AS PER GTU SYLLABUS FOR THE SUBJECT BCT, module 5 special work part 1, another part upload soon, use full for GTU exam or mid sem exam,

1. S.S.A.S.I.T
GTU
1

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Timbering in trenches
Control of Ground
water in excavation
types of
scaffoldings
shoring, underpinningCoffer Dams
Diaphragm
Walls
Demolition of
structures

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 TIMBERING IN TRENCHES
 A trench is a type of excavation or depression in the ground that is
generally deeper than it is wide (as opposed to a wider gully, or ditch),
and narrow compared with its length (as opposed to a simple hole).
 When the depth of trench is large, or when the sub-soil is loose, the
sides of the trench may cave in.
 The problem can be solved by adopting a suitable method of
timbering. Timbering of trenches, sometimes also known as shoring
consists of providing timber planks or boards and struts to give
temporary support to the sides of the trench.

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Timbering of deep
trenches can be done with
the help of the following
methods:
1. Stay bracing.
2. Box sheeting
3. Vertical sheeting
4. Runner system
5. Sheet piling.

9. 1. Stay bracing. This method is used for supporting the sides or a
bench excavated in fairly firm soil, when the depth of excavation does
not exceed about 2 metres. The method consists of placing vertical
sheets (called sheathing) or polling boards opposite each other against
the two walls of the trench and holding them in position by one or two
rows of struts.
THE POLLING BOARDS
width 200 mm
thickness of 44 to 50 mm.
STRUTS
1OO x 100 mm for trench up to 2 m width
200 x 200 mm for trench up to 4 m width.
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2. Box sheeting. This method is adopted in loose soils, when the depth
of excavation does not exceed 4 metres.
Its consisting of vertical sheets placed very near to each other (some
times touching each other) and keeping them in position by longitudinal
rows (usually two) of Wales. Struts are then provided across the Wales.
Another system of box sheeting, shown in Fig. 2.32(b), is adopted for
very loose soils. In this system, the sheeting is provided longitudinally,
and they are supported by vertical Wales and horizontal struts.
If the height is more, braces are also provided along with struts.

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Fig. 2.32 (a) for loose soil

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Fig. 2.32 (b) very loose soil

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Fig. 2 (b) very loose soil
Fig. 2 (a) loose soil

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3. Vertical sheeting.
 This system is adopted for Deep trenches (up to 10 m depth) in soft
ground.
 The method is similar to the box sheeting except that the excavation is
carried out in stages and at the end of each stage, an offset is
provided, so that the width of the trench goes on decreasing as the
depth increases.
 Each stage is limited to about 3 m in height and the offset may vary
from 25 to 50 cm per stage.
 For each stage, separate vertical sheeting, supported by horizontal
wailings and struts are provided.

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stage height 3m
offset

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4. Sheet piling
This method is adopted when
(i) soil to be excavated is soft or loose
(ii) depth of excavation is large
(iii) width of trench is also large and
(iv) there is sub-soil water.
Sheet piles are designed to resist lateral earth pressure. These are driven
in the ground by mechanical means (pile driving equipment). They can be
used for excavating to a very large depth.

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 Shoring is the type of construction of a temporary structure to
support temporarily an unsafe structure.
 These support walls, supporting a building, structure, or trench with
shores (props) when in danger of collapse or during repairs or
alterations.
 Shoring comes from shore (props)
 a timber or metal prop use for shoring
 Shoring may be vertical, angled, or horizontal.
SHORING

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THEY CAN BE USED UNDER…..
 When walls bulge out
 When walls crack due to unequal settlement of foundation and
repairs are to be carried out to the cracked wall.
 When an adjacent structure needs pulling down.
 When openings are to be newly made or enlarged in a wall.
 Shoring is used to support the beams and floors in a building while a
column or wall is removed.
 In this situation vertical supports are used as a temporary
replacement for the building columns or walls.

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Raking Shores consist of one or more timbers sloping between the face of the
structure to be supported and the ground.
The most effective support is given if the raker meets the wall at an angle of 60 to 70
degrees.
A wall-plate is typically used to increase the area of support.
Its consists of the following components:
•Rakers or inclined member
•Wall plate
•Needles
•Cleats
•Bracing
•Sole plate
Raking Shore

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The following points are to be kept in view for the use of the raking shores:
Rakers are to be inclined in the ground at 45⁰.
However the angle may be between 45 ⁰ and 75 ⁰.
Rakers should be properly braced at intervals.
The size of the rakers is to be decided on the basis of anticipated thrust from the
wall.
The sole plate should be properly embedded into the ground on an inclination and
should be of proper section and size.
Edges on raker should not be used on sole plates since they are likely to give way
under vibrations that are likely to occur.

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 It is also known as horizontal shores
 It is a system of providing temporary supports to the party walls of the two
buildings where the intermediate building is to be pulled down and rebuilt.
 All types of arrangements of supporting the unsafe structure in which the shores do
not reach the ground come under this category.
 In this type, horizontal supports are provided for supporting temporarily the
parallel walls of the two adjacent buildings, which may tend to collapse or
damage when one of the intermediate buildings has to be pulled down and
rebuilt.
 The maximum distance of about 10 meter between the parallel walls can be
supported by single flying shore. For a distance more than 10 m, a double flying
shore, having a trussed form-work is employed
FLYING SHORES

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This is the system of shoring which is used to render vertical support to
walls and roofs, floors, etc when the lower part of a wall has been
removed for the purpose of providing an opening in the wall or to
rebuild a defective load bearing wall in a structure.
The dead shore consists of an arrangement of beams and posts which
are required to support the weight of the structure above and
transfer same to the ground on firm foundation below.
DEAD SHORES

42.  When opening in the wall are to be made, holes are
cut in the wall at such a height as to allow sufficient
space for insertion of the beam or girder that will
be provided permanently to carry the weight of the
structure above.
 Distance at which the holes are cut depends upon
the type of masonry and it varies from 1.2m to
1.8m centre.
 Beams called needles are placed in the holes and are
supported by vertical props called dead shores at
their ends on either side of the wall.
 The needles may be of timber or steel and are of
sufficient section to carry the load above.
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shoring

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shoring

47. SHORING
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48. SHORING
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49. SHORING
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50. SHORING
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51. SHORING
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UNDERPINNING
The process of providing a new foundation below an existing
foundation of an existing foundation, without dangering the stability
of an existing structure.
The method of underpinning help to strengthen the foundation of an
existing building or any other infrastructure. These involve
installation of permanent or temporary support to an already held
foundation so that additional depth and bearing capacity is
achieved.

53. CONDITION OF UNDERPINNING
 The original foundation is simply not strong or stable enough.
 The usage of the structure has changed.
 The properties of the soil supporting the foundation may have changed (possibly
through subsidence) or were mischaracterized during design.
 To increase the depth or load capacity of existing foundations to support the addition
of another storey to the building (above or below grade).
 Earthquake, flood, drought or other natural causes have caused the structure to
move, thereby requiring stabilization of foundation soils.
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1. Mass Concrete Underpinning Method (Pit Method)
Mass concrete underpinning method is the traditional method of
underpinning, as it has been followed by centuries. The method
involves extending the old foundation till it reaches a stable stratum.
The soil below the existing foundation is excavated in a controlled
manner through stages or pins. When strata suitable is reached, the
excavation is filled with concrete and kept for curing, before next
excavation starts.
in order to transfer the load from old foundation to new one, a new
pin is provided by means of placing dry sand-cement pack. This is a
low-cost method suitable for the shallow foundation.
Stages divided into sections of 1.2 to 1.5 m lengths

55. DIFFERENT METHODS OF UNDERPINNING
UNDERPINNING CAN BE MADE IN VARIOUS WAYS, BUT TWO OF THEM ARE MOSTLY USED
*PIT METHOD
*PILE METHOD
Pit method Pile Method
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By pit

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If an interior strong column exists, or if the
foundation is to be extended only to one side,
cantilever needle beams may be used in place of
central needle beam.
A jack is placed between the column and wall.

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Underpinning By Cantilever Needle Beam Method
Figure represents the arrangement of cantilever pit method of
underpinning, which is an extension of pit method.
If the foundation has to be extended only to one side and the plan
possess a stronger interior column, this method can be used for
underpinning.
Advantages of Cantilever Needle Beam Method:
•Faster than traditional method
•One side access only
•High load carrying capability
Disadvantages:
•Digging found uneconomical when existing foundation is deep

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Pile Method
 In this method, piles are driven on adjacent sides of the wall that
supports the weak foundation.
 A needle or pin penetrates through the wall that is in turn
connected to the piles as shown in figure.
 These needles behave like pile caps.
 Use where Settlement in soil due to water clogging or clayey
nature can be treated by this method.

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underpinning

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underpinning

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66. SCAFFOLDING
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 Scaffolding is a temporary frame or structure used to support people and material
in the construction or repair of buildings and other large structures.
 It is used when height of wall or column or other structural member of a
building exceeds about 1.5m.
 Scaffolding is a temporary structure to support the original structure as well as
workmen used it as a platform to carry on the construction works.
 Types of scaffolding varies with the type of construction work.
 Scaffolding is made up of timber or steel.
 It should be stable and strong to support workmen and other construction
material placed on it.

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COMPONENT
Standards
Ledgers
Braces
Putlogs
TransomsBridle
Boarding
Guard rail
Toe
board

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Standards:- These are vertical members of the frame work, supporting on
the ground or embedded into the ground.
Ledgers:- these are the horizontal members, running parallel to the wall.
Braces:- These are diagonal members fixed on standards.
Putlogs:- These are the transverse members, placed at right angles to the
wall with one end supported on ledgers and other end on the wall.
Boarding:- These are horizontal platform to support workmen & material;
these are supported on putlogs.
Guard Rail:- This is a rail, provided like a ledger, at the working level.

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Single scaffolding or brick layers scaffolding
Double scaffolding or mason’s scaffolding
Cantilever or needle scaffolding
Suspended scaffolding
Trestle scaffolding
Steel scaffolding
Patented scaffolding

73. 1. SINGLE SCAFFOLDING OR BRICK
LAYERS SCAFFOLDING
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Single scaffolding is generally used for brick masonry and is also called
as brick layer’s scaffolding.
Single scaffolding consists of standards, ledgers, putlogs etc., which is
parallel to the wall at a distance of about 1.2 m.
Distance between the standards is about 2 to 2.5 m.
Ledgers connect the standards at vertical interval of 1.2 to 1.5 m.
Putlogs are taken out from the hole left in the wall to one end of the
ledgers.
Putlogs are placed at an interval of 1.2 to 1.5 m.
Single Scaffolding

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77. 2. DOUBLE SCAFFOLDING OR
MASON’S SCAFFOLDING
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Double Scaffolding
 Double Scaffolding is generally used for stone masonry so, it is also
called as mason’s scaffolding.
 In stone walls, it is hard to make holes in the wall to support
putlogs. So, two rows of scaffolding is constructed to make it
strong.
 The first row is 20 – 30 cm away from the wall and the other one
is 1m away from the first row.
 Then putlogs are placed which are supported by the both frames.
 To make it more strong rakers and cross braces are provided.
 This is also called as independent scaffolding.

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81. 3. CANTILEVER OR NEEDLE
SCAFFOLDING
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CANTILEVER SCAFFOLDING
This a type of scaffolding the standards are supported on series of
needles and these needles are taken out through holes in the wall.
This is called single frame type scaffolding.
In the other type needles are strutted inside the floors through the
openings and this is called independent or double frame type
scaffolding.
Care should be taken while construction of cantilever scaffolding.
Generally cantilever scaffoldings are used under conditions such as
•When the ground does not having the capacity to support standards
•When the Ground near the wall is Need to be free from traffic.

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85.  Light weight scaffolding used for repair works like painting, pointing
etc.
 The working platform is suspended from roofs by means of wire
ropes or chains.
 Platform can be raised or lowered at any desired level.
4.SUSPENDED SCAFFOLDING
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87. This is also used for repair works inside the room,
up to height of 5m.
The working platform is supported on the top of
movable contrivances like tripods, ladders may be
mounted on wheels.
In Trestle scaffolding, the working platform is
supported on movable tripods or ladders. This is
generally used for work inside the room, such as
paintings, repairs etc., up to a height of 5m.
5.TRESTLE SCAFFOLDING
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89. Wooden members are replaced by steel tubes and rope lashings are
replaced by steel couplets or fittings.
Such scaffolding can be erected and dismantled rapidly.
It has greater strength, greater durability and higher fire resistance.
Can be used for stone and brick masonry construction.
6.STEEL SCAFFOLDING
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Timbering in trenches
Control of Ground
water in excavation
types of
scaffoldings
shoring, underpinningCoffer Dams
Diaphragm
Walls
Demolition of
structures

92. 92