Opportunities and advantages of 3D geologic modeling for tailings storage facilities

3D modeling can be used throughout the mine lifecycle and has proven to be a powerful tool for consultants and mining companies. One of the most significant benefits of 3D models is their ability to enhance collaboration, communication and understanding between the mine owner, design engineers and other relevant stakeholders that have a shared interest in responsible mining and site management. Tailings and mine waste management is an interdisciplinary effort that requires effective coordination and communication between a range of consultants, operators and stakeholders alike. The increased emphasis on environmental, social and corporate governance (ESG) highlights the importance for mine operators to engage and communicate with all parties involved in the planning, permitting, operation and closure of mine sites. 3D models are valuable tools that can be used for the development of geotechnical conceptual models, allowing for improved design and monitoring of tailings storage facilities (TSFs). A clear conceptual understanding of a TSF’s subsurface geology and foundation characterization is essential for proper tailings management, design and planning. Visualization with 3D modeling can simplify the interpretation of the oftentimes intricate, mine-sight subsurface settings and allows for quick and effective geotechnical conceptualization. 3D models can be used to identify data gaps, optimize field investigations and streamline the development of numerical stability or groundwater models. They can help communicate the complex nature of subsurface and TSF interactions in a clear, concise and accurate manner to both technical and nontechnical stakeholders. This article discusses some of the benefits of 3D modeling in relation to geotechnical analysis for tailings management and provides methodologies for how to improve upon some methodologies that are considered industry standards. 3D modeling 3D modeling is a digital design method that creates a threedimensional visual image of any object or surface. The virtual 3D surfaces are made up of a 3D mesh that can be thought of as a snapshot of a series of points in space. Meshes are a group of computer/user-generated vertices that are connected to form an object or surface. It is possible to produce these threedimensional objects automatically or manually by manipulating the geometry or by altering the vertices. In the past, 3D modeling was thought of as a costly and time-consuming process that required a significant amount of time and computing power. Recent improvements in computer processing and reductions in cost have made 3D modeling much more accessible and applicable to a variety of industries including computer games, films, construction, art and engineering. Geologic modeling A 3D geological model consists of a representation of the subsurface based on geological field observations, geophysical surveys and drill-hole logs. Geological models that provide accurate representations of the spatial locations and extents of rock types, and/ or ore types, are essential tools for defining mineral resources and mine planning. From land surface to deep underground, 3D geologic models provide an unparalleled representation that can be used for engineering and environmental applications related to mine waste and water management, hydrogeologic characterization and more. With its roots in mineral resource characterization, 3D geologic modeling has long been a niche software used by resource geologists to define ore bodies, prove up reserves and offer confidence to stakeholders. The applications for 3D geologic models in the mining industry have been explained in many previous publications, such as those by Leonida (2020) and Wang et al. (2012). Opportunities and software As computer processing and software capabilities have improved, the opportunities for using 3D modeling in mining have increased and expanded into other areas of the mining industry such as geotechnical engineering. With the new Global Industry Standard on Tailings Management enhancing the way the industry manages, designs and constructs TSFs, it is important to consider opportunities for improvement to current workflows. 3D geologic modeling presents opportunities to improve upon current industry-standard workflows. Geologic modeling platforms can be used to couple 3D representations of subsurface geology with geotechnical information and engineering designs to provide engineers with a digital twin of a TSF that enhances visualization, collaboration and communication, as shown in a simplified model and embankment in Fig. 1. Opportunities exist for the use of 3D geologic models in the design, construction, operation and closure of TSFs. Software options Geologic modeling software tends to be catered toward specific industries to solve specific solutions. Whether it be for resource estimation, contaminant modeling or geophysical data representation, many geologic modeling software programs exist, each with their own strengths, weaknesses and different compatibilities with other software. The following programs are commonly used to generate 3Dgeologic models: Leapfrog — 3D modeling software used in the mining, civil, geotechnical, environmental and geothermal industries. Generally used for 3D geologic, resource, reservoir and contaminant modeling.Vulcan — 3D modeling software used for mine planning and generation of geologic models for resource modelers in the mining industry.Micromine — 3D mine engineering software used for mine planning and mine design work.Deswik — 3D mine engineering software used for mine planning and mine design work.Rockworks — 3D modeling software used in the environmental, geotechnical, mining and petroleum industries to visualize geologic data. Surfer — 2D and 3D modeling software used in the geologic, hydrologic, environmental and construction industries for geologic and surface data visualization.EVS — 3D modeling software used predominantly in the environmental sector for contaminant and geologic modeling. Each of the above can be used to generate 3D geological models. However, there are few 3D modeling programs like Leapfrog that are designed, updated and integrated with other engineering software with the purpose of generating a digital twin of TSFs as described by Seequent (Seequent, 2020). The unique interoperability and general benefits of 3D modeling software, such as Leapfrog, are discussed in the following sections. Of the software investigated as part of this article, Leapfrog provided the most interoperability and is further discussed in the following sections. Figure 1 Digital twin of TSF. Figure 2 3D geologic model of TSF foundation alongside geophysical data. Leapfrog Leapfrog is a geological modeling software developed by Seequent. The software program is intuitive to use and allows engineers and scientist to tie surface designs with subsurface data in 3D. The software provides a range of interoperability with other mining, civil and geotechnical engineering software and offers several modules, including the following: Leapfrog Works is specifically developed for modeling of the subsurface for civil engineering and environmental projects.Leapfrog Geo is utilized in the mining industry to generate geologic models for mineral resource estimation.Leapfrog Geothermal is catered toward the geothermal industry for creation of geologic and reservoir models. The interoperability allows all teams a high level of collaboration and communication. Software compatibility Leapfrog offers interoperability with most mining, civil, geotechnical and environmental software programs. GIS data, surface designs, geotechnical data, geophysical surveys, instrumentation data and raw CPT (Cone Resistance, Local Friction, Pore Pressure) data can easily be imported into Leapfrog. The information can be incorporated into a single holistic 3D geologic model. Some of the scientific and engineering software programs that have interoperability with Leapfrog software include: Geostudio.Plaxis.Rocscience.OpenGround.AutoCAD Civil 3D.Groundwater Vistas (MODFLOW).FEFLOW.ArcGIS.Imago.MX Deposit. Applications for TSFs General. There are many opportunities for the application of 3D geologic modeling of TSFs, from options analyses in the design phase to monitoring during operations and the ultimate closure of the facility, as discussed in the following subsections. Trade-off studies. It is essential to consider the foundation conditions prior to construction. During trade-off studies, it is common to conduct geotechnical site investigations to assess spatial variation within the subsurface that could lead to fundamental differences in design. The information obtained through the geotechnical site investigation, including borehole hole logs, soils testing, geophysics data and surface investigations, can be used to generate a 3D geologic model of the site as seen in Fig. 2, which can be utilized and updated throughout all phases of the mine lifecycle as a digital twin of the subsurface. The embankment designs can be added to the digital twin in Leapfrog so that the subsurface and embankment design can be viewed as one holistic model. Once the TSF is conceptualized and tied in with the subsurface model, traditional 2D-cross sections can be quickly generated in Leapfrog and exported for geotechnical evaluations, such as for stability analyses. Geologic model volumes can also be exported for analysis in 3D stability modeling software. Once analyzed, the results can be brought back into the model to be visualized along with all the supporting data. Construction. Construction of a TSF presents challenges that can be simplified with the use of 3D subsurface models and a digital twin of the site. These challenges include borrow material identification, determining stripping and grubbing depths, selection of instrumentation locations and communication with construction teams. 3D subsurface models can be used to help identify borrow material and define appropriate limits for borrow areas in the vicinity of the facility through the evaluation of drill logs, test pits and surface mapping. 3D geologic surfaces can be generated to estimate material boundaries. Borrow-pit designs can be created in the model or imported to calculate the volumes of appropriate materials available. Once excavated and surveys are obtained, 3D definition of the borrow areas can assist with the creation of more accurate material quantity estimates. Selection of stripping and grubbing depths can be facilitated by tying together geotechnical data in 3D. When stripping and grubbing depths are better understood prior to construction, schedules, volume and material estimates will be more reliable. It is important to consider the surface and subsurface features when deciding where to install geotechnical instrumentation. In addition, the feasibility of installing instrumentation prior to or during construction must be considered. Construction introduces additional risk to instrumentation that can be damaged during the construction process. The use of a digital twin that considers existing surfaces, final design surfaces and construction progression and subsurface features can reduce the risks associated with installation of instrumentation during the construction process. Opportunities also exist to share 3D models with construction workers to improve their understanding of the end goal. 3D representation of earthworks can complement 2D cross sections and plan views that have been the industry standard. Monitoring TSF instrumentation During operations, it is essential to properly monitor the facility for changes in pore pressure or potential movement within the embankment. This is often done through the installation of vibrating wire piezometers (VWPs), inclinometers, settlement monuments or lidar surveys. These devices and surveys are not often coupled together with the embankment design features and subsurface in one model. Leapfrog software can be utilized to view monitoring data in a holistic manner, and can incorporate the subsurface modeling data and design features into other software for further analysis, such as of slope stability, seepage and other factors. VWP data can be imported into 3D modeling software to generate piezometric surfaces that can be analyzed in the model and tracked through time, as presented in Fig. 3. Similarly, inclinometer data can be imported as 3D traces of the casing to visualize, compare and track deviation similar to the comparison of piezometric surfaces presented in Fig. 3. Inclinometer data can be added to the model alongside relevant information — such as subsurface model, design surfaces and VWP data — to help visualize and communicate the impacts of inclination or deviation, which can be difficult to grasp in 1D or 2D software. Movement of the facility can be a key indicator that there is instability or sliding along the foundation. 3D lidar surveys can also be compared against one another in Leapfrog to better understand potential movement or changes observed at the surface. Once tied into the digital twin, information can be easily incorporated into stability analyses by exporting 2D sections or 3D geologic volumes to geotechnical analysis programs, such as Slide, Slope/W, PLAXIS and/or other software. Closure TSF closure is one of the final steps in responsible mining. Closing a TSF is an undertaking that requires years of planning and communication among teams and stakeholders. Relaying final closure plans to stakeholders and community members is required long before closure occurs. Rendering of closure plans using 3D modeling can be presented to community members and stakeholders to increase understanding of the closure process and promote informed communication. Monitoring devices can continue to be updated and the digital twin of the facility can continue to be utilized long after closure. A digital twin can assist with keeping stakeholders involved and informed. Advantages One of the beneficial aspects of 3D TSF modeling is that it can be utilized to combine the subsurface model, TSF design, monitoring and instrumentation, and other infrastructure, into a single holistic model. The 3D model can be used as a digital twin of the mine site, essentially becoming a singular location where all data relevant to the design and subsurface are stored, compiled and monitored. Every time a site investigation or TSF design change is performed, the collected data can easily be incorporated into the 3D model. This assists in the reduction of data loss, which can easily occur due to relevant data being scattered across multiple reports and teams on projects that span long periods of time. Compiling site data in a digital twin can also assist with the transition of projects to new owners and/or consults. Figure 3 Piezometric surface over time. Conclusions The industry is in the process of moving toward the goal of zero harm, and it is important to address the complexity and multidisciplinary nature of sound tailings management. Sound tailings management requires collaboration and communication among different teams, locations and stakeholders. Understanding the challenges involved in responsible tailings management is the first step toward the goal of zero harm. To improve communication, all parties must be able to visualize the problems or challenges present. The implementation of a digital twin of the mine site, initiated during the design phase and continued through closure, offers an opportunity to incorporate mine-site data in a holistic setting that improves communication and collaboration. The resulting 3D model improves visualization of the system as a whole and streamlines workflows. Digital twins of mine sites can help the industry take one step closer toward zero harm. References G. Wang et al. 2012. 3D geological modeling for mineral resource assessment of the Tongshan Cu deposit, Heilongjiang Province. China Geosci. Front. Leonida, C. 2020. From model to mine to market and back again. [Online] https:// theintelligentminer.com/2020/09/16/mining-and- 3d-modelling-technology/ Seequent 2020. How free flow of data can make Tailings Storage Facilities safer. https://www. seequent.com/how-free-flow-of-data- can-maketailings- storage-facilities-safer/

Opportunities and advantages of 3D geologic modeling for tailings storage facilities

Authored by:
G. Johnson, H.D. Lelono, M. Walden

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