Effect of Fly Ash and Steel Fiber Content on Workability and Mechanical Properties of Roadway Side Backfilling Materials in Deep Mine

Abstract

The stable bearing capacity of roadside backfill body (RBB) is the key to control the surrounding rock deformation of gob-side entry retaining (GER) in deep mining. In this paper, slump and uniaxial compressive strength tests were conducted to study the changes of the slump and RBB mechanical properties of RBB fresh mixture under the influence of different percentages of fly ash (FA), river sand, and amounts of steel fiber (SF) admixture. The results show that (1) the slump first increases and then decreases with the increase of the FA proportion, while 20% of FA proportion is the critical point. In addition, SF has little influence on slump. However, when the proportion of FA is 60% and the content of SF is 0.4%, the slump reaches the minimum value of 130 mm. (2) The peak strength and residual strength increase with the increase of the FA proportion, and the strength gain starts to decrease when the FA proportion exceeds 40%. Moreover, SF only has a small effect on the peak strength when the dosage is 0.8%. (3) The post-peak strain difference decreases with the increase of the FA proportion and increases with the increase of the SF content. The addition of SF can make up for the reduced capacity of RBB to post-peak deformation caused by the addition of FA to a certain extent. (4) The addition of fly ash does not change the brittle failure mode of RBB. Furthermore, after the addition of SF, RBB changes from brittle to ductile failure mode. This study can provide experimental and theoretical basis for improving the bearing capacity of RBB and maintaining the stability of GER.