1. Introduction to Construction Technology
Unit 3
SUBSTRUCTURE DESIGN -
FOUNDATIONS
Unit 3 Substructure Design - Foundations

2. Introduction to Construction Technology
In any building
the superstructure
the substructure (foundations)
the supporting soil
act together to give the building structural stability
Unit 3 Substructure Design - Foundations

3. Foundations are the vital link between the superstructure and the ground.
The criteria for a successful foundation are:
it should be at a minimum depth and size, without exceeding the allowable bearing capacity of any soil layer below the foundation.
it should have settlement consistent with the supporting structure
it should be able to withstand natural ground movements from frost, moisture and heat
regard is given to buildability
it should be economical

4. The principles of foundations.
The basic function of a foundation is to intercept the load exerted by a building structure and transfer this load to the supporting soil in such a way that the building will not sink into the ground (subside)
Structural stability is normally achieved in either of two ways, or indeed a combination of both.
Spread the load exerted by the building over a sufficiently wide area to prevent the supporting ground being overstressed
Divert or transfer the load to a strata, deep in the ground, which is capable of supporting the imposed load without failure

5. When a building is placed on the ground it exerts a force on the soil.
Safe foundations place that load such that the soil is not overloaded.
The ability of the ground or soil to “bear” a load varies with types of soil and ground depth

6. Typical subsoil bearing capacities
Type of subsoil
Bearing Capacity
(kN/M2)
Rocks, granites and chalk
600 – 10000
Non-cohesive soils
Compact sands
Loose uniform sands
Cohesive soils
Hard clays
Soft clays and silts
0 – 600
Peats and made-up ground
To be determined by investigation

7. To achieve this basic function the foundation must be:
Be constructed of materials that will not be degraded by chemicals found in the soil around the foundation. Normally foundations are composed of concrete and when conditions demand, the specification of the concrete will need to be altered to avoid corrosive elements in the soil.
Able to withstand the effect of frost (also applies to services buried in ground)

8. TYPES OF SOIL
Rock
The hardest rock is igneous e.g. granite and basalt. Normally they have a high safe bearing capacity, 2-3 times that of sedimentary rocks and times that of clays and sands. Generally bedrock is an excellent base to build on but unfortunately the cost of levelling and the cost of excavating service trenches outweighs the initial advantage of a good natural base.
Course grained non-cohesive soils
Gravels and sands come under this heading. When loaded they shear if unconfined. The particles slide over each other at an angle known as the angle of internal friction .
Fine grained cohesive soils
These include clays and silts. The major problem with these types of soil is that their nature changes with the level of moisture in the soil. When the soil drys out they shrink, but when the moisture content is increased the soil swells. When water trapped in the soil freezes it can cause vertical heave

9. Types of soil
Organic soils
These include peat, loam and mud. Generally unsuitable for building on. Normally mm thick. Such soil (top soil) is usually removed before building begins.
Made up soil
As the stock of quality building land diminishes, poorer ground is often used. Today made up ground is being utilised. Extreme care should be taken to ensure that such land is properly investigated.

11. Working out imposed loadsB C D E F
6.000
6.000
6.000
6.000
6.000 C1 C4 C4 C4 C4 C1 1 B1 B1 B1 B1 B1 B1 B3 B1 B3 B1 B3 B1 B3 B1 B1
SD1
SD1
SD1
SD1 B3
SD1
6.000 C2 C5 C5 C5 C5 C2 2 B1 B1 B1 B1 B1
SD1
SD1
SD1
SD1
SD1 B2 B2 B2 B2 B2 B2
9.000 C6 C3 C3 C3 C3 C6 3 B1 B1 B1 B1 B1
B1 = 406 x 130 x 39 Universal Beam C1 = 254 x 254 x 71 Universal Column Note that this building has 3 storeys
B2 = 457 x 152 x 74 Universal Beam C2 = 305 x 305 x 88 Universal Column above ground level + a concrete roof
B3 = 305 x 127 x 37 Universal Beam C3 = 305 x 305 x 149 Universal Column having the same construction as the
C4 = 305 x 305 x 79 Universal Column floors. The ground floor slab is ground
SD1 = Structural Concrete Composite Floor C5 = 305 x 305 x 186 Universal Column supported and is to be disregarded in
using Corus ComFlor 80 Composite Floor C6 = 254 x 254 x 85 Universal Column foundation assessments.
Decking- depth of slab = 150mm.
Load imposed by ComFloor Deck = 0.75kN/m2

12. QUESTION FOR DISCUSSION IN CLASS
The loads exerted by the building vary according to the size, use and form of construction used.
What loads are exerted by a building on to the ground below the building?
As discussed in unit 2, the building is exposed to both dead and live loads
Permanent or dead loads: the weight of the structure, cladding and fixed equipment Temporary or live loads : imposed loads – people furniture, non-fixed equipment. environmental or dynamic loads - snow or wind. thermal loads – temperature changes causing load on structure

13. To achieve this basic function the foundation must be:
Strong enough to prevent downward vertical loads shearing through the foundation
Capable of withstanding the opposing forces, the weight of the building and the resistance of the soil, such that the foundation will not bend
Stable so that it will not overturn .Whenever possible loads on foundations should be placed centrically.

14. To achieve this basic function the foundation must be:
Capable of withstanding changing conditions in the ground if they occur, e.g. movement caused by shrinking and swelling, water pressure, etc.
Accommodate initial settlement of the structure. It is especially important that uneven settlement does not occur.
That the installation of foundations does not overstress the ground such that adjacent existing foundations and services are damaged. It should be noted that the installation of new ground based services can undermine existing foundations. It should also be noted that where services pass under or adjacent to foundations the load exerted on them by the foundations may cause failure. In such situations, such as a sewer collapse this may in turn undermine the foundation.

15. BUILDING NEAR TREES
The combination of shrinkable soils and trees, hedgerows or shrubs represents a hazard to structures that requires special consideration. Trees, hedgerows and shrubs take moisture from the ground and, in cohesive soils such as
clay, this can cause significant volume changes resulting in ground movement. This has the potential to affect foundations and damage the supported structure. In order to minimise this risk, foundations should be designed to accommodate the movement or be taken to a depth where the likelihood of damaging movement is low.

18. Water requirements for different types of trees

19. Main types of foundations
Near Surface Foundations - spread foundations
Strip Foundations
Pad Foundations
Continuous Column Founds
Balanced Footings
Rafts:
Plain Slabs
Stiffened Edge
Downstand Raft
Upstand Raft
Cellular Raft
Buoyancy tanks
Deep Foundations
Piled Foundations
Bored Piles
Driven Piles

20. Introduction to Construction Technology
Main types of foundations
Spread foundations
Piled foundations
Unit 3 Substructure Design - Foundations

21. SPREAD FOUNDATIONS

22. Main types of strip foundations
Simplest form of foundation is the strip foundation, used to support a load bearing wall
Main types of strip foundations
Conventional strip
Deep strip
Wide strip

23. CONVENTIONAL STRIP FOUNDATIONS
Spread the load exerted by the building over a sufficiently wide area to prevent the supporting ground being overstressed

24. A good quality ‘freehand’ sketch of a simple strip foundation

26. Deep strip foundations
Tend to be used at depths greater than 1.2 m deep

27. A good quality ‘freehand’ sketch of a deep strip or trench fill foundation

28. Introduction to Construction Technology
Pad foundation
Unit 3 Substructure Design - Foundations

30. GROUND BEAMS

32. RAFT FOUNDATIONS
Spread the load over a wider area

33. RAFT FOUNDATIONS
Spread the load over a wider area

35. Introduction to Construction Technology
Raft foundation
Unit 3 Substructure Design - Foundations

36. PILE FOUNDATIONS

37. Pile Foundations
Divert or transfer the load to a strata, deep in the ground, which is capable of supporting the imposed load without failure

38. Introduction to Construction Technology
Pile foundations
Two main types displacement & replacement
Typical displacement or driven pile
Unit 3 Substructure Design - Foundations

39. Introduction to Construction Technology
Unit 3 Substructure Design - Foundations

40. Introduction to Construction Technology
Displacement or percussive piles being installed
Unit 3 Substructure Design - Foundations

41. Introduction to Construction Technology
Typical replacement or bored pile
Unit 3 Substructure Design - Foundations

43. Introduction to Construction Technology
Pile cap
Unit 3 Substructure Design - Foundations

45. BASEMENTS

51. What type of foundation would you use in the assignment?
Where would you locate the foundations?
Is there a role for a basement?