Hydrogeological Response to Longwall Mining

Reliable prediction and management of mining induced water inflows and aquifer interference is a major emerging challenge confronting the industry. The Australian coal mining industry is facing intense public and political scrutiny and hence is required to operate with unprecedented environmental accountability. The absence of robust and reliable analysis tools may significantly affect the industry's ability to gain mining approval and licenses, where significant aquifers, surface water or flooded workings are involved.

The objective of this project was to develop and demonstrate an integrated hydrogeological assessment approach with supporting tools, and to enhance industry's ability to predict the hydrogeological response to longwall mining.

The project focused on Springvale Colliery as the project site due to the availability of extensive hydrogeological data there. Within this project, systematic sub-surface and underground hydrogeological monitoring and measurements were carried out including piezometer, extensometer and water inflow monitoring during mining. On the basis of field monitoring and measurement results site hydrogeological characterisation was undertaken and a new in situ hydrogeological model was established for Springvale Colliery.

The project investigated the effects of longwall mining on strata pore pressure, permeability, and water inflow and advanced the understanding of fundamental mechanics of strata and groundwater interaction processes in order to facilitate prediction of mining induced aquifer interference and mine water inflow.

A series of 3D coupled numerical simulations of the hydrogeological response during mining were conducted, using COSFLOW, to examine the impact of various mining parameters on mine water inflows based on the Springvale Colliery conditions.

The key project results are summarised in the following:

• Overview of site monitoring and measurements   
• Hydrogeological characterisation and in situ hydrogeological model
• Mining induced groundwater pressure response  
• Mining induced strata permeability changes
• Mining induced overburden deformation
• 3D COSFLOW calibration and simulations
• Conceptual hydrogeological response model
• Impact of mining parameters