Types of foundation, Factors affecting the selection of type of foundations, steps in choosing types of foundation based on soil condition, Objectives and planning of exploration program, methods of exploration-wash boring and rotary drilling-depth of boring, soil samples and soil samplers-representative and undisturbed sampling, field penetration tests: SPT, SCPT, DCPT. Introduction to geophysical methods,

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PREPARED BY : ASST. PROF. VATSAL D. PATEL
MAHATMA GANDHI INSTITUTE OF
TECHNICAL EDUCATION &
RESEARCH CENTRE, NAVSARI.

2. Foundation is the lowest load-bearing part of a building, typically below
ground level.
PURPOSE OF FOUNDATION
1. Distribution of loads
2. Stability against sliding & overturning
3. Minimize differential settlement
4. Safe against undermining
5. Provide level surface
6. Minimize distress against soil movement

3.  Shallow Foundation (D<B)
 Spread Footing
 Combined Footing
 Strap Footing
 Mat or Raft Foundation
 Grillage Foundation
 Deep foundation (D>B)
 Pile Foundation
 Caissons or Well Foundation
 Coffers Dam

4.  Also known as a footer or footing
 It’s an enlargement at the bottom of a column/bearing wall that spreads the
applied structural loads over a sufficiently large soil area.
 Each column & each bearing wall has its own spread footing, so each structure
may include dozens of individual footings.

5.  Wall footing
 Simple Wall Footing
 Stepped Wall Footing
 Reinforced concrete footing
 Inverted arch footing
 Column footing

6.  Simple Wall Footing
A wall footing or strip footing is
a continuous strip of concrete that
serves to spread the weight of
a load-bearing wall across an area
of soil.
 Stepped Wall Footing
A footing in which the desired
width is secured by a series of
steps.

7. P C C
WALL
SIMPLE
FOUNDATION
P C C
I FOOTING
WALL
STEPPED
FOUNDATION
II FOOTING

9.  Inverted Arch Footing /Foundation is
used to be provided for multi-storeyed
buildings in olden times.
 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.

11.  Used to spread the load of the structure over a large base to reduce the load per
unit area being imposed on the ground
 Particularly useful where low bearing capacity soils are encountered & where
individual column loads are heavy.

12.  A spread footing which supports two or more columns is termed as combined
footing
 It is used when the two columns are so close to each other that their individual
footings would overlap.
 A combined footing is also provided when the property line is so close.
 Trapezoidal footing is provided when the load on one of the columns is larger
than the other column.

14.  It consists of two isolated footings connected with a structural strap or a
lever.
 The strap connects the footing such that they behave as one unit.
 A strap footing is more economical than a combined footing when the
allowable soil pressure is relatively high and distance between the columns
is large

15. Strap Footing

16.  It consists of one, two or more tiers
of steel beams superimposed on a
layer of concrete, adjacent tiers
being placed at right angles to each
other.
 Grillage foundation is the most
economical foundation in case of
transferring heavy loads from
columns to soil of low bearing
capacity.

17.  Caisson is derived from French word “caisse” meaning a box.
 It is relatively large deep foundation.
 It is a box structure in shape of rectangular, round which is sunk from the surface
of water or land to the desire depth.
 It is permanent structure and part of the sub- structure.

18. Box Caisson
Well or Open
Caisson
•Single
•Multiple
•Cylinder
Pneumatic
Caisson
 Caisson is a watertight retaining structure.
 It is used, for the purpose of placing a foundation in correct position under water.

19.  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.

20.  The caisson is sunk by filling sand, gravel, or concrete in the empty space inside.
 The place where the caisson base is to rest must be levelled and as such box
caissons are used in places where the strata of sufficient bearing capacity is
available near the ground.
 In normal practice, the soft natural bottom soil of the river bed is dredged out to
some depth and the trench thus formed is filled with sand to have a levelled base.
 The function of the sand layer is to uniformly distribute the superimposed loads
over the soil below and thus avoid tilting of the caisson.

23.  common shapes of caisson

24.  Cutting edge
 Curb
 Steining
 Bottom plug
 Well cap
 Topplug
 Sand filling

25.  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.
 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.
 Topplug : 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.

26.  This type of caisson is closed at top and open (during construction) at the
bottom. The water is excluded from the caisson chamber by means of
compressed air.
 The construction of the pneumatic caisson is similar to the types described
above, except that, the working chamber and shaft are made air-tight. In order
that the workmen may carry out excavation work underneath the caisson and
the water may not find its way inside from below, the pressure of the
compressed air in the shaft is kept just higher than that of the water at that
depth.
 Each caisson has two air locks. Through one air lock workmen go down for
working while through the other excavated material is taken out. An air lock
essentially consists of a steel chamber having two air-tight

28.  When workers working under compressed air inside the working chamber,
they suffer certain type of disease when they return to the atmospheric
pressure. This disease is known as “Caisson Sickness” or “Caisson Disease”.
 The main symptoms of the diseases are:
 Dizziness (vertigo)
 Double vision
 Headache
 Trouble to speaking
 Pain in body

29.  No person should work for more than one shift in a day. Shift should not exceed 12
hours.
 Temperature of the working chamber should be maintain 25 degree centigrade.
 The main locks should be well ventilated.
 Persons with strong heart, low blood pressure and good circulation should be
employed on the work.
 Use of alcoholic drinks should be prohibited.

30.  Medical facility or chamber should be provided nearer to the work
 The workers should take enough meal before the shift starts.
 All the passages, shafts etc. of the caisson should be well ventilated and properly
lighted.
 The worker use man locks for entry, interval and exit.

31.  A pile is basically a long cylinder of a strong material such as concrete that
is pushed into the ground to act as a steady support for structures built on top
of it.
 Pile foundations are used in the following situations:
 When a building has very heavy, concentrated loads, such as in a high rise
structure, bridge, or water tank

32.  When there is a layer of weak soil at
the surface. This layer cannot support
the weight of the building, so the
loads of the building have to bypass
this layer and be transferred to the
layer of stronger soil or rock that is
below the weak layer

33.  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.
Earth fill
Coffer Dam
Rockfill
Coffer Dam
Rockfill
Crib Coffer
Dam
Single Wall
Coffer Dam
Double
Wall Coffer
Dam
Cellular
Coffer Dam

34. Earthfill Coffer Dam Rockfill Coffer Dam

37. Crib Coffer Dam Single Wall Coffer Dam

40. Double wall Coffer Dam Diaphragm Cellular Coffer Dam

42.  On the basis of Sub soil condition
 On the basis of loads from building
 Seismic force

48.  Unequal settlement of the sub –soil
 Unequal settlement of masonry
 Sub-soil moisture movement
 Lateral movement of sub soil
 Lateral pressure on the wall
 Weathering of sub –soil due to trees and shrubs
 Atmospheric action

50.  The process of collection soil data for the assessment soil properties at a site
through series of laboratory and field investigation is collectively called Sub-soil
Exploration or site investigation
 Purpose of site investigation
 Determining the nature of soil at the site and its stratification.
 Selecting the type and depth of foundation suitable for a given structure.
 Evaluating the load-bearing capacity of the foundation.
 Estimating the probable settlement of a structure.
 Determining the location of water table.
 Determining the depth and nature of bedrock, if and when encountered
 Enables the engineers to draw soil profile indicating the sequence of soil strata
and the properties of soil involved.

51.  Collection of Preliminary Information
 Reconnaissance
 Site Investigation

52.  This step includes obtaining information regarding the type of structure to be
built and its general use. The following are examples explain the needed
information about different types of structures:
 For the construction of building:
 The approximate column loads and their spacing.
 Local building-codes.
 Basement requirement.
 For the construction of bridge:
 The length of their spans.
 The loading on piers and abutments

53.  The engineer should always make a visual inspection (field trip) of the site to
obtain information about:
 The general topography of the site, the possible existence of drainage ditches,
and other materials present at the site.
 Evidence of creep of slopes and deep, wide shrinkage cracks at regularly spaced
intervals may be indicative of expansive soil.
 Soil stratification from deep cuts, such as those made for the construction of
nearby highways and railroads.
 The type of vegetation at the site, which may indicate the nature of the soil.
 Groundwater levels, which can be determined by checking nearby wells.
 The type of construction nearby and the existence of any cracks in walls
(indication for settlement) or other problems.
 The nature of the stratification and physical properties of the soil nearby also
can be obtained from any available soil-exploration reports on existing
structures.

54.  This phase consists of:
 Planning (adopting steps for site investigation, and future vision for the site)
 Making test boreholes.
 Collecting soil samples at desired intervals for visual observation and
laboratory tests.

57. o Drilling a hole into the soil strata up to specified depth is known as boring
 Auger boring
Auger and shell boring
Wash boring
Percussion drilling
Rotary drilling

60.  A soil sample is the representative of the whole lot from which it is taken.
It completely represents all the characteristics of the lot from which it is
recovered.
 TYPES OF SOIL SAMPLES
Disturbed soil samples (DS)
Undisturbed soil samples (UDS)

61.  Open drive sampler
Split spoon sampler
Shelby tube – thin walled sampler
 Stationary Sampler
 Rotary Sampler

62. SPLIT SPOON SAMPLER

64.  Generally used for Cohesion less soils
 To determine relative density , angle of shearing resistance, UCC
 A bore hole is made using drilling tools and a hammer of weight 63.5
falling from the height of 750 mm at the rate of 30 blows/minute
 After reaching the specified depth, the drilling tool is replaced by a split
spoon sampler to collect soil sample.
 First 150 mm penetration is taken as seating drive and the no. of blows
required for that penetration is discarded
 No of blows required for next 300mm penetration after seating drive is
taken as standard penetration number (N)
 No of blows greater than 50 are taken as refusal and the test is
discontinued
 Corrections are applied to the observed N value

66.  Frictional resistance = Combined resistance – Cone resistance
 Modified Cone penetrometer is known as Refined Dutch Cone
 Cone penetration resistance is denoted as qc in kN/m2
 Unlike SPT, this method is also suitable for clayey deposits
 Unsuitable for gravels and dense sand. For such soil dynamic Cone
penetration is used

69.  The stratification of soils and rocks can be determined by geophysical methods
of exploration which messures changes in certain physical characteristics of
these materials,for example density, magnetism, electrical, resistivity etc.
 The following two geophysical methods are commonly used:
(i)Seismic refraction method
(ii)Electrical resistivity method
GEOPHYSICAL METHODS

70. SEISMIC REFRACTION METHOD
The seismic refraction method is based on the principal that seismic waves have
different velocities in different types of soil.

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