Areas of Expertise

Itasca engineers plan and design underground mines, considering the key elements required for successful design, development and operation. 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
• the development of an efficient sequence and mining schedule to optimise recovery and minimise instability
• robust design of access and infrastructure to ensure long-term stability and worker safety under in situ and mining-induced stress changes
• analysis, specification and design of ground support

Investigations have been conducted of excavation behavior at all scales, from individual boreholes, access tunnels and ore passes to complete sequencing and analysis of the largest underground mines in the world in all types of rock. Individual investigations often include analyses of various scale due to the complex interaction between overall mine advance, in situ stress and the loading conditions experienced at the tunnel scale. 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 helps companies select the mining method, sequence and ground support that will maximise ore recovery, stability and safety, while minimising development costs and ore dilution.

We have developed a method of presenting the results of rock mechanics studies that relates expected geomechanics conditions to the direct costs of a mining operation. This technique supplies mine engineering staff and management with results from numerical stress analyses and failure predictions that can be easily understood and acted upon. With a numerical model that can represent the failure conditions observed in the mine, parametric studies allow cost estimations and show how costs vary with method or sequence. This kind of cost-based rock mechanics risk assessment of mining methods and sequences allows risk levels and geomechanics-related costs to be determined and compared for methods optimisation.

Itasca specialises in assessment of slope stability and design of pit slopes. Specific services offered include geotechnical mapping and assessment of rock mass structure and in-situ properties for use in design, blast design, specification of instrumentation for monitoring slope movements, numerical modelling for stability assessment 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 all work is to assist in education and training of the mine staff during a project. This approach improves the application of the assessments better than simply providing a consulting report at the completion of a project.

We are particularly well known for our ability to examine difficult problems involving slope instabilities and remediation methods. Itasca codes are the most widely used software for slope design at most major surface mines worldwide. FLAC and FLAC3D are often used for soil or highly fractured rock slope and groundwater analyses. UDEC and 3DEC are used for slope assessments where large-scale geologic structures impact slope movements.

Design of Tailings Storage Facilities and Waste Dumps
Itasca engineers have performed design and stability analyses for tailings storage facilities, waste dumps and other impoundment structures. Related work includes analyses of leach pile drainage and stability.

Dynamic Analysis of Rock Slopes and Tailings Storage Facilities
Itasca engineers have performed many analyses of the stability of slopes and large tailings dams when subjected to earthquake or blast loading, as well as dynamic discontinuum studies for rock slopes and liquefaction analyses of soil slopes.

Itasca engineers have worked with cave mining operations worldwide and with the Mass Mining Technology project (MMT, formerly, International Caving Study), a nine-year industrially funded and managed research project. The company has used this experience to develop a suite of specialised software tools for analysis of cave mining. Their capabilities include caveability prediction, flow simulation and draw control, undercut and extraction-level design and prediction of the limits and extent of cave-induced surface subsidence. In analysing any of these situations, 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 orebodies and their potential impact on ground surface, the optimal drawpoint spacing to minimise development costs and to maximise recovery, and the level of support in access and infrastructure required to ensure worker safety and long-term stability.

We are a leader in the design and analysis of undercut and extraction-level infrastructure for underground block and panel cave mining methods. We have conducted investigations of excavation behaviour at many of the world's metalliferous caving mines. These investigations have been successful in optimising 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 drive scale that occur during undercutting and subsequent cave growth.

The behaviour of a jointed rock mass is strongly governed by the detailed micromechanics of joint slip and new fracture growth. However, consideration of all joints on the scale of an engineering problem is often prohibitive. Itasca engineers have developed a methodology called Synthetic Rock Mass Modelling (SRM) that allows for detailed consideration of the rock mass joint fabric on the scale of 10-100m. The approach can be used to derive rock mass properties such as modulus, strength and brittleness for later use in larger-scale continuum or discrete-element models.

Itasca's PFC2D/PFC3D codes are used to create an assembly of bonded particles representing a large intact rock sample. A Discrete Fracture Network is then generated which honors the joint measures derived from drilling and mapping on site (e.g. spacing, trace length, orientation). The entire network is then embedded within the bonded assembly, which is subjected to stress changes expected in the field. Joints and fractures are inserted into the PFC particle assembly using a newly developed Sliding Joint Model which allows slip and opening on planar surfaces independently of the local particle geometry.

Subjecting the SRM sample to different strain paths allows derivation of the rock mass failure envelope. Of particular interest is the ability to obtain predictions of rock mass brittleness.

Using the understanding of caved rock-flow behavior developed from PFC and from physical modeling studies, REBOP (Rapid Emulator Based on PFC3D) has been developed 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.

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

We provide services ranging from field investigations 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.

We 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 modelling to predict 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
• Numerical modelling 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 behaviour. PFC has been used to investigate the flow behaviour of broken rock once a subsidence crater has been formed at the ground surface.

Design of permanent and temporary underground excavations in hard rock, soft rock, soil and backfill is an area of extensive expertise. The time scale for design can be in 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 analytical 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 minimise the impact of stress but also to minimise the risk of creating large unstable rock wedges. Also, intersecting development (such as in the storage cavern illustrated left) 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 to ensure the safety of personnel.

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 minimise their impact.

We design ground support using techniques that combine theoretical concepts (such as the Ground Reaction Curve) with practical numerical modelling 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 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.

Our specific experience includes:

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

Barricade failure is a core geotechnical risk that is an inherent feature of any open stoping mining method that employs mine backfill. The design of backfill barricades throughout the mining industry currently relies upon simplified analytical solutions that are severely limited in their representation of geometry, material properties and the wall-barricade interface. A collaborative study has recently been completed to develop a design methodology that better represents barricade construction and the filling process. Three-dimensional numerical modelling is used to improve on analytical solutions by explicitly modelling backfill barricades.

The outcome of the study is an improved understanding of the imposed loads and failure mechanisms of backfill barricades, allowing mine operators to balance strength and safety against cost and practicality.

Itasca has conducted stability analyses for complex geometry tunnel infrastructure for road and rail tunnels by applying both the continuum code FLAC3D and discontinuum code 3DEC.

The analyses addressed various objectives such as:

• Evaluation of alternative designs with respect to excavation stability
• Influence of new tunnel infrastructure on the stability of existing near proximity tunnels
• Determining the affects of weak zones on tunnel deformations and stability
• Estimating the influence of multiple large-scale shear zones/faults on overall and local tunnel stability
• Determining the influence of local joint structure on local tunnel stability
• Determination of ground support response (shotcrete and grouted rock bolts) and its affect on stability

Innovative analysis techniques have been developed to demonstrate that the total utilisation of all rock bolts is quite low with respect to characteristic strength and strain capacities. In one case 1740 rock bolts were used with 9 bolts predicted to yield. The yielding bolts were located across a weakness zone.

Drilling can lead to formation damage and potential borehole breakouts resulting in drill string damage, borehole collapse, sand production or loss of mud.

Innovative analysis techniques have been developed to predict borehole stability for both the mining and petroleum industries.

Analysis of nearly all types of retaining structures has been conducted with the Itasca codes, including slurry-supported reinforced concrete diaphragm walls, sheet pile walls, soil-nailed walls and tieback walls. As with dams, water pressure acting within the soil mass is often a key issue. The ability to predict water pressures is an important element in understanding the behaviour of retaining structures. FLAC is used to study the flow through soil and uses the resultant pore pressures to determine effective stresses used in constitutive relations.

Recently, FLAC was used to investigate failure of the 17th Street Canal in New Orleans after Hurricane Katrina. The code was used to investigate the scenario of a gap forming along the canal side of the wall, and to study the impact of the full Katrina water level pressure acting within this gap. This mechanism is able to explain the large failure and translational displacement observed.

Itasca software is used in a variety of process engineering and materials handling applications ranging from mixing and compaction to conveying and dust production and separation.

Isolation and disposal of waste involves a combination of environmental, thermal, and time considerations that are unique in geotechnical engineering. Projects in the waste isolation field are concerned with the suitability of geologic materials for underground disposal facilities. Because storage is sometimes subject to adverse effects due to temperature and pressure in the host rock, Itasca's geomechanics expertise is particularly pertinent.

Itasca engineers and Itasca software have been used in most of the nuclear waste isolation programs in the world (almost 30), but especially in Canada, France, Germany, Spain, Sweden, Switzerland and the U.S.

The Itasca effort is led by Dr. Charles Fairhurst, who has served as Chairman of the National Academy of Sciences Waste Isolation Pilot Project (WIPP) Committee and currently serves on the Yucca Mountain Review Panel. Itasca acted as the primary geotechnical and mining consultant to the U.S. Nuclear Regulatory Commission from 1985 to 1989 in its review capacity of U.S. waste isolation activities.

Itasca pioneers the development of new methodologies and techniques to ensure safe, continuous operation of waste facilities (for instance, experimental methods of fracture characterization at waste storage sites, or new methodologies for assessing the long-term risks of flow and contaminant transport to the biosphere). Itasca codes have been documented to U.S. Nuclear Regulatory Commission standards and are currently used as a basis for design and evaluation by numerous waste isolation projects.