Abstract
Cemented paste backfill containing coal gangue and fly ash (CGFACPB) is an emerging backfill technique for coal mines that allows environmentally hazardous coal gangue and fly ash to be reused in the underground goaf. Meanwhile, CGFACPB can provide an efficient ground support and reduce the surface subsidence. Due to the difference of consolidation environment between the laboratory and the field, the mechanical properties of the cemented paste backfill vary significantly. In this paper, the core specimens were collected from an underground coal mine where the CGFACPB was used for coal mining, and the mechanical properties of the collected specimens were investigated. The cores were obtained from the underground coal mine, and then the standard cylinders or discs were prepared in laboratory. The uniaxial compressive strength (UCS), Young’s modulus, and Poisson’s ratio were determined by the compression tests, and the tensile strength was achieved by the Brazilian test. Then the internal friction angle and cohesion were calculated using the improved Mohr–Coulomb strength criterion. The results showed the development of UCS can be divided into four stages, and the final long-term stable value was about 5.1 MPa. The development of Young’s modulus had similar trend. Young’s modulus had a range from 550 MPa to 750 MPa and the mean value of 675 MPa. Poisson’s ratio gradually increased with the underground curing duration and eventually approached the stable value of 0.18. The failure type of compression samples was mainly single-sided shear failure. The development of tensile strength can be divided into two stages, and the stable value of the tensile strength was about 1.05 MPa. The development of cohesion can be divided into four stages, and the stable value was about 1.75 MPa. The stable value of the internal friction angle was about 25°. This study can provide significant references for not only the long-term stability evaluation of CGFACPB in the field but also the design of optimal recipe of the cemented paste backfill (CPB).
Highlights
Cemented paste backfill containing coal gangue and fly ash (CGFACPB) is an emerging backfill technique in the coal mines in China. e cemented paste backfill can dispose of solid waste and significantly improve the recovery ratio of coal resources and reduce the surface subsidence [1,2,3]
Due to the significant difference in geological mining conditions, backfilling process, and materials between coal mines and metal mines, the aim of this paper is to investigate the mechanical properties of in situ coring CGFACPB in the laboratory. e uniaxial compressive strength (UCS), Young’s modulus, and Poisson’s ratio were determined by the uniaxial compressive tests, and the tensile strength was obtained by the Brazilian splitting test
An experimental investigation was conducted on the mechanical parameters of CGFACPB cored from an underground coal mine. e main results are summarized as follows: (1) e ingredients of CGFACPB materials were analyzed, and the production process was introduced. e primary ingredients of CGFACPB materials include coal gangue, fly ash, OPC, and water. e field recipe of CGFACPB was described as follows: the ratio of OPC : fly ash : coal gangue was 1 : 4 : 6, and the solid concentration was 74%
Summary
Cemented paste backfill containing coal gangue and fly ash (CGFACPB) is an emerging backfill technique in the coal mines in China. e cemented paste backfill can dispose of solid waste (mainly coal gangue and fly ash) and significantly improve the recovery ratio of coal resources and reduce the surface subsidence [1,2,3]. E cemented paste backfill can dispose of solid waste (mainly coal gangue and fly ash) and significantly improve the recovery ratio of coal resources and reduce the surface subsidence [1,2,3]. CPB materials are produced by mixing solid waste (e.g., coal gangue and tailings), a single or composite hydraulic binder (e.g., Portland cement or slag cement), and water. Most of studies have been focused on metal mines (e.g., gold, iron, and copper), in which the primary materials were tailing, hydraulic binder, and water, defined as TCPB (tailing cemented paste backfill). Yilmaz et al [8] investigated the effect of curing time of TCPB with different types of binder and content on the one-dimensional consolidation characteristics using an improved laboratory apparatus. Yin et al [29] investigated the effect of solid components on the rheological and mechanical properties of CGFACPB
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