Due to the differences in mineral processing techniques, the grain-size of tailings used in the construction of a tailings pond is not commensurate. It has been determined that the hydrodynamic characteristics of mudflow resulting from the failure of tailings dams are directly influenced by grain-size, solids concentration, and the surface roughness of gully and impoundment geometry. However, the behavior and influence of the grain size of mudflow resulting from a tailings dam failure have not been sufficiently examined. To investigate the effect of grain size on the hydrodynamic characteristics of mudflow surging from tailings dam failure, the law of mudflow evolution, the change of dynamics pressure, and the velocity distributions of mudflow have been obtained via a series of flume experiments utilizing three types of grain size tailings (d50 = 0.72 mm; d50 = 0.26 mm; d50 = 0.08 mm, respectively). This study proves conclusively that with an increase in grain size, the peak value of mudflow depth notably decreases in the same section. Furthermore, it has been noted that both the velocity and the dynamic pressure raise significantly, wherein the velocity displays two distinct primary stages; namely a rapid reduction stage and a slow reduction stage. This research provides a framework for the exploration of the effect of grain size on the hydrodynamics of slurry surging from a tailings dam failure, and all presented results provide an indispensable tool in terms of the accurate assessment of potential damage in the case of a prospective impoundment failure.

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Once the flood overtopping accident of a reinforced tailings dam occurs, it will cause great property losses and serious environmental pollution to the downstream residents. In order to further study the microscopic characteristics of the hydraulic erosion of reinforced tailings dams, considering that the beginning of reinforced tailings particles is the basis of flooding and erosion of reinforced tailings dams, in this paper, a reinforced tailings hydraulic erosion facility was used to carry out the tailings particle start-up test with reinforcement spacing of 5.0, 2.5, 1.7, 1.3, and 1.0 cm, and the influence the law of critical incipient velocity of tailings particles with different reinforcement spacing was revealed. The test results show that, the smaller the reinforcement spacing, the larger the incipient velocity of the reinforced tailings sample. Based on the sediment incipient motion theory, it is assumed that the resistance direction of particle incipient motion is opposite to the particle motion direction. A reinforcement coefficient is introduced to establish the incipient velocity formula of reinforced tailings particles. This model can provide theoretical support for the study of the hydraulic erosion rate of a reinforced tailings dam.

Strength and stiffness of stabilized/solidified (S/S) sediments are supposed to be degraded by freeze–thaw cycles (FTs) when applied in constructions in cold regions. In order to reveal the degradation mechanisms, FTs were first simulated on S/S sediments in the laboratory. Then, macrotests including unconfined compression strength (UCS) tests and direct shear tests were conducted on S/S sediments at different FTs to investigate the strength and stiffness changes and microanalyses including scanning electron microscope analysis (SEM), mercury intrusion porosimetry (MIP), and nitrogen adsorption porosimetry (NAP) to investigate the microstructure changes. Macrotests show that strength indexes decrease gradually, stiffness parameters and brittleness increase first and then decrease, the compaction stage of stress–strain curves diminishes first and then increases, the decrease rate of friction angle decelerates first and then accelerates, and the decrease rate of cohesion decelerates first and then keeps stable, for S/S sediments in FTs. Microanalyses have precisely captured the damage chain of S/S sediments: meso and macropores inside sediment aggregates expand gradually during FTs; as a result, sediment aggregates are fractured and stripped off from the solidification skeleton gradually; losing support of sediment aggregates, solidification skeletons are adjusted first and then collapsed when sediment aggregate fracture reaches a limit value. Based on macro and microfindings, a damage model to explain strength and stiffness degradations by microstructure damage is successfully established. Based on the established damage model, a reasonable idea is proposed for promoting the resistance of S/S sediments to FTs.