Interstate Technical Group on Abandoned Underground Mines
Fourth Biennial Abandoned Underground Mine Workshop
Abstract: Numerical Modeling Simulation of Old Works Stability New Technologies and Practical Considerations
Matthew J. DeMarco
FHWA Central Federal Lands Highway Division
In recent years, a number of numerical modeling procedures have been developed to determine design requirements and stability conditions of planned and/or existing subsurface excavations. These methods include both 2-D and 3-D applications of finite-, distinct-, discrete-, and boundary-element codes, hosting a wide array of hybrid options (slip elements, non-elastic solutions, dynamic analyses, massive deformation solutions, "material point" wave propagation elements, etc.). Of these technologies, "quasi" 3-D boundary-element codes have emerged as being extremely applicable to both in- and off-seam stress-deformation-failure analyses for tabular deposits - particularly suitable for underground coal mine settings. Boundary-element solutions can be readily generated for actual and planned mining conditions and account for a variety of mine-specific parameters, including: multiple seams, actual topography, varying seam extraction sequences and heights, gob zones, off-seam deformations (including surface subsidence), dynamic failure potential, cascading pillar failures, etc. Two methods in particular, MULSIM/NL - a non-linear multi-seam boundary-element code - and LAMODEL - a hybrid of the MULSIM technology for generating off-seam deformations in overburden units - are commonly used in the coal industry today, providing excellent correlation with measured and observed experiences at both active and abandoned coal properties.
This paper focuses on several topics pertinent to evaluating old works subsidence conditions with numerical simulations, including estimating subsidence potential (current and future mine stability), maximum and staged subsidence sequences, and the potential for catastrophic failure conditions. To this end, several case histories will be discussed illustrating boundary-element modeling applications involving subsidence predictions along proposed pipeline alignments, complex subsidence resulting from multi-seam interaction, and cascading pillar failures accompanying subsurface coal refuse pumping. The goal of the presentation will be to educate the attendance on the myriad of design factors impacting coal mine stability assessments and to provide an overview of a powerful technology for assessing complex mining settings.