Mass haul Flashcards
What does borrow imply on a mass haul diagram
Implies that you need a borrow pit outside the roadway
What is free haul?
A set distance in contract, defining the distance of earth that must be moved for free. Standard is 300m
Overhaul distance
Distance beyond free haul. Consider wasting if possible
Define ripable rock
Rock that is too dense to be excavated without breaking it apart first with a ripper
- Not so hard that it needs to be blasted
- Various charts are published describing which materials are rippable by various machines
- Classified by seismic velocity
Define seismic velocity?
Measure of strength of P waves and S waves.
P waves (primary waves) are compression waves in materials propagated by explosion or earthquake. Faster as material gets denser.
The S-wave moves as a shear or transverse wave, so motion is perpendicular to the direction of wave propagation. Slower
Rock Breakers
Hydraulic powered jackhammers that attach to excavators
- Remove bucket and attach breaker in about an hour
- Effective in stratified or highly fractured rock of soft to medium hardness
- Useful in areas where you can’t use explosives (next to buildings, power lines…..)
What is the objective of drilling and blasting?
to fracture rock to the preferred size and leave it in the correct place for use on the road
What are some requirements of controlled blasting
Controlled blasting requires a good knowledge of rock, explosives, detonators, and delay mechanisms
How are blasting holes drilled?
Require a pneumatic or hydraulic rock drill mounted on various types of carriers
What’s a tank drill?
- All the machinery is mounted on one carrier
- Called a tank drill because the are mounted on a WWII design tank undercarriage
- Usually a pneumatic hammer
- Not very mobile due to tracks
- Very common on BC coast
What eventually replaced the tank drill
Rubber tired rock drill: All equipment on one carrier
- Rubber tires mean you don’t need a low bed truck to carry the machine between work sites
- High mobility means a large operator may replace two tank drills with one RT drill
- Hydraulic powered hammer is very fast
Describe typical bits for rock drills
- Bits used in forestry are 2 1/2 or 3 inches
- 3 inch holes drill slower but will hold more powder and therefore less holes required (good for quarry work
- 2 ½ holes are usually suited to general road construction work
Describe the drill rod
- This part connects the hammer to the drill bit
- Usually 10 and 12 foot lengths
- To drill holes deeper than rod length connect rods with couplers
- Rods are hollow to feed air to the drill bit for cooling and to eject rock dust
What are the 2 explosives categories?
- Blasting Agents
• Not cap sensitive (a blasting cap won’t set them off)
- High Explosives
• Cap Sensitive (a blasting cap will detonate)
Describe blasting agents?
- Ammonium Nitrate (94%)+ Fuel Oil (6%) is very commonly used in forestry (ANFO)
- Need a cap inserted into a high explosive primer to set them off
- Safe and inexpensive
- Not sensitive to heat, shock, or friction
- Can be mixed on site (requires a special license) or purchased premixed
What is the typical blasting agent used?
ANFO Ammonium nitrate fuel oil
- Usually poured into down holes (vertical hole)
- But can be loaded with a special air compressor in flat holes
- Must be very careful when blowing into rock with lots of natural fissures (overloading causes excessive fly rock)
- Not very water resistant
Describe high explosives?
- Nitroglycerine based products usually mixed with a stabilizer or organic filler like sawdust
- Sensitive to heat, shock, friction, moisture
- Store carefully and use them quickly after manufacture
- Nitro can cause headaches so don’t breathe the fumes
What are the typical detonating systems required?
- Electrical isn’t very common anymore
- Non electric detonating systems are often used in forestry (E-Z Det, Nonel are some trade names )
- Use explosive chords to link drill holes
– Prima-cord, E-cord, B-line
• Connectors between lines act as delays
– Delays are in milliseconds
How are high explosives packaged?
Sausages
Mmm sweet sausages
Maybe u will get a sausage Sammy this morning eh big boy?
That’s right fatty get 2. Don’t forget to breathe
Which way should a driller direct the blast?
What are the benefits of proper technique in blasting?
Direct blast UP
• Proper drilling, loading and delay techniques will:
– Minimize fly rock
– Provide proper fragment size for usable rock
– Prevent overloading of the fill slope
– Minimize damage to trees
What are the sources of energy in borehole blasting?
- Shockwave (p and S waves fracture rock)
- Gas expansion (causes heaving effect)
What is burden?
Distance from borehole to where cracking will stop. Based on rock density. Important to optimize distance to free space.
What does burden depend on?
Burden is most important design parameter in blasting ***
Depends on:
– Specific gravity of explosive
– Specific gravity of rock
– hole diameter
Define specific gravity
the ratio of the density of a given solid or liquid to the density of water. Density of rock / Density of water
