Basements

Question 1

What are the three main types of basement?

Answer 1

Retaining Wall and Raft
Box and Cellular Raft Basements
Piled Basements

Question 1

What are the grades of basement and typical performance levels

Answer 1

All related to performance level with waterproof-ness

Grade 1 - Some leakages and damp areas tolerable. Local drainage may be required.
Grade 2 - No water penetration but damp areas tolerable dependant on the intended use. Ventilation may be required to control condensation.
Grade 3 - Dry environment. No water penetration. Additional ventilation, dehumidification or air conditioning appropriate to intended use.
Grade 4 - Totally dry environment. Requires ventilation, dehumidification, or air conditioning appropriate to intended use.

Question 2

What uses would there be for each basement grade?

Answer 2

Grade 1 - Car parking, Plant rooms (excluding electrical equipment), Workshops.
Grade 2 - Workshops and Plant rooms requiring drier environment than Grade 1 storage.
Grade 3 - Ventilated residential and commercial areas including offices, restaurants, and leisure centres etc.
Grade 4 - Archives, Landmark buildings, and stores requiring a controlled environment

Question 3

What is retaining wall and raft basement construction?

Answer 3

Very common type of basement construction.

Involves open excavation, raft foundation is installed as the substructure (underneath basement footprint), retaining wall is then formed.

Question 4

Can you give me an example of how to construct a basement

Answer 4

Yes, for Quayside lodge (which was a 1 storey basement), the methodology was:

1) Secant piles are set out and installed.
2) Capping beam is then formed.
3) The excavation then began,
4) Piles were then installed within the basement floor level.
5) Basement liner wall was forming
6) Basement floor slab was then installed
7) Columns within basement begin to be formed and installed.

Question 5

What is a piled basement?

Answer 5

Superstructure loads are carried to basement level via columns
Loads transferred from caps to piles

Question 6

What are the elements of a typical basement structure?

Answer 6

Piles, retaining wall (secant or sheet), columns, Raft foundation, pile caps

Question 7

What are the some techniques to waterproof a basement?

Answer 7

Using waterproofing concrete
Mastic Asphalt tanking

Question 8

What is mastic asphalt tanking?

Answer 8

Continuous waterproof membrane to the base of the slab and walls

Question 9

What is external Mastic Asphalt Tanking?

Answer 9

Preferential method
Prevents ingress and protects the structure
Generally is sprayed on

Question 10

What is internal Mastic Asphalt Tanking?

Answer 10

Only adopted if external is not possible

Does not protect structure as external does

Question 11

What is top down / bottom up construction?

Answer 11

Top Down
The top-down method sees the top slab being constructed and then construction moves downwards to the base slab

Bottom up
Traditional technique of constructing underground structures starting from the bottom and working upwards