Using gels to replace a certain amount of cement in concrete is conducive to the green concrete industry, while testing the compressive strength (CS) of geopolymer concrete requires a substantial amount of substantial effort and expense. To solve the above issue, a hybrid machine learning model of a modified beetle antennae search (MBAS) algorithm and random forest (RF) algorithm was developed in this study to model the CS of geopolymer concrete, in which MBAS was employed to adjust the hyperparameters of the RF model. The performance of the MBAS was verified by the relationship between 10-fold cross-validation (10-fold CV) and root mean square error (RMSE) value, and the prediction performance of the MBAS and RF hybrid machine learning model was verified by evaluating the correlation coefficient (R) and RMSE values and comparing with other models. The results show that the MBAS can effectively tune the performance of the RF model; the hybrid machine learning model had high R values (training set R = 0.9162 and test set R = 0.9071) and low RMSE values (training set RMSE = 7.111 and test set RMSE = 7.4345) at the same time, which indicated that the prediction accuracy was high; NaOH molarity was confirmed as the most important parameter regarding the CS of geopolymer concrete, with the importance score of 3.7848, and grade 4/10 mm was confirmed as the least important parameter, with the importance score of 0.5667.

Based on the split Hopkinson pressure bar (SHPB) test system, dynamic impact tests of coal specimens under different impact pressures were carried out to study the relationship between the impact load and the size of crushed lump coal. Based on the theory of stress wave attenuation, the relationship between the blasting impact load in a single‐hole blasting area of a coal seam and the load applied in an impact failure test of a coal specimen in the laboratory was established. According to the characteristics of the fragmentation distribution of the coal specimens destroyed under a laboratory impact load and the requirement of the minimum cost control of coal blasting in an open‐pit coal mine, the fragmentation size range was divided into three groups: large‐diameter, medium‐diameter, and powder particles. Based on this range, the variation rule of the mass percentage of coal fragments with impact pressure was obtained. Established on the evaluation principle of the blasting effect in an open‐pit coal mine, a good impact fragmentation effect was obtained. The good pressure range is 0.30 MPa ≤ P < 0.90 MPa.

The study of the permeability of soil‐rock mixtures is important in supporting theories behind reclamation mechanisms for open‐pit mines. To avoid the influence of differences in the spatial distribution of rock within the same sample on the permeability of a soil‐rock mixture in laboratory tests, a numerical method for modelling the soil‐rock mixture based on the threshold control method was proposed. Through the statistical results of 297 CT (computed tomography) cross sections of soil‐rock mixture samples, the threshold values of pores, soils, and rocks are obtained, and a numerical model representing the reactions of the samples to real‐world conditions is obtained. A numerical model was used that could vary with different rock block proportions (RBP) and porosities. Based on Darcy’s law, it is concluded that macroscopic voids greatly increase the permeability of the sample due to their depth of penetration. The higher the stone content, the closer the permeability will be to the permeability of the rock skeleton. Therefore, during the reclamation process of the open‐pit mine, the water‐retaining layer below the humus should be compacted, and RBP should be increased to lower permeability and achieve better water retention.

Dry hot rock geothermal resources by virtue of its wide distribution, large reserves, clean and low-carbon, stable, high utilization rate, and other characteristics have been widely used. The enhanced geothermal system (EGS) is the most efficient approach for harnessing and exploiting geothermal energy from hot, arid rock formations. To investigate the impact of varying parameters on heat recovery in EGS operations, we employed the COMSOL numerical simulation software to construct a seepage heat transfer model for fractured rock masses. Essential parameters and boundary conditions were established, followed by conducting numerical simulations. Through the numerical simulation results, the temporal and spatial changes of coupling effects among seepage field, stress field, and temperature field in fractured rock mass were analyzed. We investigated the impact of water injection temperature, injection-production pressure difference, injection flow rate, and initial reservoir temperature on the heat transfer process. The findings indicate that raising the water injection temperature and injection-production pressure difference can enhance the reservoir’s heat recovery capability. However, it may also accelerate thermal breakthrough and reduce the system’s operational lifespan. The higher injection flow rate can improve the heat recovery efficiency. However, too large injection flow can cause problems in other aspects of the reservoir; increasing reservoir temperature leads to higher production temperatures, which can potentially result in dynamic catastrophes. Therefore, while ensuring the heat recovery efficiency of the system, the operation life of the system can be extended by adjusting the water injection temperature in stages, setting a reasonable injection and production pressure difference, and selecting an appropriate injection flow rate, so as to achieve the purpose of EGS optimization.

To explore the rheological mechanism of cement-coal gangue cementitious material (CGCM) slurry, the effects of the activation temperature (500C-900C) of coal gangue on the initial fluidity, plastic viscosity (η₀), and yield stress (τ₀) of CGCM slurry were considered, the variation laws of rheological parameters of CGCM slurry at different hydration ages were compared, and the rheological equations of CGCM slurry were established in this study. The results show that the rheological law of the CGCM slurry conforms to the modified Bingham model, and the significant shear thinning occurs in the CGCM slurry at low-shear speed, and relatively weak shear thickening occurs in the CGCM slurry at high-shear speed; under the thermal activation temperature of 800C, the pozzolanic activity of coal gangue reaches the highest, the hydration reaction is the fastest, and the initial fluidity of CGCM slurry at 800C is the lowest; the plastic viscosity of CGCM slurry increases gradually with the increase of thermal activation temperature of coal gangue, and the yield stress of the CGCM slurry reaches the maximum at 800C; the flow law of CGCM slurry has significant time-varying characteristics, and the plastic viscosity and yield stress of CGCM slurry increase gradually with the extension of hydration time. This study shows that the fluidity of coal gangue cement slurry has significant time-varying characteristics, which can provide effective theoretical support for the accurate application of coal gangue cement in grouting engineering.

The existence of coal mine water has an important influence on the instability of soft rock roadway in mining engineering. Considering the effect of mine water, a case study on the fracture mechanism and control technology of soft rock roadway was performed in this paper. The results showed that with the increase of moisture content, the uniaxial compressive strength of mudstone nonlinearly decreased, while the tensile strength, Young’s modulus, cohesion, and friction angle tended to a linear decrease approximately. Meanwhile, with the increase of the weakening coefficient, the axial force of the anchorage body increased gradually, while the maximum shear stress decreased gradually. With the increase of moisture content, the failure zone was further propagated into the deep surrounding rock, resulting in a larger stress relaxation around the roadway, especially in the roof and floor. Finally, the supporting technology of the roadway was proposed, and then its support principle, design process, and parameters were also analyzed in detail. The field monitoring data showed that the support technology can control the surrounding rock deformation effectively and maintain the long-term stability of the roadway.