SUBSIDENCE PREDICTION AND VISUALISATION
A SHORT COURSE
5 July 2006

CANCELED

A short course on mine subsidence prediction is to be held on the Wednesday 5th July, before Coal 2006, Coal Operators Conference, at the University of Wollongong.  At the end of the course, participants will be able to make an initial assessment of subsidence over a underground coal mine and identify if there are geological and geotechnical features that may limit the application of standard methods.  Using subsidence data from adjacent operations with the same conditions, they will be able to produce contour plans of predicted movements, tilts and strains.

The course will be presented by Dr Ross Seedsman and Walter Keilich.  A minimum of 10 and a maximum places will be available.  Registration closes on Friday 16 June.

The expectations for accurate subsidence predictions are rapidly increasing and are now in excess of the capabilities of the standard design tools.  There is a growing gap between what subsidence engineers can predict and the requirements of many current consent conditions.  This short course will review the state of the art in subsidence prediction with the aim of providing a basis on which to build a better understanding of the capabilities and limitations of the process.  The course will examine the mechanisms of subsidence before applying the more common geometrical and statistical processes.

Topics to be covered include:

Geotechnical basis of subsidence.  In the past, subsidence engineering has been based on the geometry of the mine layout and the statistics of the subsidence deformation.  Only recently, have geotechnical engineering principles been applied that allow the consideration of the nature of the overburden and underlying rocks.  Subjects to be covered include the spanning and subsequent collapse of overburden strata, the deformation and failure of coal pillars, and the deformation of roof and floor rocks.  There will be a discussion on the prediction of caving and fracturing heights above longwall goafs.  A case study from the Newcastle district will be used to demonstrate how the principles can be applied.

The general shape of the subsidence bowl and the associated tilts and strains.  The systematic deformations of the surface above extraction panels will be discussed, along with the range of deviations that are sometimes recorded (disordered subsidence).  This session will also outline the various subsidence impacts that need to be considered:- vertical movement, horizontal movement, tilt, curvature, and strain.  Particular emphasis will be placed on the disordered subsidence deformations and how they can be related to specific geotechnical conditions.

The use of empirical prediction methods.  The ‘Holla’ method, published by the NSW Department of Minerals Resources, continues to form the basis of subsidence prediction in Australia.  This method allows the prediction of 7 points on a profile. The strengths and weakness of this method will be investigated.  This section will also examine how typical subsidence cross-line survey data can be assessed.  Participants will be encouraged to supply some of their own data for analysis.

The use of the influence function method to visualise subsidence deformations  Influence function programs (such as SDPS) methods are now readily available for personal computers and provide the ability to readily produce contour plans of vertical subsidence, tilts, curvatures, and strains.  The short course will demonstrate how a CAD drawing can be manipulated, input to SDPS, and the subsidence contour plans produced.  A method to prepared predictions as a function of face retreat will be introduced.  This section will be based on case studies, and participants will be encouraged to bring their own data set for analysis. 

The place for numerical methods  The application of finite element and discrete element codes for subsidence prediction will be outlined.  While finite element methods are easier and faster to run, the need to model jointed-rock behaviour specifically will be discussed.

Design of monitoring programs  Can surface surveys provide the basis for management of physical impacts?  Is there a place for the observational method, or should monitoring be designed to validate predictions?  Can subsidence risk be managed by monitoring programs, or is there a need for better prediction?

Presenters: