1. Introduction

One of the critical engineering problems faced by the coal mining industry is coal burst. It is caused by a dynamic release of energy within the overstressed rock mass/coal during the mining process. It occurs under the effects of complex environments of geology, stress and mining conditions. It has been recognised that the unstable releases of potential energy of the rock around the excavations, mainly in the form of kinetic energy, contributes to the coal burst occurrence. Interactions between the coal and rock interface, as well as the confinement, can completely determine the failure mode and the ultimate bearing capacity of coal pillars, influencing the amount of stored energy within a pillar. Many authors define rock/coal burst

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

as a sudden, rapid rupture of the rock mass with a violent, explosive release of elastic/strain energy from the surface of an excavation, which is generally associated with a seismic event and produces rock particle ejections [1–5]. The coal burst source is the mechanism that triggers or induces the damage mechanism visible on the excavation surface. The coal burst source is generally associated with a seismic event that can be performed at a wide range of local magnitudes, normally ranging from undetectable up to 5 [6]. Indeed, mining-induced seismicity can reach moderate values of ground velocity and acceleration, and in some cases its effects on the surface can be compared with low-intensity earthquakes [7]. The mechanism that produces the seismic event is a sudden release of the strain energy that has been stored above a critical level within the rock/coal mass. Some portion of this energy is demolished by crack development, and the rest of the energy is converted into the kinetic energy [8, 9]. When the energy source is located near the roadway, the released energy may lead to coal fragmentation. At the place of the source of the energy, where it is located in a plane of weakness inside the coal mass, the released energy provokes shear displacement along the plane, which in revolve generate vibrations that persuade coal ejections when they are situated near the excavation boundaries [7]. Tarasov and Randolph [6] have explained a number of special and inconsistent behaviours of hard rock at the significant depth that are directly related to rock failure mechanisms in deep excavations. They determined that the procedures of the shear failure, with respect to the significant low friction, can be classified as the main reason to release energy. Based on the suggested frictionless mechanism, the level of the brittleness of the confined rock/coal masses might be increased under high stress conditions. This may result in reducing the overall ductility which would in line with the abrupt fracture failure. Under an energy-balance approach, the methods to predict coal burst risk are based on energy indexes such as energy release rate (ERR) [8–10], energy storage rate (ESR), strain energy storage index (WET) [11], potential energy of elastic strain (PES) or strain energy density (SED) (i.e., the elastic strain energy in a unit volume of the coal mass, which can be computed by the uni-axial compressive strength of the coal and the relevant unloading tangential modulus), and burst potential index (BPI). A combination of both analytical as well as numerical methods, where they can comprehensively evaluate the structural performance of the mine scale, would be broadly addressed in the current research. Thus, the following aims explicitly will be addressed.

2. Numerical modelling strategy

remaining hazard, associated with design process.

Numerical simulations can be considered as an individual tool to predict possible failure modes and the actual capacity of the mining setting. It is mostly useful to undertake parametric and sensitivity analyses to gain better understanding the nature and level of indecision, or

Numerically and Analytically Forecasting the Coal Burst Using Energy Based Approach Methods

http://dx.doi.org/10.5772/intechopen.71879

209

First, a finite element model is developed by taking advantage from the commercial software package ABAQUS/Explicit. All the geotechnical components, including the rock and coal, were modelled by the eight-node linear brick element (C3D8R) available in the ABAQUS library. Element C3D8R relies on reducing integration and hourglass control. The assigned meshes were established by using the structured technique available in ABAQUS. The solution to the nonlinear problem was sought using the explicit dynamic analysis procedure available

Thus, by taking advantage from the symmetrical boundary conditions, a finer mesh was assigned to the model. Finding the right input material properties would be a significant assumption, which has not been appropriately studied in the available literature. Modelling of mechanical behaviour of the coal under both compression and shear stresses would be very complicated, since there are no articulated reports which might be concerned with the uni-axial and tri-axial behaviour of coal under both static and dynamic loading conditions. According to

in ABAQUS. In the current study, Figure 1 presents a quarter of a single pillar.

Figure 1. Illustration of a typical single pillar model using ABAQUS/Explicit.


The main novelty of this research is to simulate the effect of the failure and post-failure of the engaged material as well as joint/contact properties on the energy transformation.
