SCAFFOLDING SHORING & UNDERPINNING

SCAFFOLDING/SHORING
& UNDERPINNING
VISHNU VIJAYAN
HOD-Department Of Civil Engineering
Baselios Mathews II College Of Engineering
Sasthamcotta, Kollam,Kerala,INDIA
3/25/2020 1VISHNU VIJAYAN,BMCE

SCAFFOLDING
• When the height above floor level exceeds about 1.5 m
a temporary structure ,usually of timber , is erected close
to the work to provide a safe working platform for the
workers and to provide a limited space for plant and
building materials. The temporary frame work is known
as scaffolding or simply a scaffold.
• It is useful in construction , demolition ,maintenance or
repair works.

COMPONENT PARTS OF A SCAFFOLDING
An ordinary scaffolding consists of the following parts
1.STANDARDS:- These are
vertical members of the
frame work and they
are either supported
on the ground or drums
or embedded into the
ground.

2. LEDGERS:- These are the
horizontal members
running parallel to the wall.
3. PUTLOGS:- These are the
transverse pieces which are
placed on the ledgers and
which are supported on
the wall at one end.
• They are at right angles
to the wall.

4. TRANSOMS:- These are
putlogs, but their both
ends are supported on the
ledgers.
5. BRACES:- These are the
diagonal or cross pieces
fixed on the standards.
6. BRIDLE:- This is a piece
which is used to bridge an
opening in the wall and it
supports one end of the
putlog at the opening.

7. GUARD RAIL:- This is a
rail provided like a
ledger at the working
level.
8. TOE BOARD:- This is a
board placed parallel
to the ledgers and
supported between
the put logs. It is
provided to work as a
protective measure on
the working platform.
9. RAKER:- This is an
inclined support.

TYPES OF SCAFFOLDING
1. Single scaffolding or Brick layer’s scaffolding.
2. Double scaffolding or Mason’s scaffolding.
3. Cantilever or needle scaffolding.
4. Suspended scaffolding.
5. Trestle scaffolding.
6. Steel scaffolding.
7. Patented scaffolding.

1.SINGLE SCAFFOLDING
• It consists of a single
raw of standards placed
at a distance of about
1.20m from the wall.
• The distance b/w
successive standards is
about 2 to 2.5 m.
• The ledgers are then
fixed to the standards at
a vertical distance of 1.2
to 1.8m.

• The putlog with one
end on the ledger and
other end on the wall
placed at a horizontal
distance of about 1.2 to
1.8m.
• The braces , guard rail
and toe board are
provided.

2.DOUBLE SCAFFOLDING
• This is stronger than
single scaffolding.
• Mainly used in the
construction of stone
work.
• Two rows of standards
are provided.
• The distance b/w the
face of wall and the first
row of standards is
about 20 to 30 cm.3/25/2020 11VISHNU VIJAYAN,BMCE

• The distance b/w the
two rows is about 1 m.
• The rakers and cross
braces may be provided
to make the scaffolding
more strong.

3.CANTILEVER SCAFFOLDING
• This type scaffolding are useful under
1. The proper hard ground are not available for the
standards to rest.
2. It is required to keep the ground, near wall, free for
traffic, etc.
3. Construction of upper part of the wall is to be
carried out.

• In this type the general
frame work may be single
or double scaffolding
type.
• The standards are
supported by a series of
needles or ties which are
taken out at floor levels
or through openings or
through holes kept in the
masonry.

• THESE ARE OF TWO TYPES
a. PUTLOG TYPE
b. INDEPENDENT TYPE

a. PUTLOG SCAFOLDING
• The needles are
supported at floor
levels .
• Strutted through
projections such as sills
,cornices, string courses
etc.
• The inner edge of the
needle project s
sufficiently inside and is
well strutted b/w the
floors.

b. INDEPENDENT TYPE
• Here the needles are
passing through the
openings and are
strutted on the floors
through the openings.
• The suitable timber
blocks should be inter
posed at the ends of
struts on the floor level.

4.SUSPENDED SCAFFOLDING
• This is a very light type of
scaffolding .
• Only used for maintenance
works such as painting,
pointing, white washing,
etc.
• The working plat form is
suspended from the roof by
means of ropes, wires or
chains etc.
• The platform can be raised
or lowered.3/25/2020 18VISHNU VIJAYAN,BMCE

• This type of scaffolding
does not create any
obstruction on the
ground.

5. TRESTLE SCAFFOLDING
• The working plat form is
supported on movable
contrivances such as
ladders, tripods etc.
mounted on wheels.
• This type of scaffolding
is useful for minor
repairs or painting
works inside the room.
• It used up to a height of
5m3/25/2020 20VISHNU VIJAYAN,BMCE

6.STEEL SCAFFOLDING
• Instead of timber , steel
tubes can be effectively
used for the scaffolding
work.
• The diameter of tube is 40
to 50 mm & thickness is
about 5mm.
• These are available in
standard lengths.

• This scaffolding can be
used upto any height.
• It is strong and more
durable
• Easily erected and
dismantled.
• Also it possesses high
scrap value.
• It requires skilled labour
and periodical painting.

7. PATENTED SCAFFOLDING
• Now a days , various
patented scaffoldings
are made of steel , with
special type of coupling
and frames are
available.
• Usually the working plat
form is supported on a
bracket which can be
adjusted to any suitable
height.

SHORING
• It is the construction of a temporary structure
to support temporarily an unsafe structure.
• It is essential for structures which have
become unsafe due to unequal settlement of
foundation(cause cracks in walls) or due to
removal of adjacent building or poor
workmanship( wall shows bulging out) or due
to any other reason.

Types of Shoring
1. Raking or Inclined shoring
2. Flying or Horizontal shoring
3. Dead or Vertical shoring

1.Raking or Inclined shoring
• The inclined supports are
given to the external
walls from the ground.
• It consists of wall plate,
rakers, bracings, and sole
plate
• Wall plate is placed
against wall and secured
by means of needles
which penetrate into wall
about 150 mm.

• The wall plate distribute
the pressure evenly.
• The rakers are
interconnected by
struts or braces or
lacings.
• The feet of rakers are
stiffened by braces or
hoop iron and
connected to sole plate
by iron dogs.

The points should be noted
1. The centre line of raker and of the wall meet
at the floor level.
2. The rakers prevent the outward movement of
wall and partly deflect the roof and floor loads.
3. A large factor of safety should be adopted in
the design of inclined shore to meet actual loads
4. The rakers should be preferably inclined at 45
Degree. But in actual practice it may vary from
45 to 75 degree.

5. The sole plate is usually embedded into the
ground and legs of rakers rest on the sole plate .
The sole plate should be long enough to
accommodate rakers and cleat.
6. The length of top raker can be reduced by
providing a rider raker
7. It is not desirable to do wedging as it would
damage the building which is already in unsafe
condition.
8. The necessary permission of the concerned
owner of the adjacent property should be
obtained.

2. Flying or Horizontal shoring
• In this the horizontal supports are given
to parallel walls which have become
unsafe due to the removal or collapse of
the intermediate building.
• They are of two types
i. Single flying shore
ii. Double flying shore

i. Single flying shore
• It consists of wall plate ,
needles, cleats, struts,
straining pieces and
folding wedges.

ii. Double flying shore
• When the distance
between walls is more
double flying shore is
provided.
• It is used when span
exceeds 9m and upto
12m.

Points kept in mind
1. The centre lines of flying shore and struts and
those of the walls should meet at floor levels
of two building. If floor levels are different
the frame works should be suitably designed
and made unsymmetrical.
2. A large factor of safety should be adopted in
design.
3. The struts inclined at 45degree. Never
exceed 60 degree.

4. Single flying shore used upto 9m. After that
double flying shore provided upto 12m.
5. Only one set of shoring strengthens the walls.
6.The building operations in the ground are not
obstructed by this type of shore.
7. The flying shores are inserted when old
building is removed after new building
constructed to sufficient height.
8. When one building is higher than other this
shores may be provided.

3. Dead or Vertical shoring
• In this arrangement the
horizontal members
called needles are
supported by vertical
members called Dead
shores.
• The needles are driven
at right angles to the
wall through the holes
made in the wall.

The dead shores are used under following
circumstances
1. The lower part of the wall has become
defective.
2. The foundations are to be deepened.
3. The lower part of the wall is to be rebuilt.
4. The large openings are made in the existing
wall.

The points kept in mind
1. It is possible to calculate stresses in various
members of a dead shore.
2. The needles are placed at a distance of about
1.50 m to 2m and they are suitably braced.
3. The floors are suitably support inside.
4. The openings above or near a dead shore are
suitably strutted.
5. A raking shore may be provided as an
additional safety in case of weak walls.

6. The shores should be removed at least after
7 days of construction of new work to obtain
the required strength.

UNDERPINNING
• The placing of new foundation below an
existing foundation or process of
strengthening the existing foundation is
known as underpinning.

Situations demanding underpinning
1. A building with deep foundation is to be
constructed adjoining to an existing building.
2. The settlement of existing foundation has
taken place, resulting serious cracks in wall.
3. The basement is provided to an existing
building.
4. The existing foundation are to be deepened
so as to rest them on a soil of higher bearing
power.

Methods of Underpinning
1. Pit Method.
2. Pile Method.
3. Miscellaneous Methods.

1. Pit Method
• The existing wall is
divided into suitable
sections of width about
1.2m to 1.5m.
• The holes are then
made in the existing
wall.
• The needles with
bearing plates are then
inserted through these
holes.3/25/2020 42VISHNU VIJAYAN,BMCE

• And supported on jacks.
• The pit is excavated and
the existing foundation
is taken upto the
required level.
• Following precautions
are necessary.

1. One section should be excavated at a time.
2. The alternate sections should be taken in
succession.
3. If the length of wall is more , The underpinning
starts from the middle and then extended in both
direction.
4. The proper timbering should be provided for the trench.
5. It is desirable to carry out the new foundation work in
concrete.
6. If space to support needles on outside is not available,
the cantilever needles ,projecting inside and provided
with fulcrums and loadings, may be provided.

2.Pile Method
• The piles are driven
along both sides of
the existing walls
and then needles in
the form of pile caps
are provided through
the existing walls .
• Thus existing wall is
relieved of the loads
coming on it.3/25/2020 45VISHNU VIJAYAN,BMCE

• This method is useful in
clayey soils and for
water logged areas and
for walls carrying heavy
loads.
• For underpinning very
light structure, the piles
are driven along the
structure and cantilever
needles are provided to
carry structure.

3.Miscellaneous methods
i. Cement grouting
ii. Chemical consolidation
iii. Freezing
iv. Vibrofloatation

i. Cement grouting
• This method is used to restore slab or
pavement which has settled.
• The holes are drilled in the slab and the
cement grout is forced under pressure
through these holes.
• The pressure is maintained until the cement
grout has set.

ii. Chemical Consolidation
• The soil under the existing footing is
consolidated by using chemicals.
• For this perforated pipes are driven in an
inclined direction, then sodium silicate
solution injected through pipes, then pipes
are being withdrawn. At the time of
withdrawn calcium chloride injected through
pipes.
• Chemical reaction takes place b/w 2 chemicals
and soil get consolidated.3/25/2020 49VISHNU VIJAYAN,BMCE

CHEMICAL CONSOLIDATION

iii. Freezing method
• In this freezing pipes
are driven below the
existing footing and the
soil is frozen.

iv. vibrofloculation
• This is carried out by
vibrating the sand and
there by increasing the
density which
ultimately results in
increasing bearing
capacity of soil.
• This method is useful
for granular or sandy
soil before under
pinning starts.

Thank you

SCAFFOLDING SHORING & UNDERPINNING

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