Study on Mechanical Problems of Complex Rock Mass by Composite Material Micromechanics Methods: A Literature Review

The mechanical analysis of complex rock mass is a difficult problem, which often occurs in scientific research and practical engineering. Many achievements have been made in the study of rock mass composite problems by composite material micromechanics method, but it has not been well summarized so far. This paper summarizes in detail the research status of complex rock mass problems by composite material micromechanics method at home and abroad, including the application of the Eshelby equivalent inclusion theory and self-consistent model in rock mass composite problems, and the application of the homogenization method in jointed rock mass and other rock mass composite problems such as anchored rock mass, layered rock mass, and salt rock mass with impurities. It is proposed that the structural similarity and mechanical analysis similarity should be satisfied when the composite material micromechanics method is used to study the complex rock mass. Finally, the problems that need to be further studied are put forward. The research results provide a valuable reference for the study of complex rock mass by the composite material micromechanics method.

Numerical Studies of the Dynamics of the Roadheader Equipped with an Automatic Control System during Cutting of Rocks with Different Mechanical Properties

The process of cutting rocks with a boom-type roadheader results in extreme dynamic loads and vibrations. Mining, especially in the case of hard rocks, is associated with large energy consumption, which, when combined with low process efficiency, can lead to low drilling performance. These phenomena are undesirable because excessive dynamic load leads to low machine durability, as well as deterioration of work conditions and safety. Low mining efficiency affects the economics of mining works conducted using roadheaders. However, these adverse effects can be minimized by optimizing the cutting process, thanks to the automatic control of the roadheader. The present article discusses the concept of automatic control of a boom-type roadheader’s cutting heads movement. Based on previously conducted computer investigations, it was assumed that reducing the energy consumption of the cutting process and improving the dynamic state of the roadheader (objective functions) are possible only by controlling three of the four parameters characterizing the cutting process: angular speed of the cutting heads, boom swinging speed, and cut height. The web of cut and workability of the rock can be treated as variables of a stochastic nature. This paper presents selected results of computer tests during simulated cutting of rocks with different uniaxial compressive strengths (UCS) in automatic and manual mode. In addition, the tests studied the behavior of the roadheader during the cutting of rocks with variable workability, which is typical of drilling excavations in a layered rock mass. The results of simulated cutting in automatic and manual mode were compared to assess the effectiveness of the adopted automatic control strategy. It was found that the algorithm developed for automatic control of the cutting heads’ movement allows reducing the consumption of cutting energy by up to half compared to the consumption during cutting in manual mode. Furthermore, it was found to improve the dynamic state of the machine.

Creep Structure Effect of Layered Rock Mass Based on Acoustic Emission Characteristics

Investigating the creep structural effect of layered rock mass is of great practical and theoretical significance. In this paper, taking the Muzhailing tunnel as an example, structure effect of layered rock mass based on acoustic emission characteristics has been analyzed. The study shows that creep parameters of layered rock mass are significantly influenced by structural effects, and the overall creep variable is small. The creep deformation of layered rock mass includes transient creep and steady-state creep at a low stress level. At a higher stress level, when the long-term strength of the rock sample is reached, the deformation increases rapidly, and the accelerated creep occurs in a very short period of time. The creep equation of the structural effects of layered rock mass was established based on the experimental results. Acoustic emission characteristics are analyzed during creep experiment; the study shows that the energy released at the time of initial loading and destruction accounted for most of the total energy. The initial energy release increased first and then decreased with the increase in inclination angle; as the inclination angle increased, the cumulative energy when the rock sample was damaged first decreased and then increased. The structural effect on the main frequency value at the time of failure mainly reflected in the trend that the main frequency value first increased and then decreased as the inclination angle increased. Based on the above analysis, we can recognize the structural effects of layered rock mass and provide the necessary parameters for on-site support.