Welcome to SCT's own publications library which contains a collection of recent publications and other resources with reliable research about our technology.
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Definitions of Measured Hydraulic Conductivity Zones above a Longwall Panel
Published Jun, 2022This paper presents the results of a field investigation to determine zones of hydraulic conductivity above an extracted longwall panel at United Colliery in the Hunter Valley of NSW. The hydraulic conductivity zones were determined from targeted boreholes drilled into the subsided strata above the goaf of Longwall 10, an isolated panel with a supercritical width panel geometry. Five boreholes defined the edge of caving and characterised the hydraulic conductivity within and above the caved zone. The deepest hole in the centre of the goaf was drilled to 30m above the extracted seam, providing hydraulic conductivity data through most of the subsided overburden strata. Definitions-of-Measured-Hydraulic-Conductivity-Zones-above-a-Longwall-Panel-YHeritage-MSTS-2022.pdf901 KB -
Determination of the Subsidence Mechanism for Subcritical Miniwall Panels
Published Jun, 2022Airly Mine is a miniwall operation mining the Lithgow Seam in the Western Coalfield, NSW. Airly Mine currently mines beneath the Mt Airly mesa, where the Lithgow Seam outcrops near the base of the mesa. Each miniwall panel is subcritical in its geometry with 60m wide panels and depth of cover ranging 200-270m. The surface subsidence produced vertical displacements significantly greater than the empirical predictions, up to 713mm, prompting the numerical modelling approach discussed in this paper. The numerical rock failure modelling assessment illustrated the mechanism for the magnitude of subsidence experienced at Airly Mine. Determination-of-the-Subsidence-Mechanism-for-Subcritical-Miniwall-Panels-Y-Heritage-MSTS-2022.pdf1.8 MB -
Measurement of the caved zone above a longwall panel United Colliery
Published Feb, 2022This paper presents the results of a targeted goaf borehole program to define the edge of the Longwall 10 caved zone at United Colliery, Hunter Valley NSW. Longwall 10 is an isolated panel with a supercritical panel geometry. Three of the five boreholes defined the edge of caving, while two boreholes characterised the centre of the goaf. The location of the caved zone was depicted from a combination of total water loss during drilling that coincided with a subvertical fracture at the location of total water loss. The boreholes showed the caving angle from the pillar ribs to be 21 degrees on the up dip side and 19 degrees on the down dip side of the panel. An additional borehole drilled 10 metres (m) towards the goaf centre on the up dip side showed a caving angle increase to 25 degrees from the adjacent borehole, indicating the arc shape of the caved zone. The caving angle coincided with a high strain fracture zone and connectivity to the goaf. This caving angle information can inform assessments for hydraulic/gas connectivity and geotechnical engineering applications such as multi-seam overmining or opencut/underground interaction. (Note that the caving angle is not the same as the abutment angle, which the latter is a calculated angle
based on pillar load.)
Y-Heritage_Measurement-of-the-caved-zone-above-a-longwall-panel-United-Colliery.pdf1.3 MB -
Mechanics of Rib Deformation Observations and Monitoring in Australian Coal Mines - Yvette Heritage
Published Jul, 2018The risk of fatalities from rib failure is still prevalent in the coal mining industry. This risk has prompted further research to be conducted on rib deformation in order to understand the mechanisms of rib failure, with the long-term objective being to improve rib support design. This paper presents the results of ACARP research project C25057, which investigated the mechanics and drivers of rib failure. The results of rib deformation monitoring at three different mines in Australia provides rib deformation characteristics for overburden depths ranging from 160 m to 530 m. Monitoring includes deformation during development drivage conditions and during the longwall retreat abutment stress environment. The rib deformation monitoring covered three different seams: the Goonyella Middle Seam, Ulan Seam, and Bulli Seam in the Bowen Basin, Western Coalfield, and Southern Coalfield, respectively. The observed mechanisms driving the rib deformation ranged from bedding shear failure along weak claystone bands to vertical shear fractures to kinematic failures driven by shear failure dilation. The variation in mechanisms of rib failure, together with the seemingly consistent method of rib support design, prompts the question: What exactly is the role of rib support? Mechanics-of-Rib-Deformation-Observations-and-Monitoring-in-Australian-Coal-Mines-Yvette-Heritage-2018.pdf6.1 MB -
Mechanics of Rib Deformation at Moranbah North Mine A Case Study - Yvette Heritage
Published Feb, 2018Moonee Colliery are longwall mining in the Great Northern seam at depths ranging from 90m to 170m. Surface infrastructure above the first four longwall panels includes the Pacific Highway and several residential and commercial properties.
This paper describes the pillar design approach used to manage surface subsidence in the area. The approach is based on previous detailed subsidence and pillar monitoring in nearby Wallarah Colliery and measurements of subsidence throughout the Lake Macquarie area for a wide range of pillar sizes and overburden depths. Undermining the Pacific Highway requires consideration of not only the amount of subsidence but also the timing and nature of subsidence. Various options were considered and a design developed to control surface subsidence to acceptable levels. This paper summarises the results of previous monitoring and outlines the issues considered in the longwall panel design for subsidence control at Moonee Colliery. COAL-2018-Mechanics-of-Rib-Deformation-at-Moranbah-North-Mine-A-Case-Study-Y.Heritage-2018.pdf2.6 MB -
Validation of a Subsidence Prediction Approach of Combined Modelling and Empirical Methods - Yvette Heritage
Published Nov, 2017Subsidence 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
Published Feb, 2017Gas 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 -
A Combined 2D and 3D Modelling Approach to Provide Adequate Roof Support in Complex 3D Excavations - Yvette Heritage
Published Jul, 2015Traditional methods for assessing effective roof support can be difficult to apply to complex 3D excavations. Through worked examples, this paper illustrates the successful approach of combined 2D and 3D numerical modelling to understand the mechanisms of rock failure for unique excavation geometries. The modelling approach provides adequate roof support recommendations for complex 3D excavations in Australian coal mines. A-Combined-2D-and-3D-Modelling-Approach-to-Provide-Adequate-Roof-Support-in-Complex-3D-Excavations-Y.Heritage-2015.pdf2 MB -
Using Helium as a Tracer Gas to Measure Vertical Overburden Conductivity Above Extraction Panels - Yvette Heritage - Winton Gale
Published Feb, 2009This 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 -
Successful Construction of a Complex 3D Excavation Using 2D and 3D Modelling - Yvette Heritage
Published Aug, 2017Austar Coal Mine (Austar) successfully constructed an underground coal storage bin at a deep mine in challenging conditions. SCT Operations (SCT) was involved in various geotechnical assessments related to the bin excavation including vertical separation of the bin drift and underlying seam roadways, bin top area roof design and support and seam roof support at the bin base. Traditional
methods used for determining support recommendations can be difficult to apply to complex three dimensional excavations. SCT used a combination of two dimensional and three dimensional numerical modelling using FLAC 2D and FLAC 3D to understand the key drivers and modes of failure about the bin excavation.The staged process of construction and an interactive approach between Austar and SCT enabled review and validation of the modelling process to occur throughout the construction. A key lesson from this program of work is that there is value in an interactive approach whereby site monitoring and review of model properties during construction provides early validation of the model. This ensures that natural geological variability, which can have significant impacts on rock failure and deformation, can be incorporated into the model as an ongoing process. Successful-Construction-of-a-Complex-3D-Excavation-Using-2D-and-3D-Modelling-Y.Heritage.pdf1.7 MB