Desertation on Comparison of Foundations

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CHAPTER: 1

INTRODUCTION

1.1 GENERAL :

Construction of structures involves setting up of foundation which is the lowest part of a building

or a bridge and which transmits weight to underlying soil. There are two classes of foundations,

these are: shallow and deep ones. The major subject of the paper is modelling and design of

shallow foundations. A shallow foundation is a footing planned to take a shape of rectangle or

square which supports columns, other structures and walls. As per the provision of civil

engineering, a foundation is considered to be shallow when it is less than si feet in depth or

when its depth equals its width.

According to !aolocci "#$$%&, 'a foundation supports the weight or load of any construction

work such as building, bridges and roads. The design used to model a foundation depends on the

type of soil, load of the building, materials used and the purpose of the construction(. )odeling

and design of shallow foundations includes the techniques and requirements of civil engineering

that must be put in place while setting up a foundation. There are various types of shallow

foundation such as mat*slab, spread footing and slab* on + grade. pread footing foundation is

mostly used in construction of commercial structures and basements. This type of shallow

foundation includes strips of concrete that help in transfer of wall or column loads to bedrock.

everal factors control spread footing such as penetration that results due to near surface layers,

leading to changed volume because of shrink, swell or frost heave.

)at*slab foundations are used in the distribution of heavy walls or column loads constructed

across the whole building and help to reduce pressure created from construction materials. This

type of shallow foundation is constructed at a close range with ground surface or in construction

of lower part of basements. )at*slab foundations can also be used in construction of high rise

buildings where the foundation is thick and requires etensive reinforcement to ensure that there

is uniform transfer of load.

Another type of shallow foundation is slab*on* grade that is used in structural engineering for

structures formed from mold set ground. This foundation is elevated through a concrete slab

placed in the mold, thus creating no space between the structure and bed rock. lab*on*grade iscommon in construction works found in warmer climate where there is no need for heat ducting,

ground free-ing and thawing. The advantages of using this form of shallow foundation is that it

is cheap, sturdy and less vulnerable to insects, such as termites for eample.

n their argument, /eng 0 teadman "#$$1& have formulated that 'shallow foundations are

commonly used in structural constructions through the application of various models and

1



designs. This creates an environment for providing strong construction work that lasts for a long

period of time(. 2ther forms of foundations such as deep, piles, caissons and piers are mainly

used to establish strong foundation for prime structures. The provisions of civil engineering do

not provide overwhelming constructions that are threat to human life and the environment. The

use of shallow foundations has advantages and disadvantages.

Advantages of shallow foundations are that

3 t is cost effective hence affordable

3 There is no need of eperts to provide labor for shallow foundations

3 )aterials used are concrete and easily available.

3 The construction procedure is simple.

4isadvantages of using shallow foundation

3 5imitation capacity is soil structure

3 6oundation is always subjected to torsion, moment and pullout

3 ettlement is a major problem

3 The ground surface is sometimes irregular making the structures sloppy.

7hen designing a shallow foundation, there are two common aspects that must be considered.

6irstly, the pressure on applied foundation should not be more than the bearing capacity of the

supporting soil. econdly, foundation settlement should not be ecessed due to the impact of pressure on applied foundation.

1.2 OBJECTIVE

The aim of our project will be to analy-e strip and square isolated footing keeping the same soil

conditions and compare them to check the suitability of it. The methodology involves the testing

of soil sample for its various characteristics such as specific gravity, water content and load

bearing capacity.

2



CHAPTER: 2

REVIEW OF LITERATURE:

2.1 Introducton

6oundations are designed to have an adequate load capacity depending on the type of subsoil

supporting the foundation by a geotechnical engineer and the footing itself may be designed

structurally by a structural engineer. The primary design concerns are settlement and bearing

capacity. 7hen considering settlement, total settlement and differential settlement is normally

considered. 4ifferential settlement is when one part of a foundation settles more than another

part. This can cause problems to the structure which the foundation is supporting. 8pansive clay

soils can also cause problems.

2.2 Found!ton t"#$%

6oundations are mainly of two types: "i& hallow foundations.

"ii& 4eep foundations.

"i& hallow foundations

hallow foundations are used when the soil has sufficient strength within a short depth below the

ground level. They need sufficient plan area to transfer the heavy loads to the base soil. These

heavy loads are sustained by the reinforced concrete columns or walls "either of bricks or

reinforced concrete& of much less areas of cross*section due to high strength of bricks or

reinforced concrete when compared to that of soil. The strength of the soil, epressed as the safe

bearing capacity of the soil, is normally supplied by the geotechnical eperts to the structural

engineer. hallow foundations are also designated as footings.

n shallow foundation, generally, the depth at which the foundation is placed is less than its width

i.e. the ratio of depth of foundation to its width is less than unity. This type of foundation spreads

the load of superstructure into the ground laterally. 9ence shallow foundations are generally

known as spread footing. 6rom design point of view, shallow foundations are classified as

follows:

3



"a& 7all footing

"b& solated column footing or pad footing

"c& Combined footing

"d& Cantilever or strap footing

"e& )at foundation

The various types of shallow foundations are discussed below.

7all footing + n order to spread the load carried by the wall into the soil, a wall footing is

provided. The foundation is continuous along the direction of the wall. n such a foundation

depth to width ratio is #: or #:; i.e. the base width is generally two or three times more than the

width of the wall at ground level.

pread footing+ n cases of multiple columns in footing, it is used. 7hen a footing is to be made

common for two or more columns in a row, it is called combined footing. This type of footing is

normally used along the walls of the buildings at property lines where the footing for the column

cannot etend outside the limit of structure. imilarly, when columns are closely spaced or the

4



supporting soil is of low bearing capacity and the footings are to be combined, this footing is

used. t can be either trape-oidal or rectangular in shape.

trap footing: * <nder certain conditions when we have to compromise and it is not possible to

further etend an edge footing beyond the boundary of a site due to the presence of an adjoining

property, strap footing is used.

n strap footing, the edge column footing is combined with interior column footing by means of a

strap beam. uch footings are known as strap footings.

)at foundation + when a common foundation is provided for columns in two or more rows, the

footing is called a mat or raft foundation. n case of low bearing capacity of the soil and when the

foundation requires quite large area for load distribution, mat foundation is provided. )at

foundation is considered more economical than other foundations if the total area of isolated

footing needed for a foundation covers more than => ? area of the building.

)at foundation is most suited in clayey soil as the whole area under the foundation contributes

to the load distribution and this is more effective. ometimes a mat foundation is used as a

floating foundation in a deposit of very soft clay for controlling total as well as differentia

settlement.

"ii& 488! 62<@4AT2@:*

n deep foundation, the depth at which foundation is placed is greater than its width. The depth to

width ratio of the foundation is usually greater than to =. <nlike shallow foundations, deep

foundations distribute the load of superstructure into the ground vertically rather than laterally.

6ew eamples of deep foundations are:* !ile foundations, pier foundations and wells or caissons

foundations.

!refabricated piles are driven into the ground using a pile driver. 4riven piles are either wood,

reinforced concrete, or steel. 7ooden piles are made from the trunks of tall trees. Concrete piles

5



are available in square, octagonal, and round cross*sections "like 6ranki piles&. They are

reinforced with rebar and are often prestressed. teel piles are either pipe piles or some sort of

beam section "like an 9*pile&.

6oundations relying on driven piles often have groups of piles connected by a pile cap "a large

concrete block into which the heads of the piles are embedded& to distribute loads which are

larger than one pile can bear. !ile caps and isolated piles are typically connected with grade

beams to tie the foundation elements togetherB lighter structural elements bear on the grade

beams, while heavier elements bear directly on the pile cap.

7hen the epected loads from superstructure cannot be supported on shallow foundations, deep

foundations are provided.

&'u!r$ Footn(:

6



CHAPTER :)

THEORETICAL E*PLANATION

7



).1 U%n( t+$ r(+t t"#$ o, ,ound!ton on t+$ r(+t %o-.

The type of soil on which a foundation is to be established contributes to the strength of

structures constructed. 9owever, to get the right type of soil that supports strong foundation isthe major challenge faced by civil engineers. 2ne important item that civil engineers need to put

into consideration is establishment of a strong structural foundation. There are different types of

building foundations such as raft, piling and footing that are considered when setting up a

structure. t is necessary to check the condition of soil before putting up a structure. This helps to

provide a strong surface that supports the load of the walls and roof. The condition of soil is done

through soil investigations carried out by soil engineers who provide a report that is used by

architects to determine the type of foundation to be used in a particular area.

The type of soil is used to determine the type of foundation to be used in structural construction.

6or instance, clay type of soil is considered to epand during wet season and contract during dry period hence it is not recommended to be used on shallow foundation. The reason of a problem is

because the active -one of epansive clay is always near the surface. andy loam soil does not

change with moisture content or temperature and soil engineers recommend this type of soil. t is

in a position to support slab foundation and applied pressure, but the major challenge is soil

erosion. This happens when there is heavy rainfall that erodes the foundation and this calls for

slab jacking that aims at repairing the slab to avoid further damage.

).2 W!t$r t!-$ -$/$- !nd $!rn( c!#!ct"

earing capacity refers to the maimum value of pressure that the foundation on which a

structure stands can support. The depth of a foundation is dependent on the type of the soil under

which the foundation stands. A good foundation has the capacity to transmit the load of a

structure evenly below the ground surface. 9owever, the ground surface is greatly influenced by

the depth of the water table. n construction and design, water table represents the surface that

separates between saturated and unsaturated groundwater -ones. 4epending on the depth of the

bed rock, the water table may be high or low. n some areas, the depth of water table keeps on

shifting depending on the seasons of rain. 7hen the rainfall is high, say during spring, water

table rises nearer to the surface while on the other hand descending considerably to lower

grounds during the summer.

The depth of water table at any given time affects the modeling design, especially in the case of

the shallow foundations. n all cases, the ultimate depth to which one can put utili-ation of

underground space is dependent on the depth of the water table.

8



).) T+$ E,,$ct o, B$!rn( C!#!ct"

The effects of bearing capacity of shallow foundations are caused by the progressive failure

which might be influenced by the soil type. The granular soils acquire the behavior of nonlinearstrength. ts strength is not uniformly distributed. Dranular soils acquire the property of

progressive failure.These parameters are considered in designing shallow foundations since they

determine their strength. n order to design shallow foundations to take the required load, data is

collected for the performance of others foundations. This enables the ability to include all

strength parameters which take care of shear force.

9



CHAPTER : 4

0ETHODOLOG

.1 oil mechanics site investigations are conducted to discover the characteristics of the soil at

the particular location. There are different methods of soil investigation. After the soil samples

are analy-ed, a report is prepared recommending the type of foundation to be used.

.2 T+$ Pur#o%$% o, Bu-dn( Found!ton%

The foundation is the lowest part of a building. t transmits the load of the structure to the soil

below. The main purposes of a foundation are:

• To distribute the load from the building over a large area

• To load the substratum evenly so as to prevent unequal settlement

• To take the structure sufficiently deep into the ground to prevent

overturning

efore a foundation is decided, it is necessary to determine the characteristics of the soil at the

site of construction. This is done by conducting soil investigations.

.) TE&T& CONDUCTED

.).1 W!t$r cont$nt t$%t

This test is done to determine the water content in soil by oven drying method as per : %>

"!art & + #$%;. The water content "w& of a soil sample is equal to the mass of water divided by

the mass of solids.

A##!r!tu% :*

i& Thermostatically controlled oven maintained at a temperature of ##> E =o

Cii& 7eighing balance, with an accuracy of >.>? of the weight of the soil taken

iii& Air*tight container made of non*corrodible material with lid

iv& Tongs

Pr$#!r!ton o, %!3#-$

10



The soil specimen should be representative of the soil mass. The quantity of the specimen taken

would depend upon the gradation and the maimum si-e of particles as under:

Proc$dur$

i& Clean the container, dry it and weigh it with the lid "7eight F)#F&.ii& Take the required quantity of the wet soil specimen in the container and weigh it with the lid

"7eight F)F&.

iii& !lace the container, with its lid removed, in the oven till its weight becomes constant

"@ormally for hrs.&

iv& 7hen the soil has dried, remove the container from the oven, using tongs.

v& 6ind the weight F);F of the container with the lid and the dry soil sample.

REPORTING OF RE&ULT&

The water content

w G H)*);I J H); *)#I3#>>?

7ater content test results are shown below.

.).2 &#$c,c (r!/t" t$%t

O4$ct/$

6or determination of specific gravity of soil solids by pycnometer method.

11



R$,$r$nc$ &t!nd!rd

: %> "!art & + #$1= + )ethod of test for soil "!art *Drain si-e analysis&

E'u#3$nt 5 A##!r!tu%

o !ycnometer

o ieve ".%= mm&

o Kaccum pump

o 2ven

o 7eighing balance

o Dlass rod

Pr$#!r!ton %!3#-$

After receiving the soil sample it is dried in oven at a temperature of #>= to ##=>C for a period of

#L to hours.

Proc$dur$

#. 4ry the pycnometer and weigh it with its cap"7#&

. Take about >> g to ;>> g of oven dried soil passing through .%=mm sieve into the

pycnometer and weigh again"7&

;. Add water to cover the soil and screw on the cap.

. hake the pycnometer well and connect it to the vaccum pump to remove entrapped air

for about #> to > minutes.

=. After the air has been removed, fill the pycnometer with water and weigh it "7;&.

12



L. Clean the pycnometer by washing thoroughly.

%. 6ill the cleaned pycnometer completely with water upto its top with cap screw on.

1. 7eigh the pycnometer after drying it on the outside thoroughly "7&.

C!-cu-!ton%

The pecific gravity of soil solids "Ds& is calculated using the following equation.

7here

7# G 8mpty weight of pycnometer

7 G 7eight of pycnometer M oven dry soil

7; G 7eight of pycnometer M oven dry soil M water

7 G 7eight of pycnometer M water full

13



CHAPTER : 6

14



&ITE &TUD

15



6.1 &t$ d$t!-%

52CAT2@ : Kill !aundha, 4ehradun

48!T9 26 9AN4 TNATA : >.$m

TN<CT<N8 : # tower of = floor

8@4 <8 : Nesidential building

AN8A : >>m

62<@4AT2@ TO!8 : quare footing

62<@4AT2@ 48!T9 : #.=m

16



6.2 C!-cu-!ton% o, %+!--o7 ,ound!ton %$tt-$3$nt%

n construction theory, designers use equations to calculate the foundation settlements and the

resultant rates of deformations on the bed soil under the pressure of the structure. The performance of bed calculations follows under two limiting states. 6irst is the state of

performance and the second limiting state is the state of safety. n the second state, a predicted

finite deformation is not supposed to eceed those established in the condition under which

structures and other buildings are only meant to support normal habitation. This state is in most

times used as the basic criteria to measure the safety of a structure. n cases of bed calculations,

an etra constraint is included under which the average pressure eerted by the structure on the

ground is not supposed to be greater than the computed value of resistance of the supporting soil

to the pressure eerted on it. A common resolution has been that, in order to raise the limit of

safety by >?, the calculated limiting deformations should be less than >? of the limiting

values. This occurrence is eplainable by use of the facts that acknowledge the presence of patches which eperience plastic deformation.

These regions develop with the progressive increase in the loading. uch developments form

beneath the edges of foundations until a point where the linear relationship between the load

from the structure and resistance from the ground beneath it fails. This linear union between the

load and resistance stands in the situation of application of elasticity theory. According to 9ooks

law of deformation of linearly elastic material, stress "load& and strain "resistance& are applied.

Application of layer by layer accumulation of resistance values enables a designer to account for lack of uniformity in soils in reference to deformity across the allowable limits of a compressible

soil layer. '4esigners also apply other engineering methods of settlement computation. 7hen we

apply the law relating to stress and strain for a given constant thickness that is compressible, the

increase in settlement becomes proportional to the increase in the loading(. eyond a point of

limit, the settlement tends to increase more rapidly than the load. The formation of regions with

plastic deformations increases the rate of accumulation of settlement with increase in loading.

This leads to the ehaustion of fatigue of the supporting bed hence interfering with its bearing

capacity. 6urther loading from the structure becomes absolutely impossible as the soil or ground

have reached its deformation level from the shear strains in it. Computations have gone further to

prove that, by limiting pressure or structural load to the level of resistance, predictablesettlements are maintained at lower levels than their limiting values. The etra allowable loading

is left to cater for any eventuality of inadvertent loading.

17



6.) For3u-!$ u%$d

T$r8!(+9% B$!rn( C!#!ct" T+$or"

Assumptions:

ased on !randtlPs theory "#$>& for plastic failure of metal under rigid punches Ter-aghi derived

a general bearing capacity equation. All soils are covered in this method by two cases which are

designated as general shear and local shear failures. Deneral shear is the case wherein the loading

test curve for the soil under consideration comes to a perfectly vertical ultimate condition at

relatively small settlement as shown by curve # in 6ig.;. 5ocal shear is the case wherein

settlements are relatively large and there is not a definite vertical ultimate to the curve as in curve

in 6ig.;. "oil is loose relative to a general shear failure&. The following assumptions were

made in the analysis.

• The footing is continuous.

• The weight of soil above the base level of footing is replaced by equivalent

surcharge "6ig.&, where is the unit weight of soil.

• The shear resistance of the soil above the base level of the footing is neglected.

• The base of the footing is rough.

• The failure surface is composed of a straight line ac and the logarithmic spiral dc or cg .

• The soil wedge abc beneath the base of footing is in elastic state and moves with the footing.

• The base angle of the wedge abc is equal to .

• The principle pf superposition is valid.

afe earing Capacity * The safe bearing capacity is obtained as per the followings. 5et Qnet be

the net bearing capacity. The net bearing capacity, as per the definition is obtained as:

Qnet G Qult + q G Qult + R4f

Qnet G #JR@RMq"@q + #& Mc@c

Qnet G #JR@R MR4f "@q *#& M c@c

18



Qs G QnetJ6 M R4f G H#JR @R M R4f "@q + #& M c@cI M R4f

7here:

c G Cohesion of soil "k@Jm&,

g G effective unit weight of soil "k@Jm;&.

4 G depth of footing "m&,

G width of footing "m&

@cGcotf"@q + #&,

@qGe";pJ*fJ&tanf J H cos"=MfJ&I,

@gG"#J& tanf"kp Jcos f * #&,

e G @apierPs constant G .%#1...,

k p G passive pressure coefficient, and

f G angle of internal friction "degrees&.

The limitation of the Ter-aghiSs theory is that it is applicable only for the shallow foundation.

The theory has been derived for the case of general shear failure. 6or local shear failure the

following modification has been proposed by Ter-aghi.

Cm G "J;& c

ɸm G "J;& tan ɸ

The reduction in shear parameters is due to the shear strength not being fully mobili-ed. The

bearing capacity factors for use in general equation of Ter-aghi should be based on the values of ɸm.

19



5imiting Condition for 5ocal and Deneral hear 6ailure:

earing capacity for footing having limited dimension + The equation developed by Ter-aghi is

for strip foundation, which is considered as two dimensional. The case of footings with finite

dimensions is considered as three dimensional problem. ased on eperimental results Ter-aghi

suggested following modification for other footings such as square, circular, rectangular etc.

quare 6ooting

Qult G #.c@c M R4f @q M >.R@R

Circular 6ooting

Qult G #.c@c M R4f @q M >.;R@R

Nectangular 6ooting

Qult G c@c H#M>.J5I M R4f @q M >.=R@RH#*>.J5I

20



CHAPTER :

BEARING CAPACIT CALCULATION&

4ATA:

7idth of foundation G #.= m

4epth of foundation 4 G #.= m

<nit weight of soil R G #$ k@Jm;

G ;Lɸ

earing capacity factors G @c, @q, @Ƴ

@c G L=.;1, @q G $.;1, @Ƴ G =

Calculations for quare 6ooting:

<ltimate bearing capacity, qf G #.;c@c M R4@q M >.R@R

qf G #$3#.=3$.;1 M >.3#$3#.=3=

G 2;22.<) =P!

@et <ltimate earing capacity, qn G #.;c@c M R4@q M >.R@R + R4

qn G #$3#.=3$.;1 M >.3#$3#.=3= + #$3#.=

G 1<<.) =P!

Calculations for trip 6ooting:

<ltimate bearing capacity,qf G c@c M R4@q M >.=R@R

qf G #$3#.=3$.;1 M >.=3#$3#.=3=

G 21>.?) =P!

@et ultimate bearing capacity, qn G c@c M R4@q M >.=R@R U R4

qn G #$3#.=3$.;1 M >.=3#$3#.=3= + #$3#.=

21



G 21?.)) =P!

Co3#!r%on% $t7$$n %'u!r$ 5 %tr# ,ootn(%:

&@UARE FOOTING &TRIP FOOTING

', 2;22.<) =P! ', 21>.?) =P!

'n 1<<.) =P! 'n 21?.)) =P!

I, ,!ctor o, %!,$t" % t!=$n !% )

&!,$ $!rn( c!#!ct" '% .?1

I, ,!ctor o, %!,$t" % t!=$n !% )

&!,$ $!rn( c!#!ct" '% >1

22



CHAPTER >

CONCLU&ION

CHAPTER: >

REFRENCE&

Carpenter, T. ">>#&. 8nvironmental, Construction and ustainable 4evelopment*Kol.#.

@ew Oork: Vohn 7iley 0 ons

23



Cremer C., !ecker A., 4avenne 5. ">>#&. 'Cyclic macro*element for soil*structure

interaction: material and geometrical non*linearities(, nternational Vournal for @umericaland Analytical )ethods in Deomechanics,Kol. =: #=%*#1.

Da-etas D. "#$$#&. '6oundations vibrations(, 6oundation 8ngineering 9andbook, nd

ed., Kan nostran Neinhold.

Drimes, 4., et al. ">>L&. 'Civil 8ngineering 8ducation in a Kisuali-ation 8nvironment:8periences with Ki-class(. Vournal of 8ngineering 8ducation, Kol.$=, pp.L%=*L$>

5e !ape O., ieffert V.!. ">>#&. 'Application of thermodynamics to the global modeling

of shallow foundations on frictional material(. nternational Vournal for @umerical andAnalytical )ethods in Deomechanics, Kol. =, pp. #;%%*#>1.

@egro !., !aolucci N., !edretti ., 6accioli 8. ">>>&. '5arge*scale soil*structure

interaction eperiments on sand under cyclic loading(, !roc. #th 7orld Conference on8arthquake 8ngineering, Auckland, @ew /ealand.

@ova N., )ontrasio 5. "#$$#&. 'ettlements of shallow foundations on sand(,

DWotechnique, Kol. #, , pp. ; * =L. @ova N., )ontrasio 5. "#$$%&. 'ettlements of shallow foundations on sand: geometrical

effects(, DWotechnique, Kol. %, #, pp. L * L>. !acheco, )., 4an-iger, 6. 0 !into, C. ">>1&. '4esign of hallow 6oundations under

Tensile 5oading for Transmission 5ine Towers: An 2verview.( 8ngineering Deology,Kol.#>#, pp.L*;=.

@ova N., )ontrasio 5. "#$$#&. 'ettlements of shallow foundations on sand(,

DWotechnique, Kol. #, , p. $.

Cremer C., !ecker A., 4avenne 5. ">>#&. 'Cyclic macro*element for soil*structure

interaction: material and geometrical non*linearities(, nternational Vournal for @umerical

and Analytical )ethods in Deomechanics,Kol. =: #L#. !acheco, )., 4an-iger, 6. 0 !into, C. ">>1&. '4esign of hallow 6oundations under

Tensile 5oading for Transmission 5ine Towers: An 2verview.( 8ngineering Deology,

Kol.#>#, p.1 Neese, 5., senhower, 7. 0 7ang, . ">>=&. Analysis and 4esign of hallow and 4eep

6oundations. @ew Oork: Vohn 7iley 0 ons, p.%1

24

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Desertation on Comparison of Foundations

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