Mining Engineers Toolbox - Mine Backfill Properties

Mine backfill is defined as the material or materials used to fill the cavities created by mining so as to establish and retain safe working conditions, economically. Recently, mine backfill is employed in strategies to reduce surface environmental impacts.

Benefits	Costs
ECONOMIC: Backfill allows higher extraction ratio Backfill reduces dilution Aids in pillar recovery	ECONOMIC: Backfill costs money particularly if binders are used Backfill introduces delays in the mining cycle Additional manpower and infrastructure Additional dewatering costs Dilution due to backfill
SAFETY: Backfill improves regional stability in the mine Backfill can reduce risk of rockbursting	SAFETY: Risk due to bulkhead failure and liquefaction of tailings Risk due to collapse of consolidated backfill walls
ENVIRONMENT: Backfill provides a means of disposing of waste rock and mill tailings, thereby minimizing surface disturbance	ENVIRONMENT: Groundwater contamination

Cut and fill stoping is performed in steeply dipping orebodies where the hangingwall or footwall is not sufficiently competent to maintain the stable spans required for open stoping methods. The method involves the incremental development of a horizontal slot shaped excavation. Fill is placed in the stope after each horizontal slice is taken. Overhansd cut and fill can be either mechanized or captive.

Mechanized cut and fill mining refers to cut and fill stopes that are accessible by rubber tired equipment from the regular mine access development. Mechanized cut and fill stopes can be very productive with stope widths in excess of 40 m in good ground conditions and stope lift heights of 4 to 8 metres. Drilling is typically carried out using 2 or 3 boom drill jumbos using a breasting pattern. Backfill is normally a quick draining hydraulic sandfill with no binder added. Sometimes binder is added at the end of a backfill pour so the surface of the fill has the bearing capacity to support the rubber tired equipment.

Typical equipment used in mechanized cut and fill stopes includes : Drill Jumbos, LHD’s, Trucks, Scaling Machines, Scissor Lifts, Bolting Jumbos

Captive Cut and Fill refers to mining of stopes where equipment remains in the stope during the life of the stope. Captive cut and fill is generally used in narrow vein type stopes. The cost of captive cut and fill is very high relative to other methods. Drilling is typically carried out using jacklegs (breasting) or with stopers (upholes). Ore is mucked by slushers into steel millholes that are carried up through the fill. Backfill normally consist of a quick draining hydraulic sandfill with no binder.

Typical equipment used in captive cut and fill stopes includes : jacklegs, stopers, slushers, Cavo loaders

This technique is similar to conventional overhand cut and fill except that ground conditions do not permit opening up the stope to the full width of the orebody. Depending on the amount of dilution that can be tolerated some binder is required for the initial drift(s) on a level. Drift and fill can be mechanized or captive.

This method involves mining sequentially in horizontal lifts beginning at the top of a stope and working downwards. A binder is added to the backfill to create a stable roof under which to work. Typically cement is used as a binder. The lower portion of the fill pour will typically have a high cement content (14%) and the upper part of the pour would have a lower cement content (3-5%). Undercut and fill can be mechanized or captive.

Typically dry waste rock fill added to the top of a longhole stope to limit the length of exposed wall.