Increasing the strength of backfill has been the subject of much research._x000D_
In the former Soviet Union most methods concentrated on the fill mixture including chemical additives, binder re-grinding, water electromagnetic activation and the use of vibration and turbulent activation. For the most hart, this research has been confined to the laboratory where the results vrerc not representative of field conditions. These methods also were directed at increasing the mass strength and were not specifically aimed at strengthening the fill where it may subsequently he exposed for instance on the side or underneath as it required for underhand cut and fill methods of mining. In the Republic of Armenia, a method of fill strengthening known as electro-activation has been adopted. The deposit it an epithermal gold deposit which to-date has been mined using underhand cut and fill with timber support. The backfill comprises cement and pumice placed in 2.5 III lifts. Central to the method of electro-activation is the placement of the electrodes in the scope in which the polarity and the electrical potential arc changing during filling. The process promotes the binding of the fill layers, the bond to the side walls and to the adjacent fill. There is a significant increase in the compressive and tensile strength.