Mining backfill is widely used in underground mines worldwide. The stresses in backfilled stopes must be correctly evaluated because they influence the ground stability and the required strength of exposed (horizontally or vertically) cemented backfill. The stress estimation can be accomplished by numerical modeling with or without the use of interface elements between the backfill and rock walls. To date, most numerical models have been developed without the use of interface elements, and only a few have used interface elements with the same shear strength as the backfill. Stress changes resulting from the addition of interface elements or from the variations in the shear strength of interfaces have never been investigated. In this study, these aspects were analyzed with two-dimensional (2D) (plane-strain) numerical models. The stress changes resulting from the variation of the backfill’s shear strength were also analyzed. The results show that the stresses decreased as the interfaces’ shear strength increased but were relatively insensitive to the variation of the backfill’s shear strength. When the interfaces have the same shear strength as the backfill, the consideration of interface elements is not necessary in numerical models because the stress distributions with or without consideration of interface elements are almost identical. When the interfaces are weaker than the backfill, the stresses obtained by the two numerical models can differ considerably, and the interface elements should be used in numerical models.

The improper handling of smelting slag will seriously pollute the environment, and the unfilled roof of the goaf of the mine will threaten the safety of the mine. Expansion materials have attracted more and more attention because of their excellent properties. In this paper, copper-nickel smelting slag that has some active ingredients of gelling is used instead of traditional aggregate and some part of cement in order to reduce its pollution to the environment and its costs. For safety reasons, hydrogen peroxide was chosen as the foaming agent. Sodium silicate and hexadecyl trimethyl ammonium bromide (CTAB) are used as additives. Our results showed that after 28 days of curing, the material has better mechanical properties and the early compressive strength of the material was enhanced by sodium silicate. The efficiency of foaming was improved by CTAB. It also proves that copper–nickel smelting slag can be used in expansion material. At the same time, the utilization rate of the copper–nickel smelting slag of this formula can reach 70%, reduce its pollution to the environment.

Materials with sufficient strength and stiffness can transfer nonlinear design loads without damage. The present study compares crack propagation speed and shape in rock-like material and sandstone when subjected to seismic acceleration. The nonlinear extended finite element method (NXFEM) has been used in numerical simulation. It assumes the model has a pre-existing crack at 0° from the horizontal. The mechanical properties of the model, crack propagation shape, and crack speed were selected as the main parameters. The nonlinear stress and strain along the crack have been compared in two simulated models. NXFEM and Artificial Neural Networks (ANNs) were used to predict the displacement. The simulation results illustrate that the materials’ crack propagation mechanism and mechanical properties control the stress, strain, and displacement at the selected points in the model. In addition, crack propagation in materials is related to elastic-plastic stresses and strains along the crack path. The speed and shape of the crack are associated with the mechanical properties of the materials. The prediction of crack paths helps to understand failure patterns. Comparison of the seismic response of the rock-like material with sandstone helps to assess the stress, strain, and displacement levels during cracking. This study’s findings agree with the literature report and field observations.

In the two-step open stope subsequent filling mining method, the determination of the strength model for the backfill-rock interface is of great engineering significance to study the stress distribution and stability of the backfill in the stope. Considering the deformation mechanism of the interface and the interaction of the asperities, a strength model for backfill-rock with irregular interface has been proposed based on fractal theory, which can effectively describe the shear mechanical behavior of interfaces with random roughness. The model has been compared with the two-body mechanistic model and good agreements have been achieved. The results show that the shear strength of the interface changes non-linearly with increasing fractal dimension D, when the fractal dimension D is in the range of 1∼1.12. The complete relationship between the interface shear strength and the fractal dimension is given, as the fractal dimension increases from 1 to 2 based on the presented model. At the same time, the quantitative relationship between the interface and backfill friction angles during direct shear testing is analyzed.

Clay soils, usually in an unsaturated state, are widely used as barrier materials in solid waste landfills. When the saturation of clay soils is high, the gas phase will be in the form of entrapped bubbles. The entrapped bubbles can directly affect the soil hydraulic behavior, which further affects solute transport in clay liner. Therefore, based on the stress balance, fluid mass conservation, and solute mass conservation equations, and combined with the relationship between pore water pressure and air pressure in unsaturated state, a coupled hydro-mechanical-chemical model has been put forward to study the influence of entrapped bubbles on solute transport process. Using the proposed model, a series of numerical calculations are carried out through the finite element simulation software COMSOL Multiphysics. The numerical results show that the increase of entrapped bubble content can enlarge soil deformation and slow down the rates of excess pore fluid pressure dissipation and solute transport. In particular, when the degree of saturation in air phase increases from 0 to 0.2, the difference of influence depth at the transport time 10 years reaches 28 cm, and the breakthrough time of solute is prolonged by 17.8 years.