2. Rock Geology and Excavation Flashcards
4 Keys to Understanding a Rock Mass
- Rock mass
- Rock structure
- Stress
- Water
What does rock mass affect?
- fragmentation
- displacement
- blast damage
How does rock porosity affect blasting?
large voids can store water + the larger the pores, the more energy lost during a blast
How does grain size affect blasting?
fine grain rocks may cause cuts to freeze
Why must rock mass conductivity be considered when designing a blast?
premature blasting may occur if the current can travel through the rock to the next drillhole
How might a rock mass containing sulfide or coal affect blasting?
can cause secondary explosions
Would mechanical boring or drill-blast be used for long straight tunnels in sed. rock?
mechanical boring
Would mechanical boring or drill-blast be used for long straight tunnels in igneous rock?
mechanical boring
Would mechanical boring or drill-blast be used for short curved tunnels in sed. rock?
drill-blast
Would mechanical boring or drill-blast be used for short curved tunnels in igneous rock?
drill-blast
What are 5 reasons to blast?
- fragmentation
- losseness
- movement
- minimum damage
- reduce over breakage
What are 5 types of surface blasting?
- bench
- throw/cast
- sinking cut
- wall control
- secondary
What are 5 types of underground blasting?
- raise
- bench
- ring
- shaft
- development
What are 8 implication of bad blasting?
- reduced excavation productivity
- secondary blasting
- reduced recovery
- increased waste volume
- increased airblast
- increased ground falls
- increased ground vibration
- increased dilution
What 4 things does fragmentation depend on?
- confinement
- coupling of charge with blasthole
- burden
- blast sequencing
Blastability Index
describes the ease of blasting; the higher the rating, the easier the rock mass is to blast
What 5 parameters does the blastability index depend on?
- rock mass description
- joint spacing
- join orientation
- rock density
- rock strength
How does confinement affect fragmentation?
lack of confinement results in loss of energy from blast hole
What is the purpose of blast sequencing?
delays allow space for the rock to move into
