A rock burst usually causes a roadway collapse or even an instant blockage. When the deformation energy accumulated in the surrounding rock exceeds the minimum energy required for the dynamic destruction of the surrounding rock of a roadway, a rock burst accident will occur. According to statistics, 85% of rock burst accidents occur in roadways. This paper establishes a strong-soft-strong structural model for the rock burst stability control of the surrounding rock of a roadway, and the anti-impact and antiseismic mechanisms of the mechanical model are analysed. The strength, stress transfer, deformation, and energy dissipation characteristics of the strong-soft-strong structure are studied. The stress criterion and energy criterion of rock burst failure in small internal structures are derived for roadway support design. The support scheme of “anchor cable active support + hydraulic lifting support + soft structure energy absorption” is proposed. A steel pipe can be inserted into a borehole drilled into the small internal structure to realize the proposed innovative protection technology for small internal structures by creating a soft structure that can release, absorb, and transfer the pressure by repeatedly cracking the coal and rock mass. The innovation of cracking technology for soft roadway structures has been realized. The roadway tested with this strong-soft-strong enhanced surrounding rock control technology met the production requirements during the mining period. The field test was successful, and the expected support effect was achieved. This work provides a reference for roadway support under similar conditions and can be popularized and applied.

Anchor cables (bolts) act as the main support system and play an important role in improving the rock burst resistance and stability of the roadway surrounding the rock. In this study, the dynamic response characteristics of the roadway surrounding the rock and the support system under different shock intensities were investigated. The following findings were obtained. The stress wave propagation process under dynamic shock was divided into a stress vibration initiation stage, a stress fluctuation stage, and a stress adjustment stage. In the stress vibration initiation stage, the surface mass of the roadway surrounding the rock started to vibrate, and the pretension of the anchor cables (bolts) was reduced; in the stress fluctuation stage, the failure of the roadway surrounding the rock intensified, and the anchor cables (bolts) were damaged to some extent; and in the stress adjustment stage, the roadway deformation of the surrounding rock and the axial forces of the anchor cables (bolts) tended to stabilize. As the dynamic shock intensity increased, the vibration velocity, displacement increment, and acceleration amplitude of the mass of the roadway surrounding the rock increased exponentially. The critical shock energy of the roadway surrounding the rock was 10⁵ J, above which the damage to the rock was aggravated. The larger the pretension of the anchor cables (bolts) was and the higher the dynamic shock intensity was, the more severe the damage to the anchor cables (bolts) was. Given the dynamic response characteristics of the roadway surrounding the rock and support elements under shock, a full anchor cable yielding support technology is proposed to effectively control the stability of the roadway surrounding the rock under dynamic shock, providing a reference for the construction of the support systems for preventing rock bursts in similar roadways.

The mechanical properties of foam concrete with sand at different low temperatures and different strain rates were studied. Foam concrete with sand at low temperatures (−10, −20, and −30°C) were tested using a split Hopkinson pressure bar (SHPB) apparatus with different impact pressures (0.15, 0.20, 0.25, 0.30, and 0.35 MPa). The experimental results show that the porosity of sand containing foam concrete with a density of 1,000, 1,200, 1,400 kg/m³ decreases with increasing density. In the same strain rate range, the lower the temperature of the same density foam concrete with sand, the greater the ultimate compressive strength. The change in strength was caused by the presence of pore water or ice in the foam concrete with sand in low-temperature conditions. The dynamic compressive strength of foam concrete with sand decreases with increasing strain rate. The macroscopic failure of foam concrete was closely related to the energy absorption and dependent on the rate. The total dissipated energy of the low-temperature foam concrete with sand increased linearly as the temperature decreased. The research results provide the low-temperature mechanical properties of foam concrete with sand, which provides a reference for the application of foam concrete with sand.

A novel method for fracturing coal is presented in this paper. A chemical solution is injected into coal under high pressure, whereby the coal is fractured and subsequently weakened by chemical erosion over time to produce an anti‐impact soft structure. In this study, the mechanical properties of coal under chemical erosion were investigated, and the fracturing design parameters were optimized. The uniaxial compression test and the split Hopkinson pressure bar (SHPB) test were used to determine the dynamic and static mechanical properties of coal after 20 days of immersion in different chemical solutions. After chemical solution erosion, the dynamic and static compressive strengths and elastic modulus of the coal decreased according to an exponential power law in the damage variable. The chemical treatment increased the duration of the pore compaction stage and decreased that of the elastic deformation stage, while decreasing the brittleness and increasing the ductility of coal. The acoustic emission (AE) curve of the immersed coal samples consisted of four stages corresponding to those of the stress‐strain curve: pore compaction‐closure, a slowly rising linear elastic regime, steady‐state prepeak crack propagation, and unsteady crack propagation at the peak strain. The increase in the damage variable of the coal sample from chemical erosion led to a lower dissipated energy, a higher fractal dimension, and a more fragmented coal sample. The effect of the investigated chemical solutions on weakening the coal mechanical properties decreased in the following order: alkaline solution > acidic solution > NaCl solution > distilled water. The experimental results provide a reference for weakening fractured coal seams.

Summary: Nanoscale plugging materials are commonly used in the petroleum industry to seal microfractures and pores within shale formations, thereby maintaining wellbore stability and preventing drilling accidents caused by formation collapse. However, the influence of inorganic salts present in the formation and drilling fluids on the dispersion properties of nanoscale plugging materials often affects their sealing performance. In this study, we focus on investigating the influence of three commonly encountered inorganic salts in the drilling process—sodium chloride (NaCl), potassium chloride (KCl), and calcium chloride (CaCl2)—on the dispersibility and sealing performance of commonly used nanoscale plugging materials such as nanosilica and nanoemulsions in shale formations, exploring the dispersion and sealing mechanisms. Zeta potential is used as a characterization parameter, and molecular dynamics simulations are used to study the effects and mechanisms of inorganic salt ions on the dispersion of plugging materials. Filtration and pressure transmission experiments are conducted to investigate changes in their sealing performance. Scanning electron microscopy (SEM) is used to observe the microstructure of the formed filter cake, providing insights into the dispersion and sealing mechanisms. The results reveal that nanosilica agglomerates at zeta potentials ranging from −18 mV to −15.5 mV, resulting in an increase in filtration volume from 93.3 mL to 171.1 mL and downstream stable pressure transmission rising from 330.98 psi to 551.98 psi. Nanosilica (modified with KH570) agglomerates at zeta potentials of −10.3 mV to −9.9 mV, leading to an increase in filtration volume from 93.1 mL to 171 mL and downstream stable pressure transmission rising from 326.98 psi to 553.35 psi. The average gyration radius of the KH570 molecule decreases from 0.347 nm to 0.337 nm under the influence of inorganic salts. In contrast, the dispersion stability of nanoscale emulsions is independent of zeta potential; however, under the influence of inorganic salts, the filtration volume increases from 92.2 mL to 170.9 mL and downstream stable pressure transmission rises from 293.03 psi to 550.98 psi. The average gyration radius of nanoscale emulsion monomer molecules decreases from 0.340 nm to 0.336 nm under the influence of inorganic salts. Microscopic examination of filter-cake morphology shows that inorganic salts not only affect dispersion stability, leading to the aggregation of nanomaterials and influencing sealing performance, but also reduce the deformability of organic particles, thereby affecting sealing performance. The properties obtained in this study provide theoretical references for the sealing performance of nanomaterials in drilling fluids, offering significant value for researchers and field engineers in selecting nanoscale plugging materials for shale formations.

Rock burst is one of the most serious risks for underground coal mines, and the associated dynamic waves generally cause roof falls and large-scale shrinkage of the roadway. The roadway is often seriously damaged by duplicated rock bursts. Previous research on the propagation and attenuation of shock waves cannot explain well the failure mechanisms of the surrounding rock of the roadway under duplicated dynamic waves. To fill this research gap, this paper presents comprehensive research on the failure and fracturing process of roadways affected by repeated shock waves using field tests and numerical analysis. A numerical model as per UDEC Trigon logic was developed and calibrated using mine earthquake shock waves, during which a user-defined FISH function was adopted to document the quantity characteristics of fractures (i.e., shear-slip and tension). The damage to the roof was assessed based on the quantity of fractures. At the same time, the simulation analysed the evolution trend of the failure zone of the roadway roof and the fracture development area, which agreed well with the field tests. According to the spread and extension characteristics of fractures in the surrounding rock under repeated shock waves, new support materials and schemes were proposed and applied at the mine site. The results show that the scheme has controlled the deformation of the roadway effectively and satisfied the safety and efficiency requirements of the mine.