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  • Validation of a Subsidence Prediction Approach of Combined Modelling and Empirical Methods - Yvette Heritage

    Subsidence prediction is often required outside the limits of empirical databases where we look to other methods to expand our understanding of overburden caving and subsidence effects. Computer modelling, through simulation of rock failure and
    overburden caving, provides a means to extrapolate beyond current experience and to investigate other aspects of caving processes that are becoming increasingly important; aspects such as multi-seam interactions, irregular overburden geologies and groundwater interactions.

    This paper describes examples and a range of useful outcomes from modelling simulations of rock failure and overburden caving to illustrate how modelling is being used to extend understanding of multi-seam mining scenarios, irregular overburden geology, “greenfield” mining areas, increasing overburden depths and the requirement to understand overburden fracture formation and vertical hydraulic connectivity. A case study from the Bowen Basin is used as an example of the value of combining modelling and an empirical approach to improve subsidence prediction and provide validation and calibration of the prediction methodologies for future subsidence prediction. Validation-of-a-Subsidence-Prediction-Approach-of-Combined-Modelling-and-Empirical-Methods-Y.Heritage2017.pdf2.5 MB
  • Connectivity of Mining Induced Fractures Below Longwall Panels A Modelling Approach - Yvette Heritage - Winton Gale - Adrian Rippon

    Gas make into active longwall panels is an important issue in ventilation and gas drainage design. A method of simulating the mining induced fracture network and associated increase in hydraulic conductivity is a necessity for improved mine design, hazard management planning and gas drainage efficiency. This paper identifies and illustrates the key components in determining the connectivity of lower gas sources to an active goaf. Computer modelling identifies the formation of cyclic fractures that form below the longwall face and extend down back below the goaf. These cyclic fractures form when the stress conditions are high enough and the strata properties allow for shear failure to extend down through the strata.

    The mining induced fracture formation and stress redistribution creates increased hydraulic conductivity of the floor strata below the active goaf. The stress redistribution and fracture volume also reduce the pore pressure below the goaf, allowing gas desorption to occur from lower seams. The combination of gas desorption and increased hydraulic conductivity allows gas connectivity from gas sources below the seam to the active goaf. A monitoring program at a NSW mine as part of ACARP Project C23009 allowed for preliminary validation of the concepts illustrated from the computer modelling. Preliminary field gas flow measurements are within the range of connectivity expectations based on rock failure modelling of longwall extraction. This report presents the first validation results for the modelling approach presented in this paper. Further results from ACARP Project C23009 on optimisation of gas drainage will follow in future publications. Connectivity-of-mining-induced-fractures-below-longwall-panels-A-Modelling-Approach-Y.Heritage-W.Gale-A.Rippon-2017.pdf1.3 MB
  • Using Helium as a Tracer Gas to Measure Vertical Overburden Conductivity Above Extraction Panels - Yvette Heritage - Winton Gale

    This paper investigates helium injection into the goaf as a tool to measure goaf to surface connectivity. Laboratory studies confirmed a relationship between gas velocity and fracture conductivity through helium injection. Field trials of helium injection into the goaf were successfully conducted to determine whether a connection exists between the surface and the goaf. A repeatable technique of borehole helium injection, with a borehole drilled into the highly permeable caved zone of the goaf, proved to demonstrate more quickly whether a connection to the surface exists. Using-Helium-as-a-Tracer-Gas-to-Measure-Vertical-Overburden-Conductivity-Above-Extraction-Panels-Y.Heritage-W.Gale-2009.pdf281 KB
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