Master of Engineering
Department of Civil and Mining Engineering
Nemcik, Jan Anton, Practical applications of three-dimensional stress change measurements and displacements in underground coal mines, Master of Engineering thesis, Department of Civil and Mining Engineering, University of Wollongong, 1989. http://ro.uow.edu.au/theses/2369
Theoretical advances in mathematical analyses, numerical modelling and computer technology has significantly increased the knowledge of stress distribution around underground excavations. The complexity of rock behaviour, especially of the sedimentary soft rock type has made exact mathematical predictions very difficult. The need for alternative methods was clearly defined.
In the past various methods to measure in situ stresses were developed. Early measurements were in most cases limited to one dimension and were often used to measure the magnitude of vertical stress concentrations around the mine openings.
No detailed discussions on the historical stress measurement development is attempted here since many publications dealing with the topic are readily available.
To understand the behaviour of strata around the mine openings located within laminated and often strain softened rock, it is necessary to conduct a detailed underground geotechnical investigation.
In general, the geological complexity and rock behaviour in most underground coal mines requires in situ investigation of: a) geological structure of roof rock, coal and the floor rock, b) geological disturbances such as faults, fractures and other discontinuities associated with displacement c) detailed stress/displacement measurements as mining takes place.
Results are then used for mine planning purposes, mine sequencing, pillar design and design of efficient roof reinforcement.
No detailed 3-dimensional stress measurements in coal mines were conducted till recent advances in usage of CSIRO 3-dimensional soft inclusion stress cells developed by ACIRL. The stress cells were originally designed for overcoring stress measurements. 3-dimensional stress measurements were often used in metalliferous mines for some time to measure long term stress changes in stopes. Despite many problems new techniques were developed and verified to efficiently record the full three dimensional stress changes in the coal measures as adjacent coal extraction takes place.
The following text deals with a short history of the stress and displacement origins and the monitoring techniques used. Two detailed case histories of extensive geotechnical installation are presented with monitoring and interpretation of strata behaviour in underground coal mines.