Appalachian Research Initiative for Environmental Sciences: UK Mining Engineering Tasks

The Office of Surface Mining Reclamation and Enforcement (OSMRE) has proposed a new rule (NR) for regulation of coal mining to improve the balance between environmental protection and providing for the Nation’s need for coal as an energy source. The proposed rule, which was published on 27 July 2015, aims to “better protect streams, fish, wildlife, and related environmental values from the adverse impacts of surface coal mining operations and provide mine operators with a regulatory framework to avoid water pollution and the long-term costs associated with water treatment.” Furthermore, the proposed rule requires that “each permit (should) specify the point at which adverse mining-related impacts on groundwater and surface water would reach that level of damage…” and that “…the proposed changes would apply to both surface mines and the surface effects of underground mines.” It is well documented that ground movements due to underground mining may affect surface water bodies including rivers, streams, swamps, wetlands, lakes, farm dams or other water retaining structures. Overburden geologic structure and thickness, distance from the full extraction area, mine conditions and extent of surface movements all are key parameters in determining the degree of impacts on streams and the recovery cycle of the water resource due to longwall or secondary extraction room and pillar sections. At the same time it is also documented that undermined streams can recover after a period of time with, or often without, the application of mitigation measures. In view of the proposed rule, the quantification of potential damage at the planning stage, as well as the assessment of alternate mine planning scenarios will be an important step. This proposal aims at developing the tools needed to accomplish such a task both for mountainous regions (i.e. the Appalachian coal basin) as well as for flat terrain such as the Illinois coal basin. It will based on a well-accepted ground deformation prediction methodology, which is already used by OSMRE and state and federal agencies and the US coal mining industry for subsidence planning, prediction, and control. This technology is implemented in the Surface Deformation Prediction System (SDPS) software package which utilizes the influence function method for subsidence prediction -- a well-established and accepted technique. The influence function methodology implemented in SDPS to calculate final surface deformations relies on a several subsidence engineering parameters, i.e., the angle of influence, the supercritical subsidence factor and the edge effect offset distance. Empirical relations are available that allow the estimation of the edge effect offset (of the location of the inflection point of the subsidence profile from the rib of the excavation) as a function of the width to depth ratio and the calculation of the supercritical subsidence factor as a function of the percent hardrock in the overburden. Although this package was initially developed over 25 years ago as a result of an integrated research effort at VPI&SU (1987), it has been constantly updated with the incorporation of new analysis features (e.g. dynamic deformations, calibration routines, long-term stability calculations, etc) since then. SDPS has evolved into a versatile prediction tool that can handle complex tasks, including multiple calibration routines, dynamic subsidence evaluation as well as an estimation of long-term subsidence effects under different scenarios. More recently (2013), the effect of sloping terrain in the prediction of horizontal displacements has been incorporated allowing for accurate three dimensional predictions of deformation vectors over undermined areas in hilly or mountainous terrain. Furthermore, The SDPS software has been tested extensively in numerous case studies. In subsidence engineering calculations, the overall response of the overburden to underground mining can be related to mine geometry, surface topography as well as overburden characteristics. The ground deformation indices that can be used for evaluating potential impacts to streams include the maximum subsidence (Smax), the maximum surface ground slope (±Tmax), the maximum tensile ground strain (+Emax), and the maximum compressive ground strain (-Emax), measured and/or predicted for the site in question. These ground deformation indices are defined in the available literature. However, in order to calculate ground strains accurately, the topography of the surface terrain needs to be accounted for. This becomes even more important in the case of linear water bodies, i.e. streams. In addition, such models should be adjusted for pillars punching into weak floor (Illinois basin) or for pillars shrinking due to elastic deformation. In all cases of numerical modeling, it is very important to verify that model results, e.g. calculated strains, match measured values. Based on the above rationale the project will be divided in to the following tasks: 2.1 Task 1: Collect stream related subsidence data including mine plan information, surface deformation information as well as geologic information. This task will involve utilizing the available database with subsidence case studies as well as securing new data. In addition, more data will be collected pertaining to the Appalachian and Illinois basin. A 2-3 day meeting will be planned with OSM personnel in Illinois to collect available data representative of Central US coal field conditions. Another trip will be planned with a mining company in Pennsylvania that may be able to provide sanitized data. 2.2 Task 2: Develop the procedure and the tools for calculating surface deformations along linear water structures (e.g. streams) under flat and undulating terrain conditions. This task will involve modifying the influence function code of the SDPS package to incorporate these new tools and procedures. In addition the influence of underground stable structures such as barrier pillars or chain pillars between consecutive longwall panels will be critically evaluated. Emphasis will also be given to surface slope generated due to underground mining. The new tools and procedures will be tested against the case studies collected in Task 1.