The Role and Importance of Geotechnical Engineering in Mining - Revisited

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What has become clearer since 2017
 

In 2017, I published an article titled The Role and Importance of Geotechnical Engineering for a Mining Operation.
 

The purpose was straightforward: to explain why geotechnical engineering had become an important part of modern mine technical services. I described two main contributions. Geotechnical engineering helps optimise mine design, and it helps manage the risks associated with ground behaviour. [1]
 

The article made another point that remains important today. Initial mine designs are developed with incomplete knowledge of the ground. Geological structure, rock mass conditions, groundwater, stress and material behaviour are never fully known at the start. I therefore argued that geotechnical information needs to be collected and reviewed as mining progresses so that the design remains appropriate for the conditions actually encountered. [1]

I would still make those points today.
 

But after another nine years of industry practice and published case histories, I would describe the role of geotechnical engineering more broadly.
 

It is not only about producing geotechnical designs and controlling ground hazards.

It is also about keeping a sound technical basis for mining decisions as our understanding of the ground changes.
 

The design is based on incomplete knowledge
 

This is the starting point.
 

An open-pit slope design depends on our interpretation of geology, structures, rock mass strength, groundwater and likely failure mechanisms.

An underground design depends on many of the same factors, together with the stress environment, mining-induced stress changes, excavation geometry, sequencing, support performance and, at some mines, seismic response.
 

We collect drilling data, mapping, laboratory test results, monitoring data and operating experience to understand these conditions. But the ground between observations still has to be interpreted. The design therefore depends on both evidence and engineering judgement.

This is not a deficiency in geotechnical engineering. It is the nature of working with the ground.
 

Uncertainty in mining geomechanics arises from natural variability, incomplete data and incomplete knowledge. The strength of the design basis therefore depends not only on the analysis, but also on the quality and relevance of the information supporting it. [3]
 

The practical implication is simple: A geotechnical design is based on the available understanding at the time it is made, together with the assumptions required to complete the design.
 

That understanding can change. When it changes materially, the design basis should be reviewed and the design or controls changed where necessary.
 

Collecting data is not enough
 

My 2017 article emphasised continued geotechnical data collection and analysis. I would now put more emphasis on what happens after the data is collected.
 

The important step is reconciliation.
 

In 2022, Julianne Armstrong cited my original article in an AusIMM Bulletin on the importance of mine geotechnical capability. She picked up the point that initial geotechnical design is carried out under considerable uncertainty and placed particular emphasis on reconciliation: comparing actual performance with the assumptions and recommendations on which the design was based. [2] 
 

That is an important distinction.
 

A mine may have excellent monitoring systems and collect large amounts of geotechnical data. That does not automatically mean that the design is being tested.
 

The useful questions are more direct.

Did the ground conditions match what was expected?

Did the important structures occur where they were predicted?

Did groundwater respond as assumed?

Did the excavation deform as expected?

Did the installed support perform as intended?

Did the expected failure or damage mechanism actually develop?
 

Where observed behaviour differs materially from prediction, the difference should be investigated and its significance for the design assessed. That is reconciliation.
 

Recent work using the observational method in open pits follows the same basic logic: predict expected behaviour, monitor actual behaviour, reconcile the two, and change the design where the difference is significant. [4]
 

The principle is simple: compare what happened with what was expected, understand the difference, and use that information in the next decision.
 

There is another important qualification. Not all significant uncertainty will be recognised in advance. Mining can expose geological conditions, groundwater behaviour or failure mechanisms that were not represented in the original design basis.
 

Reconciliation is therefore not only about checking whether known assumptions were correct. It is also one of the ways a mine discovers that its original interpretation was incomplete.
 

The strength of the evidence matters
 

A factor of safety, probability of failure or numerical-model result does not by itself tell us how strong the basis for a decision is. We also need to understand the evidence behind the analysis.

How much drilling and mapping supports the geological interpretation?

How well is groundwater understood?

How representative are the strength and deformation parameters?

Are the important structures adequately characterised?

Is the assumed failure mechanism supported by observations?

Has the model been compared with actual mine performance?

What important uncertainties remain?
 

These questions should remain visible. They should not be hidden inside a single composite confidence score.
 

Geology, hydrogeology, data coverage, parameter uncertainty, model assumptions and analytical limitations are different issues. Combining them into one number can give an appearance of objectivity while hiding the specific weakness that may matter most to the decision.
 

The broader principle is simple: the strength and limitations of the design basis should be clear when an important decision is made.
 

A mature operating sector of a mine with extensive drilling, mapping, groundwater information and years of performance history is not equivalent to a new sector supported by limited information.

The same analytical result may therefore deserve different weight in different circumstances.

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A major permanent excavation, a critical pillar, a high-stress mining front or a major extraction-sequence decision reasonably requires a stronger technical basis than a routine, short-lived excavation in well-understood conditions.
 

The practical question is therefore not only:

   What does the analysis show?

It is also:

 What evidence supports this decision, where is that evidence weak, and could those weaknesses change the decision?
 

Geotechnical engineering affects mine value
 

The safety role of geotechnical engineering is obvious. Its effect on mine value is sometimes less visible.
 

In an open pit, geotechnical understanding influences slope geometry, stripping requirements, depressurisation requirements, access and the exposure of infrastructure.

In underground, it influences stope dimensions, pillar requirements, extraction sequence, support, access development and the ability to maintain production through changing stress and ground conditions.
 

The geotechnical engineer does not make these mine-planning decisions alone. But the geotechnical basis can materially affect the options available to the mine planner and the risks associated with those options. 

This means geotechnical engineering can affect value in both directions.
 

Insufficient understanding can result in designs that expose the mine to unacceptable safety, production or economic risk.

Excessive conservatism also has a cost through flatter slopes, sterilised ore, larger pillars, reduced extraction, additional support or unnecessary restrictions on the mine plan.
 

The objective is not to be aggressive or conservative. It is to make a design decision that is justified by the available evidence, the uncertainty that remains and the consequences if the assumptions prove wrong.
 

Important decisions need the right level of review
 

Not every geotechnical decision has the same consequence.
 

A local operational adjustment is different from approving a final wall geometry beside critical infrastructure.

Changing support in a short-lived development heading is different from approving the location of major permanent underground infrastructure or a mining sequence that may affect a large part of the orebody.

The amount of review and challenge should reflect that difference.
 

The principle is straightforward: The more consequential the decision, and the weaker the supporting knowledge, the stronger the case for additional review and challenge.
 

That review may be internal or external depending on the situation. Its purpose is not to replace the site team. It is to test whether the assumptions, evidence, analysis and proposed controls are adequate for the decision being made.
 

What is the role of the geotechnical function?
 

Looking back at the 2017 article, I would now describe the practical role in six parts:

• establish and maintain the geotechnical understanding required for mine design and planning;

• provide geotechnical inputs to slope, excavation, support, sequence and infrastructure decisions;

• identify important geotechnical uncertainties and explain how they may affect the mine;

• define appropriate ground-control measures, monitoring requirements and response actions;

• compare actual ground behaviour with design assumptions and expected performance;

• update recommendations when new information or observed performance changes the technical basis of the decision.
   

The work will look different from mine to mine.
 

A large open pit does not have the same geotechnical problems as a deep, seismically active underground mine.
 

The tools will also vary. Some problems can be addressed with mapping, precedent and relatively simple analysis. Others require detailed numerical modelling, hydrogeological analysis, probabilistic methods or sophisticated monitoring.
 

But the underlying responsibility is similar.
 

The geotechnical function provides the mine with an informed view of how the ground may affect the plan, what is uncertain, what controls are required and when the existing design basis should be reconsidered.
 

Nine years later
 

The main argument from 2017 still holds. Geotechnical engineering is important because it helps mines design and operate safely while making effective use of the orebody.
 

What I would emphasise more strongly today is the need to keep the geotechnical basis of mining decisions current.
 

A design does not remain appropriate simply because it was well engineered when it was produced.
 

The mine changes.

More ground is exposed.

New structures are encountered.

Groundwater responds.

Stress conditions change.

Monitoring reveals behaviour that may or may not agree with prediction.

Mining itself provides new information.
 

Good geotechnical practice uses that information. It tests assumptions against performance, recognises where understanding has changed, and revises the design or controls when the evidence requires it.
 

That is not a new theory. It is good mining geotechnical practice made explicit.
 

Good geotechnical practice keeps the technical basis of mining decisions current.

References

1. Vyazmensky, A. (2017). The Role and Importance of Geotechnical Engineering for a Mining Operation. MinExForum, 16 March 2017.

2. Armstrong, J. (2022). Mine management failure mechanisms — a geotechnical perspective. AusIMM Bulletin, 24 February 2022.

3. Dunn, M.J. (2019). “Quantifying uncertainty in mining geomechanics design.” In Proceedings of the First International Conference on Mining Geomechanical Risk, Australian Centre for Geomechanics, Perth, pp. 391–402.

4. Villegas, F., Calderon, J. & Vasquez, P. (2025). “Observational method applied to pit slopes informing the characterisation, design and monitoring process for an open pit mine: a case study.” In Proceedings of the Fourth International Slope Stability in Mining Conference, Australian Centre for Geomechanics, Perth.