To explore the failure precursors of hard rock, a series of triaxial loading and unloading experiments were carried out on sandstone sample using the acoustic emission systems. The extreme-point symmetric mode decomposition method (ESMD method) was used to denoise and reconstruct the AE data. The AE quiet period in Scheme I becomes much more obvious with the confining pressure increasing, which can be regarded as the precursor information of the sample failure under conventional triaxial compression. Unlike Scheme I, there are no obvious precursory characteristics before failure in Schemes II and III, and the count rate reaches the maximum at the peak point. When the stress ratio ranges from 0.8 to 1.0, the fractal values of acoustic emission can be used to investigate the failure precursors of samples at a lower confining pressure. When the time ratio is greater than 0.8 under higher confining pressures, the fractal values of sandstone samples under unloading paths are rapidly reduced, which can be used to predict rock failure at higher confining pressures.

Biocement can be achieved through the microbially induced carbonate precipitation (MICP) process. Such a method can potentially be utilized as an eco-friendly method for civil and environmental engineering applications such as soil ground improvement and wind erosion control of surface soil. In this method, one key step is the effective production of ureolytic bacteria. In previous laboratory and field studies, the cultivation and production of the bacteria used for the MICP were usually expensive and time-consuming. The purpose of this study was to optimize the cultivation method of the ureolytic bacteria (Sporosarcina pasteurii), and soil stabilization tests were conducted to verify the effectiveness of the cultured bacteria used to strengthen soil against the wind-induced erosion. Bacterial cultivation methods were studied by investigating the effects of different cultivation media and conditions. Testing variables included the types and concentrations of nitrogen sources (urea or NH₄Cl), pH values (7.5–9.5), cultivation conditions (batch or chemostat condition), and different carbon sources. It was found that, with the same amount of nitrogen source, the test with pure urea had the highest biomass yield, urease activity, and specific urease activity than the other tests with pure NH₄Cl or both NH₄Cl and urea. The use of urea as the nitrogen source in the media also led to an increase in pH, which was not found in the test with pure NH₄Cl. As for the factor of urea concentration, the tests with a higher urea concentration had a higher biomass yield, urease activity, and pH. The factor of pH values also played an important role. The test with an 8.5 initial pH value had a higher biomass yield, urease activity, and specific urease activity than the tests with 7.5 and 9.5 initial pH values. In the chemostat condition, the ureolytic bacteria could be effectively produced with urease activity up to 7 mmol/L/min, as compared with around 12 mmol/L/min activity in the batch condition. Thus, the optimum nitrogen source, pH value, and cultivation condition for the cultivation of Sporosarcina pasteurii was urea, 8.5, and batch condition, respectively. In addition, when soybean milk powder or milk powder was used as the carbon source, the urease activity was around 2.5 mmol/L/min, which is also high enough to be used for biocement.

Characteristics of energy accumulation, evolution, and dissipation in conventional triaxial compression of mudstones with different moisture contents were explored. Stress‐strain relations and acoustic emission (AE) characteristics of the deformation and failure of rock specimens were analyzed. The densities and rates of stored energy, elastic energy, and dissipated energy under different confining pressures were confirmed. The results demonstrated that the growth rate of absorbed total energy decreases with the increase of moisture content, indicating that the higher the moisture content is, the less the total energy mudstone samples absorb. The dissipated energy of the soaking sample, by contrast, has the first increase speed, and natural sample comes second at the beginning. When entering the crack stable development stage, the dry sample has the fastest growing rate of dissipated energy, meaning that dissipated energy used for crack propagation gradually decreases with the increase of moisture content. The AE signals significantly enhance at the initial compression stage and plastic deformation stage with the moisture content decreasing. The AE location events at the failure moment decrease as the moisture content increasing. The time that the maximum AE even rate appears is slightly lagged behind the macroscopic failure time, and the AE even rates increase with the decrease of confining pressure. The above results indicate that the water erosion process on rock reduces the cohesive energy and cohesive force, destroys the micromechanical structure, and minimizes the energy states of rock.

Under the effect of high ground stress and water‐rock chemical interaction, the fractures in the damaged mudstone wound undergo a self‐healing process and recover the physical and mechanical properties, which has a significant impact on the wall‐rock’s stability of high level radioactive waste repository and the migration of radioactive nuclide. According to the general thermodynamics and continuum damage mechanics, an internal variable describing mudstone healing properties is introduced and an elastoplastic damage‐healing model reflecting mudstone deformation, damage, and self‐healing evolution is put forward. This model is used to simulate the triaxial compression test of mudstone under different confining pressures, whose simulated results are compared with the test data. It is indicated that the model could embody the main mechanical properties of mudstone with the healing effect in an effective way, and the healing part of the model has a great influence on the simulated results.