Cemented paste backfill (CPB) is a common environmentally friendly mining approach. However, it remains undetermined whether CPB pollutes underground mine water. Tank leaching analysis of a CPB mass in distilled water was performed for 120 d, and water quality was tested in situ for a long-term pollution assessment. Computerized tomography was also used to determine the CPB micro-pore structure and ion-leaching mechanism. The dissolved Zn²⁺, Pb²⁺ and As⁵⁺ concentrations in the leachate peaked at 0.56, 0.11 and 0.066 mg/L, respectively, whereas the Co²⁺ and Cd²⁺ concentrations were lower than the detection limit. The CPB porosity decreased from 46.07% to 40.88% by soaking, and 80% of the pore diameters were less than 13.81 μm. The permeability decreased from 0.8 to 0.5 cm/s, and the quantity, length, and diameter of the permeate channels decreased with soaking. An in-situ survey showed novel selective solidification. The Zn²⁺ concentration in the mine water was 10–20 times that of the background water, and the Pb²⁺ concentration was 2–4 times the regulated value. Although the Pb²⁺ content decreased significantly with mining depth, there remains a serious environmental risk. Mine water pollution can be reduced by adding a solidifying agent for Pb²⁺ and Zn^2+, during CPB preparation.

The green disposal of tailings solid waste is a problem to be solved in mine production. Cemented tailings filling stoping method can realize the dual goals of solid waste resource utilization and mined-out area reduction. However, the volume of the mined-out area of the open-pit method is larger than the filling capacity, resulting in the complex stratification of the underground backfill, and the strength of the backfill cannot meet the requirements. In this paper, according to the delamination situation, the specimens of horizontal and inclination angle layered cemented tailings backfill (LCTB) is made for a uniaxial compression test, and the failure process of delamination backfill is reduced by PFC. The results show that the corresponding reduction factor φ of horizontal LCTB is 0.560–0.932, and the corresponding φ value of inclination angle LCTB is 0.338–0.772. The failure mode of backfill in different layers is mainly manifested as a tensile failure. The PFC numerical simulation results are consistent with laboratory test results, which verifies the correctness of backfill failure. The research results provide a reliable theoretical basis for the strength design of backfill in goaf, which is of great significance for solid waste utilization and environmental protection.

Red sandstone tests were conducted on the rock mechanics test system to clarify the strength and failure characteristics of red sandstone under triaxial loading and different unloading confining pressure rates. Strength change rules of the red sandstone in various stress spaces were analyzed. Results show that a large initial confining pressure indicates a long yield section and large axial strain. A small unloading confining pressure rate indicates a long yield section and large axial strain at failure under the identical initial confining pressure. The confining pressure reduction increases with the unloading confining pressure rate increasing when the red sandstone fails. The stress path of unloading confining pressure weakens the red sandstone cohesion and strengthens its internal friction angle. The general octahedral shear stress formula for judging whether the red sandstone fails under loading and different unloading rates was acquired on the basis of the octahedral shear stress characteristics of the red sandstone. In addition, a 3D empirical criterion for evaluating the red sandstone strength was constructed through the deviator plane function of Eekelen and the strength envelope curve on the meridian plane. A great initial confining pressure indicates serious internal damage of the red sandstone at failure under the identical unloading rate of confining pressure. A low unloading rate of confining pressure indicates internal serious damage of the red sandstone at failure when the initial confining pressure is the same. The analysis of macroscopic failure characteristics revealed that the stress path significantly influences the failure mechanism of the red sandstone. The results are instructive for determining the stability of underground engineering of the red sandstone.

The macroscopic aspects of adding basalt fiber (BF) to concrete has been the subject of studies that document great increases in compression strength. Research into the microscopic aspects of the reinforcement mechanism is still in an exploratory stage, and the quantitative analysis and visual observation of fibers in the concrete matrix are difficult. In this paper, the reinforcement effect of fiber on concrete is studied by means of computed tomography (CT) scanning technology and digital image processing (DIP) technology, combined with the macro-mechanical properties obtained from the unconfined compression strength test, and quantitative analysis from the micro point of view. At the same time, the fiber visualization is realized with the help of Avizo. The results show that with the increase in fiber dosage, the peak stress of concrete first increases and then decreases. When the fiber dosage is 3 kg/m³, the peak stress is 44.4 MPa, which is 41.85% higher than that of ordinary concrete. Additionally, the proportion of macropores is the least, which is the best fiber dosage. It is found that when the fiber dosage is 3 kg/m³, the angular distribution of φ is relatively uniform, and the uniform distribution of fibers forms a dense network structure, which significantly increases the peak stress of concrete. However, when the fiber dosage is too high, it will lead to the accumulation of fibers and produce macropores, and these excess fibers mainly appear in the horizontal direction and do not contribute to the compression strength.

Experiments on dried and saturated marble samples were conducted at different loading rates to investigate the influences of loading rate and saturated water on the deformation, strength and brittleness indexes of marble. Strength and deformation, the applicability and variation of different brittleness indexes, and the relationship between elastic strain energy limit and brittleness indexes were analyzed comprehensively under different loading rates. The results show that the strength of marble increases with an increase in loading rate, while elastic modulus decreases and peak strain increases. The influence of loading rate on brittleness was analyzed for seven values of the latter. The results indicate that some of the indexes of brittleness cannot reflect the influence of loading rate. Meanwhile, there are two indexes that can accurately express the variation law of rock brittleness with an increase in loading rate. Moreover, these brittleness indexes increase linearly with an increase in loading rate and exhibit a quadratic function relationship with elastic strain energy limit. A new brittleness index that can comprehensively consider strength and energy is proposed to fully express the effects of loading rate and saturation on rock brittleness. In accordance with the macroscopic failure characteristics of marble, the conclusion that a brittleness index increases with an increase in loading rate was proven correct.

Dry and saturated red sandstone direct shear tests under different normal stresses were carried out in the rock shear test system to clarify the shear strength and damage characteristics. The cumulative ring count, cumulative energy, dominant frequency, secondary dominant frequency, and the effects of water saturation and normal stress on them were analyzed in detail. Results show that the cumulative ring count and cumulative energy curves of acoustic emission (AE) can be divided into linear increasing and step jump stages. The cumulative curves in the dry state have significant steps, thereby indicating that the repetitive process of “crack rapid development — energy accumulation” is significant. The cumulative ring count and cumulative energy are great when the normal stress is high. Under the same normal stress, the cumulative ring count and cumulative energy in the dry state are greater than those in the saturated state. The shear damage stresses were determined according to the cumulative curves. The failure process of red sandstone is divided into crack initiation and crack rapid development zones. The variation law of shear damage stress and shear strength of red sandstone is basically consistent. The growth rate of shear damage stress and strength of dry red sandstone is greater than that of saturated red sandstone with the increase in normal stress. The dominant and secondary dominant frequencies of dry and saturated red sandstone decrease with the increase in normal stress. The dominant frequency is less than the secondary frequency. Under the same normal stress, the dominant and secondary dominant frequencies of red sandstone shear failure in the dry state are less than those in the saturated state, thereby indicating that the shear microcrack scale of red sandstone in the saturated state is smaller than that in the dry state. The results have a certain theoretical significance to determine the shear damage degree of red sandstone by AE monitoring.