Deep mining

In recent years, a number of Chinese underground coal mines have reached a mining depths in excess of 1000m in China. An increase in depth results in a high stress environment, high gas content and pressure and lower permeability, which presents greater risks to safe mining operations.

In collaboration with China’s Huainan Mining (Industry) Group, our team has carried out integrated ground response monitoring and 3D coupled numerical modelling at several coal mines with a depth of 750m to 1000m. This has enabled the development of significant expertise that supports the design and implementation of underground coal mining at depth.

Integrated ground response monitoring

CSIRO carried out integrated ground response monitoring of stress changes, displacement and groundwater pressure at several coal mines at Huainan. The extent of influence of deep mining and dynamics of ground responses were successfully obtained. These field monitoring results have led to many new insights into the challanges of deep mining and have supported the optimisation of mining systems as well as management of gas and groundwater.

Mining induced overburden fracturing and pore pressure changes at a mine of 750m deep

Prediction of overburden responses under various mining scenarios

Thanks to field monitoring and CSIRO’s unique in-house code COSFLOW, our team is able to adequately predict and characterise the extent of deep mining impact on stress redistribution, strata failure, subsidence, pore pressure changes, and gas desorption and migration.

Stress relief is found to be an adequate factor that can affect the coupled strata-groundwater and gas behaviours.  A factor called Stress Relief Ratio was therefore developed to enable the quantitative prediction of stress relief, fractures, and permeability increase for various mining conditions. An example of prediction of mining impact under different mining thicknesses is shown in the figure below. Based on such prediction, optimisation of mining planning such as mining sequence, gas drainage and outburst management for adjacent seams can be made.

Predicting extent of mining at various parameters