Development of a new algorithm for implementing the edge effect offset for subsidence calculations

The surface deformation prediction system (SDPS) program has been developed as an engineering tool for the calculation of subsidence deformation indices through the implementation of various prediction methods. From basic user-defined input parameters, SDPS can determine subsidence indices, such as mining induced displacements, strains, tilt, etc., at any elevation between the seam and the horizontal or varying surface topography. A fundamental parameter in obtaining reliable ground deformation results is the determination of the edge effect offset. The value assigned to the edge effect offset corresponds to a virtual offsetting of boundary lines delineating the extracted panel to allow for roof cantilevering over the mined-out area. The objective of this paper is to describe the methods implemented in updating the edge effect offset algorithm within SDPS. Using proven geometric equations, the newly developed algorithm provides a more robust calculation of the offset boundary of the extracted panel for simplistic as well as more complex mining geometries. Given that an extracted panel is represented by a closed polyline, the new edge offset algorithm calculates a polyline offset into the extracted panel with respect to the user defined edge effect offset distance. Surface deformations are then calculated using this adjusted panel geometry. The Matlab program was utilized for development and testing of the new edge effect offset algorithm. After completing rigorous testing regimes, the new offset algorithm will be integrated into SDPS further increasing the speed and reliability of the program resulting in a retrospective increase in capability and flexibility.