| Chapter 21 - Backfill |
| Number |
Topic |
Rule of Thumb |
| 21.01 |
General |
The cost of backfilling will be near 20% of the total underground operating cost. Source: Bob Rappolt |
| 21.02 |
General |
Typical costs of backfill range between 10 and 20% of mine operating cost and cement represents up to 75% of that cost. Source: Tony Grice |
| 21.03 |
General |
The capital cost of a paste fill plant installation is approximately twice the cost of a conventional hydraulic fill plant of the same capacity. Source: Barrett, Fuller, and Miller |
| 21.04 |
General |
If a mine backfills all production stopes to avoid significant delays in ore production, the daily capacity of the backfill system should be should be at least 1.25 times the average daily mining rate (expressed in terms of volume). Source: Robert Currie |
| 21.05 |
General |
The typical requirement for backfill is approximately 50% of the tonnage mined. It is theoretically about 60%, but all stopes are not completely filled and tertiary stopes may not be filled at all. Source: Ross Gowan |
| 21.06 |
General |
It is common to measure the strength of cemented backfill as if it were concrete (i.e. 28 days), probably because this time coincides with the planned stope turn-around cycle. Here it should be noted that while concrete obtains over 80% of its long- term strength at 28 days, cemented fill might only obtain 50%. In other words, a structural fill may have almost twice the strength at 90 days as it had at 28 days. Source: Jack de la Vergne |
| 21.07 |
Hydraulic Fill |
The quantity of drainwater from a 70% solids hydraulic backfill slurry is only one-quarter that resulting from one that is 55% solids. Source: Tony Grice |
| 21.08 |
Hydraulic Fill |
Hydraulic backfill has porosity near 50%. After placement is completed, it may be walked on after a few hours and is “trafficable” within 24 hours. Source: Tony Grice |
| 21.09 |
Hydraulic Fill |
It takes two pounds of slag cement to replace one pound of normal Portland cement. In other words, HF with 3% normal cement and 6% slag cement will exhibit the strength characteristics of one with 6% normal cement alone. Source: Mount Isa Mines |
| 21.10 |
Hydraulic Fill |
Because the density of hydraulic fill when placed is only about half that of ore, unless half the tailings can be recovered to meet gradation requirements, a supplementary or substitute source of fill material is required. Source: E. G. Thomas |
| 21.11 |
Cemented Rock Fill |
A 6% binder will give almost the same CRF strength in 14 days that a 5% binder will give in 28 days. This rule is useful to know when a faster stope turn-around time becomes necessary. Source: Joel Rheault |
| 21.12 |
Cemented Rock Fill |
As the fly ash content of a CRF slurry is increased above 50%, the strength of the backfill drops rapidly and the curing time increases dramatically. A binder consisting of 35% fly ash and 65% cement is deemed to be the optimal mix. Source: Joel Rheault |
| 21.13 |
Cemented Rock Fill |
The strength of a cemented rock backfill may be increased 30% with addition of a water reducing agent. Source: John Baz-Dresch |
| 21.14 |
Cemented Rock Fill |
The size of water flush for a CRF slurry line should be 4,000 US gallons. Source: George Greer |
| 21.15 |
Cemented Rock Fill |
The optimum W/C ratio for a CRF slurry is 0.8:1, but in practice, the water content may have to be reduced when the rock is wet due to ice and snow content of quarried rock or ground water seepage into the fill raise. Source: Finland Tech |
| 21.16 |
Cemented Rock Fill |
The actual strength of CRF placed in a mine will be approximately 2/3 the laboratory value that is obtained from standard 6 inch diameter concrete test cylinders, but will be about 90% of the value obtained from 12-inch diameter cylinders. Source: Thiann Yu |
| 21.17 |
Paste Fill |
Only about 60% of mill tailings can be used for paste fill over the life of a mine because of the volume increase, which occurs as a result of breaking and comminuting the ore. Source: David Landriault |
| 21.18 |
Paste Fill |
Experience to date at the Golden Giant mine indicates that only 46% of the tailings produced can be used for paste fill. Source: Jim Paynter |
| 21.19 |
Paste Fill |
The inclusion of the slimes fraction (“total tails”) means that at least some cement must always be added to paste fill. The minimum requirement to prevent liquefaction is 1½%. Source: Tony Grice |
| 21.20 |
Paste Fill |
Very precise control of pulp density is required for gravity flow of paste fill. A small (1-2%) increase in pulp density can more than double pipeline pressures (and resistance to flow). Source: David Landriault |