Underground » Strata Control and Windblasts
Quantifying the hydraulic characteristics of the longwall overburden and surrounding surficial area that is influenced by the longwall extraction is crucial to determining the impact of mining on the local groundwater and surface water systems, understanding water flows to the mine workings and gas flows through the goaf region. Groundwater and surface water impacts are contentious issues for a number of mines in Australia, and quantifying the hydraulic characteristics can assist to reduce controversy from such cases. Similarly, for mines with gas issues, quantifying the hydraulic characteristics allows more accurate estimation of gas flows within the goaf and to drainage boreholes from multiple overlying seams, and a more thorough assessment of gas risks.
This project estimates the hydraulic characteristics of the longwall overburden and the surrounding surficial area. The estimates are provided as formulae that are easily applied to common mining scenarios. Estimates of uncertainty are also provided. It is envisaged that these estimates of hydraulic properties and their uncertainties should be used in groundwater models to determine the influence of mining on the surrounding water systems.
The estimates are based on comprehensive parametric numerical modelling of 34,464 mining scenarios, each representing a different longwall panel width, depth, extraction thickness and overburden geology. In previous ACARP projects this modelling approach has supported and agreed with field observations and empirical approaches, and the current modelling also agrees with recent mine measurements.
In this work, the hydraulic characteristics of the overburden and surrounding surficial area are encoded into 9 metrics which are defined and discussed in the report.
An equation along with the numerical values in a table are the main practical output from this project. They are encoded into a Microsoft Excel workbook and a python script for ease of use, available as an attachment and from the author - andrew.wilkins@csiro.au. Also included are the processed results from the numerical simulations. It should be noted that care should be taken when extrapolating the results outside the bounds described in Section 2.1 of the report.