The value of early geotechnical assessment

VALUABLE data for geotechnical interpretation and integration into effective Australian underground mine planning may often be available, yet is not always fully appreciated or utilised, particularly in the early stages mine planning or in due diligence studies. IMC Consultants detail the strategies and benefits associated with early prioritisation of geotechnical evaluation and impact on mine planning. <b>By Chris Hanson, Principal Geologist/Geotechnical Engineer, IMC Consultants Pty Ltd.</b>

Angie Tomlinson
The value of early geotechnical assessment

Unidentified, misinterpreted, or ill defined adverse geological and related geotechnical resource characteristics can pose significant business risk to underground coal projects and operations.

Preliminary resource definition in the early conceptual mine planning stages attributes significant focus (entirely warranted) on resource quality and structural geology constraints. Yet detailed geotechnical data analysis and interpretation, which may have a substantial down stream impact and sensitivity with respect to future mine planning strategies, at times is given lower priority, or scoped and resourced in the later stages of a bankable feasibility study.

Through extensive mine planning experience and observation of down stream process impacts, IMC have found there is often data available for geotechnical analysis which does not readily stand out or is not adequately understood or utilised, available at the early (conceptual) stages of mine planning. It can be manipulated to provide key geotechnical hazard assessment at minimal cost, and provide a framework for understanding and optimising the mine planning process.

Although there is no single prescribed strategy for resource evaluation from a geotechnical perspective, potential business risks and mitigation approaches can and should be adopted early in the planning process. IMC has recognised this for some time. The following outlines the strategies and follows with key analyses adopted by IMC in mine planning from a concept level:

Comprehensive analysis and interpretation of geological data from a geotechnical perspective

Primary consideration should be given to the likely mine planning implications arising from geotechnical interpretation. Significant expenditure is often attributed to the acquisition of exploration data, yet at times there appears an imbalance between resources attributed to data acquisition, processing and presentation, compared with that dedicated to comprehensive interpretation and risk assessment of relevant geotechnical data and subsequent integration into mine planning processes.

There is almost always relevant geotechnical detail that can be manipulated from any form of geological exploration, that should be appropriately assessed in the conceptual mine planning process onwards.

Opportunity and constraints with respect to resource coal quality and structure are always (rightly) key drivers in determination of project viability and mine layout. Geotechnical characterisation is not always given the same priority at this stage. In this context, IMC recognise that there are major benefits in utilising and integrating a team of experienced professionals from the early stages of mine planning studies and in due diligence studies who have:

Comprehensive practical geological, geotechnical underground operational mining and exploration experience;

A comprehensive understanding of and previous experience in conceptual through to bankable feasibility level mine planning studies and due diligence studies for an extensive range of resources and clients;

IMC recognise major benefits in applying appropriate expertise and strategy at concept level relating to:

Minimising costs and resources otherwise dedicated to projects or resource areas that may not ultimately be viable;

Presenting a balanced and authentic assessment of project potential such that viable projects are not overlooked at the outset;

Providing capacity (through experience base) for formulation of hazard plans, risk ranking, and risk assessment during the mine plan process so that critical issues and strategies are developed and integrated into the mine plan process;

Targeting future exploration and scoping feasibility studies to ensure that critical issues are addressed in appropriate depth and in a timely fashion with respect to landmark requirements in project development.

Evaluating and comparing mine planning options and sequences incorporating assessed geotechnical risk parameters against other key drivers such as optimising resource extraction, resource quality and economic return

Due consideration, risk analysis and sensitivity analysis of various planning options based on key components including resource quality, economic, geological and geotechnical parameters is essential in delivering the ultimate goal – a mine plan that optimises economic return and delivers few surprises. The key in achieving such a balance is to integrate the key components under the same analysis, rather than treat each in isolation.

In a typical mine planning process, resources are assessed based on (minimum) prescribed guidelines, mine planning options are formulated, and productivities and capital are assigned within an economic model and scheduled to arrive at a calculated cash flow, rate of return over a fixed period. The typical involvement of relevant parties in this process is as follows:

Qualified geologists assess the resource quality, seam characteristics and structure, provide a resource status classification and, in combination with others, devise and manage exploration programs to reach required resource status classification.

Qualified mining engineers assess reserves based primarily on geological constraints provided by way of a plan from geologists. Underlying geotechnical concepts are factored in, often based on a broad assessment of regional stress data and anticipated ground conditions, from the information provided by geologists. In general, mining engineers are responsible for generating mine planning options and economic models from which reserves are generated and classified based on the assessed recoverable resource.

Business analysts and coal quality experts traditionally have a role in assessing key economic assumptions and sensitivities flowing forward, usually in the form of market placement and exchange rate or price fluctuations.

As with consideration of mine planning components and parameters, IMC view a holistic approach with individual parties working together as a team, rather than in isolation in defined roles on projects, as critical for delivery of an impartial and comprehensive mine planning process.

Through experience, IMC have recognised a number of key data sources that frequently exist at a conceptual mine planning stage, from which priority geotechnical assessments can easily be made and assessed in balance with other important factors, (including hydrological, gas etc).

The following outlines some of the data and associated analysis that IMC regard as necessarily required to address key issues at this here to read on.

A growing series of reports, each focused on a key discussion point for the mining sector, brought to you by the Mining Monthly Intelligence team.

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