Due to improved mechanical properties, nano-alumina (NA) addition has been considered as an interesting method to promote the performance of cement composites. To investigate the enhancing effect of NA on the fire resistance of cement-based composites, the physical and mechanical properties of NA-modified cement composites (NAMCCs) were experimentally measured after exposure to high temperatures (up to 800 °C). The variation mechanism of the physical properties of NAMCCs with increasing temperature was explored using X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. Increasing temperature leads to a gradual decrease in density and ultrasonic wave velocity but an overall increase in mass loss. The addition of NA particles effectively improved the mechanical properties of hardened cement pastes after heat treatment at all the temperatures studied. The compressive strength, elastic modulus and flexural strength all gradually decrease with increasing temperature. Combined with the changes in XRD and SEM, three regions are identified for the variation in mechanical performance in the temperature range of 20~400 °C, 400~600 °C and 600~800 °C. Finally, the relation between the physical and mechanical parameters of these regions was evaluated.

High-solid-water material is a kind of soft rock-like material with significant plastic deformation characteristics, and creep performance is its important material property. In order to study the effect of creep on the properties of high-solid-water materials, this paper first conducts creep tests of high-solid-water filling materials under different loading methods, performs creep data analysis based on the Boltzmann superposition principle, carries out the creep experiment of high-solid-water materials under different water contents to analyze the creep characteristics of high-solid-water materials, and then processes the curve of graded loading based on the Boltzmann superposition principle to obtain the strain–time curve of axial creep under different constant stress. Finally, the instantaneous curve is compared with the creep stress–strain curve. It is concluded that the high-solid-water filling materials with water content of 61%, 65% and 69% meet the transportation requirements and filling requirements, and the total coagulation time increases slightly with the increase in water content. The curve treated by the Boltzmann superposition principle has the same trend in the overall creep process and the creep curve loaded separately. With the increase in loading stress, the total strain of the material gradually increases, and with the increase in the water content of the material, the rate of change in the total strain of the material also increases. The long-term strength of high-solid-water materials decreases with the increase in water content. The specimen will eventually cause irreversible failure under long-term stress during the fourth-stage loading.

Establishing the relationship between the deformation of coal samples and acoustic emission response is the basis for the deformation prediction of coal samples. Using a combination of laboratory tests and theoretical analysis, acoustic emission tests of the uniaxial loading process were conducted on coal samples in the study area and the test results were analyzed, focusing on the rule of variation of acoustic emission counts with loading time. Based on the analysis of stress, strain, time, and acoustic-emission parameters variation, the relationship between the deformation of coal samples and acoustic emission response was established and analyzed. The analysis results show that during the loading process, the acoustic emission counts show the characteristics of stage changes, which can be divided into three stages: the initial stage with sporadic acoustic emission events, the middle stage with a stable increase of acoustic emission events, and the final stage with the rapid increase of acoustic emission events. This stage division has good consistency with the deformation stages of coal samples. Moreover, the acoustic emission counts have obvious and easily identifiable characteristics of changes in the deformation process of coal samples. The acoustic emission count can be used as a sensitive indicator in this study area to predict the deformation of coal samples. It provides a reference for the application of acoustic-emission prediction technology in this study area, which is important to improve the accuracy of geohazard prediction.

To improve the effect of gas drainage, with the aim of overcoming the problem of air leakage of conventional sealing materials, this study proposed the concept of gas drainage borehole sealing with active support and developed a new type of sealing material with the properties of permeability, fluidity, expansibility, early strength and compressive resistance through orthogonal tests. Using a specially designed active support testing device, this study analyzed the development law of borehole fracture under the action of active support force, which was then verified via field tests at a mine in Henan Province, China. The results show that the higher the expansion rate, the smaller the internal friction angle and cohesion, which is reflected in the sharp decline in the peak strength of the sealing material. The active support force of the sealing material has a significant time effect. It increases rapidly at first, before its growth rate slows down and tends toward a certain value. The greater the active support force provided by the sealing material, the smaller the radius of the plastic zone and breakage zone; this observation is also true of the displacement around the borehole. The active support force of sealed boreholes can effectively inhibit the development of cracks around the hole and reduce the generation of gas leakage channels. Under the action of the same burial depth and active support force, the larger the mechanical parameters of rock, the smaller the radius of the plastic zone and the breakage zone, as well as the smaller the displacement around the borehole. As has been proven by engineering practice, under the same conditions, the gas drainage concentration of the new sealing material is 47.5%, which is 84.8% higher than that of the original sealing material.

In recent years, tunnel-boring machines (TBMs) have been widely applied in deep coal mining. Turning is an inevitable challenge in TBM tunneling, and a TBM turning roadway exhibits greater instability than a straight roadway, as engineering experience has indicated. This study aimed to explore the failure mechanism and evaluate the support performance of a deep-turning roadway. Several numerical models were established to investigate the deformation of the roadway, the stress distribution, and the failure zone of the surrounding rocks under different tunneling conditions. The results show that the tunneling depth influences the failure pattern of the turning roadway: deep tunneling with high in situ stress can cause asymmetric failure of the turning roadway, while shallow tunneling with low in situ stress does not. Moreover, the change in turning radius, namely the change in roadway geometry, does not influence the stability of the turning roadway. In addition, the support actions for both the straight and turning roadways do not differ significantly, and the amount of controlled deformation of the surrounding rocks is proportional to their natural deformation.

Coal is the main energy source in China. In the process of coal resource mining, the surrounding rock of roadways is often in the complex stress environment of “three heights and one disturbance”. At the same time, rocks in the stratum are often in a three-way unequal pressure state under the action of geological structure, and conventional rock mechanics tests cannot study the mechanical properties of rocks under actual stress conditions; thus, this is based on the self-developed true triaxial multifunctional fluid–structure coupling test system to study the damage mechanical Properties of Sandstone. The results are shown as follows: With an increase in loading rate, the peak damage D_cr of sandstone decreases, but the initial damage D_a increases in the elastic stage, and the brittleness of sandstone weakens. With the increase in the unloading rate, D_cr increases, but D_a decreases in the elastic stage, and the sandstone brittleness increases first, then decreases. In addition, the peak maximum principal strain ε_1maxfirst decreases rapidly and then slowly; the peak minimum principal strain ε_3max increases first, then decreases slowly, and increases slowly; the peak intermediate principal strain ε_2max decreases slowly; and the peak volume strain ε_vmax increases rapidly first and then slowly with increases in the loading rate. With an increase in the unloading rate, ε_1max increases rapidly first, then decreases slowly, then increases rapidly and finally increases slowly; ε_3max first decreases slowly, then increases slowly, and finally decreases slowly; and ε_2max increases slowly then decreases slowly. ε_vmax decreases rapidly first and then increases slowly with increasing loading rate.