Study of the spatial strength distribution patterns and microstructure characteristics of ultra-fine tailings cemented paste backfill

In this study, the spatial distribution of the mechanical strength of ultra-fine tailings cemented paste backfill (UCPB) in underground stopes was examined, and the micro-mechanism responsible for differences in spatial strength performance via changes in particle deposition was elucidated. To better understand this phenomenon, we constructed a similar backfilling stope model using the ultra-fine tailings of a gold mine. We manufactured specimens at different spatial locations and conducted a novel series of tests, including uniaxial compressive strength, shear strength, and conventional triaxial tests, to obtain the strength parameters in different spatial distributions. The strength parameters for the different UCPB locations in this model were revealed and examined along with the original pore and particle size distributions. Computer tomography (CT) and scanning electron microscopy (SEM) observations before and after the UCPB failed revealed that the particle deposition effect at different positions was the primary cause of the size effect. The strength distribution pattern demonstrated that the UCPB material has an apparent spatial effect. Consequently, considering the position relationship between the stope and filling mouth is crucial when designing the strength of adjacent mining rooms. This research may guide both backfill study and design.