Oversize rock fragments are highly undesired in a sublevel caving (SLC) operation as they affectthe production cycle, equipment, and infrastructure. In this study, afield test was carried out inMalmberget mine to analyse the impact of oversize fragments on the production cycle and thecosts of different procedures for handling such fragments. The tests involved monitoring ofdumping oversize fragments in two orepasses, one with a grizzly and the other one withouta grizzly, using cameras. The cycle times of load-haul-dump (LHD) machines weredetermined for both orepasses. The results indicate that the grizzly increased the availabilityand productivity of the orepass despite increasing the cycle time of the LHD machines.Moreover, installation of a boulder breaker system along with the grizzly can furtherincrease the productivity and the cost of such a system will be paid offin a shorter time interms of enhanced productivity.

Rock fragmentation is vital in a sublevel caving operation. The oversize fragments are the most undesiredfragmentation category because of their challenges; as such, they require special attention. This study carried outa field test in one of the LKAB’s iron ore mines in northern Sweden to analyse the occurrence of oversizefragments. The analysis involved correlation and regression tests and was performed for different types of rockmasses. The results showed that an increase in the percentage of solid rock mass caused an increase in thepercentage of oversize fragments. The other rock types, including slightly fractured, highly fractured, and rockmass with minor and major cavities, tended to have a reduced percentage of oversize fragments. The resultsindicate that oversize fragments can be predicted using linear regression or partial least square regression modelswith R2 values of 0.78 and 0.73, respectively. 

This research was conducted to evaluate the association of rock fragmentation with different unit operations of a sublevel caving (SLC) production cycle. Drilling, charging, and blasting, as well as the nature of the rock mass, can affect the fragmentation observed at the drawpoints. Similarly, loading the blasted material from the drawpoints and dumping to the orepasses are strongly influenced by the nature of the fragmentation, particularly the oversize rock fragments.

The aim of this research was to evaluate the operational and economic impacts of different fragment sizes in a production cycle of an SLC operation. It also investigated the possibility of predicting rock fragmentation in SLC blasting based on the nature of the rock mass.

The required data for this research were collected from LKAB’s Malmberget iron ore mine. The loading operation of the blasted rock was filmed, and images of Load-Haul-Dump (LHD) buckets containing blasted rock were extracted from the video recordings. The blasted rock inside the buckets was categorized as fine, medium, coarse, and oversize fragmentation, based on the median fragment size (X 50 ). Measurement While Drilling (MWD) data were used to classify the rock mass based on the extent of rock fracturing, and statistical analysis was performed to predict the fragmentation. The results showed that the percentage occurrence of fine and medium fragmentation classes and oversize fragments have better correlations and can be better predicted using MWD data than other fragmentation types. The impact of dumping oversize fragments to orepasses with and without a screening device was evaluated. The results showed an increase in the cycle time of the LHD machines for the orepass with the screening infrastructure.

The results suggest that the drill monitoring technique has the potential to predict rock fragmentation, particularly oversize rock fragments. In addition, the variations in fragmentation during loading should be considered to allocate the best resources for handling different fragment sizes properly and improve density-based ore grade estimations. Grizzlies, along with boulder breakers, should be used to prevent oversize fragments from entering the orepasses and to increase the overall productivity of the operation.

Sublevel caving operation relies on the estimation of ore grade at drawpoints, as the mine management uses grade to decide whether the material at a certain ring should be loaded or abandoned. Grade is estimated in various ways, including visual estimation, density-based calculation, and sampling and assay methods. The grade estimation at the world’s two largest underground iron ore mines owned by LKAB in northern Sweden is based on the density difference between ore and waste. The calculations assume a constant swell factor, a theoretical fill of 100%, and a linear relationship between bucket weight and material grade. This study evaluated these assumptions in detail based on the loading data for 12,237 buckets and concluded that the method has some shortcomings which render the assumptions invalid. Further research is required to deal with these shortcomings to improve estimation of the material grade.

In Sweden, as in many other countries, the construction andinfrastructure sector are of large and growing importance for the economyand society. For instance, the construction industry’s turnover equals 11% ofthe Swedish gross domestic product (GDP) (Byggföretagen 2021), and theSwedish Transport Administration plans to invest SEK 799 billion during theperiod 2022-2033 (Regeringen 2021). At the same time, the cost ofinfrastructure projects has increased more than the consumer price index(CPI) (Trafikverket (2021)), partly due to a poorer development of theproductivity compared to other industries. An improved productivity andefficiency in the transport infrastructure and construction industry istherefore necessary. One way to increase productivity, improve theoccupational health and safety, and sustainability is through automation anddigitalization of the construction industry.The aim of the present report has been to identify ongoing initiatives andexisting research trends in construction automation with a focus on civilengineering, both nationally and internationally; and to identify potentialsand challenges that exist for the development of construction automation.Furthermore, the prerequisites for the implementation of automation in theconstruction industry have been studied. The research questions were studiedthrough a literature study and two thematic days on the subject.The results from the literature study shows that a clear increasing trendexists, both nationally and internationally, in automation, digitization androbotisation in the construction industry. The same trend can also be seen incivil engineering for roads, bridges, tunnels, as well as in the mining industry.With the mining industry as a role model, construction companies,universities, suppliers and clients together with small and medium-sizedenterprises (SMEs) should come together to develop a common vision and astrategic roadmap to enforce automation and digitization of the constructionindustry. A development of both technical, organizational and financialstructures is required, where an attractive business ecosystem can bedeveloped, enabling the upscaling of construction automation.Interdisciplinary collaborations, test-beds at an early stage, competencedevelopment, new financing infrastructure and a common vision are crucialto create conditions for construction automation.

Fragmentation analysis is an essential part of the optimization process in any mining operation. The costs of loading, hauling, and crushing the rock are strongly influenced by the size distribution of the blasted rock. Several direct and indirect methods are used to analyse or predict fragmentation, but none is entirely applicable to fragmentation assessment in sublevel caving mines, mainly because of the limitations imposed by the underground environment and the lack of all the required data to adequately describe the rock mass. Over the past few years, measurement while drilling (MWD) data has emerged as a potential tool to provide more information about the in-situ rock mass. This research investigated if MWD can be used to predict rock fragmentation in sublevel caving. The MWD data obtained from a sublevel caving mine in northern Sweden were used to find the relationship between rock fragmentation and the nature of the rock mass. The loading operation of the mine was filmed for more than 12 months to capture images of loaded load-haul-dump (LHD) buckets. The blasted material in those buckets was classified into four categories based on the median particle size (X₅₀). The results showed a strongercorrelation for fine and medium fragmented material with rock type (MWD data) than coarser material. The paper presents a model for prediction of fragmentation, which concludes that it is possible to use MWD data for fragmentation predict ion.

Ground vibrations from blasting are one of the main challenges faced by mines located near populated areas. To confront this challenge, Luossavaara-Kiirunavaara Aktiebolag’s Malmberget underground iron ore mine in Sweden tested a change in blast design. Specifically, it tested production holes with smaller diameter to decrease the explosive detonated per delay and thereby lower the ground vibrations. However, smaller holes normally increase hole deviation and may also influence the chargeability of the holes, both of which have a negative effect on fragmentation. Therefore, a detailed evaluation was required before a final decision could be made. To evaluate the fragmentation, field tests were carried out in two drifts of an ore body in the mine. Cameras were mounted in both drifts to record the fragmentation in every loaded bucket. The recording was configured to start by a motion detection parameter; consequently, every movement underneath the cameras was captured. The recording process continued for over a year and resulted in more than 15,000 videos. To analyse such an enormous data for fragmentation, an internally developed quick rating system (QRS) was used to evaluate a total of 7,258 loaded buckets. Blasted rock in the load–haul–dump buckets was classified as fine, medium, coarse, or oversize based on the median fragment size (X50). This paper explains the experimental setup of the test and the analysis procedures. The test results showed that smaller diameter boreholes tend to reduce the median fragment size slightly, and therefore favour the reduction of borehole diameter to deal with the ground vibration problem. The influence of borehole deviation and chargeability was not specifically investigated in this test and need further research to better understand subsequent fragmentation variations.

Variations in rock fragmentation are very likely to occur in a sublevel-caving operation. This study conducted a comprehensive test in an iron ore mine to monitor rock fragmentation. The results show a clear trend in fragmentation variations from start to end of production from a ring. These variations suggest an increase in coarse and oversized fragments with increasing material extraction from the rings that can be linked to increased overburden and drill hole deviations in the upper part of the rings. These problems can be addressed by shortening the drill hole length or directional drilling but need further investigations.

Geologists, mine planners, geotechnical, and mining engineers always strive for maximum information to get a better insight of the rock mass before interacting with it. Over the recent decades, close-range terrestrial digital photogrammetry (CRTDP) has been increasingly used for data acquisition and to support the conventional methods for rock mass characterization. It provides a safe, time-saving and contact-free way to gather enough data to minimize user dependent biases. However, it requires an expensive camera, fieldwork and some software to extract the information from images. In addition, it can over-estimate the rock fracturing sometimes due to weathering of the rock face or poor blasting practices. Measurement while drilling (MWD) data include the responses of different drilling parameters to the variations in the rock mass. MWD data are produced in large quantity, as they come from every hole drilled. These data correspond to the inside variations of rock rather than the surface ones counted in photogrammetry.

In this paper, structural data are obtained from different bench faces of an open pit mine using a commercial software package, ShapeMetriX3D (by 3GSM). These data are compared to the MWD data of the boreholes that were blasted to produce these bench faces to establish certain relationships between drilling parameters and rock mass structures. Half casts of the boreholes with MWD data were visible on the bench faces of the pre-split wall that allowed a better correlation. The results show abrupt changes in MWD parameters for open joints or cavities with some infilling material and overall increases or decreases in parameters for closely spaced bedding planes, fractures or foliations. The results are promising and suggest the method can be used to characterize the rock mass, modify the charging of explosives in blasting operations and facilitate the geological modeling of the rock mass.

This research is carried out to better understand the nature of the rock mass and to have a better anticipation of rock fragmentation before blasting the rock mass. Current practices of assessing rock mass usually involve techniques that focus on the surface or outcrop of the rock mass such as scanline surveys, window surveys, photogrammetry and laser scanning etc. These techniques generally lack the ability of providing sufficient information about the rock mass as well as bear various inherent constraints such as safety issues, time requirements, user biasness, equipment requirements and reproducibility of results. Similarly, the rock fragmentation is predicted using different mathematical equations known as fragmentation models. However, these models ignore some key factors that significantly affect the nature of fragmentation such as chargeability of blastholes, drilling information e.g. borehole deviation and require numerous rock parameters which are not well known in most cases. These models are often site-specific and are mostly developed for surface mines. Therefore, their application in underground mining is not so common.

The aim of this research is to investigate the possibility of eliminating the constraints and supporting the current practices of rock mass assessment and rock fragmentation prediction. In this regard, drill monitoring technique has been selected as a potential tool for analysing the rock mass and forecast the rock fragmentation.

To test the selected technique, measurement while drilling (MWD) data was collected from three different mines. The variations in MWD data were analysed to identify different zones and structures present inside the rock mass. The results were compared to 3D images obtained by close-range terrestrial digital photogrammetry for validation, which showed a close agreement with each other. Similarly, MWD data was used to classify the rock mass into five different classes i.e. solid, slightly fractured, highly fractured, having cavities, and major cavities in a sublevel caving operation. The loading operation of the blasted rock was filmed and digital images of LHD buckets containing blasted rock were extracted from the video recordings. The blasted rock inside the buckets were categorized as fine, medium, coarse and oversize fragmentation based on their median fragment size (X₅₀). A statistical analysis was carried out to see the correlation between MWD based rock mass classes and fragmentation classes. The results showed that fine and medium size fragmentation has better correlation and can be predicted with higher accuracy using MWD data as compared to coarse and oversize fragmentation.

The results suggest that the drill monitoring technique has the potential to assess rock mass as well as predict rock fragmentation to some extent. It can be used to differentiate between a weak or strong rock mass or between a fractured or competent rock mass. It can be used to differentiate between joints, cavities or foliations etc. It can also be used to predict finer and medium size fractions of the blasted rock with reasonable accuracy. However, the coarser and oversize fragmentation didn’t have a reliable correlation with MWD data. The potential of using drill monitoring technique for rock mass assessment and rock fragment prediction can be further explored and validated using other established rock mass and fragmentation assessment techniques. It can largely overcome the time, cost and safety constraints associated with the methods already in practice.