Ground Support Design Research Articles

Probabilistic Approach for Q-based Ground Support Design

For tunnel, cavern, and shaft design, the inherent variability in a given rock mass domain makes accurately estimating rock mass quality and support requirements difficult. To capture the variability in rock mass properties when using the Q system, a methodology incorporating a statistical analysis of measured Q input parameters and Monte Carlo Simulation was developed to perform a probabilistic ground support design approach. Probability and cumulative density function curves were then developed using the mathematical program MATLAB to guide in estimating ground support based on all potential rock mass conditions. To illustrate the proposed approach, two hypothetical tunnels were designed based on real data from two previous projects. Finite Element Modelling was used to evaluate the suggested Q rock support performance in a range of rock conditions for one of the hypothetical excavations to validate the proposed approach. This method demonstrated that associating a range of potential ground conditions instead of a single deterministic value for each input parameter can provide a quantifiable measurement of uncertainty within a given rock mass domain. Additionally, the approach provides insight into the design criteria for ground support in underground excavations to potentially reduce overly conservative and costly recommendations.

Elastic–plastic criterion solution of deep roadway surrounding rock based on intermediate principal stress and Drucker–Prager criterion

AbstractExcavation‐induced rock failure and deformation near an underground opening boundary is closely associated with the intermediate principal stress, strain softening and rock mass dilation. By combining theoretical analysis and numerical simulation to explore the mechanical evolution of the roadway surrounding rock during excavation. The elastic–plastic criterion solutions for surrounding rock stress, displacement, and the plastic zone of a circular roadway were deduced by including the intermediate principal stress, strain softening and rock mass dilation, based on the Drucker–Prager criterion and the nonassociated flow rule. Furthermore, ABAQUS finite element software was utilized for numerical simulations to scrutinize the influence of mechanical parameters on stress redistribution, surface displacement, and plastic range. The results of the numerical simulations verify the reliability of the theoretical analysis and affirm the high consistency of the results with the theoretical solution. The research findings indicate that the strength of surrounding rock is significantly influenced by the intermediate principal stress, and the deformation and failure of rock mass are primarily impacted by rock mass dilation, while strain softening mainly affects the thickness of the fractured zone. Moreover, the study reveals that enhancing the residual strength of the surrounding rock can improve its resistance to deformation and failure. Furthermore, the excavation of the roadway is observed to increase the original rock stress in the surrounding rock, but increasing the ground support strength effectively controls the deformation and failure of surrounding rock. Ultimately, the research outcomes offer valuable references for engineering calculations and ground support design of surrounding rock in deep roadways.

Numerical and Analytical Determination of Rockburst Characteristics: Case Study from Polish Deep Copper Mine

A simplified analytical method useful for ductile ground support design in underground mine workings is presented. This approach allows for maintaining the stability of sidewalls in rectangular openings extracted in competent and homogeneous rocks, especially in high-pressure conditions, favoring rockburst event occurrence. The proposed design procedure involves the typical assumptions governing the limit equilibrium method (LEM) with respect to a triangular rock block expelled from a sidewall of a long mine excavation subjected to normal stresses of the values determined based on the Maugis’s analytical solution concerned with stress distribution around the elliptical opening extracted within the homogeneous infinite elastic space. This stage of the local assessment of rock susceptibility to ejection from the walls of the excavation allowed for determining the geometry of the block whose ejection is most likely in a given geological and mining situation. Having extensive information about the geometry of the excavations and the properties of the surrounding rocks, it was possible to make an exemplary map of the risk from rockburst hazard, developed as the 2D contours of safety indexes’ values, for special-purpose excavations such as heavy machinery chambers, main excavations, etc. in conditions of selected mining panel of the deep copper mine at Legnica-Głogów Copper Basin, Poland. Another important element of the obtained results is the calculated values of the horizontal forces potentially pushing out the predetermined rock blocks. These forces are the surplus over the potential of frictional resistance and cohesion on the surfaces of previously identified discontinuities or on new cracks appearing as a result of overloading of the sidewalls. Finally, the presented algorithm allows us to perform quantitative tracking of rockburst phenomena as a function of time by determination of acceleration, velocity, and displacement of expelled rocks. Such information may be useful at the stage of designing the support for underground workings.

Geological Strength Index Relationships with the Q-System and Q-Slope

The Q-system and Q-slope are empirical methods developed for classifying and assessing rock masses for tunneling, underground mining, and rock slope engineering. Both methods have been used extensively to guide appropriate ground support design for underground excavations and stable angles for rock slopes. Using datasets obtained from igneous, sedimentary, and metamorphic rock slopes from various regions worldwide, this research investigates different relationships between the geological strength index (GSI) and the Q-system and Q-slope. It also presents relationships between chart-derived GSI with GSI estimations from RMR89 and Q’ during drill core logging or traverse mapping. Statistical analysis was used to assess the reliability of the suggested correlations to determine the validity of the produced equations. The research demonstrated that the proposed equations provide appropriate values for the root mean squared error value (RMSE), the mean absolute percentage error (MAPE), the mean absolute error (MAE), and the coefficient of determination (R-squared). These relationships provide appropriate regression coefficients, and it was identified that correlations were stronger when considering metamorphic rocks rather than other rocks. Moreover, considering all rock types together, achieved correlations are remarkable.

A new adaptive compressible element for tunnel lining support in squeezing rock masses

The so-called “Non-Deformable Support System” and “Yielding Support System” have been used in tunnel ground support designs in squeezing rock conditions. According to the convergence confinement method, it serves as a pivotal role to use yielding elements in the primary support for expressway tunnels in squeezing rocks. The elements of yielding support are able to convert the radial displacement into circumferential tangential closure without affecting the support capacity of the lining system, which prevents from damage in the primary lining composed of mesh, steel arch and shotcrete. This paper introduces a new adaptive compressible element that significantly improve the deformability of support lining in squeezing rock. The new compressible element features by its straightforward mechanistic principle, compact design form and convenient construction and installation. The load–displacement curves of the compressible element were obtained by laboratory compression tests. Field tests were carried out in Qinghe tunnel of Zhaolu Expressway in Yunnan Province, China. The settlements of the tunnel in three sections, the contact pressure between the surrounding rock and the ground support and the stress in steel arches were monitored during the excavation of the tunnel. Based on the monitoring data, it is concluded that when two symmetrical and longitudinal compressible elements are installed in the lining, the support pressure required at the equilibrium is greatly reduced, and the support pressure at the rock support contact is more evenly distributed. The construction measures of the compressible elements were elaborated through the field application. Finally, the advantages and suggestions for the improvement of the compressible element were summarized.

Probabilistic Approach for Q-Based Ground Support Design

Probabilistic Approach for Q-Based Ground Support Design

Assessing the conditions at the boundary of excavations in bedded or foliated rocks

Routine ground support design requires a rapid analysis tool to allow sensitivity studies on the impact of variations in the nature of bedded or foliated rock masses. A heuristic technique based on the adoption of an equivalent transversely isotropic continuum has been developed that includes a shear modulus that reflects the spacing of bedding partings or foliations . This results in the prediction of much higher stresses around an excavation when compared to an isotropic assumption. A unique relationship between a continuum shear modulus and spacing is not possible because the shear stiffness of bedding partings or foliations increases with increasing vertical stress. The heuristic can be applied to sectors of an excavation where the boundary is sub-parallel to the partings being considered. By adopting an anisotropic stress model, rock mass failure can be modelled using an isotropic brittle strength model. A re-examination of published data on overbreak in jointed quartzites and a moderately foliated rock mass at high depths collaborates the use of the technique. The heuristic technique produces similar failure zones to those predicted using an isotropic stress/ubiquitous joint approach. • Adopting transverse isotropy significantly increases the estimated stress changes near the excavation boundary compared to an isotropic assumption. • Combining a transversely isotropic material model with brittle rock failure concepts results in a useable heuristic for analysing excavation in bedded rock. • A shear stiffness of 3 GPa/m has been adopted for bedding partings or foliations under low normal stress. • Simple elastic anisotropic stress models can be used, but implementation requires the use of design sectors for different excavation faces.

Utilising the scientific method to demonstrate that slender beam/column behaviour is the dominant behavioural mechanism leading to roof/rib failure

As per most other earth science engineering problems, the underground coal geotechnical environment and the way in which roof and rib support interacts with the rock mass are complex issues. It is therefore generally recognised that without prudent simplification, the complexity of the problem will overwhelm all current geotechnical methods of modelling, not least for the reason that a rock mass can never be characterised to a level that allows a “non-simplified” analysis. The fact that numerical models, which are commonly purported to be a “simulation” tool and the so-called epitome of advanced geotechnical engineering, always need to be “calibrated” to a known reality is taken to be conclusive proof of this statement. While the problem should not be oversimplified (i.e. the dominant failure mechanisms or critical data input parameters should not be ignored), without question judicious simplification is at the heart of all engineering design, to the point that it has a well-established name – “reductionism”. The hypothesis addressed in this paper, is that horizontal and vertical stress-driven slender beam and column behaviour (which includes unstable Euler Buckling) are respectively the dominant (but not only) roadway roof and ribline behavioural mechanism that (if not controlled) can lead to excessive deformation, failure and eventual collapse. As a part of the Scientific Method, a hypothesis can only be tested via real-world observations, measurements and analyses in establishing it is a credible Theory. Utilising the Scientific Method, this paper demonstrates that slender beam/column behaviour is the dominant instability mechanism within a coal mine roof/rib subject to elevated horizontal/vertical stress conditions and therefore, must be representatively accounted for in any credible empirical, analytical, or numerical approach to coal mine roof/rib stability assessment and associated ground support design.

Re-analysis of Abutment Angle Method for Moderate and Deep Cover Retreat Room and Pillar Mines and Investigation of Loading Mechanics Using Finite Volume Modeling

Mining-induced stresses in underground coal mines play a significant role in pillar and ground support design, hence in the safety of mining operations. In the US, Analysis of Longwall Pillar Stability (ALPS) and in Australia, Analysis of Longwall Tailgate Serviceability (ALTS) software are used for designing Longwall coal mine layouts; and in the US, Analysis of Retreat Mining Pillar Stability (ARMPS) software is used to design retreat room-and-pillar mine layouts. All these software determine the adequacy of the design by comparing the estimated loads to the load-bearing capacity of the pillars and they use the “abutment angle” concept and a square decay stress distribution function to calculate the magnitude and distribution of the mining-induced loads. The abutment angle concept has been successfully applied to US longwall coal mines with the use of ALPS and ALTS in Australia. ARMPS uses the same concept for retreat room and pillar coal mine design in the US. The suggested abutment angle for coal mines in the US was derived as 21° by the back analysis of underground stress measurements from the 1990s and implemented in ALPS and ARMPS. The ALPS methodology was re-examined and calibrated for Australian conditions with additional Australian stress measurements and resulted in the original ALTS methodology which has been continually improved and expanded with additional cases. In this paper, some recent stress measurements are back-analyzed, and the abutment angles are investigated to verify the applicability of using 21° in retreat room and pillar mines with different depths and mining dimensions. For shallow mines, the derivation of the 21° abutment angle is supported by the new case histories. However, at depths greater than 200 m, the abutment angle was found to be decreasing with increasing depth. In this study, a new equation for the calculation of abutment angle for moderate and deep cover cases was constructed and tested for its applicability in retreat room and pillar mines. The differences in the mechanism of complete side abutment loads in shallow and deep cover mines are further analyzed by applying the finite volume modeling (FVM) approach to two case study mines, one shallow, and one deep cover. A 2D model of each mine is created and one-side and two-side abutment loads of consecutive panels are analyzed. Analysis of the deep cover mine indicated that the prior panel gobs provide a considerable amount of support to the overburden strata. These higher gob loads prevent a higher percentage of overburden loads from being transferred to the active panel workings, and this is in agreement with the lower abutment angles observed for deep cover mines. The findings of this study should only be used for retreat room-and-pillar mines’ production pillar loads since these are calculated geometrically using the abutment angle concept.

Ground Support Design of Underground Openings in Seismically Active Mine: A Case Study from a Lead and Zinc Underground Mine

Ground control is multi-tasking and continuous process for the stability of underground openings. Balya underground lead and zinc mine is an important case study area due to its deepest working condition and the highest production amount among Turkish underground metalliferous mines. Mining-induced seismicity needs to be investigated especially for deep as well as tectonically active mine sites. Increasing depth will increase the stress around an underground opening that is a key factor of rock-burst hazard. Rock burst potential can be estimated from analytical approaches based on the relation between rock mass strength and stress around openings; however, one of the best way is to monitor the mining-induced seismicity. The support system is designed based on the actual geotechnical conditions determined from the excavated working face prior to support applications in the mine. Empirical methods are then used to make a decision about the support system. If the location is designated as a seismically active region based on micro-seismic event results, support components are selected as a dynamic support system that must absorb the energy released from the surrounding rock masses. The purpose of this study is to investigate seismically active locations according to mining-induced seismicity and the support system design principles for that locations to protect the openings against seismic loads.

Understanding the Impact of Test Configuration on Welded-Wire Mesh Laboratory Test Results

Underground mines use a combination of rock reinforcement and surface support elements to maintain the structural integrity of excavations in rock. The design of an effective ground support system requires an understanding of the mechanical behaviour of individual ground support components and how they interact under load. This paper reviews the mechanical behaviour of welded wire steel mesh routinely used in underground mines. It further reviews the advantages and limitations of using testing rigs used to quantify the performance of mesh. In particular, it illustrates the impact of rig configuration and testing parameters on mesh performance. The main focus of this work is the development and calibration of 3D discrete element method of numerical models capable of reproducing mesh behaviour under specific testing configurations. The developed models successfully reproduced the load redistribution on the mesh wires, the load–displacement response, and failure mechanisms observed in laboratory tests. The calibrated models were subsequently used to determine the impact of testing rig configurations, including loading plate dimensions and orientation, and mesh dimensions on the performance of mesh under load. This work has significant practical implications on how to interpret results obtained from different testing rigs. Furthermore, the results of this work can provide guidance towards designing new testing rig configurations as well as demonstrating the need for the development of testing methods and procedures. Finally, it illustrates the challenges that have to be overcome if the explicit modelling of mesh will be a reliable part of the ground support design process.

Fundamentals of modern ground control management in Australian underground coal mines

Underground coal mining is inherently hazardous, with uncontrolled ground failure regarded as one of only several critical risks for multiple fatality events. Development, implementation and management of overarching systems and procedures for maintaining strata control is an important step to mitigating the impact of ground failure hazards at a mine site operational level. This paper summarised the typical pro-active ground control management system (PGCMS) implemented in various Australian underground coal mines. Australia produces approximately 100 million tonnes a year of metallurgical and thermal coal from approximately 30 of the world’s safest longwall mines operating in New South Wales and Queensland. The increased longwall productivity required to achieve both high levels of safety and profitability, places significant emphasis on the reliability of pro-active ground control management for longwall mining operations. Increased depths, adverse geological conditions, elevated variable stress regimes and weaker ground conditions, coupled with an industry wide need for increased development rates continue to make ground control management challenging. Ground control management is not only about ground support and pillar design though but also a structured process that requires a coordinated effort from all levels of the workforce to both minimise the occurrence of adverse geotechnical events and mitigate the potential risks when they do occur. The PGCMS presented in this paper is proven to provide both a safer and more productive mine environment through minimisation of unplanned delays. The critical elements of the method are presented in detail and demonstrate the utility and value of a ground control management system that has potential for implementation in underground coal mining globally.

Identifying and mapping potentially adverse discontinuities in underground excavations using thermal and multispectral UAV imagery

Geotechnical mapping, rock mass characterization, and inspections of underground excavations are critical to ensuring that excavation geometry and ground support design are appropriate for stable conditions. A lack of access, poor timing, or hazardous conditions are all factors that can prohibit engineering personnel from collecting high-quality data in the field. Advances in unmanned aerial vehicles (UAV) and portable sensor technology now allow engineering personnel to remotely capture data from underground workings that can be used for developing designs, generating inputs for analyses, and making more informed decisions. Ground falls are a source of many accidents in the underground environment, and they are the focus of many geotechnical investigations and analyses. In this study, the authors investigated how portable UAV-mounted thermal and multispectral imagers could be used to detect and quantify adverse geological discontinuities in hard rock masses that are structurally controlled. Multiple thermal, multispectral, RGB (red, green, and blue), and LiDAR (light detection and ranging) data sets were captured from 5 flights in sub-level open stopes at the Barrick Golden Sunlight Mine in the state of Montana in the western United States of America. Using off-the-shelf software, the thermal, RGB, and multispectral images were processed to create individual three-dimensional point clouds and meshes, which were georeferenced using the LiDAR data. Discontinuities identified in the three-dimensional point clouds and meshes were mapped using tools found in the freeware CloudCompare. One of the thermal models identified wedges that had developed in the crown pillar of an open stope, and 4 of the multispectral models contained enough detail for mapping individual discontinuities. The results of this investigation indicate that these portable imagers are viable tools that can be used to aid engineering personnel in identifying and mapping adverse geological discontinuities and unique rock mass composition. The techniques for capturing, processing, and interpreting thermal and multispectral imagery captured in underground excavations are described in this paper and can be used as the basis for future investigations at individual underground sites.

Statistical Analysis of the Capabilities of Various Pattern Recognition Algorithms for Fracture Detection Based on Monitoring Drilling Parameters

Ground conditions, including characteristics of fractures, joints, bed separations, and strengths of rock layers, are critical factors for proper design of openings in underground mining and construction projects. Correct understanding of geologic conditions allows for improvement and optimization of ground support design and minimizing incidents of ground failure and instabilities in underground workings. Rock bolts have been widely accepted as the preferred method of ground support in almost all forms of rock excavation applications. The concept of monitoring drilling data to evaluate characteristics of geological features of interest in the rock surrounding the underground opening is a very attractive option for developing the geological model of the ground on real-time basis. This includes information on distributions of joints and bed separations, locations of voids, and strengths of rock layers, which enables the automated and rapid evaluation of ground conditions while drilling is in progress. Several smart drilling systems have been developed and proposed to detect joints; however, they offer limited capabilities and have exhibited difficulties in identifying joints with small apertures. The current study was focused on developing a more sensitive method to locate joints with smaller apertures along the hole being drilled with an instrumented roof bolter. A series of full-scale drilling tests were carried out in samples which contained simulated joints with different inclined angles in controlled laboratory conditions. New joint detection programs, with improved capabilities based on various pattern recognition algorithms, have been developed and used for analysis of data recorded in the full-scale drilling tests. To precisely locate joints, composite parameter was also used to offer more accurate detection. This paper reviews the laboratory testing program, data analysis, logic/algorithms used in the programs, statistical analysis of the detection results, and comparison of the various algorithms for this application.

Automated Core Logging Technology for Geotechnical Assessment: A Study on Core from the Cadia East Porphyry Deposit

Abstract The Cadia East porphyry deposit, located approximately 20 km south of Orange, New South Wales, Australia, contains a significant resource of copper and gold. This resource is hosted within the Forest Reefs Volcanics and is spatially and temporally associated with the Cadia Intrusive Complex. To extract ore, the underground mine currently uses the block cave mining method. The Cadia East geotechnical model provides data inputs into a range of numerical and empirical analysis methods that make up the foundation for mine design. These data provide input into the construction of stress models, caveability models, ground support design, and fragmentation analysis. This geotechnical model encompasses two commonly used rock classification systems that quantify ground conditions: (1) rock mass rating (RMR) and (2) rock tunneling quality index (Q index). The RMR and Q index are calculated from estimates of rock quality designation (RQD), number of fracture sets, fracture roughness, fracture alteration, and fracture spacing. Geologists and geotechnical engineers collect information used to produce these estimates by manually logging sections of drill core, a time-consuming task that can result in inconsistent data. Modern automated core scanning technologies offer opportunities to rapidly collect data from larger samples of drill core. These automated core logging systems generate large volumes of spatially and spectrally consistent data, including a model of the drill core surface from a laser profiling system. Core surface models are used to extract detailed measurements of fracture location, orientation, and roughness from oriented drill core. These data are combined with other morphological and mineralogical outputs from automated hyperspectral core logging systems to estimate RMR and the Q index systematically over contiguous drill core intervals. The goal of this study was to develop a proof-of-concept methodology that extracts geotechnical index parameters from hyperspectral and laser topographic data collected from oriented drill core. Hyperspectral data from the Cadia East mine were used in this case study to assess the methods. The results show that both morphological and mineralogical parameters that contribute to the RMR and Q index can be extracted from the automated core logging data. This approach provides an opportunity to capture consistent geologic, mineralogical, and geotechnical data at a scale that is too time-consuming to achieve via manual data collection.

Ground behaviour analysis, support system design and construction strategies in deep hard rock mining – Justified in Western Australian's mines

Development of deep underground mining projects is crucial for optimum extraction of mineral deposits. The main challenges at great depth are high rock stress levels, seismic events, large-scale deformation, sudden failures and high temperatures that may cause abrupt and unpredictable instability and collapse over a large scale. In this paper, a ground control and management strategy was presented corresponding to the three stages of projects: strategic design, tactical design and operational design. Strategic design is results in preparing a broad plan and primary design for mining excavations. The tactical design is to provide detail design such as stabilisation methods. Operational design stage is related to monitoring and updating design parameters. The most effective ground control strategies in this stage are maintenance, rehabilitation, monitoring and contingency plan. Additionally, a new procedure for design of ground support systems for deep and hard rock was proposed. The main principles are: static and/or dynamic loading types, determination of loading sources, characterisation of geological conditions and the effects of orientation of major structures with openings, estimation of ground loading factor, identification of potential primary and secondary failures, utilisation of appropriate design analysis methods, estimation of depth failure, calculation of the static and/or dynamic demand ground support capacity, and selection of surface and reinforcement elements. Gravitational force is the dominant loading force in low-level stresses. In high stress level, failure mechanism becomes more complex in rock mass structures. In this condition, a variety of factors such as release of stored energy due to seismic events, stress concentration, and major structures influence on ground behaviour and judgement are very complicated. The key rock engineering schemes to minimise the risk of failures in high-stress levels at great depth involve depressurisation and quality control of materials. Microseismic and blast monitoring throughout the mining operations are required to control sudden failures. Proper excavation sequences in underground stopes based on top-down, bottom-up, centre-out and abutment-centre were discussed. Also, the performance of a ground support system was examined by field observation monitoring systems for controlling and modifying ground support elements. The important outcome of the research is that the proposed procedure of selecting ground support systems for static and dynamic situations was applied in several deep underground mines in Western Australia. Ground behaviour modes and failure mechanism were identified and assessed. Ground demand for static and dynamic conditions was estimated and an appropriate ground support system was selected and evaluated in site-specific conditions according to proposed method for ground support design at great depth. The stability of rock masses was confirmed, and the reliability of the design methodology for great depth and hard rock conditions was also justified.

Application of rock mass classification systems for performance estimation of rock TBMs using regression tree and artificial intelligence algorithms

Existing rock mass classification systems, such as Rock Quality Index “Q”, Geological Strength Index (GSI), and Rock Mass Rating (RMR) are often used in many empirical design practices in rock engineering contrasting with their original application. For example, these models which were originally introduced for ground support design are being used in estimation of TBM performance in various ground conditions. Previous use of standard rock mass classification systems in TBM performance prediction has had limited success due to the nature of the weights associated with the input parameters as evidenced by low correlations between their output and Penetration Rate (PR) of TBM in various field applications. This limitation can be mitigated by revising the weights assigned to input parameters, to better represent influence of rock mass properties on TBM performance using multivariate regression analysis and artificial intelligence algorithms, including regression tree and genetic programming. This paper offers a brief review of the applications of common rock mass classification systems for performance prediction of TBMs and development of a new model which is based on the input parameters of RMR system for this purpose. The proposed model has been developed based on the analysis of a comprehensive database of TBM performance in various rock types and offers higher accuracy and sensitivity to rock mass parameters in predicting machine performance.

Brittle overbreak prediction in deep excavations for hydrothermally altered and heterogeneous rockmasses

In massive rockmasses under high in situ and deviatoric stresses, brittle spalling is the dominant damage process and failure mode and can result in significant depths of overbreak outside the excavation design dimensions during and after construction. Significant work has been done by researchers to develop empirical and mechanistic prediction tools for brittle overbreak in homogeneous rockmasses. Brittle overbreak in heterogeneous rockmasses that contain hydrothermal veins and breccia can behave quite differently than homogeneous rockmasses, with the result that the existing tools for homogeneous rocks are inadequate. In this study, overbreak profiles and excavation observations from part of the undercut level in the New Mine Level project at the El Teniente copper–porphyry mine in Chile and intact laboratory test data from the four local rockmass units are used to develop new functions based on brittle rock mechanics to improve the prediction of the depth of brittle overbreak for similar excavations in heterogeneous rockmasses. The dacite porphyry unit, which has few stockwork veins, most closely resembles the expected homogeneous brittle overbreak development. The stockwork mafic complex unit exhibits overbreak that exceeds the homogeneous prediction because the planar, pervasive quartz veins act as crack attractors and develop maximum crack propagation after initiation and immediate strength loss. The anhydrite breccia unit and a brecciated contact zone contain large clasts of contrasting mineralogy that act as crack arresters, resulting in minimal overbreak. The proposed functions to predict depths of brittle overbreak around tunnels in these heterogeneous rocks can ultimately be used to aid in excavation and ground support design.

Ground support design for dynamic loading conditions: A quantitative data-driven approach based on rockburst case studies

Abstract There are considerable challenges associated with the design of ground support for seismically-active underground mines. It is extremely difficult to establish the demand on ground support as well as the capacity of a ground support system. The resulting dynamic or impact loads caused by mining-induced seismicity are difficult to anticipate and quantify. The performance of a ground support system is defined by the load distribution and interaction between several reinforcement and surface support elements. Consequently, the design of ground support in seismically-active mines tends to evolve, or be modified based on qualitative assessments of perceived performance or response to significant seismic events or rockbursts. This research is motivated by a need to provide quantitative and data-driven design guidelines for ground support systems subjected to dynamic-loading conditions. Rockburst data were collected from three deep and seismically-active underground mines in the Sudbury basin in Canada. The constructed database comprises 209 seismic events that resulted in damage to mine excavations and ground support. These events were associated with damage at 324 locations within the three mines. The developed ground support design strategy, based on these documented case studies, identifies areas where the use of dynamic or enhanced support should be employed. The developed design methodology provides guidelines for the zoning of mine locations in which installation of enhanced support is recommended, the specifications for an optimal ground support system, and the timing or sequence of installation.

Considerations for effective ground support in evaporites

Evaporites, such as salt and potash, pose unique problems to ground-support designs that are not encountered in other rock types. Evaporites are subject to continual creep and no amount of ground support can successfully arrest this process. Common ground-support techniques that are useful for most rock types may reduce the effective life of bolts in evaporite mines and create unseen hazards. A different approach to ground support must be applied to provide long-term support in areas where high creep rates are present. The goal of effective ground-support designs in these situations is not to contain and prevent the rock from moving; rather, the ground-support design must be able to move along with the rock and contain any fully detached slabs until additional remediation measures can be undertaken. The most appropriate ground-support designs will consider the expected movement of the rock and the duration that the area needs to remain accessible.