Block Cave Mining Research Articles

Analysis of induced stress during construction and production stages of drawbells in block caving mines

Drawbells are large constructions that allow the flow of the broken ore at the production level within the drawpoints. The results of drawbell construction are crucial for a successful mine plan extraction in a block caving mine. Analysis and integration of all the topics related to a drawbell can improve the performance of the surrounding area of drawbells, particularly the damage associated to induced stress during the different stages of a block caving operation. The improvement of operational aspects related to the drawbells would decrease the risk of failure, particularly in deep mines subject to large stresses, which are more likely to experience sudden violent or progressive failure. A large-scale numerical model was developed to analyse different mining sectors using sub-models. It was found that the geotechnical response is highly correlated to the stress field, which also controlled the resulting seismicity. In a scale of a drawbell, the drawpoint drift roof and the bridge pillar between the drawbell and the undercutting level were found the most critical zones in the design. When geological structures are present, they can be activated in the construction at an earlier stage and, therefore, could easily become critical in the resulting rock mass damage.

Geotechnical analysis of blasting sequence and resulting shapes of drawbells in block cave mines

ABSTRACT Drawbells allow disassembled ore to be extracted from the production levels in block cave mines. As part of the construction process, blast damage must be minimised, enabling the remaining rock mass surrounding the drawbell to sustain the induced stress during the different stages of a block-caving operation for a successful mine plan extraction and ore recovery.This paper proposes two approaches for the geotechnical evaluation of drawbell blast performance. Initially, the expected dynamic burden is calculated along the length of the blasthole and used to assess surveyed blast holes. Secondly, the design compliance is evaluated using the Radial Distance of Over/Underbreak concept, which compares designed and scanned shapes relative to height and radial orientation.The results have identified confined blast zones at the top and around the corners of drawbells. Excessive confinement may cause damage to the pillars and negatively impact the stability of the production level.

The effect of notches on breakdown pressure during hydraulic fracturing at various stress regimes

High stress environments are becoming more common as the trend and need to develop deeper block cave mines economically and safely continue. Hydraulic fracturing (HF) is considered to be a powerful tool in the success of hard rock block cave mines as it assists with caveability, economic recovery, and seismic risk mitigation. Therefore, determining critical design parameters such as breakdown pressure and the impact of notching on this parameter is paramount for designing and implementing a successful preconditioning campaign. To better understand the impact of notches on the breakdown and propagation pressure, a series of lab experiments were undertaken with variations in stress regime, stress magnitudes and the presence and number of notches were evaluated. This enabled us to explore the impact of confining pressure and spacing of notches on the breakdown and fracture propagation pressures. Various types of samples including Adelaide Black Granite, Engineered plastic (PMMA) were tested to give ranges and balance for homogeneity and real-world mining applications. We observed the fracture initiation and propagation through breakdown pressures along with acoustic emission measurements. The experimental results confirm that increasing confining stress on a sample increases the breakdown pressure. The works also validate the non-impact of axial stresses and the variation of tensile strength on a sample on the breakdown pressure.

Analysis of SLAM-Based Lidar Data Quality Metrics for Geotechnical Underground Monitoring

Adverse ground behavior events, such as convergence and ground falls, pose critical risks to underground mine safety and productivity. Today, monitoring of such failures is primarily conducted using legacy techniques with low spatial and temporal resolution while exposing workers to hazardous environments. This study assesses the potential of novel simultaneous localization and mapping (SLAM)-based light detection and ranging (Lidar) data quality for rapid, digital, and eventually autonomous mine-wide underground geotechnical monitoring. We derive a comprehensive suite of quality metrics based on tests in two underground mines for two state-of-the-art mobile laser scanning (MLS) systems. Our results provide evidence that SLAM-based MLS provides data of the quality required to detect geotechnically relevant changes while being significantly more efficient for large mine layouts when compared to traditional static systems. Additionally, we show that SLAM-specific processing can achieve an order of magnitude better relative accuracy relevant for change detection than quality metrics derived from traditionally deployed tests would suggest while reducing SLAM drift error by up to 90%. In collaboration with an operating block cave mine, we confirm these capabilities in field tests on a mine-wide scale and, for the first time, demonstrate methods of rockfall detection using MLS data. While more work is required to investigate optimal collection, processing, and utilization of MLS data, we demonstrate its potential to become an effective and widely applicable data source for rapid, accurate, and comprehensive geotechnical inspections.

Numerical modelling of rock mass bulking and geometric dilation using a bonded block modelling approach to assist in support design for deep mining pillars

As underground mining operations move deeper and the stresses encountered become more adverse, mine pillars are experiencing increased stress-induced damage and rock mass bulking. This has led to significant challenges in designing effective support systems, leading to costly mine development, production delays and support maintenance and rehabilitation requirements. Efforts to assess rock mass bulking have relied almost exclusively on the use of continuum modelling techniques, employing plasticity theory to predict the depth of brittle failure and associated post-yield deformations. However, rock mass bulking in high stress environments is largely driven by brittle fracturing resulting in geometric dilation, which involves shearing and buckling of spalled rock pieces as they deform into the excavation. Continuum techniques are inherently limited in their ability to model this behavior. This paper presents the results of research investigating the application of discontinuum-based numerical modelling techniques for assessing rock mass spalling and bulking in highly stressed pillars. The 3-D distinct-element program 3DEC is used to develop a bonded block modelling approach, referred to here as 3DEC-BBM. The method developed allows for the explicit modelling of brittle fracturing, spalling and geometric bulking, and the corresponding support responses, in reaction to the simulation of different mine stress paths and operation scenarios. Several different support strategies are investigated to test their effectiveness as a means to improve displacement-based support design in highly stressed pillars. These are based on the simulation of an extraction-level drawpoint pillar for a block cave mining operation that is exposed to the abutment stresses from an undercut passing over it. Based on the results, three key findings are presented and discussed: (1) Adding a small support pressure has a significant impact on the performance of the pillar. However, the benefits gained by further increasing this pressure diminish and have a less dramatic impact on spalling damage and bulking with increasing effort. (2) It is crucial to install appropriate support before the undercut passes over the extraction level pillars. The depth of damage and amount of bulking can increase significantly during pillar unloading following passing of the undercut. Extra confinement applied to the failed pillar skin allows it to carry more load and thus provide more confinement to the pillar core, helping to limit further damage and bulking. (3) The addition of support pressure through shotcrete and rock bolting performs similarly to “perfectly” installed steel sets . Thus, a heavier support system will not necessarily result in better pillar performance.

Stress modelling using cellular automata for block caving applications

In underground mining, rock mass stress is commonly modeled as a continuum. However, in block cave mining discrete modelling should be used to properly represent the stress over the extraction level in the broken column where there are high rock columns of large rock fragments. Unfortunately, we lack methods that use discrete modelling of stress in the broken column at block caving scale. In this work, we propose a vertical stress model of granular material to simulate static and dynamic flow conditions. The model is developed within a gravity flow simulator based on cellular automata to simulate the scale of the problem and flow conditions. The vertical stress model proposed is calibrated through four experimental models for the static condition. Then, based on the results from experimental testing, the dynamic condition is calibrated and compared with different flow scenarios. The results show that the proposed model can correctly simulate the vertical stresses in static conditions as well as dynamic conditions under the different flow setups tested. This vertical stress model with its flow simulator based on cellular automata has the potential to be applied at block caving scale once calibration parameters are defined.

Investigation of Gas and Airflow Distribution in a Block Cave Mine

Investigation of Gas and Airflow Distribution in a Block Cave Mine

Investigation on influential factors of bulk ore sortability based on fractal modelling

The uptake of bulk ore sorting technology is hindered by little knowledge in assessing its applicability for certain mine operation. The applicability of the bulk ore sorting technology, referred to as ‘sortability’, is a multi-folded concept and is influenced by many factors. Researchers have investigated the influence of some of the various factors, but few have done this in a holistic perspective and in a quantitative manner. In this research, nine influential factors of ore sortaibility were integrated in a mathematical framework based on fractal modelling approach. Box-Behnken design was applied and 130 block cave mine operations were hypothesized under different values of the factors. The influence of the factors on the ore sortability were investigated and factors of significant influence were identified. Results showed that ore property, sorting efficiency, metal price, processing cost and operation scale were the most significant factors in affecting the sortability for a mine operation. The research is intended to improve the understanding on the bulk ore sortability for mine productions under different conditions, and to provide a holistic perspective for applying the bulk ore sorting technology.

A hybrid extraction level layout design for block caving

ABSTRACT The most widely used production level layouts in block cave mines have been the El Teniente and Herringbone. However, these patterns face some challenges that can be improved, such as reducing LHD cycle times, improved pillar geometries for a better production level stability and enhancements in time and cost during construction. In that context, this work proposes a hybrid extraction level design for Block Caving, integrating productivity and geometry to achieve a balance based on experience and theory. A methodology is proposed to compare with El Teniente layout in terms of constructability, ground support, and main operational parameters. The results indicate that a hybrid layout offers advantages compared to the El Teniente layout based on the area and input variables analysed. Although further studies are recommended for industrial validation, the results obtained here show that the proposed layout is feasible and has the potential to be applied in block cave mining.

Physical Modeling of the Controlled Water-Flowing Fracture Development during Short-Wall Block Backfill Mining

Abstract Short-wall block backfill mining (SBBM) technology is an effective method to solve the environmental problems in the mining process. Based on the technical characteristics of SBBM technology and the physical similarity criterion, the physical similarity models for comparing the control effects of water-flowing fracture (WFF) development using short-wall block cave mining (SBCM) and SBBM were established, and the deformation and the WFF development of overlying strata above gob were monitored. The test results determined that the composite materials of 5 mm thick pearl sponge+5 mm thick sponge+10 mm thick paper+6 mm thick board were adopted as the similar backfill materials by comparing the stress-strain curves between the similar backfill materials and the original gangue sample. When the backfilling body was filled into the gob, it would be the permanent bearing body, which bore the load of the overlying strata accompanied with the protective coal pillar. At the same time, the backfilling body also filled the collapse space of overlying strata, which was equivalent to reduce the mining height, and effectively reduced the subsidence and failure height of the overlying strata. Compared with SBCM, the test results showed that the maximum vertical deformation, the height of water-flowing fractured zone, and activity range of overlying strata using SBBM were reduced by 91.4%, 82.5%, and 64.9%, respectively. SBBM had a significant control effect on strata damage and WFF development, which could realize the purpose of water resource protection in coal mines.

Comparison of normalized and non-normalized block caving comminution models

In block cave mining, rock fragmentation is a key parameter that influences the production level design and mine planning. Fragmentation occurs mainly by natural breakage during the caving process and in the draw column. The breakage that occurs within the column is known as secondary fragmentation. Secondary fragmentation has been successfully described using the block caving comminution model, which replicates the fragmentation mechanics between particles under drawn and vertical loads in a draw column. This model is based on a kinetic and population balance approach, in which non-normalized and normalized assumptions can be used depending on material and comminution system behaviour. In this paper, the non-normalized and normalized approaches are applied and compared to laboratory data to determine which assumption should be used for secondary breakage in block caving. Approaches are compared graphically, with the mean square error and the Fisher test with a false-rejection probability of 0.05. Based on a statistical analysis, the results show that the normalized model can be applied to all the rock types tested.

Mechanism of Rockburst Prevention in Deep Thick Coal Seams with Cemented Paste Backfill: A Case Study

Abstract The aim of this study is to explore a safe mining method to effectively excavate the deep thick coal seams in rockburst-prone mines. Based on the theory of elastic foundation and geological conditions of the Xinhe Coal Mine, the cemented paste backfill (CPB) is proposed to prevent rockburst. In this study, the roof fracture mechanism of block caving mining (BCM) and CPB methods are established. Then, the stress evolution of the surrounding rock and the subsidence of roof strata with these two methods are compared. The results show that the maximum bending moment appears in the middle of the roof, and the value is far below the critical bending moment of the roof by using the CBP. While using the BCM, this value exceeds the critical bending moment of the roof, which may trigger rockburst-related problems. In addition, there is no first weighting and periodic weighting phenomena by using the CPB method as the overburden pressure is gradually transferred to the backfill body, resulting in a safer mining condition. Furthermore, the engineering application indicates that the frequency of daily microseismic events and the burst energy are significantly reduced by using the CPB.

Optimisation of life-of-mine production scheduling for block-caving mines under mineral resource and material mixing uncertainty

ABSTRACT This paper presents a methodology to integrate mineral resource uncertainty from scarce orebody sampling and material mixing uncertainty due to ore flow into the life-of-mine production scheduling of block caving mines. Geological uncertainty is integrated using a Sequential Gaussian Simulation workflow and material mixing uncertainty by simulating material flow using a Cone of Movement concept. A case study is presented in which the uncertainty-based workflow is compared with a deterministic workflow. The stochastic optimisation yields a 4.97% increase in the NPV and a robust production schedule that meets production targets under both sources of uncertainty.

Investigation of airflow characteristics under parallel fan conditions in a block cave mine

ABSTRACT Block caving is an efficient underground mining method for extracting massive and low-grade ore deposits, which are too deep for traditional open-pit mining. However, in the case of orebodies with uranium mineralization, the extraction of broken rock from drawpoints will bring harmful radon gas into working areas. Airborne diesel particulate matter and dust produced from mining activities also contribute to the emissions on the production level. Maintaining relatively negative pressure in the cave by installing exhaust fans is one of the most effective approaches to mitigate gas emission concerns. The selection of proper fan systems is highly related to airflow behavior within the cave. Due to the dynamic caving process and complex cave structure, estimation of cave airflow resistance through field studies is difficult. This study developed a 1:100 scaled experimental and numerical model to investigate the effects of cave parameters (cave porosity, particle size, and undercut structure) on airflow resistance under parallel fan conditions. Results showed that cave airflow resistance increases with decreasing cave porosity and particle size; cave airflow behavior is significantly affected by undercut drift closure and the use of additional fans. This study provides valuable information to optimize ventilation system design in block cave mines.

Productivity Analysis of Raisebore RB-50X for Raise Slot Drilling at Extraction level GBC PT. Freeport Indonesia

PT Freeport Indonesia is the largest gold and copper mine in Indonesia, located in Mimika Regency, Papua Province. In its operation, PT. Freeport Indonesia applies two mining systems, namely open pit mining and underground mining. Underground Mine at PT. Freeport Indonesia consists of DOZ, Big Gosan, DMLZ, Kucing Liar, and GBC, with one of the methods applied by PT. Freeport Indonesia is a block caving method. The Grasberg Block Cave mine has entered the production stage since September 2018, but in its operation the GBC Mine is still developing its operational area to meet production targets (development). The development cycle (cycle development), which is the main operation carried out, namely drilling and blasting, loading & transporting (mucking & hauling), primary support, and secondary support. To support the main operations, it is necessary to have main support consisting of access and area, ventilation, water and water, electricity, pull of tests, surveys, and dewatering. In the blasting process at the drawbell, one free face is needed which functions as the direction of rock collapsing in the blasting process on the drawbell. Making free face or commonly known as slot raise using a rasiebore machine from PT. Redpath for slot raise drilling. Meanwhile, in the drilling stage, the slot raise has a problem that has resulted in delays in the drilling process for the RB-50X raisebore tool. The impact of the delay in making the slot raise resulted in not achieving the production target due to a delay in the blasting process, where the blasting process in the drawbell area functions to break the rock so that it falls and can be transported to the crusher to enter the rock sizing process.

A hybrid approach to predict hang-up frequency in real scale block cave mining at El Teniente mine, Chile

The in-situ ore fragmentation and probability of occurrence of hang-ups at draw points are the most significant factors on the performance of block cave mining. In this study we develop a hybrid methodology to study the uncertainty in the block geometry in the context of blockiness variable and hang-up frequency at a cave mine. This hybrid approach is based on the combination of geostatistical simulation, probabilistic discrete fracture network, geometrical and topological characterization of the fracture networks and supervised Poisson regression models. Our results and hybrid predictive models provide guidance on the systematic characterization of the fractured rock mass at a cave mine for its design, evaluation of production rates, and for risk evaluation purposes. This study can serve as a reference for the rock block geometry analysis in other related fields.

A Hybrid FEM/DEM Approach to Estimating Rock Block Breakage due to Gravity Free-Fall

An understanding of the fragmentation of rock blocks from gravity free-fall has applications to rock fall analysis as well as block cave mining. In the case of a rock fall, blocks splitting mechanics can reduce the overall block energy and therefore reduce the travel distance of the blocks. Conversely, splitting may result in a larger number of smaller fragments that may still pose a risk despite their reduced dimensions. In the case of block caving, splitting of blocks it is believed to aid the flow of the ore column, to reduce the potential of hang-ups, and to allow for easier extraction and processing of the ore. Traditional methods for block fragmentation analysis use empirical relationships and rule-based approaches that heavily rely on the block geometry, rather than block-to-block interactions. In this paper we present a study of fragmentation processes using a hybrid finite-element/discrete-element method (FEM/DEM). The approach is capable to account for the numerical instability generally associated with the simulation of high velocity surface interactions and subsequent fracturing. To date the analysis has focused on the simulation of free-falling blocks onto a fixed surface. The initial and final block breakage has been compared against parameters including the roughness and curvature of the impacted surface, and the rock block orientation in space during free fall. We believe the results could provide useful insight into designing catchments for rock fall, as well as an increased understanding of the complexities of secondary fragmentation estimates and the range of fragmentation that could be expected in block caving.

Procedure for estimating broken ore density distribution within a draw column during block caving

ABSTRACT Broken ore density (BOD) is an important parameter in planning a block cave mine. However, its assessment is complicated by the heterogeneous nature of its distribution within a draw column, varying from a denser central plug-flow zone and decreasing outwards towards outer perimeter shear bands. The BOD further decreases immediately above the drawpoint due to the development of a loosening zone that develops in response to mucking. This makes determining BOD a challenging task, hindered by the inability to measure it in situ. To address this, several key factors influencing BOD are investigated including the influence of primary and secondary fragmentation, air gap thickness, draw rate and column height. Data is used to link primary and secondary fragmentation to broken ore size distributions. From these, a conceptual framework and empirical procedures are presented for evaluating BOD within draw columns during block caving for feasibility and early stage mine planning and design.

Insight in ore grade heterogeneity and potential of bulk ore sorting application for block cave mining

A block cave mine operation was investigated in terms of ore grade heterogeneity and the potential of bulk ore sorting application. The grade heterogeneity within the caved material was measured for different draw points and mining zones, in terms of Distribution Heterogeneity and Fractal Dimension. The potential of bulk ore sorting was assessed by comparing the Net Smelter Return before and after a hypothetical bulk ore sorting system was implemented. Results showed that the potential of applying bulk ore sorting was influenced greatly by the heterogeneity within the mined material. A certain level of heterogeneity was necessary in considering the mine production as ‘sortable’. The sortability would also vary for different mining areas depending on heterogeneity level of the production. Peripheral zones of the orebody were considered with the highest level of heterogeneity and the most significant potential of bulk ore sorting application.

Simultaneous multi-sector block cave mine production scheduling considering operational uncertainties

ABSTRACT The main objective of this study is to provide a practical and near-optimal mine production schedule for block caving operations considering operational uncertainty. The problem is defined in the context of goal programming optimization to meet the operational objectives, including tonnage and grade as daily production targets. The considered operational constraints include drawpoints and ore pass design, draw rate, mine production, and transportation capacities in different operational levels, tonnage and grade constraints, and mine production targets in the presence of several mining sectors. The developed model is verified and validated using historical operational data obtained from an actual block caving operation. The practicality and flexibility of the framework are examined through three different operational scenarios and compared with the real block caving operation mine plans and historical production data.