BUILDING TECHNOLOGY

SEMESTER 4
CREDIT 3
TOTAL HOURS 45
LEVEL: BACHELOR OF ENGINERING ( CIVIL)
Unit 2. Foundation
2.1 Introduction:
Foundation is the lowest part of a structure which provides a base for
the super structure. It includes the portion of structure below the
ground level as well as the concrete blocks, piles, raft, grillage, etc.
provided to transmit the loads (dead & live loads) of the structure to
the sub-soil.

2.2 Essential requirement of a good foundation

1. Foundation should be deep enough to increase stability and
prevent overturning.
2. Foundation base should be rigid to minimize settlements
especially for the case when super-imposed loads are not evenly
distributed.
3. Foundation should be wide enough so as to distribute the weight of
the super-structure over large area.
2.3 Types of Foundation
1. Shallow Foundation
2. Deep Foundation
A. Shallow Foundation:
• Depth of foundation is less than or equal to width (i.e. D < B).
• It transmits superimposed load to the soil at a level close to the ground
floor of the building.
TYPES:
1. Spread footing or pad foundation or isolated foundation
It is the base of the transmitting the load to the soil, which is large in
width in order to distribute the load over wider area. It supports either one
column or one wall.
i. Single footing for a column
ii. Stepped footing for a column
iii. Wall footing for wall
iv. Stepped footing for wall
v. Grillage foundation
2.3 Types of Foundation
1. Shallow Foundation
2. Deep Foundation
A. Shallow Foundation:
• Depth of foundation is less than or equal to width (i.e. D < B).
• It transmits superimposed load to the soil at a level close to the ground
floor of the building.
TYPES:
1. Spread footing or pad foundation or isolated foundation
It is the base of the transmitting the load to the soil, which is large in
width in order to distribute the load over wider area. It supports either one
column or one wall.
i. Single footing for a column
ii. Stepped footing for a column
iii. Wall footing for wall
iv. Stepped footing for wall
v. Grillage foundation
 .
2 Combined footing
A footing which supports two or more columns is termed as combined footing
This type of footing is provided under the following circumstances;
i. When columns are very near to each other & their individual footings overlap.
ii. When bearing capacity of the soil is less, requiring more area under individual
footing.
iii. When the end column is located at or near the property line & its footing cannot be
extended on the side of the property line.
Types
i. Rectangular combined footing
ii. Trapezoidal combined footing
iii. Combined column wall footing
3. Strap Footings
If the independent footing of the two columns is connected by a beam,
then it is called as strap footing. The strap footing is provided when
columns are placed in large distance such that trapezoidal footing
becomes quite narrow, with high bending moment. The strap beam,
assumed to be infinitely stiff, serves to transfer the column loads on to
the soil with equal and uniform soil pressure under both footing.
4. Continuous Footing
Continuous footing support a row of limited width and continue under
all columns.
5. Mat (Raft) Foundation
 A raft foundation is a combined footing that covers the entire area beneath a structure
and support all the walls and columns.
 It is a flat concrete slab, heavy reinforced with steel, which carries the downward loads
of the individual columns or walls.

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Types of mat/ raft foundation
1. Solid Raft
2. Slab and Beam foundation
3. Cellular Raft
 2.4) Deep Foundation
 Deep foundations are those in which the foundation is very large in comparison to
its width.
 They transfer the superimposed load to the soil at a level that is at great distance
from the lowest floor.

Types of Deep foundations

A. Pile foundation
B. Pier foundation
C. Well or caisson foundation

A) Pile foundation
Pile foundation is that type of deep foundation in which loads are taken to low level by
mean of vertical member which may be timber, concrete or steel. Pile foundation may be
used instead of raft foundation where no firm bearing strata exists at a reasonable depth
and the loading is uneven.
Uses of pile foundation
1. When load of super structure is heavy.
2. The top soil has poor bearing capacity.
3. Water table is high.
4. Compressive soil.
5. Canal or deep drainage lies near the foundation.

Types of Pile Foundation

a) Types of piles according to uses
i. Friction piles
ii. End bearing piles
iii. Compaction piles
iv. Tension pile or uplift pile
v. Batter pile
vi. Sheet pile
b) According to material use
i. Steel Piles
ii. Cement Concrete Piles
iii. Timber Piles
iv. Composite Piles: made of two or more than two materials.

Methods of pile driving can be categorized as follows:

1. Drop hammer method

2. Explosion

3. Water jet

4. Vibration
B) Pier foundation:
A pier foundation consist of a cylindrical column of large diameter to support
and transfer large super–imposed loads to the firm strata below. The
difference between pile foundation and pier foundation lies in the method of
construction. Though pile foundations transfer the load through friction and
bearing, pier foundations transfer the load only through bearing.

Generally, pier foundation is shallower in depth than the pile foundation. Pier
foundation is preferred in a location where the top strata consist of
decomposed rock overlying a strata of sound rock. In such a condition ,it
becomes difficult to drive the bearing piles through decomposed rock. In the
case of stiff clays, which offer large resistance to the driving of a bearing pile,
pier foundation can be conveniently constructed.

• Used when a heavily loaded building is to be situated in sandy soil or soft

soil.
• This method consists in sinking vertical shafts upto hard bed and filling
them with concrete.
• The diameter of shaft and their center to center spacing depends upon the
loading condition, nature of soil and depth at which hard bed is situated.
C) Caisson or Well Foundation
 These are the box like structures circular or rectangular in plans which are sunk from the
surface of either land or water to the desired depth.
 The term caisson has been derived from the French word ‘CAISSEE’, meaning Box.
 These are much large in diameter than the pier foundation.
 These are used in major foundation works such as bridges piers, abutment in river/lakes,
etc.
 It is commonly used where foundation under water is done.
Methods of Dewatering of Foundations
Construction of footings of various buildings, powerhouses, multistory buildings and many other
structures requires excavation below the water table into water-bearing soils. Such excavations
require lowering the water table below the slopes and bottom of the excavation to prevent raveling or
sloughing of the slope and to ensure dry, firm working conditions for construction operations. De-
watering is done to lower the water table to achieve above mentioned goals.

Purpose of Dewatering

Construction sites are dewatered for the following purposes:

1. To provide suitable working surface at the bottom of the excavation.
2. To stabilize the banks of the excavation thus avoiding the hazards of slides and sloughing.
3. To prevent disturbance of the soil at the bottom of excavation caused by boils or piping. Such
disturbances may reduce the bearing power of the soil.

Methods of Dewatering

Following methods are used for Dewatering,

1. Sump pumping
2. Well point systems with suction pumps
3. Shallow wells with pumps
4. Deep wells with pumps
5. Drainage galleries
6. Other methods
 2.5 Basement:
Introduction
A basement is part of a building that is either partially or completely below ground level.
The potential benefits of basements include:
1. An increase in floor area without an increase in the size of the footprint of a buildings
or a significant impact on the size of the garden.
2. An increase in space to support growing families without the need to move house.
3. Semi-basements can make good use of sloping sites since constructing a basement
will negate the requirement for leveling the site.
4. If an existing house is located in a sensitive area, for example an Area of Outstanding
Natural Beauty, where there are restrictions on development, the construction of a
basement can allow the addition of extra space that would otherwise not be allowed.
5. Houses with basements can have improved energy efficiency since the basement will
have fewer exposed external walls.

TYPES OF BASEMENTS:
1. MASONRY
2. POURED CONCRETE BASEMENTS,
3. PRECAST PANEL BASEMENTS
Drainage Consideration
Basement floor drains need to be filled regularly to prevent the trap from drying out and sewer gas from escaping
into the basement. The drain trap can be topped up automatically by the condensation from air conditioners or
high-efficiency furnaces. A small tube from another downpipe is sometimes used to keep the trap from drying
out. Some advocate the use of special radon gas traps. In areas where storm and sanitary sewers are combined,
and there is the risk of sewage backing up, backflow prevention devices in all basement drains may be
mandated by code and definitely are recommended even if not mandated.

Basement waterproofing
Basement waterproofing involves techniques and materials used to prevent water from penetrating the basement of
a house or a building. Waterproofing a basement that is below ground level can require the application of
sealant materials, the installation of drains and sump pumps, and more.

Purpose
1. Waterproofing is usually required by building codes for structures that are built at or below ground level.
Waterproofing and drainage considerations are especially important in cases where ground water is likely to
build up in the soil or where there is a high water table.

2. Water in the soil causes hydrostatic pressure to be exerted underneath basement floors and walls. This
hydrostatic pressure can force water in through cracks, which can cause major structural damage as well as
mold, decay, and other moisture-related problems.

Methods
Several measures exist to prevent water from penetrating a basement foundation or to divert water that has
penetrated a foundation:

1. Interior wall and floor sealers

2. Interior water drainage
3. Exterior drainage
4. Exterior waterproofing coatings
Types of water proofing
1. Horizontal
Vertical
lVertical

2. Vertical
 2.6 Introduction on bearing capacity of foundation soil

In geotechnical engineering, bearing capacity is the capacity of soil to support the

loads applied to the ground. The bearing capacity of soil is the maximum
average contact pressure between the foundation and the soil which should
not produce shear failure in the soil. Ultimate bearing capacity is the
theoretical maximum pressure which can be supported without failure;
allowable bearing capacity is the ultimate bearing capacity divided by a factor
of safety. Sometimes, on soft soil sites, large settlements may occur under
loaded foundations without actual shear failure occurring; in such cases, the
allowable bearing capacity is based on the maximum allowable settlement.

Types of soil
Soil Exploration / Investigation :
Although information on the soil exposed at the ground surface is very valuable,
geotechnical engineers also need to evaluate the sub-surface conditions by taking
samples by boring or by digging exploratory pits. These activities are called subsurface
exploration.

The extent of exploration depends on the importance of the structure, the complexity of
the soil conditions and the budget available for exploration. A detail soil exploration
programmed involves deep boring, field tests and laboratory tests for determination of
different properties of soils required for the design of any structure.

Purpose of soil exploration is:

(i) To determine the basic properties of soil which affect the design and safety of structure
i.e., compressibility, strength and hydrological conditions.

(ii) To determine the extent and properties of the material to be used for construction.

(iii) To determine the condition of groundwater.

(iv) To analyses the causes of failure of existing works.

 Methods of Soil Exploration
(i) Auger boring:
Soil auger is a device that helps in advancing a bore-hole into the ground. These are
used is cohesive and other soft soil above water table. Hand operated augers are used
up-to a maximum depth of 10 m and power driven augers are used for greater depths.

Auger boring

Boring is done by pressing the auger into the ground and rotating it with the handle at
the top. As soon as the auger is filled with soil, it is taken out and soil is removed from
the blades. Samples obtained are disturbed samples.
Methods to Improve Bearing Capacity of soils
Some of the methods to improve bearing capacity of soils:
1. Increasing the depth of the footing is the simplest method of improve the bearing
capacity of soil, This method is restricted to sites where the sub-soil water level is
much below and deep excavations do not increase the cost of foundations
disproportionately.
2. Drainage is a well known method to improve the bearing capacity of certain soils.
Drains (with open joints) are laid in trenches just at the footing base. The sub-soil
water thus collected is drained out through a system of pipe drains provided outside
the external walls of the building.
3. By blending granular material, like sand, gravel or crushed stone into the natural soil
by ramming. The layer of soil thus formed is much stronger and is of improved
bearing capacity.
4. By confining the soil in an enclosed area with the help of sheet piles. This method is
used with advantage in shallow foundations in sandy soils.
5. By driving sand piles. This method is based on the principle of reducing the void
volume of the natural soil. Holes are made in the soft soil with the help of wooden
piles or other means and then sand is filled in the holes and rammed. These are
called sand piles. Bearing capacity of soft soil can be appreciably improved by driving
sand piles at close spacing.
2.7 Geo Textile:
Definition Of Geotextile

A geotextile is typically defined as any permeable textile material used to increase soil
stability, provide erosion control or aid in drainage. More simply put, if it is made of fabric
and buried in the ground it is probably a geotextile! Geotextiles have been in use for
thousands of years dating back to the Egyptian Pharaohs. These early geotextile
applications were basically natural fibers or vegetation mixed directly with soil. Modern
geotextiles are usually made from a synthetic polymer such as polypropylene, polyester,
polyethylene and polyamides. Geotextiles can be woven, knitted or non-woven. Varying
polymers and manufacturing processes result in an array of geotextiles suitable for a
variety of civil construction applications.
Insert Beam Detailing Pictures
 2.8 Causes of failure of foundations &
preventive measures
Causes of Failures of Foundations
The main causes of failure of foundations are as follows:
1. Unequal settlement of the sub-soil
2. Unequal settlement of the masonry
3. Withdrawal of moisture from the sub- soil
4. Lateral pressure on the superstructures
5. Horizontal movement of the earth
6. Transpiration of trees and shrubs
7. Atmospheric action.

Preventive measures to be taken are as follows:

1. Foundation should be taken beyond the depth up to which rain water can reach.
Ingress of rain water and harms associated with it can therefore be avoided.
2. Suitable underground drains should be provided to maintain the water table at a
definite level.
3. After the masonry work is completed, the sides of trenches should be carefully filled
with earth and well consolidated. A gentle slope should be provided so as to keep rain
water away from the wall.
4. Plinth protection should be provided and given due consideration.
 2.9 Methods of setting out foundation trenches

SET OUT THE FOUNDATION FOR A BUILDING BY USING CENTER LINE METHOD
Aim:
To determine the setting out the foundation for a building, using center line method.

Instruments Required:
Theodolite, Pegs, Arrows, Measuring Tape or Chain, mason’s square, ball of string, lime powder.

Planning and organization:

A small area is to be kept ready for setting out a simple rectangular building of size 6m x 3m. The site
has to be cleaned off any vegetation and made level. or given plan.

Given:
A hall 6m x 3m internal dimension has to be constructed. The wall are 230mm thick. The width of the
foundation is 900mm. Set out the building, mark foundation trench.
 Procedure:
1. Study the plan of the building and note down the internal dimensions and also the width
of the foundation.
2. Prepare the center line sketch of the building.
3. Remove the any vegetation in the construction site.
4. Setting out a straight line slightly greater than the length of the front wall. The frontage is
to be located with respected to other features is site plan such as road etc., this line will be the
center line of the front wall.
5. Now mark the two ends of the front wall.
6. Drive two pegs a little away from the ends marked and tied a string accurately.
7. At two ends, set out perpendicular strings using masons square.
8. Stretched strings of the sidewalls and ties\ with pegs a little beyond the required.
9. Repeat the same for other side walls.
10. Now, stretched strings through the points C and D indicates the ends of the centers lines of
the side wall give a rectangle bounded by strings. This rectangle indicates the center line of the
building.
11. Measuring the four sides of the rectangular and check its accuracy as per the center line
sketch prepared.
12. Check the angles of the corners.
13. Measure the diagonals and check for its accuracy.
14. If items 11,12,13 are satisfied the rectangle is marked.
15. Mark the width of foundation of wall on ground have the wide on either side of the center
line marked and apply lime powder to indicate outline of the foundation trench.

RESULT:
The foundation marking is done for the given layout.
C
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