Numerical modelling techniques for studying longwall geotechnical problems under realistic geological structures

Zhang and Wong 
(2018) emphasise that Voronoi logic reduces 
kinematic freedom of polygonal blocks that 
facilitates tensile failure. Meanwhile, Trigon logic 
increases the kinematic freedom of triangular 
blocks that facilitates shear failure. The two GBM 
logics may misrepresent realistic failure 
mechanisms if they do not sufficiently represent 
the texture and shape of minerals constituting 
rock mass. 
Figure 6. Longwall roof stability model with Trigon logic (Gao et al., 2014a). 
 Dung Tien Le, Tung Manh Bui/Journal of Mining and Earth Sciences 62(3), 87 - 96 93 
4. Conclusions 
This paper presents a systematic 
understanding of numerical modelling techniques 
for studying longwall geotechnical problems 
under realistic geological structures. The 
modelling techniques derived from conventional 
and advanced continuum and discontinuum 
methods were reviewed in detail with emphasis 
on their mechanics formulation and applications. 
For FDM - based techniques, the current study 
confirms that they well represent the micro - 
mechanics of rock mass failure rather than 
explicit caving caused by unjointed or moderately 
bedded coal seam/roof strata in longwall. The 
continuum formulation of the programs, on the 
one hand, limits the complete and large 
detachment of elements in the domain. On the 
other hand, it may break down the calculation 
process when many discontinuities (e.g., 
geological structures) are incorporated. For DEM 
- based techniques, the study finds a wide use 
from longwall entry stability to coal wall spalling, 
roof caving, and roof fracture. Conventional joint 
generator built in the programs is found to be 
limited to modelling deterministic fractures 
which are persistent. DFN logics are seen to be 
suited for explicit representation of stochastic 
fractures as in practice, but their use in longwall 
problems is currently limited and mainly in 2D. 
Note that due to the 3D nature of geological 
structure distribution, the 2D modelling must be 
implemented with care for retaining the 
representativeness of the problem’s structure. At 
the same time, GBM logics are suited for the 
representation of explicit failure and caving 
development along well - calibrated fictitious 
fractures. This study suggests that the successful 
selection of a proper modelling technique should 
be based on the physical principles of longwall 
problems, textures and shapes of materials 
constituting problems, and mechanics 
formulation of the numerical program used for 
modelling. 
Author contributions 
Dung Tien Le reviewed and wrote the 
introduction and discussion; Tung Manh Bui 
collected documents and wrote the conclusions. 
Acknowledgements 
This research is funded by Hanoi University 
of Mining and Geology, Vietnam. 
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