Experimental study of the “short-term” pressures of uncemented paste backfill with different solid contents for barricade design

Abstract

The successful application of paste backfill in underground mines depends on the stability of a confinement structure, called barricades, constructed at the base of stopes to hold the backfill slurry in the stopes. The stability analysis of barricades needs the knowledge of the pressures during or shortly after the placement of the paste backfill exerted on the barricades. The recommendation of slight construction of barricades for paste backfill given in the few handbooks on paste backfill implicitly indicates that the paste backfill pressure is very small. This does not correspond to the field pressure measurements reported in the literature, which indicated that the pressures of paste backfill during and shortly after the placement can be as high as the iso-geostatic overburden pressure. To understand this dilemma, the difference between the paste backfill defined in the handbooks and that used in underground mines is for the first time highlighted. The former requires a high enough solid content and the backfill should be unsaturated. In practice, enough water has to be added in the backfill to facilitate its transportation by pipes. The solid content cannot be as high as that required in the handbooks. The dilemma between the recommendation of handbooks and field pressure measurement is for the first time solved. However, this analysis tends to indicate that the pressure of paste backfill depends on the solid content. To verify this hypothesis, a series of laboratory tests were conducted to measure the vertical total stresses of paste backfill having different solid contents at the end of filling operation. The results show that the vertical total stresses decrease as the solid content increases. The solid content should be taken into account in the pressure estimation of paste backfill for the design of barricades.