The Impact Behavior between Coal Gangue Particles and the Tail Beam Based on Rock Failure

In top coal caving mining, common impact occurs between coal gangue particles and tail beam. Little attention has been paid to the effects of coal gangue particles failure on impact force and tail beam response theoretically, numerically, and experimentally. This paper aims to reveal the influence of coal gangue particles failure on the impact effect of tail beam. First, this paper incorporates the theory of rock failure and energy consumption to assess the impact process of coal gangue particles on the tail beam. A new model to simulate the actual failure conditions of rock particles was developed: the brittle damage-fracture particle model. By comparing damage phenomena and simulation data, the brittle damage-fracture particle model was proved to be correct. Based on this model, a dynamic simulation of brittle coal gangue particles impacting the tail beam was conducted. Then, the dynamic responses of the particles and tail beam were analyzed. The results show that particle failure significantly affects the impact force and dynamic response of the tail beam. The impact effects of coal and gangue particles on the tail beam and their failure energy consumption also differed significantly. This paper stresses the importance of coal gangue particle failure conditions for research on top coal caving mining. Theoretical support is provided for the research of coal gangue identification technology based on the tail beam vibration signal.

Comparative analysis of acoustic and electromagnetic emissions of rocks

Comparative analysis of acoustic and electromagnetic emissions recorded during the intact rock samples deformation and dynamic rupture of simulated crustal fault is presented. Specialized machines for uniaxial compression and shear tests of rock samples with identical data acquisition systems for both test cases were employed. Increase of acoustic emission was observed accompanied by significant rise of intensity and amplitude of electromagnetic signals at high stress of the rock samples under the uniaxial compression or dynamic failure in the spring-block model. Such correlation is consistent with the previous conclusions that an increase of electromagnetic emission may be considered as a rock failure precursor. Any specific characteristics of the detected electromagnetic signals to be used for prediction of impending rock failure or the earthquake fault rupture were not found. The similarity of electromagnetic signals and their spectra obtained at the press equipment and the spring-block model suggests that in both cases, the signals observed are generated by the crack formations and shear. The electromagnetic emission appeared only in dry samples. The samples saturated by water with the salinity of over 0.1% demonstrated no electromagnetic emission.

Brittle deformation

By nature, brittle deformation is discontinuous. It is often studied through mechanical tests, both in laboratories and outdoors, in mines and quarries. Brittle deformation also concerns civil engineering (road maintenance, strength of retaining structures such as bridges, dams, galleries etc.) and is well integrated with investigations in rock mechanics. Hydraulic fracturing is extensively used in the geothermal sector, for oil or gas production enhancement, or recovery of shale gas. Along with in-situ stress measurements, it has expanded the interest of geologists within the domain of rock mechanics. A solid knowledge of the mechanisms governing rock failure is necessary to understand the processes operating at the origin of earthquakes and volcanic eruptions, as well as the genesis of ore vein deposits. Beyond the elastic threshold of mechanical tests, rock failure takes place after development of a certain amount of non-elastic deformation. The fact that a progressive transition exists between ductile and brittle deformation suggests that these two behaviours are not mutually exclusive. Indeed, the study of the brittle-ductile transition paves the way to new concepts that enrich our understanding of the mechanisms of failure, in turn allowing practical applications. In this chapter, a presentation of the relationships between fracture orientation and principal stress directions will be followed by an examination of the macroscopic and microscopic aspects of brittle deformation.