Foundations Flashcards
0
Q
Functions of foundations are
A
- to transfer load of structure to soil
- to prevent settlement of structure
- to resist lateral forces
1
Q
Types of foundations
A
- strip footing/foundation
- pad (spread) footings
- raft foundations
- pile foundations
2
Q
To design a foundation, we need:
A
- site plans
- site geotechnical investigation report (soil types and properties, load bearing capacity of soil, ground water table)
- static and dynamic loads from structure
- constraints on site
3
Q
How to identify soil:
A
- by field identification
- by lab tests
4
Q
Field identification:
A
- greater than 2mm = gravel
- from 2 - 0.06 mm = sand
- from 0.06 - 0.002 = silt
- less than 0.002 = clay
5
Q
Lab tests for soil ID:
A
- sieve test
- liquid limit test
- plastic limit test
- triaxial compression test
6
Q
Soil description
A
G: gravel S: sand M: silt C: clay O: organics
W: well graded (different sized particles)
P: poorly graded (homogenous)
H: high plasticity
L: low plasticity
7
Q
Types of foundations by behavior:
A
- shallow foundations: strip, spread (pad), combined, raft footing.
- retaining wall
- deep foundations: pile, caisson.
8
Q
Pad/spread/isolated footing:
A
- excavation from 1 to 3 m (or 5 m)
- usually under a single column located in middle of footing
- distributes load from column to soil
9
Q
Combined footings
A
- usually support two columns of unequal loads
- suitable when interior columns are too close
10
Q
Strip footing
A
Wide strip of reinforced concrete that supports loads from bearing wall.
11
Q
Raft foundation
A
- primarily a shallow foundation
- expanded continuous footing usually analyzed as a single unit
- usually used on houses or 10+ high-rise buildings.
12
Q
Pile foundations
A
- more expensive than shallow foundations
- will overcome problems of soft surface soils by transferring load to stronger, deeper stratum, therefore reducing settlement.
13
Q
Caisson foundation
A
- deep foundation used in dams, bridges and off-shore structures
- up to 3m dia hole boring
- over 50m depth
- metal shell, box or casing is placed in hole, reinforcing and cast-in-place concrete.
14
Q
Serviceability limit
A
- until crack appears
- 1.0 G (dead load) + 1.0 Q (live load)
