation system to
be used. This decision cannot normall be made until the surface and subsurface conditions are
known in some detail and the general size, shape, and location of the building are determined.
In some cases it may be necessary to proceed with an approximate design of several possible
foundation schemes so that the results can be compared. The majority of foundations for small
structures are selected to meet the minimum requirements of building regulations or standards
set by various regulating authorities or financing institutions. Although satisfactory structural
safety and first-cost economy are usually achieved, the life cycle costs and performance of
shallow foundations on deep deposits of active clay subsoil are often poor.




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Chapter-2

Types of foundation
Foundation are generally divided into two main types

   1) Shallow foundation
   2) Deep foundation


   1) Shallow foundation
A shallow foundation is a type of foundation which transfers building loads to the earth
verynear the surface, rather than to a subsurface layer or a range of depths as does a deep
foundation. Shallow foundations include spread footing foundations, mat-slab foundations,
slab-on-grade foundations, rubble trench foundations, and earthbag foundations.

Shallow footings are, usually, embedded a meter or so into soil. One common type is the spread
footing which consists of strips or pads of concrete (or other materials) which extend below the
frost line and transfer the weight from walls and columns to the soil or bedrock. Another
common type is the slab-on-grade footing where the weight of the building is transferred to the
soil through a concrete slab placed at the surface.




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        Fig.2: Shallow foundation.




Types of shallow foundation
Shallow foundation is generally divided in to different parts. They are given below.

   a)   Spread foundation
   b)   Grillage foundation
   c)   Raft foundation
   d)   Inverted arch foundation

   a) Spread foundation
The foundations constructed by invreasing the area at the base of structure by means of
offsets, are called spread footing foundations. In such foundations spread is given under the
base of a wall or a column by providing offsets. This spread is known as footing and the
foundation itself is called spread footing. Broadly spreaking, all the types of shallow foundations
mentioned above can be refferred to as spread footing foundations. Spread footing
foundations consists of strips or pads of concrete (or other materials) which transfer the loads
from walls and columns to the soil or bedrock. Embedment of spread footings is controlled by
several factors, including development of lateral capacity, penetration of soft near-surface
layers, and penetration through near-surface layers likely to change volume due to frost heave
or shrink-swell. These foundations are common in residential construction that includes a
basement, and in many commercial structures. But for high rise building it is not sufficient.

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     Fig.3: Spread footing.

   b) Grillage foundation
The foundation which cosists of one or two tiers of wooden or rolled steel sections with space
filled up with concrete is known as grillage foundation. This is so called because the bed
constructed in this type of foundation is called grillage. Thistype of construction avoids deep
excavation and provides the necessary area at the base of the structure to reduce the intensity
of pressure within the safe bearing capacity of the soil. His type of foundation generally used
for heavy structure columns piers and stanchions etc. the grillage foundation generally consist
of steel I section (R.S.J) laid in single or double larges. The second larger. The number of R.S.J.S
and their distanced a part depend upon the load of the structure and the bearing capacity of
the soil. To construct a grillage foundation a trench of the required width and depth is
excavated. The surface the trench is leveled and rammed. Over the rammed surface a layer of
cement concrete is spread and is well compacted so as to make if impervious. R.S.J.S are of
desired dimensions are laid at regular intervals. The lower flanges of the R.S.J.S are embedded
in to the concrete by pouring rich cement mortar the R.S.J.S are connected together by pipes
and bolts




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       Fig.4: grillage footing .


The object of this type of foundation is to spread the load over a large horizontal area at the
base of a structure. Grillage foundation is classified into the following two types.

           I. Steel grillage foundation
           II. Timber grillage foundation

For construction the steel grillage foundation a trench is excavated to the calculated width and
about 0.90 m to 1.50 m deep. Bottom of the trench is rammend and levelled. Then a layer of
lean cement concrete about 30 cm thick is laid and compacted.



   c) Raft foundation
The foundation consists of a thick R.C.C slab covering the whole area in the from of a mat is
known as raft foundation. Raft slabs are very quick and easy to build and they can be completed
with a minimum amount of disturbance to the site and when completed the site is clean and
accessible for loading up materials for the next stage of the works. Raft slabs are as the name
suggests foundations that cover the whole surface area of the building in one continuous piece.
They are often joined when the area is too large for a single pour, but the rebar though the
construction joints keep the slab working as a whole. In general they work well with flat sites.
When the land has a slope to it the formwork and the fill at the lower end can get a bit of a
handful and so at some stage a decision has to be made between using a raft slab and a strip
footing on a sloping site.

Method of construction.

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The whole area is dug out to the specified depth and 30 cm more wide than the area to be
covered.




   Fig.5: raft foundation.

The bed is compacted and sprinkled over with water. Thena layer on lime concrete or lean
cement concrete is laid to a suitable thickness to act as a bottom cover. After this the
reinforcecement is laid as illustrated . the reinforcement consists of closely spiced bars placed
at right angles to one another. Then the cement concrete ( 1:2:4 )is laid and copacted to the
required thickness. Then concrete slab so laid is the properly cured. When loads are excessive
thick concrete beams running under the columns can also be constructed.



   d) Inverted arch foundation
The foundation cosisting of inverted arches between the piers is known as inverted arch
foundation.

In this type of foundation the load from the piers is transferred to the soil by constructing
arches in inverted position at their base as illustrated . th rise of the inverted arches is aout one
fifth ot one tenth of the span and the are usually build in half brick rings. The position of arches
may be either along the row of piers or across the row of piers or in both the direction
dependiong upon the nature of soil and the type of load to be takesn by them. Inverted arches
are sometimes built under and between the bases of piers, with the idea of distributing the


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weight of the piers over the whole length of the footings. The intermediate wall may either be
supported by steel beams or arches, as preferred.




              Fig.6: Inverted arch foundation.

It is better to build the arches before putting in the skewbacks, and for the latter 1 to 6 Portland
cement concrete possesses specific advantages, as the concrete can be deposited between the
ends of the arches and rammed evenly and simultaneously, thus giving a solid and uniform
bearing against the ends of the arches, tending to prevent unequal settlement and cracking.




   Chapter-3

Deep foundation

Deep foundation constructed sufficiently below ground level with some artificial arrangements
sush as piles , wells etc. at their base are called deep foundations. A deep foundation is a type
of foundation distinguished from shallow foundations by the depth they are embedded into the
ground. A deep footing is used to transfer a load from a structure through an upper weak layer
of soil to a stronger deeper layer of soil. There are different types of deep footings including
helical piles, impact driven piles, drilled shafts, caissons, piers, and earth stabilized columns.
There are many reasons a geotechnical engineer would recommend a deep foundation over a
shallow foundation, but some of the common reasons are very large design loads, a poor soil at
shallow depth, or site constraints (like property lines). There are different terms used to
describe different types of deep foundations including piles, drilled shafts, caissons and piers.

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The naming conventions may vary between engineering disciplines and firms. Deep foundations
can be made out of timber, steel, reinforced concrete and pre-tensioned concrete.




Fig.7: deep foundation.

Types of deep foundation
Deep foundations are generally divided in to different parts. They are given below.

   a) Pile foundation
   b) Well foundation
   c) Caisson foundation



   a) Pile foundation
A foundation supported on piles is called a pile foundation. A pile foundation ususally consists
of a base of spread footing or grillage supported by piles at their bottom. Piles distribute the
load of structure to the soil in contact either by friction alone or by friction combined with
bearing at their ends.




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    Fig.8: pile foundation.

            a) When the soil is very soft and solid base is not available at a reasonable depth to
               keep the bearing power within safe limits.
            b) When the grillage and raft foundation are very expensive.



Classification of piles
piles are classify in two types, which are given below.

1) Bearing pile
2) Friction pile


1) Bearing piles:- The piles which rest on hard strata and act as columns to bear the load of
the structure are known as bearing piles. When the bedrock is within a reasonable depth, the
piles are typically extended to the rock, Point Bearing Piles. These types of piles are the most
common in practice, and in the software they are modeled as ordinary columns, with or
without the influence of the soil.

2) Friction pile:- The piles which do not rest on a hard strata and bear the loads on account of
frictional resistance between their outer surface and the soil in contact are called friction pile.
Or which transfer loads mainly by frictional resistance along the shaft; and endearing piles in


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which load is primarily transferred to the surrounding soil of through the pile base. Depending
on the structural requirements.




     Fig .9: bearing & friction pile.




   b) Well Foundation

With these the building rests upon a number of hollow cylinders, or wells, of brick work or,
masonry which form supports in the same way as hollow piles or tubular foundations. The
masonry is first built to a height of about 4 feet upon a wooden curb or frame of the size of the
work; this is then undermined and allowed to sink its full depth into the ground; another 3 or 4
feet is then added, the structure is again undermined, and so on until the required depth has
been attained. The masonry must be of first-rate quality, and the undermining must be equal all
round, or the work will be strained and crack. Well foundations are extensively used for
ordinary buildings in India; but in this country they have been restricted to cases in which a
support is required for heavy wharf walls and other structures. Pile Engines of various kinds are
used for driving piles into the ground.

all of them a heavy block of iron or wood called a " ram" or "monkey" is raised by a rope or
chain over a pulley to the top of an upright frame and then allowed to fall suddenly upon the
head of the pile, being guided in its descent by arrangement which vary considerably in
different engines.



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   Fig.10: well foundation.




   c) Caisson Foundation
Is a retaining, watertight structure used, for example, to work on the foundation of a bridge
pier, for the construction of a concrete dam, or for the repair of ships. These are constructed
such that the water can be pumped out, keeping the working environment dry. When piers are
to be built using an open caisson and it is not practical to reach suitable soil, friction piling may
be driven to form a suitable sub-foundation.

Types of caisson foundation
   a) Open caisson
   b) Box caisson
   c) Monolithic caisson

   a) Open caisson



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Open caissons are similar to box caissons except that they do not have a bottom face. They are
                                             river-beds)
suitable for use in soft clays (e.g. in some river beds) but not for where there may be large
obstructions in the ground. Open caissons used in soft grounds or high water tab tables, where
open trench excavations are impractical, can also be used to install deep manholes, pump
stations and reception/launch pits for micro tunneling, pipe jacking and other operations.




   Fig.11: open caisson.

   b) Box caisson

                             ated
Box caissons are prefabricated concrete boxes with sides and bottom and are set down on
prepared bases. Once in place they will be filled with concrete to become part of the
permanent works, for example the foundation for a bridge pier. One problem with box caissons
is that hollow concrete structures float and so they must be ballasted or anchored to prevent
this until they can be filled with concrete. Box caissons except that they do not have a bottom
                                                            river-beds) but not for where there
face. They are suitable for use in soft clays (e.g. in some river
may be large obstructions in the ground.




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Fig.12: box caisson.




    c) Monolithic caisson
The bottom has been satisfactorily cleaned and leveled off; the working chamber is at once filled with
concrete. As soon as Monoliths are, as their name suggests, larger than the other types but are
similar to open caissons. They are often found in quay walls where resistance to impact from
ships is required. A pneumatic caisson is essentially a large inverted box on which a pier is built,
and inside of which work may be done because the water is forced out of the box by
compressed air. If an inverted tumbler is forced down into a bowl of water, If the tumbler is
forced to the bottom of the bowl, the possibilities of working on a river bottom are somewhat
exemplified. It is, of course, necessary to have a means of communication between this working
chamber and the surface; and it is likewise necessary to have an air-lock through which

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workmen (and perhaps materials) may pass. When the caisson has sunk to satisfactory subsoil,
sufficient concrete has been placed to seal the chamber effectively against the entrance of
water, the air-locks may be removed, and then the completion of the filling of the chamber and
of the central shaft is merely open-air work.




       Fig.13: monolithic caisson.




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