Understanding the Potential for Extrusion Failure in Tailings Dams

December 12, 2023   |  

The Fundão Dam failure at the Samarco Mine in Brazil and the Nerlerk berm slope failure in the Beaufort Sea were the result of liquefaction flow events brought on by the extrusion of materials within the foundation of the structure. This process is referred to as liquefaction by extrusion failure. 

In many cases, liquefaction by extrusion failure is difficult to predict because it can develop with no apparent warning (e.g. excess pore pressures will not develop prior to failure). 

While unpredictable, certain conditions make extrusion failure more likely. These include: 

  • Soft material exists which can deform laterally with minimal confinement as vertical or shear load increases.
  • Overlying material lacks ductility (e.g. clean sand) and cannot strain to match the soft material extrusion.
  • Ductility contrast between the soft extruding material and the sand can result in reduction in lateral confinement of the sand.
  • Saturated sand can collapse, and dry sand can crack.

Evaluating Extrusion Failure in Tailings Dams

In a tailings dam, the potential for extrusion failure can increase with rising water levels due to post-construction drain failure or flood storage or from foundation deformations in a soft or weak unit beneath the dam.

The following steps can be used when evaluating the potential for liquefaction by extrusion failure in a tailings dam:

Step 1:
Characterize the state parameter of the tailings using cone penetration tests (CPTs). CPTs are in situ tests where a cone on the end of a series of rods is pushed into the ground at a constant rate, and nearly continuous measurements are made of resistance to penetration of the cone and of a surface sleeve.
Step 2:
Identify the material properties of the tailings through laboratory testing, including triaxial tests on reconstituted samples.
Step 3:
Calibrate a critical state soil model to the laboratory and field behaviour, including the stress path of interest. A critical state soil model is a theoretical framework for understanding the behaviour of soil in response to changes in density and stress.
Step 4:
Prepare a 2D deformation model of the tailings dam to assess the potential response of the tailings to increasing pore pressures or foundation deformations. The model can show which conditions are more likely to result in liquefaction by extrusion failure.

Safe and Sustainable Dam Design

Because of the danger associated with these stress paths, it is common practice for upstream-constructed facilities to be designed using a precautionary approach in which the dam is designed to remain stable in the event of liquefaction. In some cases, involving pre-existing or older facilities, it is not possible to take such pre-emptive measures and an understanding of the potential for triggering liquefaction is required. 

In such situations, critical state soil models can be used to analyze the potential development of these stress paths and the potential response of the tailings.

Categories:   Blog   |   Mining

Applying the Hierarchy of Controls to TSF and Dam Safety

July 19, 2023   |  

Understanding Controls

A control is an act, object, or system that must be in place to minimize, prevent or mitigate an unwanted event. In the context of Tailings Storage Facility (TSF) or dam safety, controls typically focus on protecting the public and environment from the impacts of a dam failure, unplanned discharges, or groundwater contamination. Failure mode controls can be described as either preventative (in advance of the event) or mitigative (after the event has occurred).

Although generally more applicable to worksite health and safety, another way to think about controls that is probably more familiar is the Hierarchy of Controls from the National Institute for Occupational Safety and Health (NIOSH):

Controls for TSF and Dam Safety

We can expand on the concepts of preventative and mitigative controls by applying the hierarchy of controls to TSF and dam safety. The modified Hierarchy of Controls is:

Elimination, or physically removing the hazard: Which risks can be eliminated from the design at the outset? This is part of the design process, and is supported by early stages of the design, such as site selection, tailings technology selection (and the multi-criteria analysis), and the risk assessment. For example:

  • Selecting a TSF location away from sensitive downstream areas;
  • Assessing alternative tailings management technologies that present lower risks to people and the environment;
  • Assessing the risk of potential options for types of facilities and determining which risks can be eliminated early on, such as selecting options where risks related to dams can be reduced (e.g., in-pit disposal or co-management with other mine waste materials with higher strength properties).

Substitution, or replacing the hazard: How can we adjust the design once the site and tailings technology are selected to reduce risk? This includes developing a robust design that has looked for opportunities to incorporate risk reduction measures. Examples include:

  • Designing for extreme loading conditions (for example, sufficient storage capacity to store multiple flood events;
  • Undertaking sufficient site investigations to support the design; and
  • Design to industry standards appropriate for the dam safety classification of the structure.

Engineering Controls: these are physical structures that isolate people from the hazard, placing a barrier between the hazard and people or the environment. In the context of a TSF and dam safety, these may include:

  • Upstream structures that divert flows away from the TSF or dam, reducing the loading during flood events;
  • Buttresses or extensions constructed after the initial construction to provide support to the embankment in a specific area based on performance monitoring;
  • Construction of filters or drains to manage seepage after the dam has been constructed, such as inverted filters or granular filters on the downstream slope;
  • Downstream structures that protect the environment or people in the event of a dam break;
  • Seepage recovery wells and reclaim systems (more related to environmental impacts); and
  • Sediment collection ponds at the toe of the dam (more related to environmental impacts)
Governance and Operations: these are controls related to the effective management, OMS (operations, maintenance, and surveillance) activities, and governance of the facility. Examples include:

  • Robust surveillance system, including routine inspections, instrumentation monitoring and analysis;
  • Developing and maintaining a tailings or dam safety management system;
  • A dedicated team to manage the TSF or dam, including an accountable executive, engineer of record, and responsible tailings facility (or dam safety) engineer;
  • On-going risk assessment and risk management throughout operations, and implementing performance-based risk-informed safe design principles;
  • independent review and continuous improvement through a plan-do-check-act process;
  • Developing and implementing a comprehensive OMS Manual including triggers and Trigger Action Response Plans, with standard operating practices and procedures;
  • Routine and preventive maintenance program; and
  • Governance structure, with defined roles and responsibilities and adequate available resources.

Mitigative Controls: these are the systems and activities that are implemented once a failure event (or unwanted event) is imminent, or already underway. These are the last things in place to protect people and the environment. Examples include:

  • Activating the Emergency Response Plan;
  • Alarms or warning systems for people in the downstream area;
  • Using the emergency spillway to discharge excess water from the TSF or water management facility;
  • Mobilizing the mining fleet to construct buttresses or emergency freeboard; and
  • Rapidly drawing down the TSF or dam reservoir via pumping and/or reclaim system.

Critical Controls

Controls that are established to either prevent or mitigate a high consequence event are referred to as “critical controls”. In other words, a critical control is a preventative or mitigative control which, if not carried out effectively, could lead to a failure or significant increase in risk of failure. Even if other controls are in place, the failure or absence of critical controls significantly increases the risks. The most common critical controls are: the design elements and configuration with robust governance, followed by routine surveillance and instrumentation monitoring, pond management (including freeboard and beach width), and quality assurance/quality control during construction.

This blog post was developed based on shared ideas with Karen Chovan of Enviro Integration Strategies Incorporated.
Categories:   Blog   |   Mining

Designing Flow-Through Rockfill Underdrains in Unpredictable Climates

March 1, 2023   |  

Papua New Guinea experiences high annual rainfall, has rugged topography, and is one of the most seismically active zones in the world. These conditions have presented challenges to the diversion of surface flow at mine sites in the region.

Flow-Through Rockfill Underdrains in PNG

KCB has been involved in the design of flow-through rockfill underdrains for mine sites across BC and in Papua New Guinea (PNG). Flow-through rockfill underdrains have been used at mines to pass flows beneath waste dumps, rather than constructing diversion channels around the dumps. Mines with flow-through rockfill underdrains are common in BC, but KCB has done considerable work over the years with flow-through rockfill underdrains at the Porgera, Hidden Valley and Ok Tedi mines in PNG. The stable dump at Porgera, known as the Kogai dump, has a rock underdrain that has been in operation for about 30 years; the Hidden Valley Western Sector waste dumps have underdrains in operation for over 10 years.

Underdrains are typically built from durable, non-acid generating rock from the open pit. Rock is either dumped from a high dump (> 20 m high) to segregate the rock as it falls, so that the coarsest rock forms the drain at the toe of the dump, or it is screened by size and placed by conventional methods. Underdrain rock must be comprised of strong, durable rock that can withstand the stresses imposed by the overlying waste dump, and resistant to mechanical breakage and chemical weathering.

Many of the dumps in PNG could not be built without the rock underdrain as it is not possible to divert the creek base flow or flood flow. Heavy rainfall needs to be diverted, and natural soil and rock, and waste rock is highly erodible. The rock underdrains act as diversions to allow the dump stability and then serve to pass the creek flow during the mine's operating life and closure.

Designing Flow-Through Rockfill Underdrains using Wilkins’ Formula

Design principles for flow-through rockfill underdrains have been developed from civil engineering applications, including Wilkins’ formula for estimating flow capacity for non-Darcy turbulent flow in rockfill:

Q = flow in m3/sec
W = Wilkins constant, ranging from 5.24 m0.5/sec for crushed gravel to 7.33 m0.5/sec for polished marbles
i = hydraulic gradient
e = void ratio
m = hydraulic mean radius of the rock voids (m)
= void ratio/surface area per unit volume
= e*d/8.4 for coarse angular rock where d is the rock diameter in metres
A = area of rockfill transverse to flow (m2)

KCB's design of flow-through rockfill underdrains uses Wilkins ’ formula with a factor of safety of 10 applied to the calculated area. The design allows for a period of ponding for storms (e.g. 24-hour 100-year return) at the upstream face of the dump where the drain inlet is located. Design flood volumes can then be discharged over a reasonable period, often 7 days.

Categories:   Blog   |   Mining

Improving Efficiencies in Collecting 20-Year-Old Undisturbed Soil in Alaska

January 24, 2023   |  

KCB has supported tailings management at the Greens Creek Mine near Juneau, Alaska for nearly two decades. A section of the mine is located in Admiralty Island National Monument, an ecologically sensitive area that is home to one of the largest populations of brown bears in the world and various species of wildlife.

As part of an environmental upgrade project, KCB was tasked with excavating a portion of the mine’s tailings pile and collecting undisturbed soil samples that had been buried for up to 20 years.

A Modified Method to Soil Collection

Collecting undisturbed soil samples is an important component of most site investigation programs. The standard method of collecting undisturbed samples is by piston tube sampling in drill holes or block sampling in test pits.

The corner of the existing tailings pile was going to be excavated which would expose tailings that had been buried in the pile for more than 20 years. This provided an opportunity to collect undisturbed samples of these tailings for advanced geotechnical laboratory testing. The conventional method of block sampling was not practical due to the impact on construction schedule and issues with handling and transporting such samples from the site.

KCB devised a modified method and sampling device to collect undisturbed tube samples from ground surface. The sampling device could be placed directly on a prepared surface to recover in situ samples. The sampler consisted of a hydraulic ram to push modified Shelby tubes into the tailings. The tube was then retrieved by hand and trimmed and sealed. With this approach, multiple samples could be collected from an area without disrupting construction and the samples were manageable for handling and transport from the site to the testing laboratory in California.

Benefits of a Hybrid Sampling Method

While the hybrid sampling method proved to be simple, efficient, and cost effective, the sampling device was heavy and awkward to maneuver, and relies on the weight of people to provide the reaction force for the jack to drive the tube into the ground. In stiff soils, several people are needed to collect samples. However, these challenges could be overcome without impacting sample quality and allowed the team to collect more samples that would have been able using conventional methods.

Categories:   Blog   |   Mining

3D Block Modelling of Tailings Dams

November 7, 2022   |  

Tailings dams are often progressively raised during mine operations to offset the start-up capital cost and to reflect changes in the operation. The potential to use mine waste – whether it is waste rock from open pit mining or the sand-fraction from cycloning of whole tailings – for construction of the raises presents the opportunity to offset costs, reduce mine waste storage footprints, and improve the safety of the dam.

The efficient use of mine waste in tailings dam construction is reliant on alignment between the overall mine plan and the tailings management plan (e.g., timing of dam raises). The ability of the tailings management plan to “speak the language” of the mine plan is a key to success.

Mine planners typically use 3-dimensional “block models” of the deposit to track the type, quantity, and timing of materials within the open pit (e.g., high-grade ore, low-grade ore, waste). A similar approach can be applied to the development of a tailings dam in support of planning alignment.

What is a Block Model?

A block model is like a series of Lego® blocks, each with a unique spatial location and extent, and associated attributes and metadata, including material type, and completion data for example. The block models can be filtered by attribute and assessed by planners for upcoming fill placement and construction sequencing. Ensuring alignment with the mine waste plan, as far as practical, can aid in ensuring the appropriate materials are available and placed in the right location at the right time.

The 3D Building Blocks

Generating a 3D block model starts with a 3D model of the dam using design and drafting software (e.g. AutoCAD or Civil3D) to create a series of wireframes, or triangulated meshes representing shapes or surfaces comprising the dam.

Each wireframe connects to adjacent wireframes to make a 3D model, without gaps or overlaps. Wireframes are developed using construction sequence records, drill hole or test control data, and design information. Former TSF models can be developed from historic aerial photography and terrain models as it was constructed.

The accuracy of a 3D block model depends on the amount and quality of available data and the minimum block size. Higher accuracies will require a greater amount of data and more computational effort. Consider that a 1 x 1 x 1 block size will generate 100 times the volume of information compared to a 10 x 10 x 1 block size.

Block Factor and Sub-Blocking

There are several methods for building block models, including block factor and sub-blocking. The block factor method generates blocks of a consistent dimension and volume and is calculated using the percentage of the block that falls within the wireframe. The sub-blocking method subdivides blocks into smaller blocks to “best fit” the wireframe.

The block factor method yields a more accurate volume of the solid wireframe, at the expense of its geometry; whereas the sub-blocking method yields a more accurate geometry of TSF components such as embankment zones, drains, or filters. The sub-blocking method also generates a far greater quantity of data than the block factor method.

Categories:   Blog   |   Mining

Calculating Passive Treatment of Effluent in Constructed Wetlands

October 4, 2022   |  

Natural Versus Constructed Wetlands

As opposed to natural wetlands, which are typically found at topographic depressions or in areas with high slopes and low permeability soils, or between stream drainages when land is flat and poorly drained, modern treatment wetlands are constructed systems that have been designed to emphasize specific characteristics of wetland ecosystems for improved treatment capacity.

The technology for passive effluent treatment in constructed wetlands has evolved over the last several years into new system configurations and a much broader range of treatment applications. Passive treatment is often attractive to mining proponents because they are relatively low-cost and low maintenance when compared to other treatment alternatives.

Formula for Effluent Treatment

Effluent treatment in a wetland is influenced by a variety of biological processes and biogeochemical cycles that are not always easy to predict and design for. Other factors, including metal species, metal concentration, flow volume, water temperature, and pH all factor in the applicability of wetland treatment. A simple calculation can provide you with a rule of thumb area required to meet the necessary retention time for treatment, helping to determine if a treatment wetland is a feasible alternative.

The formula is: A = [Qd (Ci – Ct)] / RA

A = required wetland area (m2)
Qd = mean daily flow-rate (m3/day)
Ci = mean daily influent contaminant concentration (mg/L)
Ct = required concentration of contaminant in final discharge (mg/L)
RA = area-adjusted contaminant removal coefficient (g/m2/day) (dependent on metal)

It is important to note that the contaminant removal coefficient varies significantly by metal; and, certain metals (e.g., zinc) are not so easily remediated. For example, a calculation for a site with an inbound flow rate of 5 m3/min and iron and zinc at equal concentrations and equal regulatory discharge limits is shown below. A wetland for zinc removal would require over 100 hectares of area, not practically feasible. The removal of iron requires significantly less area.

Categories:   Blog   |   Mining

Employee Spotlight – Eugene Cheung

September 21, 2022   |  

Eugene Cheung leads the Electrical Engineering team at our Vancouver office. He joined KCB in 2010 and is proud to be an Associate.

1. What does a typical day look like for you?

I find an early start enables me to warm up and get into gear before the daily barrage of e-mails and back-to-back meetings begins. My personal goal is to respond to every inquiry before the next day starts, albeit I’m not always successful! Like others, I’m still trying to perfect my multi-tasking: switching between writing letters/reports/memos, marking-up design drawings, coordinating workflows, and welcoming guests at my desk. I also try to look ahead to navigate the forest through the trees. Although I don’t travel for work as frequently as before, I still try to take advantage of chances to visit new sites and participate in equipment testing as opportunities arise. Otherwise, travelling to warm and sunny destinations is my preference!
Eugene R and R’ing in Jamaica and the Bahamas

2. What has been the most fulfilling part about your role?

I feel a significant component of engineering consulting is akin to working in the customer service industry. As a result, my most fulfilling aspect is to keep clients happy (some harder than others!), such that they’re eager to return with more business. And just like in customer service, there inevitably will come times when issues have to be professionally resolved; it’s extremely gratifying if I can help turn frowns upside down. As a side note, I’ve definitely tried to apply the experience I’ve gained while serving as the president of my condo strata over the past 15 years, including interfacing with various personalities in the building and team members of the Pattullo Bridge Replacement Project (literally being constructed right outside my bedroom window!).
New Pattullo Bridge in-river and in-soil footings being installed (April 2022 to September 2022)

3. What is something you find challenging about your role?

Planning, organizing, and optimizing productivity. I think my affinity for this challenge formed while growing up on such min-max video games as Civilization and Master of Magic. Since then, I’ve graduated to playing Stellaris and defeating the toughest aliens on XCOM2 (ironmode legend mode). At work, I enjoy the dynamics of managing my own workload, as well as thinking ahead to overall project deliverables and how that translates to day-to-day activities for the team. At the same time, it’s also important that I recognize that everyone is at a different place in their career, works at a unique pace, and handles stress differently. Additionally, since some staff prefer an early start and some prefer a late finish, I try to be available as much as possible to keep workflows moving, and to fill in any gaps that form.
Eugene and his wife Dawna at the Grand Cayman Islands and Brooklyn Bridge

4. What is your biggest achievement?

I was awarded the Governor General’s Academic Medal (first-in-class) upon graduating high school. Growing up in a traditional Asian household culminated in this focal point. However, it was not long afterward, when I progressed to university and into the working world, that I realized there are many, many other brilliant people more capable than myself, all with distinct talents and working as a team towards common objectives.

5. What advice would you give someone pursuing a career in your field?

Like most things, engineering isn’t as simple as it used to be. Beyond the traditional fields of civil, mechanical, and electrical, there are numerous subfields from which to choose. An education in electrical engineering may center on computers, software/tech, telecommunications, semiconductors, and others, or a combination thereof. Then within those subfields are varying roles in research & development, manufacturing, sales, design integration, and construction. In my case, working in the area of power engineering within consulting and at KCB allows me to maintain exposure to many of these areas, which keeps me on my toes! Thus as advice, I’d recommend someone interested in engineering to research and speak with a variety of engineers to gain an overall perspective on the types of engineering careers that would best suit their personal situation. During one’s studies, I recommend giving strong consideration to internships (albeit I didn’t have the chance to do so having studied and graduated during the “.COM Bubble” era when co-op opportunities were limited). Finally, since several engineering industries are cyclical, with some industries even at the risk of obsolescence, it’s important to select an engineering field and role based on one’s outlook.
Eugene at Powell River while Generator G1 is undergoing construction and commissioning

6. What qualities do you think make a good engineer?

I think soft skills are critical. Here are a few that my engineering role models possess:
  • Honesty – good engineers are true to others and to themselves. The trust of technical judgment goes no further than the trust of character.
  • Self-improvement – good engineers are humble, open-minded, and learn from their mistakes.
  • Positive attitude - finally, good engineers are innovative, energetic, and optimistic, with a willingness to tackle all sorts of difficult and unexpected challenges.

7. What is your favourite thing about working at KCB?

Aside from staff and project work, I feel KCB’s unique position within engineering consulting cannot be understated. Specifically, KCB is a mid-size engineering company that has been taking a leading, active role on relatively large projects that are typically only awarded to gargantuan engineering conglomerates nowadays. This has provided the company and staff the ability to be flexible, creative, and responsive to our clients’ needs, presenting rewarding personal and business growth opportunities.
Categories:   Blog   |   Mining

Could “Smart” Bridges Be the Way of The Future?

August 30, 2022   |  

Our Bridge Infrastructure is Aging

The 2021 American Society of Civil Engineers report card for America’s infrastructure found that the national backlog for bridge repair exceeded $125 billion. The report also found that 42% of all bridges were at least 50 years old and that 46,154 (7.5%) were considered structurally deficient. In Canada, the 2019 Canadian Infrastructure Report Card found that 9,661 (12.4%) bridge and tunnel structures were in poor or very poor condition. As North America’s bridge infrastructure continues to deteriorate, and a growing population pushes demand for mobility to new highs, researchers have recognized an opportunity to apply technology to support the operation and maintenance of these critical assets.

Oak Street Bridge, Vancouver, BC

Sensor-Based Monitoring (SBM) of Bridge Assets

Much research over the past two decades has focused on the development of structural monitoring approaches to collect quantitative data relating to bridge performance (e.g., accelerations, displacements, strains). However, significant challenges remain surrounding how this data can be effectively used by asset owners and engineering consultants to assess bridge conditions and inform operation and maintenance decisions. As a result, the use of monitoring has largely been limited to academic studies and very targeted applications.

Key Questions

This raises a number of important questions: What is preventing the widespread use of sensors to monitor bridge infrastructure? And what information would a sensor system need to produce to prove to be useful for bridge owners and engineering consultants?

To investigate the answers to these questions, an anonymous survey was circulated amongst industry and academic participants to get their insights into the current state of the use of sensors for monitoring bridge infrastructure. KCB recently presented the findings of this survey at the 11th International Conference on Short and Medium Span Bridges.

Civil EIT, Millar Coveney, at the 2022 International Conference on Short and Medium Span Bridges

Survey Results

Respondents identified a lack of knowledge about sensor-based monitoring (SBM) and a lack of requirements for regular bridge operation and maintenance as the primary reasons they had not previously used or implemented an SBM system. Respondents also felt that to be widely used and accepted in practice to support bridge operation and maintenance, an SBM system would need to offer the following benefits:
  1. Provide monetary value in the form of reduced operation and maintenance costs,
  2. Locate and identify potential damage indicators,
  3. Estimate the likely remaining service life of the asset, and
  4. Reduce the bridge inspection frequency.
Perhaps the most notable conclusion from the survey was the seemingly widespread interest in SBM for bridges, even among structural engineering professionals without prior experience using SBM. A total of 73.1% of survey respondents reported having previously used SBM, and 85.7% of those who had not expressed an interest in using it for asset operation and maintenance if it could provide more reliable data than visual inspections. These conclusions validate the importance of SBM research and the need for continued investigation to easily interpret data and to quantify financial benefits.

Next Steps

Based on the survey results, respondents felt that a useful SBM system should provide value to asset operators with minimal engineering analysis required for decision-making. Furthermore, asset operators should be able to quantify the accuracy of the information provided by an SBM system since they are ultimately responsible for invoking maintenance action. Sensor limitations and assumptions about SBM data could be quantified to develop confidence intervals for output data to further assist with decision-making. The potential for applying a mathematical framework to support decision-making related to operation and maintenance is worth exploring in future research. Similarly, the value of applying a reliability-based framework of analysis to SBM should be explored.

The large datasets produced by SBM systems over the life cycle of a bridge could lend themselves well to the application of artificial intelligence and machine learning algorithms to recognize trends and is worth exploring in future research. Given the amount of time needed to capture these datasets and observe changes in bridge performance, the effect of prolonged environmental exposure on sensor networks also merits further investigation.

To gain buy-in from asset owners, a cost-benefit analysis should be performed to determine the financial viability of proposed SBM packages over the life cycle of the asset. The installation and operation costs of the system should be compared against potential savings on operation and maintenance, and traditional bridge inspection costs. An SBM system designed to collect data from several different bridge components could be deployed in phases using a cost-benefit analysis to determine the optimal order and timing of installation for each sensing option.

Looking Ahead

With the rapid advancement of technology in the 21st century, many companies have realized that data generated by their operations can be collected and used to optimize their business practices. Advancements in the field of artificial intelligence have turned the once labour-intensive task of parsing large datasets into a powerful and increasingly accessible tool to help businesses improve their bottom line. In many cases, industries that fail to collect data to improve their business practices are falling behind in this competitive digital and technological landscape. It is imperative we do not allow bridge engineering to be one of those industries.

Read the full paper here.
Categories:   Blog   |   Mining

Portable Light Percussion Drilling: A Practical Solution for Challenging Site Conditions

July 8, 2022   |  

Some geotechnical site investigations face challenging conditions such as poor site access, restrictions on the operation of heavy equipment, and limited budget and time to complete the program. In these situations, the use of portable light percussion drilling systems can be a practical and efficient method for obtaining soil samples. In KCB’s project work at the Fruta Del Norte mine in Los Encuentros, Ecuador, these systems have been an invaluable tool because of their mobility and ease of use.

The Fruta Del Norte mine is located in the province of Zamora, in the jungle region of Ecuador. KCB has been working at the mine since 2009 undertaking site investigations, geotechnical assessments, and feasibility studies at the tailings storage facility (TSF) and Plant Site. The mine is in a densely vegetated jungle where the presence of thick residual soil horizons and high yearly precipitation (3000 mm per year) make the logistics for field programs difficult.

To manage some of the challenges in recovering soil samples at the project site, the KCB team adopted a portable light percussion drilling system. The system is a portable gas-powered percussion drilling apparatus with a core sampler. It operates by advancing steel gouges and/or core samplers into the ground by a telescopic drilling method, where progressively smaller diameter gouges are driven into the soil. The soils contained in each gouge is sampled through a window in the side of the tube. Depending on the drilling apparatus’s specifications, some have drilling depths of up to 10 m.

Light percussion drilling system - Fruta Del Norte project, Ecuador


  • Low cost compared to conventional drilling rigs.
  • Easy transportation and operation.
  • High penetration rates (up to 3 holes of 6 m per day).
  • Good recovery up to 6 m depth.
  • Very good recovery in ‘cohesive’ fine-grained soils.


  • Disturbance of each sample is unavoidable.
  • Requires a few people to manoeuvre the equipment.
  • Poor recovery of wet coarse-grained soils with the supplied core sampler, and at depths below 6 m.
Categories:   Blog   |   Mining

Decision Analysis: A Structured Approach to Improving Project Success

June 21, 2022   |  

Decisions are a part of our everyday life. They can include a low-stake decision like buying a cup of coffee before your drive into the office, or a high-stake decision like buying a house. As engineering professionals, your project work requires a multitude of decisions and the opinions of stakeholders throughout the process. Decisions made in a project setting often require a more structured approach to produce a rational and auditable methodology for determining a choice between competing options.

A decision analysis process can help build consensus among stakeholders, consider a wide range of options, identify potential risks, and develop a plan with specific actions. There are several that are commonly used in project management including the Kepner-Tregoe method and Multiple Accounts Analysis. The advantage of a decision analysis process is it can bring together informed people in many fields (fields of interest are called accounts) and can include social, environmental, technical, and cost aspects of a project. These fields of interest often have competing requirements and different risk profiles which the process describes in plain language and evaluates from different stakeholder viewpoints, often in a workshop setting.

Define the Problem

The first step when conducting a decision analysis is defining the problem. During this step, you will develop a thorough description of the situation, its purpose, and identify a core team of stakeholders from a variety of fields (geotechnical, environmental, operations, finance, etc.) who can contribute. The core team should determine the purpose of the decision and any constraints that will guide the scope of the process. It is during this step that you will consider multiple criteria, identify the account structure (social, environmental, technical, cost, etc.), and define assumptions.

Establish the Objective

Once you have developed an understanding of the problem, you can establish the objectives of the decision. Start by compiling a list of objectives and divide them into “musts” and “wants”. "Must” objectives are criteria that must be met for an alternative to be successful (e.g. regulatory criteria). “Want” objectives provide the means of differentiating between options (e.g. maximize opportunity to reach passive care) and do not need to be met for an alternative to succeed.

Identify Alternatives

In this step, you will identify alternatives to meet the decision. These can be achieved through a matrix of elements to develop various options which are discussed throughout the process. If any alternatives do not fulfill all the “must” objectives, screen them out.

Engage Stakeholders

Now, compare the alternatives to the defined objectives. (This is typically undertaken in a workshop setting with key stakeholders and a capable facilitator guiding the process.) Rank each alternative based on its ability to achieve the objectives. For this step, alternatives must meet all the “must” objectives and are evaluated against the “want” objectives. Assess your results by conducting sensitivity analyses and a risk assessment to reduce the overall risk to as minimal as possible.

Make your Decision

Decide on an alternative based on how it ranks above other alternatives, its costs, and risks. Once a decision has been made, develop an action plan, documenting the approach and rationale of the decision, to move the project forward. This step usually includes a forward high-level work plan for the project.

Tips when conducting a decision analysis:

  • Be clear on the situation appraisal and problem analysis prior to undertaking the decision analysis.
  • Have the right people in the room to make decisions. Identify and include key stakeholders to increase the success of the decision analysis process.
  • Achieve consensus at each step.
  • An objective framing workshop is a useful way to engage decision makers and identify policy, strategic and tactical objectives.
  • Characterize each alternative with a supporting body of knowledge enough to compare each option without prior judgement.
  • It can be as simple or complicated as it needs to be. But do not over-complicate. Not all the answers are needed to make an informed decision.
Categories:   Blog   |   Mining