Ask the Experts: Site Characterization and Planning of Mine Hydrology Programs

Name: Ask the Experts: Site Characterization and Planning of Mine Hydrology Programs
Uploaded: 2024-07-01T23:06:36.000Z
Duration: 2 h 52 min 41 s

Introduction to the Webinar

Overview of the Webinar Series

Jillian Nunan introduces herself as part of the Geotechnical Center of Excellence at the University of Arizona, kicking off a series of five webinars focused on mining hydrogeology topics.

The first webinar's topic is "Site Characterization and Planning of M Hydrology Programs," with a panel ready to answer questions.

About the Geotechnical Center of Excellence (GCE)

The GCE is an industry-funded, member-led center that fosters collaboration between academia and industry for geotechnical research and education.

Their goal is to bridge gaps in knowledge through research projects and educational courses, such as "Water and Mine Operations" and "Slope Stability."

Course Information

A 30-hour online professional development course titled "Water and Mine Operations" is currently available for registration.

The course was developed in partnership with Pau Associates and acknowledges support from GCE member companies.

Panel Introduction

Meet the Expert Panel

Jillian introduces Benjamin Meyer, a software engineer assisting with the webinar logistics.

Jeff Beal, Global Technical Adviser at Pau Associates, is introduced but unable to speak initially.

Simon Sha will join later; he is a principal hydrogeologist also from Pau Associates.

Additional Panel Members

Travis White from Anglo-American joins as a principal hydrogeologist.

Gus Roland serves as country manager for South Africa at Pau Associates, while Jim Wile represents Rio Tinto Kennecott Copper.

Webinar Participation Guidelines

How to Engage During the Webinar

Participants can submit questions via Zoom's Q&A function; they can also upvote questions they find relevant.

Questions may be submitted anonymously, with some pre-submitted queries being addressed during the session.

Recording Information

The webinar will be recorded for later access on GCE’s YouTube channel and course site.

Planning a Mine Hydrology Program: Common Pitfalls

Introduction to Mine Hydrology Challenges

The webinar begins with an introduction to the topic of planning a mine hydrology program, emphasizing the importance of site characterization.

The panel is asked about common pitfalls or challenges in planning such programs, setting the stage for expert insights.

Key Pitfalls Identified by Gus

Neglecting Available Information: Many planners overlook existing data on mining sites, leading to unnecessary drilling campaigns without proper analysis.

Information Overload: There is often a tendency to seek excessive information before making decisions, which can delay progress.

Lack of Integration: Failing to collaborate with other technical teams (geotechnical, geological, etc.) limits the value derived from available data and resources.

Recommendations for Effective Planning

Initial Gap Analysis: Engage with site personnel to understand existing knowledge and perform a gap analysis before initiating new data collection efforts.

Focus on Simple Steps First: Prioritize gathering essential weather and rainfall data and confirm existing groundwater monitoring programs before expanding investigations.

Leverage Ongoing Work: Coordinate with ongoing drilling projects to maximize information extraction from each borehole rather than adding instrumentation late in the process.

Insights from Travis

Underappreciation of Hydrogeology: Hydrogeology is often only considered after issues arise; proactive engagement is necessary for effective management.

Baseline Characterization Gaps: There are significant gaps in baseline characterization that need addressing; utilizing existing drilling information can save costs and improve outcomes.

Importance of Economic Justification

Selling Hydrogeological Value: Emphasizing the economic benefits of hydrogeological work (e.g., dewatering programs improving MPV) helps justify its necessity within larger mining projects.

Integration with Mine Planning Teams

Understanding Infrastructure and Water Management in Mining

Importance of Pre-Planning for Access

The necessity of vertical wells in mining operations requires careful design to maintain infrastructure, especially when access points are elevated.

Effective pre-planning is crucial for ensuring access to older operations as development progresses, particularly regarding geological holes that may not have been initially planned.

Maximizing Resources through Coordination

Utilizing existing holes for additional installations like vertical wellpoints (VWPs) can be a cost-effective strategy, providing significant benefits despite being unplanned.

Gathering water level data from multiple holes is essential; inconsistent groundwater heads indicate low flow systems while consistent levels suggest interconnected systems.

Analyzing Groundwater Flow Systems

Marrying water head observations with structural geology helps interpret the overall groundwater flow system effectively.

Packet tests measure local permeability but often mislead broader interpretations; they are most useful in low-permeability units or shaft characterizations.

Common Errors in Groundwater Modeling

Over-reliance on packet test data can lead to significant errors in conceptual models due to their limited scope of measurement.

Early career lessons emphasize the importance of integrating groundwater heads with geological structures for accurate modeling.

Cost-Efficiency and Innovative Techniques

Water levels and pore pressures are relatively inexpensive to obtain compared to larger hydrogeological wells, making them an ideal starting point for investigations.

New methodologies involve using reverse circulation drilling near VWPs to gather cross-sectional information about formations, enhancing understanding of wider-scale interactions.

Serendipitous Characterization Opportunities

Unplanned events during drilling programs can provide valuable insights into groundwater behavior; awareness and open-mindedness during data collection are key.

Groundwater and Surface Water Management in Mining

Importance of Early Involvement in Drilling Programs

Early involvement in drilling program planning is crucial for effective testing and monitoring, especially when water supply wells are nearby.

Gathering information from abstraction wells can provide valuable insights; even limited data can be beneficial compared to having none.

Considerations for Surface Water Management

Surface water management is essential as it can significantly impact mining operations, particularly during heavy precipitation events.

Managing surface water involves collaboration with mine operations teams to maintain infrastructure that may become clogged with mud due to rainfall.

The challenges of managing mud on-site highlight the need for effective strategies to handle overland flow during significant weather events.

Use of Packers in Pump Testing

In regions like South Africa and Zambia, Packers are utilized to isolate fracture zones for pump tests, which helps understand groundwater behavior.

Isolating zones using Packers creates cross-hole stress, which is an important consideration when interpreting results.

Addressing Limited Data on Pore Pressure

When pore pressure or water level data is scarce, alternative monitoring methods must be employed to assess slope stability risks.

Research indicates that over 50% of global slope instabilities are linked to surface water; thus, correlating rainfall with geotechnical data is vital.

Techniques for Monitoring Without Piezometers

While drilling holes and installing piezometers (Pomers) remains the best practice, other methods such as geophysics can provide background data about the water table.

Technological Advancements in Mining and Geotechnical Monitoring

The Role of Technology in Mining Surveys

Modern technologies like drones and thermal imagery have revolutionized mining surveys, allowing for quick data collection and mapping within minutes.

Drilling is emphasized as a critical component for risk assessment; without proper drilling and characterization, addressing geological risks becomes challenging.

Importance of Instrumentation in Drilling

Effective mineral exploration relies on extensive drilling to define ore bodies; lack of instrumentation can lead to missed opportunities.

The costliest aspect of any installation is often the drilling itself; leveraging existing holes for instrumentation is recommended to optimize resources.

Enhancing Data Collection with TDR Cables

Installing Time Domain Reflectometry (TDR) cables at a minimal additional cost can help monitor slope movements effectively.

Even without TDR cables, using Peters (pressure sensors) can provide valuable geotechnical data, aiding in identifying potential shear zones.

Site Characterization Using Peters

Questions arise regarding the quantity of Peters needed for effective site characterization; focusing on critical sections is essential.

When dealing with low-density data, distinguishing between quality VWP (Vibrating Wire Piezometer) data versus poorly coupled cemented VWPs is crucial.

Guidelines for Instrument Placement

Prioritize placing instruments in areas flagged by geotechnical assessments or where failure mechanisms are predicted to occur.

Geotechnical Monitoring and VWP Management

Importance of VWP in Geotechnical Investigations

The discussion emphasizes the necessity of monitoring mass types along major structures, highlighting that surface movements often lead to further investigations with drilling rigs for core sampling.

It is recommended to maintain a stockpile of vibrating wire piezometers (VWPs) to ensure timely installation during critical moments when drilling occurs.

Installation Strategies for VWPs

Opportunistic installations are valuable; it’s suggested to install VWPs before abandoning drill holes, ensuring they are grouted properly for effective data collection.

VWPs should not be treated as permanent infrastructure; they can be lost or damaged, and their placement should be strategic to maximize utility.

Value of Data from VWPs

The primary value derived from VWPs is the information they provide rather than the physical components themselves. Cost-effectiveness increases with the duration of data collection.

Emphasis on understanding that the cost associated with VWPs is justified by the quality and relevance of data obtained, which informs geotechnical decisions.

Mining Through VWPs: Experiences and Techniques

A question arises regarding experiences in mining through recovered VWPs. One participant shares a successful case involving deep multi-level installations where cables were recovered without damage.

The method involved leaving part of the cable suspended while using expanding foam in empty casing sections, allowing safe recovery during mining operations.

Best Practices for Logger Recovery

It’s crucial for monitoring personnel to coordinate closely with drill and blast teams to protect loggers from being damaged during operations.

If telemetry cannot be used, recovering loggers before blasting is essential as it preserves valuable data collected prior to potential loss.

Success Rates in Mining Through VWPs

Mining Techniques and Data Recovery in VWP

Procedures for Successful Mining

Several procedures can enhance success rates in mining, with operators successfully mining through PWP (Piezometer Water Pressure) installations over more than ten benches without instrument failure.

Cost of Recovery vs. Value of Data

The cost of recovering BWP (Borehole Water Pressure) is justified as it ensures continuity of data, which is deemed more valuable than the recovery costs themselves.

Quality Assessment of VWP Data

To distinguish the quality of VWP data, one should observe if all Pomer sensors show similar heads and responses; this could indicate potential issues but does not automatically mean the data is incorrect.

In cases where old geological exploration holes are nearby, similar sensor responses may reflect actual system conditions rather than installation errors.

Installation Integrity and Data Reliability

Identifying real versus fake data can be challenging; however, significant discrepancies like unusually high piezometric levels compared to local groundwater levels can signal problems.

Proper installation records are crucial. It’s important to track grout levels during installation to ensure integrity and avoid ambiguous data interpretations later on.

Grouting Guidance for VWPs

Specific grouting guidance includes using prescribed grout mixes that often contain Bentonite to prevent cracking.

Grouting Techniques and Data Monitoring

Importance of Grouting Without Bridges

Emphasizes the necessity to avoid bridges during grouting, suggesting that grouting should be done from the bottom of the hole upwards.

Highlights using pressure data to monitor grout flow, noting that higher density grout will change pressure readings on sensors.

Data Quality and Analysis

Stresses the importance of maintaining detailed notes for troubleshooting issues with Peter sets once operational.

Recommends reviewing raw data for potential errors in frequency or digit readings, as well as temperature measurements.

Installation Considerations

Discusses using a TDR reader to measure cable length in the ground up to certain depths, which can help identify structural features affecting hydrostatic pressures.

Mentions potential issues with hydrostatic pressure stacking due to structural damage zones or old boreholes not properly abandoned.

Data Logger Preferences and Quality Control

Raw vs. Processed Data

Points out that some data loggers record both raw data and processed engineering units, which may introduce errors if incorrect factors are applied.

Advocates for using data loggers that output raw data for better accuracy in analysis and flexibility in applying conversion factors later.

Drilling Orientation Guidelines

Optimal Drilling Angles

Advises against drilling at a 45° angle due to difficulties in cleaning holes; recommends angles either less than or greater than 45°.

Suggests keeping drill holes parallel to pit slopes while avoiding overbreak zones that could distort measurements.

Targeting Geotechnical Zones

Encourages positioning Pomers close to predicted geotechnical formation zones for accurate monitoring.

Describes recent practices of angling Pomers behind walls (60° - 70°), allowing observation of pressures before advancing mining operations.

Geotechnical Instability Factors

Structural Influences on Stability

Geotechnical Insights on Slope Stability

Horizontal Piezometers and Their Importance

The discussion emphasizes the significance of horizontal piezometers (posos) in geotechnical stability, particularly when structures are subparallel to slopes.

It is noted that installing horizontal piezometers at a 7-degree angle downwards simplifies installation and drilling processes.

Current projects utilize vertical water pressure (vwp) measurements with time-domain reflectometry (TDR) to assess pressures behind walls and shear zones effectively.

Drilling Techniques and Data Collection

The approach involves constraining drilling depths based on data from horizontal drain holes, enhancing the understanding of slope stability.

A paper discussing challenges in characterizing slope-parallel structures has been authored, indicating ongoing research in this area.

Early Warning Systems for Instability

Shallow vertical holes near high wall crests serve as effective early warning systems for potential instability due to rainfall or surface water.

Emphasis is placed on not solely focusing on deeper measurements; unsaturated zone data can also provide valuable insights into pore pressures.

Lessons Learned from Field Studies

An example is shared where deep multi-level piezometers missed significant changes because they were too far from the pit edge, highlighting the need for strategic placement.

Confidence Levels in Feasibility Studies

A question arises regarding confidence levels in pre-feasibility and feasibility studies, specifically how these levels are calculated.

Confidence levels are described as subjective, influenced by factors such as pumping tests and responses from borehole water pressures (bwp).

Subjectivity in Geotechnical Analysis

The complexity of hydrogeological systems makes it challenging to assign objective confidence levels; reliance on empirical data is crucial.

Key parameters affecting groundwater models include storage and permeability, but their influence can be inconsistent across different geological contexts.

Geological Influence on Stability Assessments

Geology plays a critical role in determining stability; often, unexpected geological conditions lead to instabilities that challenge predictive models.

Feasibility Studies and Instrumentation in Geotechnical Analysis

Minimum Drill Holes for Feasibility Studies

There is no set minimum number of drill holes required for feasibility or pre-feasibility studies; it varies based on rock characteristics.

The judgment on the number of drill holes needed depends on the expertise of specialists assessing the site.

Characterization of Rock Units

It's crucial to characterize different rock units, including pore pressures and structural impacts on water movement.

Monitoring pore pressures should extend below anticipated failure depths to ensure comprehensive data collection.

Importance of Instrumentation

Different changes in rock mass characterization necessitate instrumentation in zones with poor rock mass to monitor pore pressures effectively.

Data analysis should include transient responses, particularly during significant water infiltration events like snowmelt.

Data Collection and Analysis

A minimum of one to two years' worth of data is essential for evaluating water movement through slopes and its impact on pore pressures.

Understanding recharge events can inform geotechnical modeling, especially when direct measurements are unavailable.

Dewatering Trials and Confidence Levels

For dewatering feasibility studies, achieving 10% drawdown during pumping trials indicates a confidence level around 15% regarding system behavior predictions.

Geological factors introduce subjectivity into geotechnical analyses, complicating numerical sensitivity assessments.

Understanding the B Hole Magnetic Resonance Tool

Overview of the BMR Tool

The B hole magnetic resonance tool (BMR), developed from earlier technologies, measures water presence by inducing polarity flips in hydrogen atoms using radio frequency energy.

Challenges with Mineralogy

Accurate interpretation requires a deep understanding of insitu mineralogy since certain minerals contain significant hydrogen that may affect readings.

Limitations of Measurement Scope

Understanding Geotechnical Impacts and Dewatering in Mining

Analyzing Geological Data

The interpretation of geological data from adjacent holes can be misleading if not analyzed carefully, as spikes may not directly indicate water-bearing structures.

It's crucial to critically assess whether measurements are indicating the presence of pore water or other minerals, rather than making assumptions based on initial readings.

Geotechnical Considerations for Ramp Dewatering

When using pre-advancing ramps as a dewatering option, one must consider the geotechnical impacts on ramp stability and adjacent benches.

Extra benches added to walls during dewatering can affect wall stability; understanding the behavior of these walls is essential before proceeding with ramp advancements.

Balancing the benefits of pre-dewatering against potential slope stability risks is necessary, as every action in mining has unintended consequences.

Assessing Depressurization Effectiveness

A participant asks about assessing the effectiveness of depressurization programs on slope stability; this question highlights ongoing concerns in mining operations.

Future webinars will cover various topics related to water management in mining, including hydrogeological modeling and dewatering techniques.

Tools for Monitoring Slope Stability

To evaluate if a depressurization program affects slope stability, monitoring pore pressure changes through instruments like TDR (Time Domain Reflectometry) and inclinometers is recommended.

It’s important to correlate pore pressure data with geotechnical tools such as radars and prisms to determine any movement or stabilization effects accurately.

Challenges in Depressurization Programs

There can be instances where reduced pore pressure does not lead to slope stabilization; further investigation into underlying causes may be required.

Understanding Water's Role in Stability

Integration of Data for Stability Analysis

The integration of data from radars, drains, and wells is crucial for understanding the role of water in stability.

Installing TDRs (Time Domain Reflectometers) or inclinometers alongside piezometers enhances the understanding of pore pressure effects on shear strength.

Movement Detection and Surface Influences

Subsurface movements are often detected by TDRs or inclinometers before surface movements are visible on radars or prisms.

Precipitation can complicate signals related to depressurization and movement rates, necessitating careful monitoring.

Impact of Rainfall on Depressurization

Additional water entering a slope may replenish pore pressure faster than it can be removed through pumping or drainage.

Rainfall and infiltration can lead to spikes in movement rates, which may delay the effectiveness of depressurization efforts.

Upcoming Webinar Details

Future Topics in Hydrogeological Modeling

The next webinar is scheduled for July 31st at 3 p.m. Arizona time, focusing on conceptual hydrogeological models.

Key topics will include pore medium vs. fracture flow, excavation damage zones, water balance, and global benchmarking.

Guidelines for Site Characterization

References for Characterization Studies

Jeff emphasizes that large open pit books serve as essential references for site characterization studies.

The guidelines need updates; particularly the slope design book will undergo revision soon with hydrology included as a module.

Resources for Further Reading

Recent papers on horizontal drains and slope depressurization provide valuable insights but are condensed within existing guidelines.

The LOP project website offers comprehensive guidelines relevant to evaluating water impacts on pit slope stability.

Closing Remarks from Panelists

Acknowledgments and Future Engagement

Panelists express gratitude towards participants and encourage them to bring unanswered questions to future webinars.