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The statues of seepage in broken red sandstone may become unsteady due to the effects of water erosion, so it is important to consider the effect of mass loss on the permeability of broken red sandstone. In this study, the seepage property and water outburst were measured through a self-made variable mass seepage experimental system. In the test, the particles of broken red sandstone satisfied the Talbol grading theory. The influences of Talbol index n on the hydraulic, mass loss of particles, porosity and permeability were investigated. The experimental results show that the seepage process in the broken red sandstone usually experiences three stages: the initial stage, mutation stage and stabilization stage. Broken specimens can bear water erosion at the initial stage. However, the internal structure of specimens produces instability because the seepage of small particles gradually increases in the mutation stage. Finally, stable underground watercourses of the specimen were formed at the stabilization stage. It is also found that the mass loss, the peak of mass loss rate, the final porosity after seepage, the permeability at the mutation and stable stages were negatively related to the Talbol index n of the specimen. The seepage mutation occurred sooner for smaller n. The permeabilities of specimens with different Talbol indices differed by more than 10 times after seepage mutation.

It is of great significance, for economic, environmental and security reasons, to investigate the strength characteristic of underground cemented paste backfill (CPB). Consequently, an ultrasonic test, uniaxial and triaxial compression experiment, and acoustic emission (AE) monitoring were carried out on CPB, for which the particles satisfied Talbot gradation. The homogeneity of CPB specimens was evaluated by ultrasonic pulse velocity (UPV). The stress–strain behavior and AE characteristic of CPB specimens under different Talbot indices and confining pressures were investigated. The effects of the particle size distribution and the confining pressure on the peak strength of CPB were analyzed. The strength parameter model of CPB under the coupled influence of the particle size distribution and the confining pressure was constructed based on the Mohr–Coulomb strength criterion. The results show that the peak strength of CPB is positively linear with confining pressure, however, the relationship between its strength parameters and the Talbot index can be characterized by a quadratic polynomial function. This suggests that there is an optimal gradation of particles reflected in the maximum strength of CPB.