Baogui Yang

Cemented coal gangue-fly ash backfill (CGFB) slurry has commonly been used to control subsidence damage caused by underground coal mining. This paper discusses the characteristics of CGFB slurry fluidity in its pipe transportation. A general description about the components of the CGFB is provided involving the percentage of composition, particle size distribution (PSD) and rheological performance. The CGFB flow characteristics of the slurry pipeline were simulated in a straight pipe and 90° elbow pipe, respectively, combined with the pressure loss and conveying velocity distribution. With the help of the commercial computational fluid dynamic (CFD) code FLUENT, the modeling was conducted with various slurry feeding velocities. These results showed the local resistance loss in a bending pipe is significantly higher than the resistance in a straight pipe under the same conditions associated with CGFB transportation. The velocity distribution of the slurry solid particles in the slurry’s movement forward is more decentralized as the hydraulic inlet velocity increases. Based on these simulation data, a correlation was developed to predict the resistance loss of the CGFB slurry as a function of the hydraulic inlet velocity, pipe diameter and CGFB slurry rheological characteristics.

Clogging pipelines is one of the most common and urgent problems in paste backfill mining. The aim of the present study was to solve the problem of pipe blockage in paste backfill mining. In this paper, paste mixed with coal gangue, fly ash, cement, and additives is used to investigate the influence of three air-entraining agents (AEAs) (including sodium dodecyl sulfate (SDS), triterpene saponin (SJ), and sodium abietate (SA)) on the flow characteristics and strength characteristics of the paste. A series of relevant tests was conducted on the paste, such as air content experiments, slump and expansion experiments, viscosity and yield stress tests, and the uniaxial compressive strength (UCS) test. The results show that the air content of the paste increases with increasing AEA content, but the increase is limited and reaches a maximum at 0.9 AEA. The slump of the paste increased by up to 10–13 mm, and expansion increased by up to 66–130 mm compared to the paste without AEA. The viscosity of the paste decreased by up to 0.13–0.20 Pa·s, and the yield stress decreased by 81.47%–93.7% of the original. The strength of the paste was also reduced, and after 28 days of curing, the strength was reduced by up to 1–1.2 MPa. Taking into account the strength requirement of 3 MPa for the paste from the Linxi mine, it was considered that the dosage of 0.9 B was a good choice, as it could better change the flowability of the paste and reduce the pipeline transportation resistance and transportation energy consumption. At the same time, the strength was also acceptable. The study in this paper can provide a reference for performance studies of pastes mixed with coal gangue, fly ash, cement, and additives as materials.