14-6.

SHORING

Definition: Sometimes the structures are to be temporarily supported. This 1s

achieved by what is known as the shoring. It is essential for structures which have become
unsafe due to unequal settlement of foundations or due to removal of the adjacent
building or due to any other reason. For safe structures, the shoring is required to
prevent movements when certain additions and alterations are being carried out.
as follows:
The circumstances under which the shoring is required can be summarised
 Art. 14-7]7 Scaffolding, Shoring and
Underpinning 301
adiacent structure is to be
(i
a k s developed due to unequal dismantled:
settlement of foundation
repaired, in a wall are to be
.dofective walls
(iii of a building are to be
necessary to the tioors or dismantled
and rebuilt and
roofs connected
that wall;
to support is
large
iv openings are required to be made in the main walls
walls of a building shoWing signs of of an existing building;
bad workmanship; bulging out or
leaning outwards due to

/1 Materials: The shoring can be carried out either

in timber
or in steel tubes
or in combination of timber and steel tubes. The
timber surfaces should be coated
th a preservative so as to
give Protection against wet rot.
(9) Duration: There is no limit for the duration of shoring and it ranges from
weeks to years.

Requirements:
(3) The loads
coming shoring vary widely in nature
on
and
Lance the requirements of each case of shoring should be studied separately and
designed accordingly.
(4) Approval: T'he shoring should be carried out as per prevailing rules and
regulations of the local authority and necessary approval should be obtained.

14-7. TYPES OF SHORING

Depending upon their supporting characteristics, the shores are classified into the
following three categories:
(1) Raking or inclined shores
2) Flying or horizontal shores
(3) Dead or vertical shores.
A brief description of each type of shores is given below.

shores (fig. 14-6): In this arrangement, the inclined supports

4 Raking or inclined shown in fig. 14-6.
given to the external walls from the ground as
and sole plate
rakingshore consists plate, needles, cleats, rakers, bracing
of wall wall and is secured by
in the figure. The wall plate is placed against the
Snown distance of about 150 mm. The
which penetrate into the wall for a
woll needles The needles, in turn, are secured by
cleats

Plate distributes the pressure evenly. braces or

interconnected by struts or
nailed to the wall plate. The rakers are
re similar braces and/or hoop
iron and they are
T h e feet of rakers are stiffened by should be noted:
of iron dogs. Following points
Led with the sole plate by means
should meet at the
floor level.
() The and of the wall
*"C
centre-line of the raker deflect the
and partly
(ii) the outward
movement of the wall
lakers prevent
roof and floor loads. inclined shores as

in the design of
ii A large factor of safety should be adopted
it is the actual loads. However, in
difficult to assess
with the ground.
at 45°
iv) The rakers should be referably
inclined
from 45° to 75.
The top
may vary
actual
en ice, the angle of
inclination

than 75°
with the horizontal.
be inclined steeper
o u l d not
 Building Construction Ch. 14
302
a rider raker as shoWn
of top raker can be reduced by providing
The length
( in fig. 14-6.
embedded in the ground and the legs of rakers reet

The sole plate is usually

(vi) The sole plate should be long enough
shown in fig. 14-6.
on the sole plate
as
on the outside.
In case of soft ground
rakers and a cleat
to accommodate all to distribute pressure on a
on a timber platform
the sole plate is placed
greater area.

Wall plate Fourth floor

Cleat

Needle Needle

Third floor

Cleat

Iron dog
Second floor

Rider raker First floor

Top ofraker
Fo ng wedges

Bracing

Cleat Plinth
G L
-Hoop iron
Sole plate

Raking shore
FIG. 14-66
(vii) It is not desirable to do wedging as it would damage the building which is
already in an unstable condition.
(vii) The necessary permission of the concerned owner of the adjacent property in
which the raking shores are to be erected should be obtained.

(2) Flying or horizontal shores (fig. 14-7 and fig. 14-8): In this arrangement, the
horizontal supports are given to parallel walls which have become unsafe due to the
removal or collapse of the intermediate building.
Art. 14-7] Scaffolding, Shoring and
Underpinning 303
inale flying shore
consists of wall
1ding wedges plate, needles, cleats, struts, straining
a n df o l d
as
shown in fig. 14-7.
The flying shore should have pieces
than
p-thirtieth
one-t
of the clear span and width not less than
not less
a
depth
one-fiftieth of its length.
Floor
Floor
Needle Cleat

Straining piece
Flying shore Strut
Floor Floor
Wall plate,
Folding wedges

Floor Floor

Single flying shore

FIG. 14-7
Following points should be noted:
The centre-line of flying shores and struts and those of walls should meet at
the floor levels. If the floor levels of the two buildings are at different levels,
the framework may be suitably designed and made unsymmetrical.

i A large factor of safety should be adopted in the design of flying shores as

it is difficult to assess the actual loads.

Floor
Floor
Cleat
Needle
Strut

Straining piece

Floor
Floor Brace
+Post

Wall plate
Flying shore
Floor
Floor

Double flying shore

FIG. 14-8
inclination
the angle of
(ii) The struts are generally
inclined at 45°
and in no case,

sho S
should increase 60.
304
Building Construction
Ch. 14
for a maximum distance of about
(iv This type of shoring is suitable
walls. But when the distance is between
between the adjacent parallel to
shore is provided as shown in f
12 m, a compound or double flying 14-8
It should be seen that both the horizontal shores are symmetrically nllaced
with respect to the floor levels.
two walls.
(v) Only o n e set of shoring strengthens
are not obstructed by this type of shorine
(vi) The building operations on the ground ing.
inserted when the old building is removed and thev.are
(vii The flying shores are
is constructed to a sufticient height to
kept in position till the new building
provide necessary stability.
than the other, the raking shores may be provided
(viii) When one building is higher
on the horizontal shores.
erected at a distance of about 3 m to 5 m in
ix The flying shores are generally
and horizontal struts are introduced, if necessary, to act as lateral bracino
plan
between the adjacent flying shores.
Dead vertical shores arrangement, the horizontal
(fig. 14-9): In this
(3) or
vertical members known as the dead
members, known as the needles are supported by
shores. The needles are driven at right angles to the wall through the holes madein
the wall. A dead shore is used under the following circumstances:

(i) The lower part of the wall has become defective.

(ii) The foundations are to be deepened.
(iii) The lower part of the wall is to be rebuilt or reconstructed.
(iv) The large openings are to be made in the existing wal.

Floor

Needle Proposed opening

Dog
Bracing

Dead shore

Floor support||

Sole Plate

Section Elevation
Dead shore
FIG. 14-9
Following points are to be noted:
(i) It is possible to calculate the stresses in the
various members of a dead sho
(ii) The needles are
placed at a distance of about 1.50 m to 2 m and re

suitably braced. The they

folding wedges, sole plate, dogs and braces are used
shown in fig. 14-9.
Art. 14-10] Scaffolding, Shoring and
Underpinning 305
:ii The floors are
suitably supported inside.
.The openings above and near
a dead shore
A raking shore may be
are
suitably strutted.
(V weak walls.
provided as an
additional safety especially in case of

T h e shores should be removed at least after

7
work. This period is necessary for the new work to days
of construction of
new
obtain the required strength.
fsiil The sequence of removal should be
needles, strutting from openings, the
floor strutting inside and raking shores, if It is desirable to allow an
interval of two days between each of these any.
operations.
14-8. UNDERPINNING

Definition: The placing of new foundation below an existing foundation or the

proces of strengthening the existing foundation is known as the underpinning of foundations.
Following are the situations demanding underpinning:

(i) A building with deep foundations is to be constructed adjoining to an

existing
building.
(ii The settlement of existing foundation has taken place, resulting in serious
cracks in the wall.
(ii The basement is to be provided to an existing building.
(iv The existing foundations are to be deepened so as to rest them on a soil of
higher bearing power.
14-9. POINTS TO BE ATTENDED TO BEFORE UNDERPINNING

Following important points should be carefully attended to before the work of

underpinning commences:
(1) Shoring and strutting: The necessary shoring and strutting should be provided
to the structure to make it safe for carrying out the process of underpinning.

2) Examination of structure: The structure should be carefully examined before

underpinning is commenced and poor masonry work should be suitably rectified.
3) Repairs: It is necessary to carry out urgent repairs such as grouting of eracks,
Insertion of tie rods between walls, etc. before commencing underpinning
the and
4 Checking arrangement: The levels may be marked on structure t
Ement of structure during underpinning should be checked and recorded.

is art rather than a

operation: The process of underpinning
an
19 Expensive
cience Lue guess-work
to advance made in the science of soil mechanics,
much in
hod
plnning is eliminated. But still it remains an expensive operation.
used needle, the bearing plate is provided
earing plate: When R.S. joist is
as

9avoid the
crushing of mason
14-10. METHHODS OF UNDERPINNING
wing are the methods of underpinning:
(1) Pit method
(2) Pile method
3) Miscellaneous methods.
306 Building Construction Ch. 14
14-10-1. PIT METHOD (fig. 14-10)
In this method, the existing wall is divided into suitable sections of width about
1.20 m to 1.50 mn.
The holes are then made in the existing
wall. The needles with bearingplates Existing wall
are then inserted through these holes Bearing plate
and supported on jacks as shown
Needle
in fig. 14-10. The pit is excavated and
the existing foundation is taken upto Jack
G
the required level. Following precautions
are necessary:

) One section should be excavated 4-

Timbering for trench
at a time. oooo

ii) The alternate sections should New foundation

be taken in succession.
ii) If the length of wall is more, Section
the underpinning is started from
the middle and it is then
extended in both the directions.
iv The proper timbering should
be provided for the trench. Existing wall
( v I t is desirable to carry out the
new foundation work in concrete.
vi If space to support needles on
outside is not available, the
Plan
cantilever needles, projecting
inside and provided with fulcrums Pit method
and loadings, may be adopted FIG. 14-10
as shown in
fig. 14-11. A hydraulic jack is placed between the needles and fulcrum.

Loading Existing wall

Bearing plate -

Needle
Hydraulic jack -
G
L
Fulcrum-

Inside New
foundation

Underpinning pit
Support by cantilever needles
FIG. 14-11
Art. 14l0-3]
Scaffolding, Shoring and
14-10-2. PILE
METHOD (fig. Underpinning 307
14-12)
In this method, the piles are
the ides of the driven
along both existing wall
nd then needles in the form of Existing wall
pile G
caps are provided through the existing
wall as shown in fig. 14-12. Thus the Pile cap
existing wall is relieve of the loads
ming on it. This method is useful in
soils and for
clayey
and for walls
water-logged areas
carrying heavy loads. For
underpinning very light structures, the
piles are driven along the structure and Concrete piles -
then brackets or cantilever needles are
provided to carry the structure.
Pile method
14-10-3. MISCELLANEOUS METHODDs FIG. 14-12

Following are some of the

specialised underpinning methods which may sometimes
be successfully adopted:
(1 Cement grouting
(3) Freezing
2) Chemical consolidation (4) Vibroflotation.
Each of the above method will now be
briefly described.
(1) Cement grouting: This method is used to restore slab or
settled. The operation is pavement which has
simple. The holes are drilled in the slab and the cement
pressure through these holes. The pressure is maintained untilgrout
is forced under
cement grout has set. the

(2) Chemical consolidation: In this Existing wall

method, the soil under the existing 3 m-
t0oting is consolidated by using chemicals. Working pit Perforated pipes
The
precedure for chemical consolidation
is as follows:

) The perforated pipes are driven

in an inclined direction as shown
in fig. 14-13. The inclination slopes
are so adjusted that the entire
area under the existing footing New footing
Comes under the command of the Consolidated soil
inclined pipes.
When the pipes are being driven, Chemical consolidation
the solution of sodium silicate in FIG. 14-13
water is injected through the pipes.
(ii The pipe
'pes are then withdrawn and during
the withdrawal of pipes, the calcium

chloride is injected through the pipes.

iv magnesium
chemical reaction takes place between these
two chemicals and the soil
e
is consolidated.
This is useful when the soil consists of sand
or granular materials
and the
cOst of con
nod
of consolidation, site of work, etc.
a t i o n depends on nature of soil, depth