MIGS. Mining Initiative on Ground Support Systems and Equipment. Presentation and Summary of Achievements

Transcription

1 MIGS MIGS Mining Initiative on Ground Support Systems and Equipment Presentation and Summary of Achievements

2 RTC Front cover. Rock bolt and screen covered in surface corrosion, picture taken in one of the MIGS II consortium members mine The MIGS Consortia of Nordic Rock Tech Centre AB. 2

3 MIGS Introduction Ground support has a significant impact on safety and tunnelling/development advance rates, both in mining and construction. Since 2007, the Rock Tech Centre s MIGS consortium has managed and represented the collective and non-competitive interests of the global mine operating and service industry, seeking to advance the capability of ground support and installation equipment technology through pursuing: A rationalized approach to ground support system design and testing; A standardization of equipment functionality and productivity improvements; Innovative methods of monitoring support systems and interaction with the rock mass; Increased ductility in support system capacity for deep mining applications; Exchanges of technical and operational information on ground support, equipment and related subjects. This executive report comprises a description of the MIGS program together with summaries of the achievements from the 10 completed work packages of MIGS I ( ) and a summary from 1 completed and 5 on-going work packages of MIGS II ( ). The full reports and other types of documentation from the projects are available to MIGS members. Value proposition Improvement in technology and methodology within the area of ground support is paramount to the achievement of higher productivity, lower costs and increased operational safety. Our objective is to deliver state-of-the-art and practical recommendations to common issues that are expected to improve mine safety and/or productivity. With the combined expertise and experience from multiple companies and universities, we are well- equipped to take up both daily and future challenges. The degree to which the MIGS consortium has been successful in achieving and communicating this objective may be measured by the completion of 15 Work Packages and the convening of at least the same number of technical Workshops over a total period of 7 years. As a partner, you can increase your safety and productivity by having access to all the knowledge contained in final reports, together with participation in future projects and workshops. You will also have an opportunity to influence the direction of future work undertaken by the RTC MIGS program. Mr. Johan Hedlin Program Director Dr. Graham Swan Technical Program Manager 3

4 RTC The MIGS consortia MIGS I MIGS II

5 MIGS The MIGS program - How does it work? The Mining Initiative on Ground Support Systems and Equipment (MIGS) program runs over a three year period, with a fixed cost/year/partner decided by the founders of MIGS I and later endorsed by the MIGS II membership. The fixed cost forms the basis of the MIGS program budget, and is divided among the separate work packages (projects and sub-projects) and a project management fee. Ideally, a MIGS work package is a short-term industrially focused project (sometime comprising sub-projects) of around 3-18 months, of which we normally run 2-3 in parallel. Each work package gets a designated technical project leader, who is recruited on a consultant basis from inside or outside of the consortium and who is responsible for the project s progress and reporting. The technical project leader has support in the form of a working or reference group, comprising personnel from the consortia members with a special interest in the area in question. Work packages are free to arrange workshops or similar events, as long as this is within budget. The first three work packages are normally pre-determined during the initiation of any given three year phase, and although a preliminary plan exists for the first year, it is not unusual that the consortium decides to replace some of the later project ideas or introduce new ideas due to follow-up on findings from earlier projects or new developments in other areas. This has created a flexible program that is continuously updated, including results and lessons learned from executed projects. In addition, the fixed cost per year creates a low economic risk for the program partners, knowing the exact operating cost for program membership, while it also ensures that funding is secured for follow-up projects during the duration of the program. Members of the MIGS consortium normally meet during a 1-2 day workshop two times per year, alternating between locations. We prefer to have these meetings at or near a partner s location, enabling study visits to illustrate the challenges faced in the work packages. Of course, it is possible to participate through video link or phone as well. In addition, RTC arranges monthly status report meetings that are open for all participants in the projects to call in to, to listen and discuss the progress of the different sub-projects. The board of the project the High Level Group (HLG) comprising one representative from each member company, meets by phone/video at least four times per year (two in connection with the workshop events) to review the progress of the work packages and budgets and to take any necessary decisions as whether to start new or to close old projects. RTC is responsible to record the meetings and to store these minutes, protocols, technical documentation, etc. on the RTC project database, and to make this information accessible to the MIGS members. For project partners there are several advantages with a multiple-year program, 5

6 RTC compared to running a number of single projects. For example, it creates a good basis for long-term cooperation where many development costs can be shared on a generic level, and opens the possibility to learn from each project since the results are owned by the same consortia. In addition to maintaining control over the scientific contents/outputs, the partners also have full control over the project program s budget, which is continuously updated and presented in economic reports. If you would like to know more, please don t hesitate to contact us or visit: 6

7 MIGS WP-1 Design Requirements for Ground Support Equipment The first project in 2007 that the MIGS consortium identified the need for was to provide an inventory of bolting and shotcreting equipment and operating characteristics. The work was based upon a questionnaire submitted to 20 mining companies (although with poor response), and a MIGS Consortium Workshop. Among the main findings were that the experience teaches that getting suppliers to agree on certain equipment standards can be futile since standards can become obsolete and hamper development. However, some standards do need to be agreed on, particularly in the area of health & safety and a way forward was suggested in the final report. WP-2 State-of-the-Art, Ductile Ground Support Systems & Elements Together with WP 1 in 2008, the need was identified to provide a review of ductile ground support systems and elements currently used by mines. This work package was based upon a literature study, interviews with 24 experts from 6 different countries, together with visits to 10 mines, 1 civil tunnel, 1 bolt supplier and 3 mining research institutions. From the study, some general conclusions were drawn, e.g. mines subject to high stress/deformation of brittle or soft, squeezing ground use ductile ground support with the aim to dissipate dynamic/squeezing energy within the reinforced portion of rock (Fig. 2-1). A reasonable philosophy given currently available ductile support elements is to construct a system in 3 tiers or layers: 1. surface retention tier, to prevent unravelling failure; 2. First holding tier of short ductile bolts, to retain the rock within the failure zone; 3. Second holding tier of long ductile cablebolts, to secure the reinforced failure zone to competent rock. Research and development should focus on a new philosophy of support systems as well as alternatives to de-bonded cablebolts giving greater ductility for the second holding tier application. Figure 2-1. Shotcrete lining with deformation gaps used in civil tunnels in soft rock is expensive and not practicable in hard rock mining. Besides, how does the rock know that it should fail where the deformation gaps are? 7

8 RTC WP-3 Monitoring of Ground Support Response During 2009 a state-of-the-art study of ground support response monitoring (capability and potential) for use mainly with bolts, cablebolts and shotcrete in mining was carried out. The project idea was to identify areas where a step-wise evolution of a monitoring system for ground support response seems feasible, that is robust, reliable, automatic, on-line and that can be integrated with other types of data for an overall interpretation of rock and ground support behavior (Fig. 3-1 to 3-2). In addition, work was carried out focusing on monitoring shape changes to underground openings based upon a field study conducted in one of the consortium members mines. The findings tell of a rather primitive development area where there is a general lack of objectively to measure rock mass response in general and ground support response in particular. Visual inspection of rock break-outs and ground support failure is the basic method currently being used and deformation at the periphery of mine excavations is measured, but only for selected stopes or selected sections. With the exception of micro-seismic systems, little or no systematic and meaningful continuous monitoring data is collected by mines that relate to ground support response. This needs to be addressed in some way. WP-4 Ductile Surface Support, Conceptual Design The decisive factors that must be considered in the design of ductile surface support, including both theoretical and practical aspects, were identified and described in WP 4. The following definitions were found relevant: Conceptual design is a description of design in terms of principle behavior; Surface support is rock support installed and acting on the surfaces of the openings; Ductility is the ability to absorb deformations or strains from both static and dynamic loads by maintaining a sufficient bearing capacity. The results addressed the need of two basic design loading categories: 1) normal design loads associated with rock mass conditions, tunnel geometries and static stress field, and 2) deformations associated with mining activity, together with dynamic loading associated with seismic events. It is evident that current types of rock bolts and surface support with shotcrete do not have adequate ductility or energy absorption capacity to manage severe deformation or seismic-induced dynamic loads. Due to the complex nature of the problem a more probabilistic-based approach to defining the concept of a safe design was recommended. Independently, a literature survey on ductile shotcrete was made available in a 2009 report prepared by researchers at Luleå University of Technology. As well as providing basic information on fibre-reinforced shotcrete, polymer-modified and 8

9 MIGS Figure 3-1. Example of a non-destructive test for rock bolts called the GRANIT system developed at the University of Aberdeen. Figure 3-2. Photogrammetric method being used to obtain 3D surface measurement data whose accuracy is dependent upon the accuracy of reference points used to scale the paired photographs. 9

10 RTC strain-hardening cementitous composites are also reviewed. The most important results and conclusions from this study were that a plain cement matrix has a strain capacity of c. 0.35% compared to so-called Strain Hardening Cementitous Composites (SHCC) which have been reported as achieving as much as 3.5% and because concrete is a strain-rate sensitive material, comparisons of static with dynamic flexural toughness often show significant differences. WP-5 Overview of Test Methods for Ground Support During , this WP provided an overview of past and current methods used for testing ground support elements and systems used in tunnels and drifts. A distinction was made between small-scale material specification testing and full-scale support element performance testing under different loading conditions. Among other things, it was found that, with the exception of specific shear tests, all tests on support tendons evaluate performance under uniaxial loading conditions, this despite the commonly observed fact that uniaxial support situations are the exception rather than the rule. Performance testing also needed to focus more on the interaction between grout and support tendon since this governs the load transfer mechanism between support and rock mass. In summary, this WP concluded valuable input on focusing future WPs, as using numerical modelling to determine the in situ performance of support elements. WP-6 Sprayed Shotcrete Nozzleman Training Course A 71 page training manual for certified shotcrete nozzle operators is available, with course content covering the subjects of: mix design, equipment, expected Features of a Spraymobile High standards of safety Simple operation with interactive display Operation with remote controll Practically pulsation-free conveyance Automatic adjustment of lance movement and spraying head motion Proportinal admixture dosing Formulation calculation and dosing control Auxiliary systems for cleaning and maintenance (incl. water tank) Lights for workstation illumination Figure 6-1. Mobile wet mix concrete spraying equipment specification, Part 1. 10

11 MIGS Figure 6-2. Application: Nozzleman spraying position, from the Safety & responsibilities section of the Instruction Manual (MIGS internal documentation). design performance, pre-application checks, operating procedures, surface finishing/curing and standardized testing methods (Fig. 6-1 & 6-2). WP-7 Simulation of Multi-Function Ground Support Equipment This work package was initiated to establish a basis for the proposition that a multi-functional equipment package associated with the ground support cycle will necessarily result in higher productivity and lower cost benefits. Both single and multi-heading scenarios were considered. The report dealt with the simulation of multi-function equipment for development purposes only a) using realistic production scenarios, based upon MIGS partner mines, and b) based upon a set of detailed assumptions concerning the equipment operating practices (Tab 7-1). Although cost conclusions proved hard to acquire from this theoretical simula- Table 7-1. Selected parameters used to compare the various simulations. 11

12 RTC tion study, it was concluded that multi-functional equipment fits best in a single or limited number of faces scenario and the most productive multi-functional equipment will be those that perform activities that occur strictly in sequence in the activity cycle. However, time-studies of specific machines were suggested to be the case of a future WP. WP-8 Bolt Requirements & Function The main objective for this work package was to explore the possibility of harmonizing and rationalizing the design process for bolt types & requirements across the spectrum of mines & ground conditions (Fig. 8-1): do we really need the wide variety of bolt types, lengths, plates, nuts, etc. in mining? A discussion document was prepared that provided i) a benchmarking study on design process issues, followed by ii) known effective quality assurance procedures. This then led to the development of a set of harmonized guidelines for desirable bolt support design requirements & function (Fig. 8-2), and the ensuing discussion was recorded. These discussions highlighted the fact that bolt & equipment suppliers need to know what mining companies need and the weaknesses with current ground support systems. They also suggested that the best way to proceed would be to assign a project coordinator to work directly with the consortium s mining companies and prepare a set of practical guidelines for ground support design for a) squeezing ground conditions, and b) rockbursting conditions with dynamic loads. Figure 8-1. Overview of the basic ground support design process and related considerations that are considered to be best practice guidelines for support type selection in mining. 12

13 MIGS A compilation of support design principals used by MIGS mining companies was made, showing that many factors affect the final choice of support design. WP-9 State-of-the-Art, Thin Spray-On Liners (TSLs) This work package conducted in 2011 provided a review of the past 20 years of research and development into TSLs, based upon a literature study and direct contact/experience working with various universities, suppliers and mining companies where laboratory tests and trials have been performed in Canada, Australia and South Africa. The report covered the spectrum of issues that TSL s in mining has raised, e.g. desirable TSL characteristics for different types of ground condition, health & safety given airborne isocyanates, lessons learnt from the many and various underground trials, together with an assessment of the gap between operational performance vs. standard laboratory tests. WP-10 Workshop on the Usefulness of Seismic Systems The consortium arranged a workshop on mine seismic systems their use in the monitoring and understanding of seismic hazard for the purpose of mitigating the risk of mining-induced rockbursts (Fig. 10-1). This workshop was open for the MIGS consortium partners. Contributions included presentations from invited experts with many years of experience from e.g. the Institute of Mine Seismology, and from consultants and MIGS Consortium mining companies. WP-11 Ground Support Productivity This work package investigated the bolting equipment productivity process and problems, as a follow-up on the earlier benchmarking study of WP 8. It proposed to do this by first obtaining data and time study observations that would provide answers to the following questions in relation to a specific mine operation: Type of rock condition supported? Blasted rock surface condition? Ground support element(s) & equipment used? Details of the installation process & cycle times? Equipment maintenance times? Justification of the equipment being used? Phase 1 of the project began by collecting existing process/equipment information and time-study data from mining companies, equipment suppliers, academic institutions and literature study. The study included the commonly used ground support elements and two different levels of mechanization. 13

14 RTC Figure Visit to one of the MIGS II partners mines for a WP 11 meeting and workshop in January During the mine visit, a tour was given to illustrate rock support installation, maintenance schedules & logistic requirements for the timely distribution of support elements. 14

15 MIGS Figure Suggested classification of the unit times for rock reinforcement. The second phase of the project, developed in a workshop setting, brainstormed for new ideas regarding the definition of productivity from the perspective of mine operators and equipment suppliers. In doing this, the fact that it is difficult to measure productivity in both a structured and relevant way, was being recognized. Based upon conclusions from the workshop session, a suitable model was derived that should be adopted in all future references to the process of bolting in a mine environment (Fig. 11-2). Throughout the project due consideration was given to the subject of fully mechanized versus manual bolting rigs. The argument in favor of both levels has been expressed independently yet rarely has there been an objectively posed comparison as was reported by this project. The results will be published in a scientific journal during WP-12 Ground Support Monitoring A strong recommendation from MIGS I WP-3 on Monitoring Ground Support was that future efforts should be directed at achieving a step-wise evolution of a monitoring capability that would also be robust, reliable and automatic. To this end any new work package on the subject should first target a Level 1 capability: Has the Bolt Failed? This project began with a survey of techniques currently employed by major mining companies for monitoring rock bolts, together with a short literature review on the general use of fiber-optic sensors for monitoring deformation in rock me- 15

16 RTC Table 12-1 Truth table of Bolt Status based upon observations made from the measurement of Active Bolt Length (L), Bolt Plate Load (P) and Bolt Plate Displacement (D). The status colours indicate different levels of concern: green=none; yellow=bolt likely functioning, but follow-up recommended; red=bolt likely ineffective, but follow-up necessary. chanics applications. In brief, it was found that the main focus is on axial strain and bolt integrity but that the equipment used is both expensive and complicated to install. Next, information was requested from the same mining companies on what the most wanted capability/characteristics of a bolt monitoring device would be. With the information gathered from the completed mining company surveys, a Request for Proposal (RFP) was prepared detailing the desired characteristics of a bolt monitoring device, with particular emphasis on the fact that it should be robust, cheap and practicable given mine operating conditions. Unfortunately this approach failed to find any promising solutions from known suppliers of geotechnical monitoring equipment. Finally an international organization called InnoCentive was contracted in the hope that their large crowd of solvers would find a solution to our re-drafted and highly focused challenge document. Figure D Laser Mapping s demonstration in one of the MIGS partners mines during the MIGSII spring meeting in The equipment used is shown at the left and a screenshot from one of the resulting videos on the left, not including interpretations of rock surveys. 16

17 MIGS Figure D survay of the underground loop used in the demonstration of the Dougal system and its capability to detect rock/bolt movement. After working through more than 60 idea proposals, some ingenious, it was decided that none met the must have cost and practicality criteria that are required for mining application. Finally, using an approach intended to get at the desired data via an indirect route, an underground evaluation was undertaken at LKAB s Kiruna Mine (Fig & 12-3) of the accuracy and data processing capability of the latest optical scanning technology to detect and discriminate bolt plate movements at the surface of an excavation. The company chosen to demonstrate this technology was UK-based 3D Laser Mapping. Various scanning survey parameters were explored with the objective of achieving a measuring accuracy of 2mm. Figure Left: Damage from a rockburst event observed at one of the MIGS II partners mines. Right: Underground visit of MIGS II members to one of the MIGS II partners mines during the Sudbury Workshop held in the spring of

18 RTC Figure Numerical modelling result showing predicted shock wave damage to a supported tunnel wall given a simulated rockburst event. These simulations aim to illustrate the interaction between rock support and the rock mass during a seismic event, with the objective of improving the design and selection of appropriate support elements under dynamic loading conditions. WP-13 Rockburst Case Histories: Lessons Learned from Support Damage This project was inspired by the opportunity to agree a collaborative project on a safety-related topic between the Canadian Mining Industry Research Organization s (CAMIRO) Deep Mining Research Consortium (DMRC) and the Rock Tech Centre s MIGS program. The DMRC was undertaking a case histories write-up on damaging rockburst events at Canadian mines during the period and was looking to include LKAB s Kiruna mine, making a total of 9 case histories. From this study it would be a valuable exercise, if at all possible, to extract the various Lessons Learned across the spectrum of mining methods, rock types & structures, depths and ground support systems used. It was therefore agreed between the two parties MIGS & the DMRC that at the completion of the nine Case Histories, with funding from the DMRC, MIGS II would attempt, under WP 13, to learn the lessons with an equivalent amount of spending. Under the agreement all products from both initiatives would be freely shared between the two parties, meaning that there would be no exchange of cash. The nine mines contributing to the Case History study all have experienced multiple damaging rockburst events in the recent past which have been documented using state-of-the-art (at the time) microseismic monitoring systems, together with photographs and visual observations (Fig. 13-1). A careful review of 9 DMRC Rockburst Case History documents has been made to highlight the lessons that 18

19 MIGS can be learned in general. The resulting list has been catalogued below in five categories: Ground Support, Failure Mechanisms, Mine Design Strategies, Mitigation Tactics and Global Monitoring Systems. During the course of formulating this work it was recognized that the formal rockburst reporting protocols that are being used by mining companies leave something to be desired. Accordingly a review of those being used by mining companies in Sweden, Canada and Australia to record rockburst-related groundfalls was made and reported in October The report confirmed that the type of information and level of detail contained in such reports is quite variable; detailed or forensic studies are never reported or even acknowledged in these protocols. A final phase of this work package has been the development of a new numerical modelling capability, as a means of responding objectively to the important question: in a burst-prone mine is there a preferred and unequivocal way of assessing the true scale of support system effectiveness? This has meant building into the model the capability to simulate a variety of ground support element types, together with observing the mechanics of a seismic wave passing through fractured rock and interacting with the various support elements (Fig. 13-2). Results from this important but challenging piece of work by Dr Ping Zhang of LTU were summarized in an early 2015 report. WP-14 Ground Support - State of the Art The objective with WP14 was to undertake a State-of-the-Art (SOTA) review of new, evolving ground support elements and systems that have been, or are in the process of being, implemented in the mining industry since WP2 in Each new element/system is evaluated in terms of its current stage of development and implementation by the international mining industry. Wherever possible the study includes operational data of added value, specific to the where s, why s and to what extent these are being used. Figure Containment achieved by a multi-tier ground support system comprising shotcrete, weld-wire mesh, mesh strapping, rebar and yielding D-Bolts. The final report concludes with summary tables of findings specific to reinforcement/bolt elements, surface support liners and ground support accessory elements. 19

20 RTC Figure Documented stages observed during stages in the operation of a recently installed fully mechanized bolting rig in WP15 to be compared with the results of WP11. WP-15 Mechanized Bolter, Follow-Up Study This work-package was initiated based upon some of the findings from WP-11, where the productivity of both fully- and partly-mechanized ground support equipment was studied. Results from WP-11 suggested that, comparing the two, a significant difference in overall productivity exists depending upon the level of mechanization, though questions remained due to the difficulty of comparing the data sets. This is simply because of differences in the study methods, mine applications, work procedures, etc. With this in mind a second detailed time study of a fully mechanized bolting rig was agreed to (Fig. 15-1), but under similar mine operating conditions as was undertaken under WP-11 on the partly-mechanized bolters. The study was conducted at one of the MIGS consortium mines on one of their recently installed mechanized bolter rigs. WP-16 Corrosion of Rock support Elements Corrosion is known to have a negative influence on the performance of rock support elements by weakening the structure of the support element, creating a false sense of security in underground operations. A number of techniques have been applied to mitigate the effect of corrosion, as e.g. coatings, encapsulations and usage of corrosive resistant alloys. However, coatings may be scratched and bolts may be nicked, creating flaws which will affect the metals corrosion resistance. At the same time, mines are going deeper, entering a domain with higher rock pressures together with warmer and potentially more aggressive environments with respect to corrosion of the rock support elements. WP-16 Figure Rock bolt and mesh covered with surface corrosion, a common sight in many mines. 20

21 MIGS has conducted a critical review of published literature relating to the occurrence of in-mine corrosion on ground support elements. Based upon this review, recommendations are being formulated for further work directed at obtaining a better understanding of causes, leading to a more reliable, practical set of guidelines for its detection and mitigation and onwards MIGS III At the end of 2014, the preparations began for another three year period, MIGS III, following the successful scope of the MIGS I and II programs. During these first seven years, we have collected a large project portfolio covering different types of projects pursuing the MIGS objective. The initial work packages for MIGS III will be decided upon the initiation of the program, possibly aiming to follow-up work of completed work packages or to cover new unexplored areas of importance to ground support that we think we would benefit to pursuit entirely based upon the wishes of our consortium partners. We welcome our old as well as new potential partners to these discussions and, if you would like to know more or are interested in participating in the MIGS program, please contact us for more information or visit: 21

22 RTC Notes...! 22

23 MIGS 23

24 MIGS Mining Initiative on Ground Support Systems and Equipment RTC ROCK TECH CENTRE Moving Theory into Practice