Effective mine designs require collaborative efforts between geology, mine planning, mine production, and geotechnical engineering groups. The cycle of design, execution, measurement, and feedback should be continuous. Employing a well-documented and standardized approach is essential to ensuring a coherent, consistent and efficient system.
The necessary systems and processes within a technical services department are covered in a number of management plans and procedures, the purpose of which are to ensure that ore extraction is executed safely and efficiently. This article discusses a methodology for establishing effective systems and processes within the mining geotechnical department. The discussion stems directly from an underground open stoping operation, but would be generally relevant at most underground mines.
Geotechnical processes methodology
The establishment of appropriate processes within a geotechnical department allows for systematic collection of geotechnical data, and ensures that data is readily accessed for analysis and reported to key stakeholders. The following steps can be taken to achieve this:
- Review of the current capabilities of the geotechnical group members, including development of a skills matrix.
- Review of the current processes and gap analysis.
- Compilation of a workflow diagram.
- Identifying the documentation required for each step in the workflow diagram.
- Compilation of procedures for each process, compatible with other departments and existing processes.
- Compilation of databases and reports to a set format to maintain consistency.
- Training and coaching of staff to implement the new procedures.
- Review of management plans to reflect the new systems and processes.
A geotechnical workflow diagram incorporating all processes in the department, including interactions with external parties, can be used to illustrate the relationship between individual tasks. Including the workflow diagram in the introduction of each procedure helps establish the context for that task/procedure. An example is illustrated in Figure 1.
Figure 1. Geotechnical workflow diagram
The documentation required for each step in the workflow should be identified. Existing documentation should be reviewed, otherwise new procedures compiled using the mine’s current templates and document control systems. This is important to ensure that site personnel can take ownership of the information and easily update it.
A team performance plan can be used to establish the purpose and key performance indicators of the geotechnical group. It should state the team purpose, key result areas (for example: safety, quality, stope dilution, and design optimization), and outline the roles of, and key performance indicators for each team member. An example is shown in Table 1.
Table 1 Goals and strategies of the geotechnical engineering group
|Goal||Strategies and action||Key performance indicators|
|Minimize dilution in stopes caused by rock instability.||Provide rock mass and backfill stability analyses for each stoping area and each stope with clearly stated recommendations.||Provide a risk assessment approach to stope and backfill analyses with an understanding of acceptable levels of dilution. Completed for each stope and stoping area 1 month prior to extraction.|
|Eliminate exposure of personnel and equipment to rockfall hazards.||Check designs of every excavation, recommend appropriate ground support systems, regularly inspect all excavations and check the quality of ground support.||QA/QC of all ground support, inspect all mining areas at least once per week. Reported upon monthly (or immediately if a safety concern). Designs are checked immediately.|
|Optimize stope designs.||LOM planning and back-analysis of all stopes for dilution. This information is used for future stope designs.||Mining method selection and sequencing is completed in accordance with the planning schedule. Every stope is back-analysed as soon as the CMS is available. Key information is provided to the mine planning and production engineers immediately.|
|Prevent inundation to the underground mine.||Ensure the mine is not at risk of water or backfill inundation. Provide technical support to the fill management team.||Provide recommendations for risk mitigation of inrush hazards. Provide documentation to ensure that water or backfill inundation does not occur as soon as the certainty exists.|
A skills matrix lists all the geotechnical team members, their job title, the various skills and skill gaps, and training requirements including mandatory competencies.
The department should follow a schedule to ensure the tasks are completed on time. The schedule would cover all routine tasks including data collection, QA/QC, monitoring, and delivery of designs. The core logging schedule is usually governed by the geology department. All other tasks are governed by the mining schedule and are updated following each mine planning meeting.
A ground control management plan (GCMP) should document the history and evolution of the geotechnical aspects of the mine, describe the geotechnical setting, and explain the way in which ground related hazards are managed.
A seismic hazard management plan (SHMP) should outline the key processes used in understanding and managing conditions that lead to seismic events and related risks. The primary aim of the SHMP is to assist in identification, management and mitigation of seismic hazards.
A fill management plan (FMP) is a primary document outlining the key processes of backfill operations encompassing the entire process from harvesting the mill tailings to deposition of the fill slurry into the stopes.
The management plans follow two simple rules in order to be relevant and accessible:
Be concise – present all information in a summary format, with reference links pointing out to detailed drawings, tables and descriptions.
Be accurate – the document should only reflect what is actually being done on site and not be aspirational.
The following procedures are typically required for the geotechnical department for an underground open stoping mine:
- Data collection: core logging.
- Data collection: geotechnical mapping.
- Monitoring: inspections.
- Monitoring: instrumentation.
- QA/QC: ground support installation.
- QA/QC: ground support testing.
- Design: stope analysis and reconciliation.
- Other required procedures might include seismic system operation, seismic data analysis and extensometers monitoring, shotcrete QA/QC, as well as a number of procedures related to backfill operations.
All procedures should state the purpose, scope, and task frequency, and describe the methods in detail to undertake the tasks effectively and safely. They should describe how information is stored and reporting protocols for non-compliance with stated tolerance levels.
Databases and reports
Databases should be established for each task that involves the collection of data, i.e. core logging, mapping, monitoring, and QA/QC.
The monitoring and QA/QC databases can be linked to graphs that measure quality and compliance, and changes over time. These graphs can be used as the basis for periodic reports which provide relevant information to the mining department. Examples are shown in Figure 2.
Figure 2 Example of graphs providing various measures of quality and compliance
Periodic geotechnical reports should summarise status of geotechnical hazards at the mine, and present results for monitoring, QA/QC, key tasks completed, and note any geotechnical related accidents/incidents such as falls of ground, significant seismicity or failure of ground support. Periodic reporting helps to identify deficiencies or areas in which further work is required including outstanding action items required to mitigate any operational geotechnical hazards. Conversely, thorough periodic reporting can also be used to track improvements with time as processes and systems are implemented and improved, and convey these successes to mine management.
Senior Geotechnical Engineer
Owen Watson AMC