2.

Foundations and basements

Building Technology (EG 626 CE)

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Foundation
Definition of foundation
 It is the lowest part of structure. It provides base for super
structure. It transmits loads to soil below. It is a part that is
below the ground level.
Function of foundation
 To transmit all superimposed loads (wind, vibration, dead and
live loads).
 To withstand against all kinds of settlements (against failure of
underlying soil).
 To give stability to structure by resisting in firm base.
 To prevent lateral movement of supporting materials.
Characteristics
 Wide enough section to distribute weight over larger base area
within safe bearing capacity.
 Evenly loaded condition that prevents unequal settlement.
 Deep enough preventing overturning and increasing stability.

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Foundation
Types of foundation
 Shallow foundation
 Deep foundation
 Shallow foundation
 The depth of the foundation is less than or equal
to its width.
 It is placed immediately below the lowest part of
the superstructure.
 Deep foundation
 It is relatively deep and need special precautions
 The purpose of deep foundation is to attain
bearing stratum deep inside the ground in case of
weak soil.
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 Shallow foundation

 Spread footing
 Independent footing
 Combined footing
 Continuous footing
 Strip footing
 Wall footing
 Inverted arch footing
 Eccentrically loaded footing
 Offset and Strap (cantilever) footing
 Raft foundation
 Slab (solid)-up to 30 cm
 Slab and beam- slab > 30 cm
 Cellular- slab >90 cm
 Grillage foundation
 Timber grillage
 Steel grillage
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 Shallow Foundation

Spread
footing

Independent Combined Continuous

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 Shallow Foundation

Strip footing

2t + 2J
wall Inverted arch Eccentric

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 Shallow Foundation

Cellular
Slab Raft Slab & beam

Raft Foundation
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 Shallow Foundation

Timber grillage
Steel grillage

Grillage Foundation
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 Deep Foundation

 Pile foundation
 Well foundation (caissons)
 Piles
 Pile is the pillar like structure driven deep in to the ground
to strengthen strength of soil below, It acts as support to
the spread footing, It is used individually or in cluster
through out wall.
 Uses of piles
 in very poor soil condition,
 in waterlogged soil (high water table),
 in filling areas,
 in areas with heavy loads,
 in compressible soil,
 in the areas where the mat or grillage foundations are
not possible.
 as the anchor in docks,

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 Deep Foundation
 Types of piles
 According to the
uses; Decking
 Bearing piles
 Friction piles
 Sheet piles Sheet

 Anchor piles Bearing

Anchor

 Batter piles Fender

Batter
 Compaction piles
 Fender piles

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Deep Foundation
Types of Piles
 According to material use;
 Steel piles (H-beam, Box piles, pipe piles, screw piles and
disc piles)
 Cement concrete piles
 Cast-in-situ piles
 Cased: Raymond, Mcarthor, Monotube, BSP base
driven, Swage etc.
 Uncased: Simplex, Franki, Vibro, Vibro-expanded,
Pedestral, Pressure etc.
 Pre-cast piles
 Pre-stressed piles
 Timber piles
 Composite piles
 Sand piles

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 Deep Foundation

 Methods of pile driving

 Drop hammer
 Stem hammer
 Water jet
 Boring
 Selection of types of pile
 Nature of structure
 Loading in structure
 Ground water table
 Length of pile required
 Availability of material and equipments
 Factors causing deterioration of piles
 Cost of piles
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 Deep Foundation

 Well foundation
 Well foundation is the water tight box structure of
wood/ RCC/steel and mostly used in the
foundation of the bridges.
 Purpose: to develop an enclosure below for plumb
and provide access shaft to reach a deep tunnel
transmitting the loads to hard bearing strata.
 Types of well foundations (Caissons)
 Box caissons
 Well foundation or open caissons- single, double
or cylindrical
 Pneumatic caissons

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 Soil and soil exploration

 Soil and its properties

 Soil is uncemented geological deposits
 It is the basis of foundation
 Property of soil decides the type of foundation
 Types of soil: Cohesive and Cohesion less
 Sub-soil exploration
 Very important phase in construction and determines the
characteristics of underlying soil.
 Soil investigation is must before undertaking construction works.
 Acquires general picture of geology of area.
 Objectives of soil exploration:
 To determine the value of safe bearing capacity of soil.
 To select economic types of foundation.
 To determine the depth of proposed foundation.
 To predict likely settlement and make allowance for that in design.
 To know underground water level and its problem

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 Method of soil exploration

 Inspection
 Naked eye observation
 Test pits
 Helps to know type of soil at small depth, pit size: 1.5*1.5 m² and depth 1.5m.
 Probing
 Hollow tube of 35-50 mm is driven to ground at about 30 cm at a time.
 Boring
 Auger
 Deep: percussion and rotating boring.
 Wash: case tube is driven along with this a wash jet is inserted, this washes the soil
below and bring it to the surface.
 Test piles
 Wood/steel piles are driven under hammer blows.
 Geo-physical methods
 Electrical method
 Electric current is passed through cathode and anode in soil and the flow of current
through cathode to anode is the measure of soil below.
 Seismic methods
 Vibrations are caused by artificial explosions and the movement of these vibration
waves measures the soil characteristics.

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 Bearing capacity of soil

 It is the ability of soil to support the load

coming over it.
 It is the strength of soil to resist maximum
load coming to its unit area causing no failure.
 Maximum bearing capacity of soil = W/ A
 Safe bearing capacity = W/(A*f)
where,
W is Total load including self weight
A is area of sole plate and
f is factor of safety

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 Methods of improving bearing capacity of soil

 Mechanical stabilization  Chemical stabilization

 Mixing different graded soil  Calcium chloride, Sodium
 Change of chloride, Polymers, Chrome
Lignin, Sodium silicate
grading of soil  Thermal stabilization
 Mixing different  Heating, Freezing
graded soil  Electrical stabilization
 Use of roller  Grouting under pressure
 Cement stabilization  Geo-textile and fabric
 Mixing soil, cement and water stabilization
 Lime stabilization  Sheet piling
 Mixing soil, lime and water
 Sub-soil drainage
 Bituminous stabilization
 Mixing of bitumen with soil

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 Suitability of different types of
foundation

 Basis of foundation design

 Total loads of building
 Nature and bearing capacity of sub-soil.
 A good foundation is judged by;
 Firm location
 Stability of structure
 Free from settlements

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 Foundation in black cotton soil

 Black cotton soil

 Good for agriculture and bad for structure.
 High shrinkage value due to change in
moisture content.
 Volume varies as 20-30% of original
volume.
 Develops very wide and deep cracks due to
excessive shrinkage
 Very weak in saturation.
 Problematic for foundation.

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 Foundation in black cotton soil

 Precautions for foundations in black cotton soil

 Foundation depth be enough below from cracks to
hard strata.
 Measures to be applied to avoid water reaching to
bottom of foundation.
 Prevent foundation from direct contact with black
cotton soil.
 If thickness of black cotton soil is high, foundation
is to be laid on piles.
 Raft foundation is the choice in this condition.
 Tie-beam in plinth is important.

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 Settlement of foundation

 Causes of foundation settlement

 Consolidation of soil particles
 Reduction of moisture content
 Heaving of soil due to pressure
 General earth movement
 Effects of unequal settlements
 Stresses in structure
 Distortion of structure fabrics
 Failure of structure
 Prevention of undue unequal settlements
 Proper foundation design
 Proper soil investigation
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 Causes of foundation failure

 Unequal settlement of sub-soil

 Unequal load distribution
 Horizontal movement of soil adjoining structure
 Lateral pressure tending overturn
 Shrinkage due to withdrawal of moisture from soil
 Atmospheric action
 Lateral escape of soil below foundation
 Nearby building construction
 Trees etc.

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Underpinning of foundations of existing
building

 Definition
 It is a process of improving and strengthening
existing foundation
 It facilitates to support structure and assist in
transferring loads to better soil strata
 Necessity
 Occurrence of excessive settlement
 Increasing load bearing capacity of foundation
 Change of functional use
 Addition in loading pattern
 Permitting to lower adjacent ground below
existing foundation
 Construction of new basement nearby
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 Underpinning

 Operation to be carried out before

underpinning
 Survey of structure
 Marking of Settlement if any
 Noticing neighbors (adjacent building)
 Setting indicators to identify probable
cracks while underpinning
 Carrying out corrective measures for
cracks etc.
 Investigate sub-soil
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 Underpinning

 Sequences of operation
 Suitable holes driven through the wall and a needle beam is
inserted & supported on the jack
 Excavation is started below foundation and footing of the
foundation is reached
 The offset of the foundation is cutoff and removed & excavation
is reached to the defined depth
 New foundation is laid in the desired depth up to the underside
of the existing foundation
 This process is repeated in stages
 Final layer of pinning work just underside of existing foundation
should be done with the mortar from rapid hardening cement
 Precautions
 Excavation in one time done for less than one fourth of length,
for weak soil it is done for less than one fifth to one seventh of
length, normally length of one bay is taken as 1.5 m
 To be carried out slowly in stages and not at a time

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 Methods of underpinning

 Pit method
 Ordinary
 Cantilever
 Pile method
 Improving of foundation by grouting
and chemical consolidation

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 Methods of underpinning

wall wall weight

Needle beam Needle beam

Jack

Existing foundation Existing foundation

New foundation New foundation

wall

GL wall
Pile cap
Perforated pipe

GL
pile

Hard strata consolidation

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 Basement

 Basement is a
space, a storey or
a floor immediately
below the adjacent
ground level.
 Retaining wall is
essential
component of
basement.

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 Basement

 Retaining wall
 Structural wall that resists lateral thrust of earth mass,
pressure of sub-soil water & support vertical loads.
 Function of retaining wall
 Strength, stability and Durability
 Resistance to overturn and horizontal slide
 Resistance to overstress in the materials of
construction
 Resistance to overstress in the soil on which the wall
rest

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 Forces acting on the retaining walls

 Active earth pressure

 Lateral pressure that tends to move or overturn the wall at all times
 This is the result of earth wedge retained and any hydrostatic
pressure of ground water
 Passive earth pressure
 The reactionary pressure that builds up to resist any forward
movement of the wall, because any forward movement will compress
the soil in front and reaction to counteract this movement builds up.
 Angle of repose
 The natural slope taken up by any soil and given in terms of the
angle to the horizontal base line
 Varies from 450 to 00 angle for wet clay, but for most soils, this angle
of repose is 300.
 Wedge of soil
 The mass of soil resting on the upper plane of the angle of repose
 Surcharge
 The additional mass of soil above the top surface of wall
 Frictional force
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 Forces acting on the retaining walls

surcharge

Mass of wall

Active earth pressure

Weep hole

Angle of repose

Friction at interface

Ground pressure

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 Factors affecting strength, stability and
durability of retaining wall

 Effect of ground water

 The sub-soil ground water reduces soil shear strength.
 Reduces bearing of the base and the soil
 Subsoil drainage is the solution for this.
 Effect of inadequate passive earth resistance
 The passive earth resistance at the front of the wall
resists sliding
 Insufficient passive pressure is not able to resist sliding
 Provision of ribs under the head and toe increased
passive pressure

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 Types of retaining walls

 Gravity or mass retaining wall

 Cantilever or L-Shaped Retaining wall
(max H=6 m)
 Base entirely in front of stem
 Base partly in front and partly behind the
stem
 Base wholly behind the stem
 Counterfort retaining wall (max H=8 m )

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 Types of Retaining wall

C
o
u
n
t
e
r Gravity or Mass Retaining Wall

f
o
r
t

Cantilever Retaining wall

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 Retaining wall

 Design principle of retaining wall

 Overturning does not occur
 Sliding does not occur
 The soil beneath the wall is not overloaded
 The materials in the wall are not overstressed
 Factors to be considered during design
 Nature and type of soil
 Height of water table
 Sub-soil water movements
 Types of wall
 Materials used in the wall
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