Areas of Expertise

Itasca specializes in assessment of slope stability and design of pit slopes on bench, inter-ramp, and global scales. Itasca routinely performs slope design services at some of the world's largest open pit mines. Specific services offered include:

• geotechnical mapping and assessment of rock mass structure and in situ properties for use in design,
• dewatering and coupling of the dewatering program to geotechnical stability of the slopes,
• blast design,
• specification of instrumentation for monitoring slope movements,
• numerical modeling for assessment of stability and design, and
• specification of slope remediation programs.

We work with mine engineers and geologists to provide practical - but technically sound - solutions to the mine's problems. One key aspect of our work is the use of data transfer algorithms that allow us to use nearly all the geotechnical and hydrogeologic data collected by the mine in our analyses. Another key aspect of our work is to assist in education and training of the mine staff during larger projects. We find that this approach improves communication and is better than simply providing a consulting report at the completion of a project.

instabilities and remediation methods. We pioneered the use of accurate and efficient methods to determine safety factors using numerical methods. The determination involves adjusting shear strength parameters to find the values that put the slope at the limit of stability (i.e., a safety factor of one). The safety factor for the slope is computed by comparing the limit parameters with actual strength parameters. This technique, called the shear-strength reduction technique, has an important advantage over more traditional limit-equilibrium solutions that are restricted to prescribed failure surface geometries (circular, log spiral, segmented, etc.). The shear-strength reduction technique allows failure surfaces to develop naturally, resulting in a more accurate estimate of the failure mode and safety factor. This development has recently been extended to estimate failure probabilities, which are becoming increasingly important in formalized risk assessment.

We use our software for slope design at most major surface mines worldwide. FLAC and FLAC3D are often used for soil or highly fractured rock slope and simple groundwater analyses. For more comprehensive ground-water flow analysis we typically use MINEDW, although other programs such as MODFLOW-SURFACT and FEFLOW are sometimes used where appropriate. UDEC and 3DEC are used for slope assessments where large-scale geologic structures impact slope movements.

Itasca offers services in backfill specification, design of backfill mixing and delivery systems, stability analysis (exposure stability and closure resistance), and instrumentation and testing of placed backfill. These services cover a wide range of backfill products (paste fills, hydraulic fill, cemented aggregate fill, and rockfill) and have been applied at mining operations throughout the world.

Itasca has also developed state-of-the-art numerical modeling methods for simulation of the deformation and yielding of backfill and backfill mats. Both two and three-dimensional models are used to examine the response of fill under static and dynamic loading conditions.

Our specific experience includes:

• design and implementation of laboratory testing programs to determine fill shear strength, tensile strength, compressibility and consolidation characteristics;
• numerical modeling stability analysis of vertical and horizontal fill exposures;
• analysis of fill closure resistance;
• design of fill exposure reinforcement requirements; and
• dynamic modeling to examine stability and liquefaction potential under rockburst and rockfall conditions.

Itasca performs geotechnical services for the planning and design of underground mines, considering the key elements required for successful design, development, and operation of the mine. These elements are largely geotechnically related and include an understanding of the:

• rock mass strength (i.e., interaction of intact rock and structure) relative to in situ stress, to predict its response to excavation;
• selection of mining methods appropriate to the ore body geometry and rock mass strength conditions;
• development of an efficient layout, sequence, and mining schedule to optimize recovery and minimize instability;
• robust design of access and infrastructure to ensure long-term stability and worker safety under in situ and mining-induced stress changes; and
• layout and specification of ground support and predictions of mining induced surface subsidence in cases of shallow operations, to optimize location of infrastructure and predict impacts on existing infrastructure and topography.

Itasca has conducted investigations of excavation behavior in all types of rock and at all scales, from individual boreholes, access tunnels, and ore passes to complete sequencing and analysis of the largest underground mines in the world. Individual investigations often employ analyses over a wide range in scale due to the complex interaction between overall mine advance, in situ stress, and the loading conditions experienced at the tunnel scale. Itasca staff also have the capability to design blasting rounds and to select mining equipment. The company has performed this work with underground mining operations worldwide and with a number of industrially funded and managed research projects. Our expertise is employed to help companies select the mining method, sequence, and ground support that will maximize ore recovery, stability, and safety while minimizing development costs and ore dilution. The following sections detail our project experience in specific underground mining methods/environments.

Itasca has performed mine design and evaluation studies in numerous room-and pillar and longwall operations in sedimentary rocks. These include: layout and pillar design in trona operations in the Green River, Wyoming, district; silver operations in Montana; design of underground limestone quarries for Vulcan Minerals; and layout and high-extraction mining in potash and salt in Canada (beneath Lake Huron) and in coal in the U.S. and South Africa. As with all problems, Itasca engineers combine a practical engineering approach with the use of numerical modeling technology as necessary. The ability to model the behavior of widely varying rock types under a wide range in scales is particularly relevant to the analysis of underground mines in sedimentary rock.

Itasca has developed a unique and robust approach to designing such mines, which recognizes the importance of understanding the rock behavior from intact specimens through to bedded sequences and the entire mine. Itasca's rock-engineering software is capable of representing the stress-strain response of continuous, blocky or bedded materials exhibiting plastic, brittle, and creep behaviors; thus, any combination of lithologies comprising the pillar-floor-roof system can be represented. For example, at the General Chemical and Solvay Mines, which are located in sedimentary formations of the Green River Basin,Wyoming, Itasca has successfully developed a robust model of the combined brittle trona seam, the weak and punching response of the oil-shale floor, and the arching response of strong overburden beds. This model is capable of reproducing the complex combination of pillar sloughing (rib rash) and floor heave experienced at different extraction levels and vertical stress levels throughout the mine. Information derived from these pillar-scale models forms an essential input to larger-scale models, which have been used extensively for design of individual panels (width, remnant stub width, and extraction ratio) as well as barrier pillars and the overall mine layout and extraction ratio. These larger-scale models have been validated through successful back-prediction of the timing and nature of large scale catastrophic collapses experienced in the region.

Itasca has worked with cave mining operations worldwide and with the International Caving Study (now called Mass Mining Technology or MMT), a nine year industrially funded and managed research project. The company has used this experience to develop practical experience in caving, as well as a suite of specialized software tools for analysis of cave mining. Software capabilities include: caveability prediction, caved rock flow simulation and draw control, undercut- and extraction level design, and prediction of the limits and extent of cave-induced surface subsidence. In analyzing any of these, the unique nature of cave mining operations is considered, particularly with respect to the evolving stress conditions that accompany cave growth. Our expertise in cave mining analysis has been used by companies to make critical decisions regarding:

• the caving potential of ore bodies and their potential impact on ground surface,
• fragmentation prediction,
• the optimal drawpoint spacing to minimize development costs and to maximize recovery, and
• the orientation and geometry of the undercut, the layout of the extraction level, and the degree of support in access and infrastructure required to ensure worker safety and long-term stability.

PFC3D simulations of draw from a block caving drawpoint (left) and a sublevel caving ring (right). These models, which are limited to a few drawpoints, are used to understand the basic mechanisms of rock flow and to predict the impact of caved and blasted rock properties on dilution entry times and hang-up potential.

Itasca is a leader in the design and analysis of undercut- and extraction-level infrastructure for underground block- and panel-cave mining methods. Our engineers have conducted investigations of excavation behavior at many of the world's metalliferous caving mines. We have also conducted feasibility studies of the transition from open pit to underground caving operations at a number of large open pits. Our engineers have been successful in optimizing the extraction level development prior to undercutting as well as developing sound designs for the level and timing of ground support. Due to the three-dimensional nature of typical undercut- and extraction level mining geometries and the complex interaction between cave shape, cave growth, and abutment stresses, three-dimensional analyses at both the tunnel and cave scales are required to simulate the loading conditions of undercut-and extraction-level drives. Three-dimensional, non-linear analysis of such mining geometries has become routine using FLAC3D and 3DEC. These codes permit careful consideration of the complex stages of loading, unloading, and yielding at both the cave and drift scale that occur during undercutting and subsequent cave growth.

Both caveability and subsidence are examined with numerical techniques developed in FLAC3D and 3DEC. The true undercut shape and direction are represented. Draw may be simulated by continuously reducing the support pressure within the undercut level to mimic a specific draw strategy. The resulting evolution in cave growth, which may indicate continuous growth or stalling, and its eventual impact on ground surface can be observed. Modeling also indicates key changes in rock mass properties that occur as the rock mass weakens and moves from an "undisturbed" to a "disturbed" condition in the region surrounding the cave.

Using the understanding of caved rock-flow behavior developed from PFC2D and from physical modeling studies, Itasca developed REBOP (Rapid Emulator Based on PFC3D) to rapidly simulate the flow of fragmented rock in cave mining operations. Along with a drawpoint layout and schedule, REBOP accepts a mine block model with expected caved-rock properties as direct input to easily set-up and run mine-specific draw simulations. REBOP can track the movement of material within caves that incorporate hundreds of drawpoints over production spans of several years. The code provides reports of drawpoint grades with time/tonnage. It has been employed at several cave-mining operations to predict waste entry and recovery as functions of drawpoint layout and as a guide to draw control strategy.

Once the location, orientation, and geometry of an excavation have been determined, long-term considerations such as the impact of future adjacent excavations on stability require consideration. Development should be located and then sequenced to minimize their impact. Design of semi-permanent and permanent underground excavations in hard rock, soft rock, soil, and backfill is an area of extensive expertise for Itasca. The design time scale can be on the order of years (mine drifts and infrastructure, tunnels, underground power houses) or on the order of millennia (underground waste isolation). We perform complete analyses using all numeric, empirical, and analytic tools available.

A number of design issues require consideration when developing infrastructure in rock or soil. Various impacts on the excavation's long-term stability - in situ or induced stress, geologic structure, intersecting development - can be assessed in order to compensate in design. For instance, all excavations should be oriented to minimize the impact of stress but also to minimize the risk of creating large unstable rock wedges. Also, intersecting development (such as in the hoist room illustrated below) can concentrate stress or form unstable brows that need to be identified for specific design considerations. We determine the optimum orientation and geometry to ensure the long term stability of the excavation and the safety of mine personnel.

Shafts are another critical part of the mine infrastructure, and Itasca has had considerable experience assisting mining companies in the design and selection of adequate support. For example, at the Silver Shaft, Lucky Friday Mine (Hecla Mining Company, Mullan, Idaho), Itasca staff performed analysis of shaft ground support and concrete lining systems for the circular (6.7 m finished diameter), 1890-m deep production shaft in highly stressed, bedded quartzite. This shaft was sunk conventionally by Redpath of North Bay, Ontario. Itasca staff performed rock-mass displacement and concrete-lining strain and stress measurements to verify support loads and functions. These measurements were used to develop guidelines for deep shaft design in combination with the U.S. Bureau of Mines' deep-shaft design initiative.

We design ground support using techniques that combine theoretical concepts (such as the Ground Reaction Curve) with practical numerical modeling tools to ensure that the appropriate ground support is installed for site-specific conditions. Then, we design instrumentation programs to validate and subsequently monitor the design over the life of the excavation.

Itasca provides consulting services to optimize blasting operations to minimize costs and maximize excavation stability. All aspects of blast design are analyzed - from layout of site blast patterns and charges to research into blasting mechanisms. We have in-house tools for blast analysis that are used to: understand blasthole-to-blasthole interaction, optimize fragmentation and throw, and minimize damage (such as back break).We can help design blast instrumentation for monitoring systems so that design performance can be assessed and possibly improved.

Surface subsidence is an inevitable consequence of many mining methods. Itasca evaluates mining-induced subsidence related to the extraction of ore from both underground and open-pit mines, together with dewatering-induced subsidence.

We provide services ranging from field investigation for acquiring geomechanical and hydrogeological properties to prediction of the magnitude and extent of subsidence related to a particular mining geometry. Traditionally, empirical and analytical methods have been used to assess the limits of subsidence from underground mining. However, these methods are restricted to simplified, regular mining geometries, and often are limited to two-dimensional problem geometries.

Itasca engineers have pioneered the use of three-dimensional numerical models to assess mining-induced subsidence. Through the calibration of observed and measured subsidence features at a number of operating and abandoned mine sites, we have developed a rigorous methodology that predicts the limits of large-scale surface cracking and ground strains capable of causing damage to surface infrastructure.

Our specific experience includes:

• field investigation of subsidence-affected land;
• numerical modeling prediction of the subsidence zone-of-influence surrounding block cave, panel cave, and longwall mines;
• evaluation of the long-term residual subsidence above subsidence affected land;
• investigation of the long-term stability of room and pillar mining excavations; and
• numerical modeling prediction of dewatering-induced subsidence.

Itasca software is extensively used for subsidence evaluation. FLAC and FLAC3D are often used to simulate subsidence within soil or highly fractured rock masses. 3DEC has been used for subsidence analysis where persistent, large-scale geologic features have a significant influence upon the subsidence behavior. PFC has been used to investigate the flow behavior of broken rock once a subsidence crater has been formed at the ground surface.

Examples of Itasca subsidence studies are shown in the figures on the following page: the top figures show an example of surface subsidence calibrated using FLAC3D; the middle figures show an example of surface subsidence due to mining below an open pit in Chile, and the calibrated fracturing limits at El Teniente mine from 3DEC (as reported by Cavieries et al., 2003); the bottom figures show a PFC analysis of mining below an open pit in Western Australia.

Prediction of subsurface subsidence in existing open pit due to underground mining.Calibrated fracturing limits at El Teniente Mine (Cavieres et al., 2003).

Geology of the pit and underground at the start of underground mining in simulation using the PFC code.Caving simulation and subsidence effects due to underground caving.

Reference

Cavieres, P., S. Gaete, L. Lorig and P. Gómez. "Three-Dimensional Analysis of Fracturing Limits Induced by Large Scale Underground Mining at El Teniente Mine," in Soil and Rock America 2003 (Proceedings of the 39th U.S. Rock Mechanics Symposium, Cambridge, Massachusetts, June 2003), pp. 893-900. P. J. Culligan, H. H. Einstein and A. J. Whittle, Eds. Essen: Verlag Glückauf, 2003.

Alternative mining and development technologies such as TBM, drill-and-blast, raiseboring, Alimak, etc. will need to be evaluated from cost, timing, safety and operational perspectives. Itasca has experience in evaluating all of these alternative techniques and has had considerable exposure to these mining technologies from experience at client mines and project sites. Examples range from large-span shallow hydroelectric caverns in China, to large openings and deep development in mines such as Kidd Creek, Creighton, and Laronde. Itasca is the geomechanics consultant on the Sudbury Neutrino Observatory Expansion at the Creighton Mine in Sudbury. In addition, Itasca has acted as consultant on mining development at Cameco's McArthur River Mine, where high pressure Radon-bearing water is an additional risk faced by the operator.

Itasca designs and optimizes dewatering systems for surface and underground mines around the world. Our experience allows us to select the most cost-effective methods for dewatering or depressurization for slope stability purposes. We design and supervise the installation of dewatering wells, sub-horizontal drain holes, monitoring wells, and drainage galleries. We are especially knowledgeable in the design of large-diameter, deep production wells, and with methods of well completion and development to ensure that each well is as hydraulically efficient as practical. Our staff comprises geologists, hydrologists, geochemists, and engineers, which allows us to tackle all aspects of the design, including water quality and disposal issues.

Itasca provides the technical expertise necessary to design successful water supply systems, including assessment of resources and safe yields and design of well fields. Itasca personnel are also experienced in providing technical support for obtaining water rights and permits.

Itasca has extensive experience in conducting field investigations for acquiring hydrogeologic and geochemical data, including:

• installation of pumping wells, point piezometers (both surface and underground), and multi-level monitoring systems;
• conducting field tests (air-lift, pumping, injection, packer tests, etc.) for estimating aquifer hydraulic parameters;
• installation of surface water monitoring systems; and
• characterization of mine wastes to evaluate the potential development of acid-rock drainage.

With respect to environmental studies, Itasca specializes in site assessment, data analysis, evaluation of impacts to water resources, selection of remediation systems, and implementation of remedial actions that lead to closure of sites where contaminated soil and ground water are encountered. Our staff of hydrogeologists, geochemists, and engineering geologists has extensive experience working with regulatory agencies to achieve practical, cost effective solutions to a broad range of environmental problems. We provide services that range from sampling of soils and water to constructing detailed models to assess the fate of chemicals in the environment. Our experience ranges from recommendations on approaches to remediate small diesel spills to detailed hydrologic and geochemical modeling for Superfund sites. We have also completed many investigations of mine dewatering and the subsequent formation of "pit lakes," and assessed their impact on the quantity and quality of water resources as part of Environmental Assessments (EAs), Environmental Impact Statements (EISs), and mine closure plans. The strong technical background and extensive experience of our staff allows Itasca to provide clients with technical overview (second opinions) and testimony as expert witnesses.

Itasca has vast experience in the use of hydrogeological and geochemical models for mining applications. We have developed a sophisticated, three-dimensional, finite element, ground-water flow program, named MINEDW, specifically for mining applications. MINEDW is in use world wide for designing dewatering or depressurization systems, predicting local and regional environmental impacts of mine dewatering, assisting in the design of water supply systems, simulating the infilling of a "pit lake" after mining ceases, and estimating pore pressure distributions within highwalls used for geotechnical design purposes. We are also well-versed and widely experienced in the use of other codes for analysis of saturated and unsaturated ground-water flow, chemical transport, and surface water systems. We maintain current versions of the following public-domain and proprietary codes in house, and routinely use them based upon the needs of the client and the project:

• MODFLOW and MODFLOW-SURFACT,
• FEFLOW,
• MT3D99,
• PEST
• HST3D, and
• HEC-1 and HEC-2

Our expertise also includes the use of geochemical models to evaluate impacts on the quality of local and regional water resources, to assist in predicting chemical characteristics of "pit lakes," and to evaluate the potential development of acid-rock drainage. The codes that we typically use for these applications include PHREEQC, CE-QUAL, and various kinetic models.

It is most important in the application of numerical modeling that:

1. the conceptual hydrogeologic model on which the numerical model is based is as representative as possible,
2. proper boundary conditions are used,
3. the mining plan is accurately incorporated into the model, and
4. appropriate sensitivity analyses are performed to define the possible range of consequences when important parameters are uncertain or highly variable.

The members of Itasca's Mining Group have the judgment and experience necessary for these critical aspects of applying numerical models.

Itasca offers short courses that cover the basic hydrogeologic and hydrogeochemical aspects related to mining operations, including how to collect hydrogeologic and geochemical data, pumping test analysis, numerical modeling, and design and implementation of dewatering systems. Our experience has been recognized by the Society for Mining, Metallurgy, and Exploration (SME), which has invited Itasca to teach a mining hydrology short course as part of its annual meetings in 1990, 1991, 1993, 1995, 1998, and 2001, and by the Canadian Institute of Mining, Metallurgy, and Petroleum (CIM), which invited us to teach a similar course at its annual meeting in 1999. At the request of several of our clients, Itasca has also presented this course at different mine sites around the world. In 2000, Itasca geochemists taught a short course on Introduction to Geochemical Modeling Tools at the International Conference on AcidRock Drainage (ICARD 2000).