Numerical investigations to assess ground subsidence and fault reactivation during underground coal gasification

Abstract. This paper aims to assess potential environmental impacts
associated with commercial-scale application of in situ coal conversion in a
target area in Hungary. The site is an environmentally protected forested
area. Parametric numerical modelling techniques were employed using a discrete
element method (DEM) to evaluate the surface subsidence and fault activation
during mining processes. The Mohr–Coulomb elastic–plastic material model
adopted to simulate rock formations. Zero-thickness interfaces with friction
and cohesive characteristics were employed to simulate geological faults. A
sensitivity study on rock formations and fault properties was conducted to
address the importance of geological parameters that have an impact on
surface subsidence as well as fault activation, which could in turn result
in pollutant migration from the deep coal seams to the surface. The
analysis of the results demonstrated that surface subsidence is affected by
the average Young's modulus of the geological strata, whereby the activation
of the faults is influenced by the friction angle between faults. Also, it
was found that shallower seams are more likely to produce surface subsidence;
i.e. as excavation depth increases, the surface subsidence decreases.
Finally, computational outputs from this work were used to develop the
web-based and interactive Environmental Hazards and Risk Management Toolkit
(EHRM) for planning and decision-making processes during in situ coal
conversion.
