The stability of underground openings is pivotal to sustainable safe mining in underground coal mines. To determine the stability and tunneling safety issues in 800-m-deep underground openings through large fault zones in argillaceous rocks in the Guqiao Coal Mine in East China, the pilot industrial test, laboratory experimentation, and field measurements were used to analyze the large deformations and failure characteristics of the surrounding rock, the influence factors of safe excavation and stability of underground openings, and to study the stability control countermeasures. The main factors influencing the stability and tunneling safety include large fault zones, high in situ stress, poor mechanical properties and engineering performance of the argillaceous rock mass, groundwater inrush and gas outburst. According to the field study, the anchor-ability of cables and the groutability of cement-matrix materials in the argillaceous rock in the large fault zones were extremely poor, and deformations and failure of the surrounding rock were characterized by dramatic initial deformation, high long-term creep rate, obviously asymmetric deformations and failure, rebound of roof displacements, overall loosened deformations of deep surrounding rock on a large scale, and high sensitivity to engineering disturbance and water immersion. Various geo-hazards occurred during the pilot excavation, including roof collapse, groundwater inrush, and debris flow. Control techniques are proposed and should be adopted to ensure tunneling safety and to control the stability of deep underground openings through large fault zones, including regional strata reinforcement technique such as ground surface pre-grouting, primary enhanced control measures, floor grouting reinforcement technique, and secondary enclosed support measures for long-term stability, which are critical for ensuring the sustainable development of the coal mine.

Goaf-side roadway driving could not only notably reduce the loss of coal resources and improve the coal recovery rates, but also greatly mitigate the imbalance between excavation speed and production needs, which are able to prolong the service life of the mine and are pivotal to sustainable and efficient development of underground coal mines. However, it is difficult to control the stability of the goaf-side roadway, especially under mining disturbance of another adjacent coal working face. In order to control the stability of the goaf-side roadway, Haulageway 1513 in the Xinyi Coal Mine of China, under mining disturbance, theoretical analysis, numerical simulation, and engineering practice were carried out to reveal the mechanism of overburden key strata fracture, stress distribution, and deformation characteristics of the surrounding rock of the goaf-side roadway due to mining disturbance. Results showed that some key strata above Goaf 1512 did not fracture due to the influence of the strata caving angles. However, these key strata would fracture and break into rock blocks when suffering from mining disturbance of the adjacent coal working face, which changed the stress distribution and increased the deformations of the surrounding rock of the goaf-side roadway. The combined techniques of pressure relief and bolt support were proposed and carried out to control the stability of the goaf-side roadway. Engineering practice indicated that the maximum deformations of the roof and sidewall-to-sidewall were 220 mm and 470 mm, respectively. The deformations of the goaf-side roadway under mining disturbance were efficiently controlled.

This paper conducts a simulation experiment research on cutter-head vibration characteristics by evaluating a soft-hard mixed stratum (the upper layer is silty soil, whereas the lower layer is moderately weathered granite of maximum UCS 142.0 MPa and slightly weathered granite of maximum 210.0 MPa). The ratios of hard rock and soil within the tunnel face were designed to be 1:1 and 1:2. Then, the cutter-head and stratum model were subjected to vibration analysis by reasonably deployed accelerometers. Results show that: 1) different conditions of heterogeneous strata mainly affected the acceleration amplitude and frequency distribution of cutter-head, in other words, the stronger hard rock, the larger the strength difference between the hard rock and soil within a tunnel face, the larger the vibration acceleration and the more concentrated the vibration frequency distribution; 2) the radial and circumferential vibration acceleration of the cutter-head in different positions were not largely different; however, axial accelerations were largely different. The axial vibration accelerations first increased and then decreased along the radial direction of cutter-head. Considering the difference between Multi-Mode Boring Test System and real cutter-head structure, the radius of joint between the cutter-head and the flange plate should be reasonably increased according to the ratio of hard rock in tunnel face; 3) with the increasing difference between the strength of the hard rock and soil, the circumferential and axial vibration acceleration multiplied. Thus, the soil remarkably reduces the vibration of the cutter-head. These results can provide some evidence of potential application for advancing manufacturing practice for cutter-head and disc cutter of shield machine.

The longevity of grouting has a significant effect on the safe and sustainable operation of many engineering projects. A 500-day experiment was carried out to study the long-term mechanical behavior of nano silica sol grouting. The nano silica sol was activated with different proportions of a NaCl catalyst and cured under fluctuating temperature and humidity conditions. The mechanical parameters of the grout samples were tested using an electrohydraulic uniaxial compression tester and an improved Vicat instrument. Scanning electron microscope, X-ray diffraction, and ultrasonic velocity tests were carried out to analyze the strength change micro-mechanism. Tests showed that as the catalyst dosage in the grout mix is decreased, the curves on the graphs showing changes in the weight and geometric parameters of the samples over time could be divided into three stages, a shrinkage stage, a stable stage, and a second shrinkage stage. The catalyst improved the stability of the samples and reduced moisture loss. Temperature rise was also a driving force for moisture loss. Uniaxial compressive stress-strain curves for all of the samples were elastoplastic. The curves for uniaxial compression strength and secant modulus plotted against time could be divided into three stages. Sample brittleness increased with time and the brittleness index increased with higher catalyst dosages in the latter part of the curing time. Plastic strength-time curves exhibit allometric scaling. Curing conditions mainly affect the compactness, and then affect the strength.

Rapid excavation could mitigate the imbalance relationship between excavation speed and production needs that plays a pivotal role in the sustainable development of large underground coal mines. This paper provides a case study on Bolter Miner Rapid Excavation Technology (BMRET) in Menkeqing Coal Mine, which has a high production of 13 million tons per year in Inner Mongolia. The temporal characterization of excavation procedures is analyzed in detail based on field monitoring data. The improvement of the roadway driving process and efficiency under a new support design is introduced, and corresponding evaluation methods, including parallel operation index ( $P_x$ ) and unit drilling-hole index ( $D_x$ ), are proposed for BMRET. A field application is conducted to verify the effectiveness of the improved BMRET, which fully considers the structure characteristic of the bolter miner machine. The performance and reliability of this new support scheme are monitored in terms of roadway convergence and axial force of cable through professional instrumentation programs in the field. The results show that the average excavation speed of the BMRET is 36.15 m/day (1080 m/month), an increase of 99.72% compared with the original excavation technology, which indicates that the BMRET could provide high efficiency in roadway excavation and effectively control the stability of deep roadways. It is pivotal to apply BMRET to ensure sustainable and highly efficient coal production. This case study provides reference and guidance for rapid excavation of deep underground roadways with similar geological conditions.