Development & Implementation of Strata Control Practices Management through Understanding Stuart MacGregor B.E Principal Geotechnical Engineer Director SCT Istanbul 2014

Theme “Unforeseen" or "unpredictable" ground conditions are often put forward as the causal factor resulting in loss of life or closure of mines. Often the responsibility is placed on front line personnel with little or no training to recognise and respond to changing conditions.

Theme The ability to manage strata control hazards, following a risk based approach, is achieved by: undertaking systematic and thorough site investigations prior, and during, mining to identify and quantify geotechnical hazards and through the systematic application of measurement, observation and design to understand the interaction of mine openings, ground conditions and application of controls. Elimination of geotechnical hazards – notably poor mine design and practices – is a powerful tool available to the geotechnical engineer early in the planning process.

We have control over this, enabling management of conditions. Mining changes the nature of the ground. How we mine and how we respond will change the outcome. We have control over this, enabling management of conditions.

Methodology The basis for a geotechnical program is a recognition that defining the variability in strata conditions is the key to minimising unforseen problems. This is achieved by the systematic and ongoing evaluation of strata control hazards, which minimises their unexpectedness.

Methodology In practice we are defining a range of geotechnical domains that have similar characteristics (rock types, defects, strength, stress conditions) that respond in a predictable manner during mining. Defining key characteristics of the strata, reinforcement and roadway behaviour for each domain enables an expected range of mining conditions to be determined. For these mining conditions appropriate mine layouts and reinforcement designs can be implemented.

Strata Control Workflow Geotechnical Characterisation Strata Control Workflow Geotechnical Design Systematic & Ongoing Evaluation

Geotechnical Characterisation Provide a base level of geotechnical data on which to conduct mine design Quantify geotechnical environment Identify specific geotechnical hazards impacting mine design Provide plans showing geotechnical domains - define the variation using maps - to assist with prediction, planning and design.

Quality & Type of Data

Geotechnical Data Synthesis

H  h Pw  = 3H - h - Pw Engineers Deal with Stress and Load Understand the source and magnitude of ground stress on your design H  h Pw Determine rock strength Constrain h Solve for H  = 3H - h - Pw

Underground & Surface SITE INVESTIGATIONS Note mining impacts on multiple systems including groundwater/inrush.

Be Aware of Hazards Posed by Caving, Fracturing & Interconnection

HAVE A DESIGN APPROACH SUITABLE FOR YOUR CONDITIONS – UNDERSTAND WHAT IS GOING ON

TYPICAL EXAMPLE OF ROOF BEHAVIOUR FOR DIFFERENT MINING STAGES Industry Training Programs

INCREASING STRESS

Longwall Support Mechanics POOR Ground Control Horizontal Stress and Displacement Indicators Vertical Stress and Displacement Indicators Longwall Support Mechanics POOR Ground Control

Geotechnical Input into Equipment Configuration & Implementation

Systematic and Ongoing Evaluation

Routine Monitoring & TARP’s Forms the basis for operational assessment A set of pre-determined triggers coupled with guidelines on the implementation of controls and responses. Needs a context.

ROUTINTE MONITORING IN ISOLATION IS NOT A MANAGEMENT SYSTEM Trigger -10mm Trigger -30mm

Implementing & Managing Change Incorrect and uncontrolled application = high risk of failure Greatest concern is uncontrolled and unsupervised application Inappropriate designs and consumables Applying the technology under inappropriate geological and mining conditions and mining layouts

Summary Mining is dynamic – with rapid changes in mining geometries and associated ground stress and displacement. Ground response is not typically linear – step changes can occur and it is important to identify and quantify. Understanding these processes enables rational and safe introduction of new mining systems and/or new mining areas. Management of strata control hazards requires systematic and ongoing integration into mining operations. Ground conditions can be managed.