Geotechnical Incident Investigations

The occurrence of damage to underground excavations is still an unfortunate reality of the mining industry. When such an incident/accident occurs, and there is damage to an excavation, the geotechnical team usually forms part of the task team who must investigate the incident/accident.

An incident is an undesired event that causes personal injury or damage to property. In underground mining this is generally related to excavation damage; which can be broadly subdivided into three main groups:

• Static failure (Wedge failure, Unravelling)

• Quasi-static failure (Squeezing)

• Dynamic failure (Seismic related, Pillar bursting)

The purpose of a forensic investigation is to reconstruct the events leading up to the incident. This includes determining all the causal factors which lead to the incident and to implement corrective actions to prevent future recurrences.

The difference between documentation and investigation is implementation.

The typical investigation process consists of six steps. Below is a list of these steps with some additional information. It is vital to conduct investigations in teams as this helps to provide perspective on the problem.

Step 1: Record the facts

Record as many facts about the incident as possible. Keep in mind how you would use this information in the analysis part of the process. The easiest way to ensure the investigation is done thoroughly, is to determine a systematic structure of investigation beforehand. Further to this, make sure that the damage locations are not disturbed until after the investigation has concluded. This ensures that the damage location can still be revisited if more checks are needed after the completion of later steps.

Step 2: Analyse the facts

Focus on putting all the facts together to get an overall picture of what might have happened. Try to determine which facts are most important and consistent with each other.

Step 3: Develop an Accident Sequence

Establish the most exact sequence of events leading up to the incident. Such a timeline is critical for determining the largest contributing factors leading up to the incident.

Step 4: Find the Causal Factors

Finding the causal factors can in many cases be the most challenging part of the process, as a certain technical understanding of the topic is needed. For example, when a ground support system fails it might be due to QA/QC problems, strength-discrepancies between the different support components, failure of a specific bolt component (e.g. nut failure) etc. If you do not have the required expertise on-site, consider getting help from other sources in your company or consider an outside expert.

Step 5: Recommend corrective actions

When determining appropriate recommendations, the investigation team should consider the entire process and aim to eliminate such an incident occurrence with minimal disruptions to the operation. It is important to involve all stakeholders in this part of the discussion to ensure the impact on the different departments is minimised. 

Step 6: Implement corrective actions

The difference between documentation and investigation is implementation. This process should not be an exercise in documentation, ensure that the investigation recommendations are implemented, monitored and adjusted (if required).

Companies follow several theoretical methodologies to ensure that investigation teams get to the most accurate conclusions. The most used methodologies are:

• 5 why’s

• Incident bowtie

• Fault tree method

• Event tree method

• SCAT (Systematic Cause Analysis Technique)

• Fishbone

Each one of these steps above needs to be done thoroughly and effectively to prevent a recurrence. Doing this process effectively will ensure the future safety and help limit revenue loss.

Require expert input into your geotechnical investigations? Contact us for your underground geotechnical needs.