Topic 5.2.1

Question 1

Construction sequence of bottom-up method for basement

Answer 1

1. Excavate and strut
2. Construct bottom-up
3. Backfill

Question 2

Advantages of bottom-up construction

Answer 2

Waterproofing can be applied to outside surface
Inside of excavation is easily accessible
Drainage systems can be installed outside the structure
Conventional construction method

Question 3

Disadvantages of bottom-up construction

Answer 3

Larger footprint required for construction
Ground surface cannot be restored to final condition until construction s complete
Requires temporary support
May require dewatering that can affect surrounding infrastructure

Question 4

Construction sequence of top-down method

Answer 4

1. Construct ERSS
2. Install foundation bored piles
3. Install steel H-piles
4. Construct ground floor slab and beams with openings
5. Excavate, cast floor slab of first basement level with openings
6. Excavate, cast floor slab of second basement level
7. Repeat until desired depth
8. Construct foundation slab
9. Construct pile caps and ground beams when formation level is reached

Question 5

Advantages of top-down construction

Answer 5

Shortened construction period
More operational space
Highly suitable for construction of tall buildings with deep basements
Can be installed in close proximity to existing structure

Question 6

Disadvantages of top-down construction

Answer 6

Higher cost
Lateral displacement of retaining wall is possible
Construction quality may be influenced
Requires highly skilled supervision and labour force