Backfill

Question 1

What is backfill

Answer 1

material excavated from a site and used for refilling once ore extraction has occured, it can provide ground support

Question 2

What are the underground backfill options used

Answer 2

*paste
*hydraulic
*rock

Question 3

What is rock fill

Answer 3

cemented and non cemented fill
Used to fill in open stope methods to provided minimisation to ground movement problems and in now engineered to improve with pillar recovery

Question 4

What is hydraulic fill

Answer 4

slurry and dense slurry fills
made of tailings and are prepared at surface plants. The fine fraction is removed and then sent to the tailings dam the remaining slurry goes to pipelines to underground voids

Question 5

What is a risk with hydraulic fill

Answer 5

Water needs to be drained out of the fill in an efficient manner. Poor water drainage could cause fill liquefication which is dangerous

Question 6

What is paste fill

Answer 6

comprises of full tailings it is the densest form of backfill

Question 7

What determines the backfill method

Answer 7

*configuration of the mining process
*stope sequence and excavation size as determined by the mining method
*depth and orientation of the orebody
*backfill material available
*cost

Question 8

What are adv and dis of rock fill

Answer 8

Adv
*high modulus (stiff)
*can use waste rock in UG

Dis
*difficult to consolidate
*requires crushing at some point
*not always available
*tailings not used

Question 9

What are adv and dis of sand fill

Answer 9

Adv
*negligible unless cemented

Dis
*cost
*difficult to control moisture
*environmental problems

Question 10

What are adv and dis of hydraulic fill

Answer 10

Adv
*easy to transport
*reduces tailings disposal
*low plant cost

Dis
*high water content
*high binder content
*slow to consolidate
*extensive bulkheads construction

Question 11

what are adv and dis of paste fill

Answer 11

Adv
*no water generated
*faster set times
*no bulkhead construction
*reduce binder requirements
*environmentally friendly as less water is used
*less underground contamination
*placement options do not have to be continuous

Dis
*difficult to transport
*pumping for horizontal runs

Question 12

What are the key backfill properties

Answer 12

UCS
Permeability

Question 13

What are extra considerations for backfill

Answer 13

*high early strength
*sustainable long term strength
*ensuring dimensional stability after placing (by meeting/exceeding design performance requirements)

Question 14

What are backfill sources from coal mines

Answer 14

*fly ash
*solid waste
*high water material

Question 15

What are adv and dis of fly ash (granular) backfill

Answer 15

Adv
*cheap material and addatives
*high strength
*backfill rate is high
*low labour system that is simple

dis
*needs special backfill support and rear scraper conveyor

Question 16

What are adv and dis of cemented backfill

Answer 16

adv
*does not absorb water leading to reduced isolation time
*no complex filtering system required
*high strength
*readily comes in contact with the roof
*low compression ratio

dis
*complex and significant investment in early period
*high power back fill pump in needed and piplines are easily blocked

Question 17

What are adv and dis of high water content backfill

Answer 17

adv
*simple
*low initial investment
*easily transported
*low labor intensity
*readily lose water and are readily pulvarised

dis
*ratio need to control the high water content material
*backfill materials are expensive and cannot permit recycling of gangues and fly ash of coal mines