Topic 5.1.1

Question 1

Methods used to support basement excavation

Answer 1

Open cut excavation
Strutted sheetpile walls
Anchored walls

Question 2

Describe open cut method

Answer 2

Sides of excavation are sloped
Slope protection (e.g. shotcrete) to maximise slope angle
Basement is constructed bottom upwards
Remaining excavated areas are backfilled

Question 3

Limitations of open cut method

Answer 3

Not practical in built-up urban areas
Soil condition is main criteria
Site is exposed to weather
Flooding usually occurs after a downpour

Question 4

Where are sheet piled walls used

Answer 4

Temporary works or as permanent retaining walls

Question 5

Where are cofferdams made

Answer 5

In high-rise buildings as temporary structures used in formation of basements

Question 6

Properties of steel sheet piling

Answer 6

Resistant to high driving stresses
Lighter in section
Can be used several times
Used either below or above water

Question 7

How do ground anchors work

Answer 7

Prestressing cable or bar with a fixed anchorage
Cable is inserted in a hole formed by rotary or percussive drilling