Document Type

Conference Paper

Publication Date


Publication Details

Ben Blacka, Adrian Rippon and Nick Le Bauti, Measurements of the height of fracturing and height of depressurisation above a longwall panel, Proceedings of the 2024 Resource Operators Conference, University of Wollongong - Mining Engineering, February 2024, 101-112.


This paper presents the findings of a program of work to determine the height of mining induced fracturing and the height of groundwater depressurisation above a longwall panel. The program of work utilised two fully cored boreholes drilled from surface at Tahmoor Colliery, located southwest of Sydney in the Southern Coalfields in New South Wales. The boreholes were drilled adjacent to and over a subcritical longwall panel, one before and one after extraction of the longwall panel.

Field measurements of the geotechnical and hydrological ground conditions in the pre and post mining boreholes were compared. Three geomechanical zones were determined in the overburden above the extracted longwall panel which correlate with ground water and hydraulic conductivity measurements.

The results show that the determined height of caving and the start of a reduced pore pressure profile (from hydrostatic) coincide at the same height above the mining horizon. The reduction in pore pressure from hydrostatic to zero pore pressure is a gradual transition, meaning the height of depressurisation (zero pore pressure) and height of caving do not necessarily coincide.

This work program provides a comprehensive dataset of changes in pore pressure, conductivity and caving for the horizons within the overburden above a longwall panel at Tahmoor Colliery. The results from this program of work reinforce the results from a previous work program at Tahmoor Colliery detailing the height of caving and height of depressurisation.

The outcomes of this program are useful in providing an understanding for groundwater modelling above extracted longwall panels.