Foundations

Question 1

What are the functions of foundations

Answer 1

To transmit combined foundation and ground loads (dead, live, wind),

Any movement of the ground caused by swelling, shrinkage, or freezing of the subsoil, should not impair the stability of the building

Question 2

What are the 5 types of soils found ?

Answer 2

Rocks
Classified as igneous, sedimentary and metamorphic
Ie granite (high bearing capacity), hard limestone

Non- inclusive soils
Ie Gravel and sand (bearing capacity depends on density, grading and particles size)

Cohesive soils (sticks together)
Ie Clay settle

Peat and organic soils
Made of fibrous vegetable matter, clay or sand silt (not stable ground for foundations)

Made up ground
Variety of material & variable compaction and settlement (unsuitable for foundations)

Question 3

What are the three main types of loads on foundations

Answer 3

Dead loads - static or constant weight created by the buildings, materials and structural elements. Ie external and internal walls, Floors, doors, windows, ceilings, roofs ,basement

Live loads- known as impose loads. They are moveable loads ie furniture, white goods, people etc. also includes variable loads caused by weather conditions such as rain or snow

Wind loads - (earthquake load) can be positive or negative. It’s the load placed on a structure by wind. Loads are calculated to combat this in high structures

Question 4

What are the two types of foundations

Answer 4

Shallow
Deep

Question 5

What are shallow foundations ? 3 points

Answer 5

Found near the finished ground surface

Depth is generally less than the width of the footing, less than 3m.

Shallow foundations are strip (trenchfill), pad, raft and short bore pile and beam

Unsuitable in weak or highly compressible soil

Question 6

What are deep foundations ? 7points

Answer 6

Found deep underground, greater than 3m

Used for structures with high loads, like deep basements and multi- storey structures

Where the soil is weak

Used when trees and vegetation are near the structure

Include pile, peers and compensated foundations

Question 7

What are the 4 types of strip foundations ?

Answer 7

Traditional shallow strip foundations
Wide strip foundations
Deep strip foundations
Trenchfill

Question 8

Draw a strip foundation

Question 9

Where is a pad foundation used and draw it

Answer 9

Used under isolated piers or columns

Question 10

Where is a raft foundation used (2 points) and draw it ?

Answer 10

Used for lightly loaded structures on soils with poor bearing capacity heavily loaded frame structures,

Question 11

Where is short bore pile and beam foundation used and draw it

Answer 11

Used when strip foundation is unsuitable due to ground conditions.
Usually depths of 2-3m long piles

Question 12

What are the 6 advantages of short, bore pile and beam foundations ?

Answer 12

Clay heave or shrinkage is not affected in clay soils

Groundwater can percolate between piles

Tree roots have little effect

No dewatering is required when piling

Less concrete used then strip

Uses precast connect beams, saves time

Question 13

What are the 2 disadvantages of short bore pile and beam foundations

Answer 13

The technique require specialist plant and labour
Piling requires a pile rig

Question 14

What are the 4 main types of materials use for pile foundations?

Answer 14

Timber, steel ,concrete and composite piles

Question 15

What are the 2 functions of pile foundations?

Answer 15

To transmit a foundation load to a solid ground
To resist vertical, lateral and uplift load

Question 16

What are the main components of pile foundation?

Answer 16

Pile cap and the piles

Question 17

Draw the pile pressure, bubble and down drag diagrams


Question 18

What are the 4 Advantages of pile foundations

Answer 18

Less excavation than deep strip foundations

Less concrete used than deep strip foundations

Quick

Constructible on shrinkable Clays

Question 19

Disadvantages of pile foundations

Answer 19

Require specialist equipment

beams and slabs require reinforcement

does not reduce ground movement around the building’s perimeter

Question 20

Draw pile and ground beam foundation

Question 21

Advantages of pile and beam foundation

Answer 21

In clay soils clay heave or shrinkage is not affected

Groundwater can percolate between piles

Dewatering not required

Reduced spoil and ground disturbance

Less concrete than strip

Precast concrete beams used, save time

Question 22

Disadvantages of pile and beam foundations

Answer 22

Cost
Specialist plan and labour required

Question 23

Draw pile and beam foundation

Question 24

Draw pile foundation

Question 25

When are deep or pile foundations suitable?

Answer 25

For the construction of multi-storey buildings- pile, piers or compensated foundations used For deep basements Suitable when the transfer of loads need to be deep within the ground and competent strata. When there is no loadbearing capacity of the soil at its geographical location. Results in depths of 3m below floor level Drainage of water runs off hard & soft surfaces effecting the topography When vegetation, plants and tress are excessive and can’t be removed

Question 26

What are the Foundation forces

Answer 26

F1 The bearing pressure exerted by the load of a building F2 the bearing capacity of subsoil on which foundations are supported.

Question 27

What is it called when the foundation forces are equal ?

Answer 27

Equilibrium state

Question 28

What is pier foundation ? (3 points)

Answer 28

Constructed at a shallow depth Normal consist of a cylindrical column of large diameter Used when there is a firm bearing of strata

Question 29

Draw the foundation forces F1 F2

Question 30

Draw combination piles

Question 31

What are the classification of piles

Answer 31

Displacement piles Non-displacement piles

Question 32

What are displacement piles

Answer 32

Piles that are driven or jacked into the ground

Question 33

Name 4 displacement piles

Answer 33

Pre-cast concrete Pre-fabricated steel Cast insitu concrete Screw pile

Question 34

What are non-displacement piles

Answer 34

Soil is removed and the pile is placed in

Question 35

Name 3 non-displacement piles

Answer 35

Bored Continuous flight auger Mini-pile/micro pile

Question 36

What are the 2 advantages of displacement piles

Answer 36

Rapid installation minimal generation of spoil

Question 37

What the 4 disadvantages of displacement piles

Answer 37

Noise and vibration Potential ground heave May not be allowed use on obstructions Potential driving induced damage to pile

Question 38

What are the 2 advantages of non-displacement piles ?

Answer 38

Limited noise and vibration Method can be used to verify ground conditions 

Question 39

What are the 3 disadvantages of non-displacement piles? 

Answer 39

Quality of workmanship and tools influences performance Generation of spoil Support to boring required in granular soils.