2. Rock Geology and Excavation

Question 1

4 Keys to Understanding a Rock Mass

Answer 1

1. Rock mass
2. Rock structure
3. Stress
4. Water

Question 2

What does rock mass affect?

Answer 2

• fragmentation
• displacement
• blast damage

Question 3

How does rock porosity affect blasting?

Answer 3

large voids can store water + the larger the pores, the more energy lost during a blast

Question 4

How does grain size affect blasting?

Answer 4

fine grain rocks may cause cuts to freeze

Question 5

Why must rock mass conductivity be considered when designing a blast?

Answer 5

premature blasting may occur if the current can travel through the rock to the next drillhole

Question 6

How might a rock mass containing sulfide or coal affect blasting?

Answer 6

can cause secondary explosions

Question 7

Would mechanical boring or drill-blast be used for long straight tunnels in sed. rock?

Answer 7

mechanical boring

Question 8

Would mechanical boring or drill-blast be used for long straight tunnels in igneous rock?

Answer 8

mechanical boring

Question 9

Would mechanical boring or drill-blast be used for short curved tunnels in sed. rock?

Answer 9

drill-blast

Question 10

Would mechanical boring or drill-blast be used for short curved tunnels in igneous rock?

Answer 10

drill-blast

Question 11

What are 5 reasons to blast?

Answer 11

1. fragmentation
2. losseness
3. movement
4. minimum damage
5. reduce over breakage

Question 12

What are 5 types of surface blasting?

Answer 12

1. bench
2. throw/cast
3. sinking cut
4. wall control
5. secondary

Question 13

What are 5 types of underground blasting?

Answer 13

1. raise
2. bench
3. ring
4. shaft
5. development

Question 14

What are 8 implication of bad blasting?

Answer 14

1. reduced excavation productivity
2. secondary blasting
3. reduced recovery
4. increased waste volume
5. increased airblast
6. increased ground falls
7. increased ground vibration
8. increased dilution

Question 15

What 4 things does fragmentation depend on?

Answer 15

1. confinement
2. coupling of charge with blasthole
3. burden
4. blast sequencing

Question 16

Blastability Index

Answer 16

describes the ease of blasting; the higher the rating, the easier the rock mass is to blast

Question 17

What 5 parameters does the blastability index depend on?

Answer 17

1. rock mass description
2. joint spacing
3. join orientation
4. rock density
5. rock strength

Question 18

How does confinement affect fragmentation?

Answer 18

lack of confinement results in loss of energy from blast hole

Question 19

What is the purpose of blast sequencing?

Answer 19

delays allow space for the rock to move into