The document discusses caissons, which are watertight structures sunk into the ground or water to excavate foundations. There are several types, including box caissons (open top, closed bottom), open caissons (open top and bottom), and pneumatic caissons (closed top, open bottom). Materials used include steel, timber, concrete. Pneumatic caissons use compressed air to work in a dry environment underground. Challenges in sinking caissons include sand blowing, tilting, and shifting of wells. Precautions must be taken to avoid the bends disease from compressed air use.

1. Caisson

2. Caisson
• Introduction
• Uses of caisson
• Material used for
caisson
• Type of caisson
• Load on caisson
• Design feature of
caissons
• Floating of caisson
• Cutting edge
• Sinking of caisson
• Problem in well sinking

3. Caissons
• The term caisson is derived from French word caisse means
BOX.
• Caisson is a watertight structure round or rectangular, which is
sunk through ground or water to exclude water and semi-fluid
material during the process of excavation of foundation and
which subsequently becomes an integral part of the
substructure.

4. Usesof caissons
the hard bearing strata for transferring the load of
superstructure.
• For the excavation for foundation of bridges, piers, abutments in
river and lakes.
• T
o serve as an impervious core wall of earth dam, when
placed adjacent to each other.
• To provide access to a deep shaft or tunnel
• T
o provide an enclosurebelow water level for installing
machinery pump.
To reach

5. Material usedforcaissons
• Steel
• Timber
• Reinforced cement
concrete
• Cast iron

6. S
teel
• It is most suitable material for the construction of a caisson.
• It have form of a double skin of steel plating and hollow space
which can filled with cement concrete.

7. Reinforced cement concrete
• It is suitable for caisson shoes.
• It becomecostly in the early stageof constructionas more
weight creates problem is handling and floating of caisson.
• It become economicalto construct a steel caissonwith
concrete lining.

8. Castiron
• It is suitable for open well type of caisson.
• New segment of C.I are bolted as the caisson sinks.
• It is not suitable for pneumatic caisson due to risk to
tension developed by the compressed air.
• The cost of C.I. caisson is more as compared to steel
and RCC.

9. Typesof caissons
• Box caisson
(Open at top and closed at
bottom)
• Open caissons
(Open at top and bottom)
• Pneumatic caisson
(Closed at top and open at
bottom)

10. Boxcaisson
• It is strong water tight vessel open at
top and closed at bottom and made
of timber, steel or RCC.
• It is build on land , cured and then
float or launched to pier site where
it is placed in position.
• Mainly it is used for shallow depth
and for light weight.

11. Conditions for Construction ofbox caisson
• Excavation for foundation is not required. The bed of foundation
can previously prepared.
• The velocity of flow of water is slow so as to give stability to
the caisson against scouring.
• The bed material is loose enough and it is possible to dredge
out this material and from a levelled bearing surface.
• The depth of water is about 6 to 8 m.

12. Open Caissons Or Wells
• Open caisson is a box of timber,
reinforced concrete, steel or
masonry which is open at the top
and at bottom.
• It used for building and bridge
foundation .
• Open caisson are also called
well
foundation.
• They are used on sandy or soft
bearing stratum liable to scour and
where no
firm bed available for large
depth below the surface.

13. TypesOf OpenCaisson
• Single well
• Multiple well
/monoliths
• cylinder

14. ShapesOf Wells
• Single circular
• Rectangular
• Twin circular
• Dumb well
• Double-D
• Twin-
hexagonal
• Twin-
octagonal

15. ShapesOf Wells

16. Factor ForChoiceOf ShapeOfWell
• The dimension of base of the pier of abutment.
• The case of sinking.
• The cost of sinking and shuttering.
• The vertical and horizontal forces acting on the
well.
• The considerations of tilt and shift during
sinking.

17. Component OfWell
• Cutting
edge
• Curb
• Steining
• Bottom
plug
• Top plug
• Well cap
• Sand filling

18. • Cutting edge
Provides sharp edge to cut the soil below during sinking
operation.
• Curb
During sinking it acts as extension of cutting edge and provide
support the well. It is made of RCC.
• Steining
It is main body of the well. Made of RCC or masonry with
minimum thickness of 45 cm.

19. • Bottom plug
Made of concrete and designed for an
upward load equal to the
soil pressure minus self weight of the
bottom plug and sand filling.
• Top plug
It supports the well cap.
• Well cap
It transfers the load from pier to the well.
• Sand filling
It transfers a portion of load from well cap to the bottom plug.

21. Well Sinking Operations
• For dry ground open excavation up to half a meter above subsoil water
level is carried out and the well curb is laid.
• Well Steining built in short height about 2 m.
• Well is sunk by excavating material from inside the curb
where excavation may carried out by worker or dredger.
• “Kentledge” is applied on well by iron rail or sand
bag to counter skin frication and loss in the weight of well due
to buoyancy.
• Pumping out the water from inside the well when well has gone
deep enough.
• A concrete plug is provide at the bottom which made bowl shaped.
• Internal space is filled with sand and top of well provide concrete with
RCC cap.

23. Multiple well/Monoliths
• The monoliths consists of multiple
wells, which are sunk together.
• The individual well of the monoliths
has got separate cutting edge and the
dredging can be done in each of the
well separately.
• It having bigger dimension so they can
not built on the site in the water.
• Therefore, they are constructed in dry
place, floated and placed in final
position.

24. Construction
• A suitable site is selected on the upstream side of the proposed bridge in a
river and a dry dock is constructed.
• Dimensionof the dry dock is bigger then monolith and it should
provided sufficient width of door.
• The monolith is constructed in the dry dock to such a height that some
portion of
it remain above water level.
• The gate of the dry dock is opened the monolith is then floated and located
in its correct position.
• Dredging operation done in sequence as four dredging well used
simultaneously
and the middle row is touched
last.
• After dredging to the required depth the whole monolith is gradually sunk
up to required level.
• The bottom is provided with concrete seal and then filled with concrete and
cap is provided at top.

26. Pneumaticcaisson

27. Pneumaticcaisson
• A pneumatic caisson is open at bottom and closed at top.
• It is useful at location where well is not possible.
• It suitable for water depth of 12 m to 35 m.
• Compressed air is used to remove water from working chamber
at the bottom and foundation work is carried out in dry
condition.
• The pressure of air in chamber is higher than water at that depth
for subsoil water may not enter in working chamber.
• The maximum pressure is limited up to 0.35 N/mm2 .

28. Construction
• The caisson is sunk in water till no problem is encounter. When
water creates problem the air lock is placed inside the well.
• There are two air locks are provided in caisson one for sending
men inside and second for removing the excavated material
with help of muck bucket and hosting rope.
• After the lock is placed in position direct entry of air is sealed
water is pumped out from the bottom and compressed air is
prevent the entry of water from bottom.
• The work of foundation is then started by sending the labour in
to working chamber.

29. Construction conti..
• The height of chamber is kept about 2m and lighting
arrangement is provided.
• The excavation material may be taken out
by a muck hoisted by a rope or cable.
• The explosive or reduction of air pressure for a short duration
may be applied.
• When a caissonhas reached the desired level a concrete seal
is provided at bottom .
• The air lock and other equipment removedand filling caisson
with suitable material.

30. Pneumatic caissonsickness
• Dizziness
• Double vision
• Headache
• Trouble to
speaking
• Pain in lag
• Etc.

31. Precautions to avoidsickness
• Work only for one shift in a day
• Duration of shift should not exceed 12 hours.
• Maintain temp. 250 C.
• Persons employed on the work should be physically fit.
• The main lock should be well-ventilated.
• Medical chamber must be provided just near the side of
work
• Etc.. As per your view

33. LoadsOnCaisson
• Vertical load
• Lateral load
• Sinking load
• Seismic forces
• Longitude force
• Wind force
• Centrifugal force in case of well on a
curve

34. Floating of caisson
• Construction of dry
dock
• Floating from bank
• Turning of caisson
• Use of compressed air

35. Construction Of DryDock
• A dry dock is constructed on the upstream side of the bridge
site.
• After construction of caisson in dock it may flooded to float
out.
• The caisson should be properly anchored when it is
floating and landing.

36. Floating frombank

37. Turning of caissons
• This method is used when depth of water is high.
• The caisson is launched upside down cutting edge is upward
and top is at bottom.
• The portion on one side is kept slightly higher than the
remaining one.
• Sand is used to maintain symmetry during launching.stone
ballast and water are then added to cause tilting of the caisson.
• When complete turning occurs, the caisson starts floating
in the water and stone ballast falls out of the caisson.

38. CompressedAir
• The completed portion of caisson is provided with a steel
dome and the compressed air is applied through it.
• The compressed air keeps out water and facilitates the
floating of caisson.
• When the caisson settles down at its proper position the steel
dome is removed.

39. CuttingEdge
• It should be sharp angle for knifing into the soil to resist the
various stresses induced by boulders blow, blasting, etc.
• It should be well protected by the steel point to avoid any
damage to the edge
• The outer edge should be vertical
• In case of pneumatic caisson it should be air tight.
• If water jet is to be used for sinkingpurposethe nozzleshould
be accommodated in the cutting edge to reduce skin friction.
• In concretecaisson the lower portion of the
cutting edge is rigidly fastened with 12 mm steel plate
with help of steel straps.

40. Typesof cuttingedges
1. Cutting edge with sharp
ends
2. Cutting edge with blunt
ends

41. Cutting edgewith sharpends
• Cutting edge shown
in fig (a) and fig. (b)
are used for open
cylinder/ caisson.
• Fig. (c ) is used for
pneumatic caisson.

42. Cutting edgewith bluntends
• a is suitable for Avg. condition
of sinking
• b is suitable when a caisson is to
be
sunk through rock
• C is suitable when it is to be built
from a land surface.

43. Factors to selection of acuttingedge
• Method of sinking to be adopted.
• Construction method of caisson
• Nature of soil
• Nature of ultimate soil stratum on which the cutting edge is to
rest while concrete is being placed for the bottom plug.

44. Sinkingof caisson
• Various method for sinking of caisson are here
below;
• Air and water jets
• Blasting
• Loading
• Sand island

45. Air and Waterjets
• Jet are provided near the cutting edge level to reduce the skin
friction
• It may be embodied in the body of the caisson or it may be
operated independently by driver or other workmen.
• The air or water is forced through the jets which ultimately
facilitates the sinking of caisson.

46. Blasting
• Explosive are used to remove any obstruction like rock, boulder
etc .
• It is reduce skin friction of hard soils.
• for blasting gelignite is used which is a absorbing powder and
blasting gelatin.
• It is powerful under water and convenient to use.
• It is necessary to take
extreme care to see that the cutting edge
of caisson is not damage during the blasting operation.

48. Loading

49. Sandisland
• It is used when subsoil condition are
such that it is not possible to kept the
caisson stable.
• In this method sinking a steel cylinder
around the site of work and then filling
this cylinder with sand or other
dredged material.
• The caisson is sunk through this
filling in
the usual manner.
• It is also known as artificial island
method.

50. Problem in wellsinking
• Sand blowing
• Tilting of wells
• Shifting of
wells

51. Sandblowing
• Sand blowing is takes place during the process off dewatering
of the well passing through sandy strata.
• The ground around the well starts breaking up to wide
cracks are seen in it.
• The fall of sand in the caisson is sudden and huge amount to a
depth of about 3 to 15 m of sand.
• This may result in a fatal accident and the equipment and
worker may get buried during sand blowing.

52. Shifting of wells
• The shifts change span
length and thereby
induced loads on the
well staining and the
foundation.
• The magnitude of the ill
effect depend upon the
size of well and depth of
which it is sunk.

53. Tilting ofwells
• Control of dredging
• Eccentric loading
• Water jetting
• Pulling the well
• Pushing by jacks
• Use of explosive
• Deposition of earth on one side and excavation on
other
• Providing temporary obstacle below the cutting
edge