Abstract: Large scale direct shear tests were performed on the furnace slags and flay ash mixtures backfill materials with three different moisture contents, 0%, 8% and 13% respectfully. The objective of the test study was focused on the effect of moisture contents on the internal friction angle of the backfill materials. The results indicate that the internal friction angle increases with the moisture content of the materials first, and then decreases. The internal friction angle reaches at the peak value at a moisture content of 8%. The tested cohesion, however, reduces with the increase of moisture content significantly and then turns to flat. It is concluded that the moisture content has the large impact on the cohesion of the backfill material but has the less effect on the internal friction angle. The maximum shear strength can be achieved at a moisture content of 8%.

Key words: Blast Furnace Slag and Fly Ash Mixture, Large-Scale Direct Shear Tests, Characteristic Analysis