Construction of substructure

2.Construction of sub structure
By- Khan Nikhat naaz

1. Job Layout
1.Site Clearance
1.Site Clearance is an important factor to
be considered in the job layout plans ,
before commencement of project work
2.There should not be any obstruction like
trees , plants , shrubs, bigger size stones,
etc.

3. Approach road should be wide so as to
allow the truck for loading and unloading the
constructional material . If site ground is
uneven , then it should be made plane , for
this contouring is done in advance.
4.In short site should be cleared by all the
way, otherwise no activity can be launched in
construction processes.

 1. A plan in which the arrangements for
placing site office, store room , labour
quarter, medical aid center , godowns
for keeping construction materials and
other facilities are properly prepared is
called as Job layout or site layout .
 2.The arrangements for processes should
be such that the work is done smoothly
and in orderly manner.
2. Preparing Job Layout

3. Job layout depends upon three factors as
follows:-
a) Location , area and topography of the site .
b) Method of construction.
c) Nature and type of work.
4. There should be proper co-relation and co-
ordination among the different units.

3.Layout for load bearing and framed
structure by Center line method

4.Layout for load bearing and framed
structure by Face-Line Method

 Correct measurement of distances , preferably
by steel tape.
 Use of level , either dumpy level or mason’s
level.
 Correct marking of face -line or center – line.
 Use of correct plumb –bob for transferring
points on ground
 Checking of distances from at least two
independent measurements .
5. Precautions while Marking Layout on Ground

6. Excavation for Foundation
• Excavation of foundation ,trenches can be done either
manually with the help of conventional implements or
with the help of special mechanical equipment.
• Excavate foundation along the line created by batter
boards.
• Excavate remainder of soil inside the perimeter.
• Don’t excavate inside soil if slab is on the grade.
• If foundation is deep , taper edges are used to prevent
the collapse.
• If soil is unstable or very deep , Use shoring method.

 Timbering and strutting is a method of
giving the temporary supports to the sides
of trench , when the depth of trench is
large or when the sub-soil is loose.
 Timbering is also called as Shoring . It
consists of timber boards and struts to give
temporary support to the side of the
trench.
7.Timbering and Strutting

 Following are the methods of timbering
and strutting :-
 1. Box sheeting
 2. Stay bracing
 3. Runner system
 4. Vertical sheeting
 5. Sheet piling

 If depth of the excavation is upto 4m and soil
is loose , the box sheeting method is used.
 It is just like box consisting of vertical sheets
held in position by horizontal row of wales
and made tighten by providing strut.
 If soil is very loose, that time horizontal sheets
are provided and supported by vertical wales
and made tighten on both sides by horizontal
strutting
 Braces are provided when the height is more.
1. Box Sheeting

 When the depth of excavation is upto 2m ,
then stay bracing method is adopted to
support the sides excavated in fairly firm soil.
 It consists of a vertical sheets or polling
boards opposite to each other against the two
walls of the trench and held these vertical
sheets in position by strutting
2. Stay Bracing

 This is used in extremely loose and soft ground
which need immediate support as excavation
process.
 This system is similar to vertical sheeting of box
system, except in place of vertical sheeting, runner,
made of long thick wooden sheet or plank s with iron
shoe at the end are provided.
 Wales and Struts are provided as usual.
 These runner are driven about 30 cm in advance of
progress of the work, by hammering.
3. Runner system

1.It is similar to the box system , only
difference is that in this case excavation is
progressed in stages by providing an
offset at the end of each stage.
2. This method is best suited for deep
trenches in soft ground.
4. Vertical Sheeting

 This method is adopted as follows :-
 When soil to be excavated is soft or loose.
 The Depth of excavation is large.
 When the Width of the trench is large.
 When there is sub soil water . Sheet piles are used to
resist the lateral earth pressure.
 These are driven in ground by mechanical means .
 They can also be used for excavating for very large
depth.
5. Sheet Piling

Vertical sheeting and vertical Runner System

 If the plinth depth do not exceed 450mm above the
ground level and if the exposed ground is back
cotton soil , then remove the black cotton soil so as to
avoid the uneven settlement of ground flooring.
 In process of plinth filling watering and compaction
should be carried out till the required level is reached
so as to from a thoroughly compacted base.
 The material for plinth filling consist of hard murum
and broken rubbles.
 On the compacted surface or consolidated plinth
filling , a concrete bed of thickness of 80 mm is done
for laying the tile work further.
Material for Plinth Filling

 Lead and lift are the terms related to excavation
of earth / soil.
 LEAD : 1.The horizontal distance up to which a
contractor will haul the material excavated and
it is included in the rates of excavation is called
as Lead. 2.The lead is 30m and called as
Standard or normal lead.
 Lift : 1. The vertical distance up to which a
contractor will haul the material excavated and
it is included in the rates of excavation is called
as Lift. 2. The lift is 1.5m and called as Normal lift.
Lead & Lift in Excavation

 SUB-STRUCTURE OR FOUNDATION is
the lower most portion of the building,
usually located below the ground level,
which transmits the load of super
structure to the supporting soil. A
foundation is therefore that part of the
structure which is in direct contact with
the ground to which the load are
transmitted.
Foundation

Purpose of foundation
 To distribute the total load coming on the structure on a
larger area.
 To Reduce the load Intensity
 To support the structures.
 To give enough stability to the structures against
various disturbing forces, such as wind and rain.
 To prepare a level surface for concreting and masonry
work.
 For the Lateral Stability.

 1. Open Foundation.
 2. Shallow Foundation :-
 Types of shallow foundation :-
 1] Stepped Foundation
 a)Wall footing , b) Reinforced concrete footing
c)Column footing :- 1.Isolated , 2. Combined
,3.Raft foundation.
 3.Deep foundation :-1. Pile foundation ,2.Well
foundation, 3.Coffer dams.
Types of foundation

 This is simply a layer of foundation
concrete provided at the base of a
column, pedestal or wall.
 This type of foundation is provided when
hard stratum is available at very shallow
depth or the work is unimportant e.g.
Compound wall , pillars for barbed wire
fencing etc.
1.Open Foundation

 When the foundation is placed immediately below
the lowermost part of structure it is called as
SHALLOW foundation.
 It can also be defined as, when the depth of
foundation is less than or less than equal to the
width;, the foundation is called as SHALLOW
FOUNDATION.
 PURPOSE: The purpose of shallow foundation is to
distribute the structural load over considerable
horizontal area .
 LIMITATION:-
1. The load carrying is considerably less as compared
with deep foundation.
2. Can not be used under marshy land, made up of
ground water or water logged area.
2.Shallow Foundation

 Stepped foundations = In this case , the base of
the foundation is made wider to distribute the
load on wider area .
 A) Wall footing : 1.It can be achieved by
constructing several courses of bricks widening
the base, the lowest course is usually twice the
breadth of the wall. 2. The sectional elevation of
brick wall footing and stone wall footing is
shown.
Stepped Foundations

B)Reinforced Concrete Footing :- When the bearing capacity of the
soil on which the wall footing is to rest is very low and when the
walls are subjected to heavy loading , under such circumstances
the reinforced concrete footing is used

 C) Column footing :-
1.Isolated : It is provided under a
column or other similar member for
the distribution of concentrated load
in the form of uniformly distributed
load on the soil below.The shape may
be square, rectangular or circular in
plan . It may be constructed either in
brick masonry , stone masonry or
R.C.C. steel grillage etc.

 2. Combined : Combined column footing is provided as a
common footing for two or more columns.
 This type of column helps in reducing the depth of
foundation and unequal settlement can be avoided.
 In this type of footing ,a common P.C.C bed is provided on
which two or more column rest.
 Combined footing is also provided when column are very
near to each other and isolated column will over lap each
other.
 Shear force calculation is important in combined footing

 C) Raft Foundation :-
 When bearing capacity of the
supporting soil is very low and heavy
concentrated structural loads are to be
supported in case of marshy land or
made of soft clay.
 It proves to be economical under water
logged area.
 Raft is acting as a floor consisting of
thick reinforcement concrete slab
covering the entire area of the bottom
of the structure.

When the depth of foundation is
more than its width the foundation is
called as DEEP foundation.
It can also be defined as , if the depth
of foundation is more than 2.00 m, it
called as deep foundation.
3.Deep foundation

1) Piles
 A).Depending upon the function :-
 1. Bearing piles
 2.Friction piles
 3.Sheet piles
 4.Anchor piles
 5.Batter piles
 6.Fender piles
 7.Compaction piles
Types of Deep foundation

1. BEARING PILES: These are driven into the ground until a
hard stratum, directly supported on hard base and pile act as
pillar to transmit the load.
 2. Friction pile : When the soil is soft to a considerable
depth the pile which is required to be driven is called
FRICTION PILE.
 The load carried by a pile is borne by the friction
developed between the side of the pile and the
surrounding is called as SKIN FRICTION.
 3.Sheet Pile :They are used to retain soil which is liable to
escape laterally when subjected to pressure or to
enclose the area for some foundation and to protect
the area from the flowing water.

 ANCHOR PILE: when piles are used to provide
anchorage against horizontal pull they are called as
ANCHOR PILE.
 BATTER PILES: When the piles are driven at an
inclination to resist large horizontal or inclined forces
then the piles are called ac BATTER PILES.
 FENDER PILES: when the water front structure or
concrete check is required to protect from impact or
abrasion caused by the ship then the fender pile is used
at the front.
 COMPACTION PILE: when the piles are driven to
increase the bearing capacity of the granular soil they
are called as compaction pile

B) Depending upon the material :-
1.Timber piles
2.Concrete piles
3.steel piles

 Economical for supporting light structures
 Timber from sal, deodar , babul , khair, is used .
 the pile cap of iron ring of about 25 mm is provided to
prevent the pile head from brooming .
 The lower end of the pile is provided with a cast iron
conical shoe.
 The load transfer mechanism is by skin friction hence
there should a minimum distance of about 60 cm
center to center
1.Timber pile

ADVANTAGES:
1. Economical.
2. Can be driven rapidly hence saves time.
3. Due to its elasticity it is recommended in region
where the piles are likely to be subjected to lateral
forces
4. Heavy machinery and skill supervision is not required.
 DISADVANTAGES:
1. Should be cut of above ground water table to
prevent decaying.
2. Timber cannot be driven in filled up ground.
3. Likely to decay by salt water or insect.
4. Restricted length .

 Concrete piles are classified as :-
 1. Pre-cast piles.
 2.Cast in – situ pile.
 3. Pre-stressed concrete pile
2. Concrete Pile

 1.PRE-CAST CONCRETE PILE:
 Precast piles are those which are manufactured in the
factory or at a place away from the construction site and
then driven to the ground at the place required.
 Pre cast pile may be square ,octagonal, or round in cross
section or may be tapering or parallel in longitudinally.
The size of these piles varies from 30cm to 50cm in cross
sectional dimension and up to 30m in length .
 Precast pile are useful in carrying fairly heavy loads
through soft material to firm strata .

 2. Cast in – Situ pile :- The piles which are cast in
position on site inside the ground , it may be
reinforced when pile act as column and when
subjected to lateral force.
 Normally the cast in situ piles are constructed with
an enlarged bulb and corrugated stem.
 A steel tube having internal diameter equal to the
diameter of the pile and 20mm thickness is driven
into the ground
 when the has been driven up to the desired depth
a charge of concrete is poured and the tube is
gradually withdrawn and thus alternate pouring and
withdrawing of tube , the pile is constructed to the
full length.
 In case the pile is to be reinforced , the
reinforcement cage is lowered in the steel tube
before pouring the concrete.

 3. Pre – Stressed concrete piles :Pre stressed piles are
stronger than the normal reinforced pile . Therefore ,
because of the reduction in cross sectional, they are
lighter and more easily handled.

 It has greater ability to withstand extremely hard driving.
 It more durable in sea water because of the crack.
 It has great column
 It has lesser handling cost because of light weight.
 It has much lager moment of inertia then the
conventional pile of the same dimension .
Advantages of concrete piles :-

 These piles cannot be driven rapidly.
 It requires skilled technical supervision heavy driving
machinery.
 To withstand handling stresses, reinforcement is essential.
Disadvantages of Concrete piles

 A steel pile may be a rolled section , a fabricated
shape or a piece of sheet piles
 Metal piles have been used in from of cast iron pipes
or solid wrought iron shaft .
 These piles are excepted to penetrate through hard
rock.
 Types of steel pile.
 H-PILES, PIPIE-PILE, SCREW PILE, DISC PILE.
 The pipes is normally filled with concrete and the
diameter varies from 25cm to 125 cm and the depth is
30m or more.
3.Steel Pile

 Caisson
 The caisson is a structure used for the purpose of
placing foundation in correct position under water.
 It is Permanent in nature.
 Used to pump out water in under water concreting
work.
 Types of caisson:
1. Box caisson
2. Open caisson
3. Pneumatic caisson
2. Well foundation
Caisson is a foundation which comes under the type of well foundation.

 Open caisson is a box of timber, metal, reinforced
concrete or masonry
 Open at both end (top and bottom)
 Whenever consideration for scour or bearing
capacity required foundation being taken to depth
of more than 5 to 7m
 Costly and uneconomical (heavy timbering
required)
 Due to greater earthwork, the progress of work is
very slow
1. Open Caisson :-

 A box caisson open at top and close at
bottom.
 It is Made up of timber, concrete or
steel.
 Built on land and floated to pier site
where it is sunk in position
 Used where bearing stratum is available
and loads are not heavy
2.Box Caisson :-

 DEFINITION: It is a temporary structure constructed in a
river or lake or any other water bearing surface for
excluding water from a given site to enable the water
building operation to be performed under dry conditions.
walls are water tight
 Temporary structure
 Built within or in pairs across a body of water
 Allows the enclosed space to be pumped out ,creating a
dry work environment.
3.Cofferdams

 1. Earth filled cofferdams .
 2. Rock filled cofferdams .
 3. Sheet pile cofferdams :-
a) Single wall cofferdams,
b) Double wall cofferdams.
Types of cofferdams

 Earthen cofferdam consist of earthen
embankment built around the area to be
enclosed.
 It can be constructed if the water depth is more
than 1.4 to1.8m and the velocity of the flowing
water is very low.
 Top width of the dam should not be less than
1.00m and the side slope may vary from 1:1.5 to
1:1.2. the inner portion called as embankment
consist of clay and sand or clay or gravel
1. Earth filled Cofferdams

 In case of a rock filled cofferdam , the
depth of water to be retained is of order
of 1.8 to 3.00m .stone or rubble is used
for embankment
2.Rock Filled cofferdams

 1.Single wall cofferdams
 If the area to be enclosed is very small and the depth of
water is about 4.5 to 6.0m then timber piles known as
guide piles are first driven deep into the firm ground
below the river bed, the distance between the piles
may vary from 1.7 to 3.5m depending upon the velocity
of the flow.
 Then Wales are bolted to guide piles at suitable
distance
 Then sheet or wooden sheet piles are driven into the
river bed along the Wales and secured by bolts to the
Wales.
 Thus , the area can be enclosed and the water is
pumped out to start the construction in dry condition.
3. Sheet pile cofferdam

 2. Double walled cofferdam
 If the area to be enclosed is very large and if
the depth of water is large then double wall
cofferdam are used instead of single wall
cofferdam.
 The construction is same , only in case of a
single wall a pair of wall with a gap between
is provided.
 This is suitable up to a depth of 10 to 12.0m
 To prevent leakage the sheet piles are firmly
driven into the ground.

For Water Logged Foundation It Is Essential To
Carry Out Dewatering Of Soil Before Carrying
Construction Activity.
 Methods Of Dewatering
1. Sumps and Ditches
2. Well Point System
3. Deep well System
4. Vaccum Method
Dewatering of foundation by
Pumping Method

 This is the simplest form of dewatering
used in shallow excavation in coarse
grained soils.
 Sallow low pits ,calls as sumps are dug
along the periphery of the area drainage
ditches.
 The water from the slope or sides flows
under gravity and is collected in sumps
from which it is pumped out.
1. Sumps and Ditches

 A well point system is a perforated pipe
of 5 to 8 cm in diameter and one metre
long covered by cylindrical wire gauge
screen known as STRAINER.
 These pipes are joined to a horizontal
pipes known as HEADER pipe.
2. Well point Systems

3. Deep well system :-This system is suited
when the depth of excavation is more than
16m.

 In this method a hole of 30cm diameter is
bored around the well point and the riser
pipe.
 It then sealed using bentonite ,soil-
cement or clay. The header pipe is then
connected to vacuum pump for removal
of water.
4. Vacuum Method

These foundations are provided
when the bearing capacity of the soil
is low and hard strata is not available
on the given site.
The most commonly constructed
special foundation are 1. Mat or raft
foundations , 2.Under-reamed piles .
Special Foundation

 When bearing capacity of the supporting soil is
very low and heavy concentrated structural
loads are to be supported in case of marshy
land or made of soft clay.
 It proves to be economical under water logged
area.
 Raft is acting as a floor consisting of thick
reinforcement concrete slab covering the
entire area of the bottom of the structure
1. Mat or Raft Foundations

 The under reamed piles are the best solution for foundation
black cotton soil.
 Bored cast in situ concrete piles having bulb shaped enlarge
base
 Such structure is anchored to the ground at depth where
ground movement due to change in moisture content
negligible
 Bearing capacity increased by increasing the number of bulbs
 Hand auger or machine auger used for boring with extension
rod
 After boring upto certain depth the base of hole is enlarged in
the form of bulb
2. Under- Reamed Piles

 Bearing capacity of soil is the is the intensity of the load
per unit area of the foundation . If the bearing capacity
is not sufficient , then the use of special type of
foundation becomes imperative.
 Bearing capacity of the sub soil or foundation soil is
measured by plate load type.
 In this method, the bearing plate is square of minimum
size 30cm square, and maximum size 75 sq.cm .
 The thickness of the plate should not be less 25mm.
BEARING CAPACITY OF THE
FOUNDATION.

1. Break direct contact between soil and masonry.
2. Construction should be taken in dry season.
3. Masonry should be start at least 15 cm below the ground level.
4. Mostly raft foundation should be provided.
5. Under reamed pile foundation is ideal foundation.
6. To take the foundation at such depths where cracks cease to
extend.
7.To provide reinforced concrete ties or band all around the main
wall of the building.
8.Under –reamed piles are ideal for foundation in black cotton
soil.
Precaution to be taken while
constructing the foundation black
cotton soil:

Construction of substructure

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Construction of substructure

Similar to Construction of substructure (20)

Recently uploaded

Recently uploaded (20)

Construction of substructure