Types of foundation

1. FOUNDATION
BY
RIMPI BARO
LECTURER, CIVIL ENGINEERING DEPARTMENT
PANDIT DEENDAYAL PETROLEUM UNIVERSITY,
GANDHINAGAR
BUILDING MATERIALS AND CONSTRUCTION

2. Foundation
• The foundation is the most
critical part of any
structure and most of the
failure is probably due to
faulty foundations rather
than any other cause. The
purpose of foundation is to
transmit the anticipated
loads of the superstructure
safely to the soil

3. Basic functions:
• To distribute the total load coming on the structure over
a large bearing area so as to prevent it from any
movement.
• To load the bearing surface or area at a uniform rate so
as to prevent any unequal or relative settlement.
• To prevent the lateral movement of the structure
• To secure a level or firm natural bed, upon which to lay
the courses of masonry and also support the structure.
• To increase the suitability of the structure as a whole, so
as to prevent it from overturning or sliding against such
as wind, rain, frost etc.

4. Design loads
The basic requirement of any building is that it should be able to carry all possible types of
loads to which it is subjected. Loads coming on a structure are:
i. Dead Load: Comprises of weight of all walls, partitions, floors, and roofs and all other
permanent construction.
ii. Live Load or Imposed Loads: Produced by intended use or occupancy. Usually
unstable or moving loads.
Material Mass (kg/m^3)
Bricks 1600 to 1920
Cement 1440
Steel 7850
Concrete, reinforced 2400
Occupancy classification UDL (KN/m^2)
Dwelling houses 2-3
Class rooms 2-3

5. iii. Wind Load: Acts horizontally on the exposed surface of walls, columns.
iv. Snow Load: Acts on roofs. Roofs should be designed for actual loads due to snow
or for the imposed loads, whichever is more severe.
v. Earthquake Load: The earthquake imposes forces in horizontal and vertical
directions

6. FOUNDATION
Shallow foundation
(Depth < Width)
(Depth = Width)
Deep foundation
(Depth> Width)
Spread Combined Strap Mat or
Raft
Pile Well or
caissons
Strip Pad End bearing Friction Compaction Sheet pile

7. Spread footing
• Supports either one wall or column.
• Strip footing: Spread footing for wall; footing provided when wall carries
light loads or when the safe bearing pressure is high, the wall rests on the
concrete base.
• Pad footing: Isolated footing for a column
Fig: Spread footing
Combined footing
Supports two columns; provided when columns are very near to each other so that
their footings overlap; bearing capacity of soil is less
If footing supports more than two columns, then it is known as Continuous footing.
Fig: Combined footing

8. Combined footing

9. Strap or Cantilever footing
• Comprises of two or more footings connected by a beam
called strap.
• If the distance between two adjacent columns is large, strap
footing is provided.
• The strap beam doesn’t remain in contact with soil and
doesn’t transfer any pressure to the soil. It is assumed to be
rigid and transfers the column loads on to the soil with
uniform pressure(C.G. of combined loads of two columns
pass through C.G. of the two footing areas).
• The strap should be properly designed to withstand shear
force and bending moments.
Figure
Mat or raft foundation
•Combined footing that covers the entire area beneath a
structure and supports all the walls and columns.
•Provided when allowable soil pressure is low or building loads
are heavy or the soil mass is erratic.
•A true raft or mat is a flat concrete slab with uniform thickness
throughout the area
Figure

10. Raft foundation

11. Grillage foundation
• A type of foundation often used at the base of a column. It
consists of one, two or more tiers of steel beams super
imposed on a layer of concrete, adjacent tiers being placed at
right angles to each other, while all tiers are encased in
concrete.
• This is dependable foundation and is used in those place
where the load of the structure is pretty high and bearing
capacity of soil comparatively poor; extends to a depth of 1m
to 1.5m

12. Grillage foundation
Grillage foundation

13. Grillage foundation
• The grillage foundation helps in distributing the load over a
wider area of subsoil.
• The grillage foundation helps in avoiding deep excavations
as the necessary base area is provided for the load of
transmission.
• This type of foundation generally used for heavy structure
columns piers and steel stanchions etc.

14. Inverted arch foundation
• Provided for multi storyed buildings in old times.
• However, with the advent of reinforced cement
concrete construction practice, inverted arch footing
is rarely done these days.
• One of the drawbacks in this type of construction is
that the end piles have to be specially strengthened by
buttresses to avoid the arch thrust tending to rapture
the pier junction.
• However, the advantage of inverted arch construction
is that in soft soils the depth of foundation is greatly
reduced.

15. Inverted arch
foundation

16. DEEP FOUNDATIONS
• Deep foundations are those founding too deeply
below the finished ground surface for their base
bearing capacity to be affected by surface conditions.
• This is usually at depths of 3 meter below finished
ground level.
• Deep foundations can be used to transfer the load to a
deeper, more competent strata at depth if unsuitable
soils are present near the surface.

17. Types of Deep Foundations
• Pile Foundations
• Caisson Foundation
• Well foundation

18. Pile Foundations
• These are relatively long, slender members that
transmit foundation loads through soil strata of
low bearing capacity to deeper soil or rock
strata having a high bearing capacity.
• They are used when for economic,
constructional or soil condition considerations
it is desirable to transmit loads to strata beyond
the practical reach of shallow foundations.

19. Pile foundations are used in the following
situations:
• The load of the super structure is heavy and its
distribution is uneven
• The top soil has poor bearing capacity
• The subsoil water level is high
• There is large fluctuations in subsoil water level
• Canal or deep drainage lines exist near the foundation
• The structure is situated on the sea shore or river bed

20. Pile Foundations
• In addition to supporting structures, piles are also used to anchor structures
against uplift forces and to assist structures in resisting lateral and
overturning forces.
• Engineers will usually group a few piles together, and top them with a pile
cap. A pile cap is a very thick cap of concrete that extends over a small
group of piles, and serves as a base on which a column can be constructed.
The load of this column is then distributed to all the piles in the group.

21. Under-reamed Pile
• These are bored cast in situ piles
•Have bulb or larger diameter at its lower
end to prevent the movement of
foundation in expansive soils subjected to
alternate expansion and contraction ; eg:
black cotton soils
•Diameters vary from 15 cm to 50 cm
•Diameter of bulb is around 2.5 times the
pile stem
•When the pile has one bulb, it is known
as single under reamed pile or else multi-
under reamed pile.

22. Classification of piles
Based on function
• End bearing pile: In end bearing piles, the bottom end of the pile rests on a
layer of especially strong soil or rock. The load of the building is transferred
through the pile onto the strong layer.
• Friction pile: Transfer loads by means of skin friction along the length of
piles
• Compaction pile: Used to compact loose granular soils, thus increasing their
bearing capacity; don’t carry any loads; hence may be of weaker material
such as sand
• Tension pile or uplift pile: Anchor down the structures subjected to uplift
due to hydrostatic pressure or due to overturning moment.
• Sheet pile: Used as impervious cut off to reduce seepage and uplift under
hydraulic structure.

23. • End Bearing Piles
In end bearing piles, the bottom end of the pile rests on a
layer of especially strong soil or rock. The load of the building
is transferred through the pile onto the strong layer. In a
sense, this pile acts like a column. The key principle is that the
bottom end rests on the surface which is the intersection of a
weak and strong layer. The load therefore bypasses the weak
layer and is safely transferred to the strong layer.
Friction Piles
Friction piles work on a different principle. The pile transfers
the load of the building to the soil across the full height of the
pile, by friction. In other words, the entire surface of the pile,
which is cylindrical in shape, works to transfer the forces to
the soil.

25. • HOW PILES ARE USED
• As pile foundations carry a lot of load, they must be designed
very carefully. A good engineer will study the soil the piles are
placed in to ensure that the soil is not overloaded beyond its
bearing capacity.
Every pile has a zone of influence on the soil around it. Care
must be taken to space the piles far enough apart so that
loads are distributed evenly over the entire bulb of soil that
carries them, and not concentrated into a few areas.
• Engineers will usually group a few piles together, and top
them with a pile cap. A pile cap is a very thick cap of concrete
that extends over a small group of piles, and serves as a base
on which a column can be constructed. The load of this
column is then distributed to all the piles in the group.

27. Pile cap

28. How piles are constructed
• Piles can be either cast-in-place or precast driven piles.
Cast-in-place piles are made in the following steps:
• hammer a thin-walled steel tube into the ground
• remove all earth left inside the tube
• lower a steel reinforcement cage into the tube
• cast the pile by pouring wet concrete into the tube
• The thin walled steel tube is called the casing, and only serves
to form a secure mould for casting concrete that is free from
earth and debris. It has no structural role to play after the
casting is complete.

29. • Some soils are highly cohesive, meaning that if
one drills a hole into the soil that is say 1 foot
wide by 50 feet deep, then the soil holds the
shape of the hole and does not collapse into the
hole and block it. If such soil is present at the site,
then one does not need to leave a casing in place:
one can use the casing to drill the hole for the
pile, and then remove it, and then cast the pile in
place. This saves costs as the same casing tube
can be used to drill holes for all the piles.

30. USE OF BENTONITE IN BORED CAST IN SITU PILES
During boring for pile, the side of the bore hole is subjected to various types of
forces & pressure like active earth pressure, overburden pressure, hydrostatic
pressure, pore pressure due to underground water, etc. due to which the side of
bore becomes unstable and start collapsing if the soil strata is weak.
In order to stabilize the side of bore the supporting fluid is to be used to counter
the above pressure. The commonly USED SUPPORTING FLUID FOR
STABILIZING IS BENTONITE.
Bentonite is commonly used as support fluid. In its natural form as sodium
montmorillonite exhibits thixotropic properties, where by it forms a gel under
quiescent /static conditions & regains its fluidity under dynamic conditions.

31. Casing

32. Pile cages

33. The tremie concrete placement method uses a pipe,
through which concrete is placed below water level.

34. • Precast Driven Piles are first cast at ground level and then
hammered or driven into the ground using a pile driver. This is
a machine that holds the pile perfectly vertical, and then
hammers it into the ground blow by blow. Each blow is is
struck by lifting a heavy weight and dropping it on the top of
the pile - the pile is temporarily covered with a steel cap to
prevent it from disintegrating.
• The pile driver thus performs two functions - first, it acts as a
crane, and lifts the pile from a horizontal position on the
ground and rotates it into the correct vertical position, and
second, it hammers the pile down into the ground.
Piles should be hammered into the ground till refusal, at
which point they cannot be driven any further into the soil.

35. SPECIAL PILES
• Pile driving is very noisy and causes massive vibrations
through the soil. For this reason, it is sometimes difficult to
use them in sensitive locations. For example, if an operational
hospital or science lab is to be extended, driving piles would
cause unwanted disturbance. Their use is also restricted in
residential areas in many countries. The vibrations could also
cause structural damage to older buildings that are close by.
In such situations it is possible to use micropiling or helical
piling, neither of which rely on hammering.
• A Micropile is a small diameter, typically less than 300mm,
drilled and grouted non-displacement pile which is heavily
reinforced and carries most of its loading on the high capacity
steel reinforcement

36. Micropiles

37. Micropiles or minipiles are small piles that are constructed in
the following way:
Step 1: a hole a little larger than the pile diameter and the full
length of the pile is dug into the ground using an apparatus
like a soil boring machine.
Step 2: a precast concrete pile is lowered or pushed into the
hole.
Step 3: a concrete grout is poured into the gap between the
pile and the earth.
Helical piles are steel tubes that have helical (spiral) blades
attached to them. These can be drilled into the ground,
meaning that the pile acts as a giant drill bit, and is rotated
and pushed into the ground from above, much like a screw
drills into wood. Once the steel pile is driven into the ground,
a pile cap is poured on top of the pile to prepare it for the
construction above.

38. Helical pile

39. Micropiles
• Size : 100mm to 350mm Diameter
• Lengths : Varies
• Structural Capacity : 20Ton to 250Ton
• Material : Grade 25MPa to 35MPa

40. • Sonic Echo Testing (IS 14893:2001) has been used successfully
for checking integrity of piles after installation. In piles
integrity test, a small metal / hard rubber hammer is used to
produce a light tap on the top of the pile. The shock travels
down the length of the pile and is reflected back from the toe
of the pile and recorded through a suitable transducer /
accelerometer (also held on the top of the pile close to the
point of impact)in a computer disk for subsequent analysis.
• The primary shock wave which travels down the length of the
shaft is reflected from the toe by change in density between
the concrete and the sub strata. However, if the pile has any
defects or discontinuities within its length these will set up
secondary reflections which will be added to the return signal.
• All piles shall be tested at a minimum age of five days after
casting, unless instructions to the contrary shall be given by
The Engineer.

42. A synthetic pile and the reflectogram

43. Based on Materials and composition
• Concrete piles
– Pre cast: Manufactured off site; Max design load 800 KN; require more
time to set; high cost; require heavy pile driving machinery, 30-50 cm
dia, 20 m or more
– Cast in situ: Max design load 750 KN;
i. Driven: driven into the ground by machinery
ii. Bored: under reamed piles, bored compaction piles
• Timber piles: Made from trees deodar, babul, teak; treated with creosote
oil as preservative; low bearing capacity; shouldn’t be driven through hard
stratum.
• Steel piles:
– H-pile: desirable in hard rock stratum; high bearing capacity; very high
cost; construction of bridges
– Sheet pile: prevent seepage of water below dams; driven into the
ground
– Box pile: driven pile; deep beams; Great lateral strength; support sea
structures.

44. • Composite piles: Lower portion of timber or steel and upper portion of
concrete; used
– Concrete and timber
– Concrete and steel

45. • Size : 250mm to 2000mm
• Lengths : 6m, 9m and 12m (Typical)
• Structural Capacity : 45Ton to 1000Ton
• Material : Grade 60MPa & 80MPa Concrete

46. • A caisson foundation also called as pier foundation is
a watertight retaining structure used as a bridge pier,
in the construction of a concrete dam, or for the
repair of ships. It is a prefabricated hollow box or
cylinder sunk into the ground to some desired depth
and then filled with concrete thus forming a
foundation. Caissons are adopted when the depth of
water is great and the foundations are to be laid
under water. Caissons are generally built on the
shore and launched in to the river floated to the site
and sunk at the proper position.
Caisson Foundation

47. It is of 3 types:
Box caissons are watertight boxes that are constructed of timbers,
concrete or steel and open at the top. They are generally floated
to the appropriate location and then sunk into place with a
masonry pier within it. Used where loads are not very heavy.
Open caissons or well are box of concrete, timber or steel that
are open both at the top and bottom and are placed and then
pumped dry and filled with concrete. These are generally used in
the formation of a pier. Most common foundation in Indian
bridges.
Pneumatic caissons are large watertight boxes or cylinders where
compressed air is used to exclude water from working chamber;
used if only head of water is more than 12m.

48. Well foundation
The choice of a particular shape of well depends upon the size of the pier,
the care and cost of sinking, the considerations of tilt and shift during
sinking and the vertical and horizontal forces to which well is subjected.

50. Description of Parts (Elements) of Well:
1. Steining:
It is the wall or shell of the well, made of
R.C.C. and which transfer the load to the
curb. It acts as a enclosure for excavating
the soil for the penetration of well.
Minimum grade of concrete used in
steining is M20
2. Curb:
It is a R.C.C. ring beam with steel cutting
edge below. The cross- section of the
curb is wedge shaped which facilitates
the sinking of the well. The curb
supports well steining. The curb is kept
slightly projected from the steining to
reduce the skin friction.

51. • 3. Cutting edge:
• It is the lowest part of the well curb which cuts the soil during
sinking. Well curb carries cutting edge for the well and is
made up of reinforced concrete using controlled concrete of
grade M25. The cutting edge usually consists of a mild steel
equal angle of side 150 mm.
• 4. Bottom plug:
• After completion of well sinking the bottom of well is pluged
with concrete. The bottom plug which is confined by the well
curb acts as a raft against soil pressure from below. Minimum
grade of concrete used in bottom plug is M15
• 5. Back fill:
• The well is dewatered after setting of the bottom plug and it is
backfilled by sand or excavated material.

52. The space inside the well between the bottom of the top plug
and the top of bottom plug is usually filled with clean sand, so
that the stability of the well against overturning is increased.
While this practice is good in case of wells resting on sand or
rock, the desirability of sand filling for wells resting on clayey
strata is doubtful, as this increases the load on the foundation
and may lead to greater settlement. In the latter case, the
sand filling is done only for the part of well up to scour level,
and remaining portion is left free.
6. Top plug:
• It is a concrete plug provided over the filling inside the well.
The top plug is an unreinforced concrete plug, generally
provided with a thickness of about 600 mm beneath the well
cap to transmit the loads from the pier to the steining.
Minimum grade of concrete used in top plug is M15.

53. 7. INTERMEDIATE PLUG
• As discussed above, for wells resting on clayey strata, it is
not preferable to fill the space inside the well completely
with sand. In such cases, sand filling is not done or sand is
filled up to the scour level. A concrete plug covering the
filling is usually provided, known as intermediate plug.
Usually, thickness of intermediate plug is taken as 500 mm.
8. Well cap:
• It is a R.C.C. slab provided at the top of stening to transmit
the load of superstructure to the stening and over which
pier is laid. The minimum thickness of the slab is about 750
mm.

54. cofferdams

55. • A cofferdam is a structure that retains water and soil
that allows the enclosed area to be pumped out and
excavated dry. Cofferdams are commonly used for
construction of bridge piers and other support
structures built within water. Cofferdams walls are
usually formed from sheet piles that are supported
by internal braces, and cross braces. Cofferdams are
typically dismantled after permanent works are
completed. Since cofferdams are usually constructed
within water, the sheet piles are installed using
preconstructed templates that permit the correct
positioning of each sheet pile from a barge.

57. Factors affecting design of foundation
• Soil types and ground water table conditions.
• Structural requirements and foundations.
• Construction requirements .
• Site condition and environmental factor.
• Economy etc.

58. Requirements of a good foundation
• Following are the three basic requirements to be fulfilled by a
foundation to be satisfactory
• Location : The foundation should be located that it is able to
resist any unexpected future influence which may adversely
affect its performance. This aspect requires careful engineering
judgment.
• Stability: The foundation structure should be stable or safe
against any possible failure
• Settlement: The foundation structure should not settle or
deflect to such an extent so as to impair its usefulness.

59. REFERENCES
• Building construction materials techniques, P.
Purushottam Raj
• Building Materials, S.K. Duggal
• Building Materials, B C Punmia
• www.civilconstructor.org