Properties of Cemented Coal Gangue-Fly Ash Backfill

Abstract

Cemented coal gangue-fly ash backfill (CGFB), which is a mixture of coal gangue, fly ash, cement, and water, is being extensively used for subsidence control and waste management. A pipe flow model is developed for predicting the flow behavior of fresh CGFB slurry in the pipe loop. This model is validated by the contrast of simulation outcomes and loop testing results. Afterwards, the uniaxial compressive strength (UCS) and ultrasonic pulse velocity (UPV) of hardened CGFB are investigated. The UCS and UPV values of CGFB increase with increasing fly ash dosage and solid content. One of the most significant evaluation criteria for CGFB is its mechanical performance, which is subjected to coupled thermo-hydro-chemical (THC) effects. A THC coupled model is developed to investigate the coupled THC behavior of CGFB and its evolution versus time. A favorable agreement between the modeling results and experimental data can validate the capability of the developed model to simulate the coupled THC responses in CGFB. Both column and block experiments are conducted to investigate the thermal, hydraulic and mechanical performance of CGFB. The results indicate that the hydraulic and mechanical behaviors of the CGFBs are significantly affected by thermal factors, contributing to a better understanding of the thermo-hydro-mechanical (THM) behavior CGFB. Furthermore, the CGFB performance is subjected to the thermal (T), hydraulic (H), mechanical (M) and chemical (C) processes and THMC coupling effects. A THMC coupled model is developed to describe and analyze the coupled THMC processes that occur in CGFB. The simulation results of the developed model are compared with the experimentally tested data from three case studies, validating the capability of the THMC model. The modeling results can also contribute to a better design of stable, durable and environment-friendly CGFB structures.