Paste and thickened tailings (PTT) technology can improve the utilization and management of tailings from processing plants. The pore size distribution (PSD) and microstructure evolution affected by the rake shear in thickening tailings beds are essential to produce a high-density tailings underflow. Continuous thickening and computed tomography (CT) scanning tests were conducted to study the PSD with and without shear. The pore morphology was studied to reveal the shearing-dewatering performance of the tailings bed. The results show that at a flocculant solution concentration of 0.01 wt % and a feed slurry concentration of 10 wt%, the underflow concentration with and without shear can reach 58.5 wt %and 55.8 wt %, respectively. The CT image reconstruction models demonstrated that the porosity of the sheared tailings bed increased with the bed height. When the bed height increased from 2.5 to 10 cm, the porosity increased from 35.1% to 41.9%, the pore fractal dimension increased from the range 1.8–1.95 to the range 2.1–2.15, and the pore quantity decreased by 21.39%. The average pore volume increased with increasing height by 13.93%, 16.57% and 12.07%. The pore structure became more complex with the bed height, and the connectivity between pores increased to form water-flow channels, which were beneficial to the drainage of sealed water.

To achieve an adjustable setting time and significantly improved early strength of a new type of sulphoaluminate cement-based double-liquid grouting material (SACDL), the effects of calcium formate, sodium sulfate, lithium carbonate, and a composite early strength agent on the setting hardening and early hydration behavior of SACDL paste were studied by means of setting time, fluidity, compressive strength, and viscosity tests. The results showed that the adsorption and osmosis of calcium formate, the complex decomposition of sodium sulfate, the precipitation polarization of lithium carbonate and the synergistic action of the composite early strength agent could accelerate the early hydration rate of SACDL, shorten the coagulation time, and improve the early strength of SACDL. The composite effect of 0.8% calcium formate and 0.5% sodium sulfate is the most significant in promoting coagulation and early strength; the initial setting time and final setting time of the slurry were shortened to 5 min and 10 min, respectively; and the 3 h compressive strength was capable of reaching 16.7 MPa, 31% higher than that of the blank group. In addition, X-ray diffraction and SEM morphology observation were used to study the composition of the hydration products and the evolution of the microstructure, which revealed the early hydration mechanism of SACDL under the synergistic effect of the composite early strength agent: (1) The solubility of tricalcium aluminate (C₃A) and dihydrate gypsum (CaSO₄·2H₂O) increased under the low content composite early strength agent condition, which increased the ettringite (AFt) formation rate. HCOO⁻ was able to penetrate the hydration layers of tricalcium silicate (C₃S) and dicalcium silicate (C₂S), accelerating the dissolution of C₃S and C₂S and promoting the early hydration of SACDL. (2) Under the condition of a high dosage of the composite early strength agent, the further increase in Ca²⁺ concentration promoted the crystallization nodules and precipitation of CH and accelerated the formation of calcium silicate hydrate (C-S-H) gel. C-S-H was filled between a large number of rod-like AFt crystals, thus making the structure more dense.

As the mine enters the deep mining stage, there is a need to enhance the compressive strength and toughness of the backfill. The objective of this study is to examine the mechanical properties of cemented tailings backfill after the incorporation of multi-size fibers and to validate the toughening mechanism of basalt fibers (BFs). To achieve this, a series of basic mechanical property tests for multi-size BFs mixing were devised, accompanied by industrial computerized tomography (CT) scanning and discrete element simulation. This study shows that the compressive strength increases and then decreases with the increase of BF dosage at a certain percentage of each size, and the splitting tensile strength gradually increases with the increase of BF dosage. The compressive strength tends to decrease and then increase, and the splitting tensile strength increases and then decreases as the fiber size ratio changes. The distribution of cemented tailings backfill and BF within the discrete element model is random. A few BF cannot play a bridging role; however, a moderate amount of BF is relatively uniformly distributed in the model to form a network structure, which generates a bond between the particles and the matrix and can effectively limit the expansion path of cracks and enhance the toughness.

Clay cement grout is frequently employed in geotechnical reinforcement projects. However, laboratory test revealed that clay cement slurry does not consolidate in a closed environment for an extended period of time, with cracks forming during the consolidation process under natural conditions, indicating that the geotechnical reinforcement poses dangers. Stone powder is a powdery solid waste similar to clay materials. Stone powder particle surfaces provide an attachment point for cement reaction, which can speed up cement hydration, with the ability to substitute clay cement slurry. According to our findings, the bleeding rate of clay cement slurry is 14.80% at 290 mm fluidity, and that of the same mass ratio (1:3) as stone powder cement slurry is 11.09%. The bleeding rate is minimal, which promotes the creation of an integral structure after setting between the slurry and lose rock and soil. Mechanical test results show that the strength of the stone powder cement slurry hardened body is 1458 kPa, whereas the strength of the clay cement slurry hardened body is 436 kPa. Microstructural analysis shows that the stone powder cement hardened body has more hydration products and is porous than the clay cement hardened body. The hardened body of stone powder cement slurry has high strength and resistance to external loads, which can increase the bearing capacity and improve the geotechnical reinforcement effect.

Layering of filling body is common in large-scale filling areas. In this paper, the cement–sand ratio of 1:8 is based on the configuration of 68%, 70%, 72% and 74%; four concentrations; and filling layers of one-, two-, three- and four-layered cemented filling samples. Combined with a uniaxial compression test and two-dimensional particle flow software (PFC2D), the mechanical properties and failure modes were explored. The results show that the concentration can strengthen the uniaxial compressive strength of the filling body while increasing the filling times weakens its power; therefore, the constitutive damage model was constructed. It was found that the initial layered damage existed in the layered filling, and the total damage showed an upward trend of first fast and then slow; the main failure modes of one-layer and two-layer backfills showed prominent shear failure characteristics, and the three-layer and four-layer fillings were closer to tensile failure. From the crack generation to the specimen failure, there is a mutual conversion between different energies.

To study the mechanism of reverse percolation and drainage of unclassified tailings, improve the disposal concentration of tailings and solve the bottleneck in the development of filling technology, this study performed semi-industrial flocculation and sedimentation tests using macroscopic continuous thickener tests and a self-developed continuous thickener test platform to observe the evolution pattern and formation mechanism of unclassified tailings flocs. Then, in situ sampling was performed on the compressed thickener zone of tailings at the bottom of the bed with the help of industrial CT scanning tests and 3D images. Avizo software was used to establish the seepage channels and construct an evolutionary model to analyze the effect of tailings dewatering and concentration on tailings concentration from a microscopic perspective. The study shows that the distribution of seepage channels is closely related to the height of the bed. As the bed height increases, the bed concentration increases; shear has a significant effect on the water flow inside the pore space. After shear, the water between the sample pores has been discharged. Therefore, the flow rate is relatively slow. Shear produces pressure and tension effects, breaking the static equilibrium between flocs and water forming seepage channels. Shear can effectively break the floc structure and release the water so that the mutual position between flocs and water constantly changes, The concentration of the tailings bed is increased.