Lecture 2 - Geotechnical Engineering contd...

Question 1

What long term bolt and dowel stabilisation techniques are there? How are they achieved?

Answer 1

Bolts, dowels, anchors - transfer load from unstable exterior to confined inferior
Rock bolts - steel bars drilled in holes fixed at inner end by resin or expansive shell, tensioned, increase normal stress across joints
Grouped dowels, steel bars drilled in holes through joints providing direct shear resistance

Question 2

How can are soil and rock anchors used to stabilise slope long term?

Answer 2

Rock and soil anchors - tensioned steel cables drilled into rock soil, drill rod removed, cable grouped into position, cable tensioned, locked on plate

Question 3

Name one kind of rock anchor

Answer 3

Duckbill rock anchor

Question 4

What is shotcrete? Why is it unpopular?

Answer 4

Shotcrete is a long term stabilisation technique whereby concrete is sprayed onto slope
Unpopular as ugly

Question 5

What do baboons provide? Give two advantages

Answer 5

Provide toe stabilisation

Cheap and simple

Question 6

Give examples of retaining structures

Answer 6

Cribs, mechanically stabilised walls and sheet piles

Question 7

How does gradient of slope effect choice of method for stabilising embankments and cuttings

Answer 7

Embankments used up to 45 degree slope
>45 degrees reinforced with geotextiles
If near vertical then retaining structures used

Question 8

What are embankments generally composed of?

Answer 8

Material from cuttings

Question 9

What is the different purposes of basal geotextiles and synthetic soil cells?

Answer 9

Basal geotextiles - prevents settlement

Synthetic soil cell - prevents failure

Question 10

How is blasting carried out? What are the key controls?

Answer 10

1. Face survey
2. Drilling of shot holes
3. Checking holes
4. Charging with explosives and stemming top
5. Detonating the explosives
6. Shotpile ready for loading
   Key controls are rock strength and fracture state

Question 11

What is the disadvantages of production blasting?

Answer 11

Untidy, less stable slope

Question 12

What is the pro and con of pre-split blasting?

Answer 12

Pro: Controlled, more stable slope
Con: Unnatural appearance

Question 13

What is ripping?

Answer 13

Mechanical excavation by steel Tyne mounted on bulldozer

Question 14

What three factors influence tunnels?

Answer 14

Rock type
Nature of bedding, fractures
Orientation of bedding, fractures