The document discusses foundations for buildings. It states that foundations transfer structural loads from a building safely into the ground, reaching below the frost line into competent soil or rock. Foundation design depends on factors like subsurface soil, loading intensity, and groundwater. Shallow foundations like spread footings are used when soils can support loads near the surface, while deep foundations like piles are needed in weak soils. Foundation selection involves considering soil strength, loads, construction methods, and effects on neighboring properties.

1. FOUNDATIONS

2. INTRODUCTION TO FOUNDATIONS
 Function of a foundation is to transfer the structural loads
from a building safely into the ground.
 It should reach the underlying soil that is free of organic
matter and unreachable by the winter’s frost.
 A larger and heavier building of masonry, steel, or
concrete would require its foundations to go deeper into
earth such that the soil or the rock on which it is founded is
competent to carry its massive loads.
 foundation design is a highly specialized field of
geotechnical engineering.
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3. Major Building Parts
Superstructure
Substructure
Foundation

4. Primary Factors Affecting
Foundation Choice
 Subsurface soil
 Ground water conditions
 Structural requirements
 Lateral earth pressure
 Intensity of loading

5. Secondary Factors Affecting Foundation
Choice
 Construction access, methods & site conditions
 Building Codes & Regulations
 Impact on surrounding structures
 Construction risks
 Environmental factors

6. SELECTION OF FOUNDATION TYPE
Selection of foundation depends on whether the load
is transfer at deeper depths or shallower depths.
Following parameters will be considered while
selecting a foundation type.
 Soil strength
 Ground conditions
 Foundation loads
 Construction methods
 Impact on adjacent property.

7. Foundation Loads
 Dead Load
 Live Load
 Wind Load
 Earthquake
 Structural Member Forces

8. SETTLEMENT IN FOUNDATION
 Uniform
 Differential
Differential settlement must be minimized, depends
on site soil conditions and distribution of loads on
columns supporting the building

9. SETTLEMENTS OF FOUNDATIONS
NO SETTLEMENT * TOTAL SETTLEMENT * DIFFERENTIAL SETTLEMENT
Uniform settlement is usually of little consequence in a building, but differential
settlement can cause severe structural damage

11. Main types of foundation
Foundations or ‘footings’ come under two main
categories
 Shallow foundation.
 Deep foundation.

12. Shallow foundations
Shallow foundations
Shallow foundations includes spread column footings without
or with tie/grade beams, individual or combined wall footing,
strip footings, stepped foundation, grillage foundation and
rafts.
The guidelines for a shallow foundation are
 They are founded near to the finished ground surface.
 The depth is generally less than the width of the footing
and less than 3m.
 They are used when the surface soils are strong enough to
support the load imposed upon it.

13. SPREAD FOOTINGS
 Made from reinforced concrete
– Square (B x B)-Usually one column
– Rectangular (B x L)-When large M is needed
– Circular (D/B<3, Rounded)-Flagpoles, transmission lines
– Continuous (Strip)-Support of bearing walls
– Combined (Cantilever)-Provides necessary M to prevent
failure. Desirable when load is eccentric and construction
close to property line.

14. Weight Distribution in footing

15. Sizes of Footings
 The width of the wall is the
height of the footing
 The width of the footing is
twice the size at the wall
 W, W, 2W is the rule

16. Footing Specifications
 Footings should extend down at least 6” into
undisturbed earth…no fillings under footing
 Footing must be at least 6” below the frost
line
 If soil is bad, increase the size of footing

17. Sizes of Foundation Walls
 Depends on lateral earth pressure and vertical
load to be supported
– Typically walls are 8” thick
 Basement walls must extend 8” above the
finished grade. Min height is 7’5”.

18. 18
Combination Spread & Strip Footing Spread Footing
Spread FootingReinforcement in Spread Footing

19. 19
Types of Spread Footing

20. 20

21. 21
Grillage Foundation

22. 22
Steped Foundation

23. Strip foundations
These are use to support
a line of loads such as a
load bearing wall.
They could also be used
where the line of
column positions are so
close that individual pad
foundations would be
pointless.

24. Raft Foundations
 These are used to spread
the load from a structure
over a large area.
 This would normally be
the entire area of the
structure.
 Raft foundations are often
needed on soft or loose
soils which have a low
load bearing capacity.

25. ADVANTAGES OF RAFT FOUNDATIONS
– Spread the load in a larger area-Increase bearing pressure
– Provides more structural rigidity
– Reduce settlement
– Heavier-More resistant to uplift
– Distributes loads more evenly

26. Deep foundations
Deep foundations
 Shallow foundations are unsuitable in weak or highly
compressible soils so, deep foundation is provided in such
areas where soil bearing capacity is very low and heavy
loads are expected. Deep foundations are usually at depths
deeper than 3m and use to transmit the loading to a deeper,
more competent strata.
 Caissons with or without sockets, end bearing or friction
piles, pile walls and piers.
 Made of concrete (precast or cast in situ) or steel or wood

27. Deep Foundations - Purpose
transfer building loads deep into the earth
Basic types
– Drilled (& poured)
– Driven
(End bearing piles for
point load and friction piles
will transfer load by friction
resistance between the pile
and the earth)

28. Pile foundations
 Piles are used to support
buildings in poor soil
conditions.
 A basic pile foundation is a
series of stilts which rest on
a solid load bearing layer.

32. Precast Concrete Plies

33. Benched Excavation

34. Backhoe
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35. DOZERS

36. Solder Beam & Lagging

37. Bank Requiring a Retention System

38. Retention System Depends On:
 Proximity to Buildings
 Type of Soil
 Water Table Level
 Temporary or Permanent
 Cost - KEY Consideration

39. Dewatering
 A process of removing Water and/or lowering the
Water Table within a construction site
 Purpose: To Provide a Dry working platform -
(typically required by Code and Specification)
 If the Water Table is above the working platform;
Options:
» Keep water out
» Let water in & remove it
» Combination

40. SOIL TYPES
 The make up of the soil has a major
influence on the choice of foundation.
 A good soil type needs to be able to cope
with loadings.
 A good soil needs to drain water well.
 A poor soil type will shrink, swell or move
depending on the loads or conditions placed
upon it.

41. SILT
 Silty soil is found in flood plains or around
lakes.
 Silt holds water well and is soft when wet.
 Silty soil is not a very good foundation
material unless it has been compressed and
hardened, or has been dried out.

42. SANDY SOIL
 Sand is usually considered favourable from
the standpoint of foundation support.
 It can be a problem though usually due to
water.
 Water raising through a sand deposit can
create an unstable condition.
 Sandy soils can hold water.

43. CLAY
 Clay is composed rock particles ground
extremely fine or reduced by weathering.
 Clay soils normally contain water.
 Clay drains slowly and compresses when
foundations are placed upon them.
 Clay has a tendency to absorb water and
swell.

44. ClaysPorous
(sandy)

45. GRAVEL
 Gravel can be well compacted and allows
water to drain freely.
 Gravel soils do not hold water.
 The variety in particle sizes in gravel means
that even when closely packed it still
contains voids and drains well.
 Gravel is least likely to be affected by
drying out.

46. Waterproofing
 Structures Below Ground subject to penetration of
ground water
 More extreme, if below H2O table
 Two basic approaches to Waterproofing
– Waterproof Membranes, or
– Drainage
– Generally - both used in tandem

47. Waterproofing Membranes
 Materials
– Liquid or Sheet (Plastic, asphaltic, synthetic rubber)
– Coatings (asphaltic)
– Cementitious Plasters & admixtures
 Accessories
– Protection Board
– Waterstop
 Unit of Measure - SF, Mils (thickness)

49. Thank You
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