Tech Talk - When Millimetres Matter: Subsidence by Design

Join Sydney Branch and WIMnet NSW for their Tech Talk - When Millimetres Matter: Subsidence by Design.

About this event

Underground coal mining in New South Wales operates under strict environmental and regulatory controls, particularly where mining may affect sensitive surface features or groundwater. A key consideration in mine planning is subsidence the lowering of the ground surface that can occur as coal is extracted underground through a longwall mining method.

This presentation will examine two case studies where mine layouts were specifically designed to limit surface movement. These involved subcritical mining geometries, where the width of extraction is constrained so that the full potential subsidence response does not develop.Because there is less historical monitoring data available for these layouts than for conventional longwall mining, traditional empirical subsidence prediction methods can be less reliable. Numerical modelling was therefore used to simulate how the rock mass would respond to mining and to estimate the resulting surface movement.

The two case studies involve miniwall mining at Airly Mine and shortwall mining at Clarence Colliery. Modelling was undertaken using FLAC2D together with in-house tools that simulate rock deformation, failure and stress redistribution as mining progresses.

The focus of the presentation is not the mathematics behind the model, but how numerical modelling can be applied as a practical mine-design tool by combining mining geometry, depth of cover and local geotechnical conditions.

Importantly, the modelling approach has been validated against actual subsidence monitoring. In one case, the model was incorporated directly into mine design, with mining successfully maintaining the required surface subsidence limit of less than 125 mm, consistent with predictions.

The case studies demonstrate how numerical modelling can provide a practical and defensible basis for mine design where historical data is limited and strict surface subsidence constraints must be achieved.

Speaker/s

Rhys Pitchers

Senior Geotechnical Engineer - SCT Operations

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Rhys Pitchers is a senior geotechnical engineer with SCT Operations. He holds a Bachelor of Science in Engineering Geology from the University of Pretoria and a Bachelor of Engineering (Honours) in Civil Engineering from the University of Wollongong. He is a Sydney Branch member of the AusIMM.