Modeling on spatial block topological identification and the irprogressive failure analysis of slopeand cavernrock mass

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Characterisation and modelling of natural fracture networks: geometry, geomechanics and fluid flow

Natural fractures are ubiquitous in crustal rocks and often dominate the bulk properties of geological formations. The development of numerical tools to model the geometry, geomechanics and fluid flow behaviour of natural fracture networks is a challenging issue which is relevant to many rock engineering applications. The thesis first presents a study of the statistics and tectonism of a multiscale fracture system in limestone, from which the complexity of natural fractures is illustrated with respect to hierarchical topologies and underlying mechanisms. To simulate the geomechanical behaviour of rock masses embedded with natural fractures, the finite-discrete element method (FEMDEM) is integrated with a joint constitutive model (JCM) to solve the solid mechanics problems of such intricate discontinuity systems explicitly represented by discrete fracture network (DFN) models. This computational formulation can calculate the stress/strain fields of the rock matrix, capture the mechanical interactions of discrete rock blocks, characterise the non-linear deformation of rough fractures and mimic the propagation of new cracks driven by stress concentrations. The developed simulation tool is used to derive the aperture distribution of various fracture networks under different geomechanical conditions, based on which the stress-dependent fluid flow is further analysed. A novel upscaling approach to fracture network models is developed to evaluate the scaling of the equivalent permeability of fractured rocks under in-situ stresses. The combined JCM-FEMDEM model is further applied to simulate the progressive rock mass failure around an underground excavation in a crystalline rock with pre-existing discontinuities. The scope of this thesis covers the scenarios of both two-dimensional (2D) and three-dimensional (3D) fracture networks with pre-existing natural fractures and stress-induced new cracks. The research findings demonstrate the importance of integrating explicit DFN representations and conducting geomechanical computations for more meaningful assessments of the hydromechanical behaviour of naturally fractured rocks.Open Acces

Inherent strength and stiffness anisotropy of laminated rocks

The variation of rock strength and stiffness, known as mechanical anisotropy, is expected at different scales: large (rock mass) - or small (intact rock) - scales. It is always mandatory for engineering applications built either on or in anisotropic rock masses to investigate the strength and deformation behavior of those masses. To achieve this goal, continuum-based constitutive models are presented to analyze the mechanical anisotropy. One of both implemented models is named ‘Transubi model’ which considers the transverse isotropic elasticity into bi-linear Mohr-Coulomb strain hardening/softening plastic framework. Experimental investigations and numerical simulations focused mainly on the influence of the mechanical anisotropy on the plastic zoning around excavated openings in laminated rocks. Later, the Transubi model was applied to a tunnel excavated in a shaly facies formation of bedded argillaceous Opalinus clay in an URL (FE-tunnel) to obtain the short-term stability insights. Overall, the research outcomes may have a prospective impact regarding the understanding of anisotropy of laminated, bedded and foliated rocks which improves the deformation behaviour predictability using continuum-based numerical modeling tools

An integrated approach to span design in open stope mining

In order to develop an appropriate mine design, a thorough understanding of the rock mass conditions and its potential response to mining is required. Rock mass characterisation is a key component in developing models of the rock mass and its engineering behaviour, and relies on disparate data collected by exploration geologists, mine geologists, rock mechanics engineers and technicians, in a variety of formats. Optimal rock mass model development requires the effective integration of all data sources, which currently requires considerable effort in collecting, managing, collating, validating and analysing this data.The importance of understanding the spatial variability of rock mass conditions has been highlighted as a major issue. The traditional approach of using simplistic models of “average” rock mass conditions can lead to sub-optimal designs, which may result in unplanned additional costs or economic implications of dilution and ore loss. The design of stope and pillars should be optimised for the prevailing rock mass conditions in the various regions of the mine.Some of the existing design tools used for open stope design have shown poor reliability in their performance predictions. Though some may have been originally developed to assist in initial stope size selection (i.e. pre-feasibility and feasibility levels), they are potentially being inappropriately relied upon for detailed design. Consideration of large scale structures on stability and their influence on local rock mass conditions are also important aspects of open stope design that are commonly over-looked. There is a need to select design methodologies that are optimised for the stage of project development. It is also important to emphasise the iterative, evolutionary and interdisciplinary nature of open stope design.This thesis proposes a framework that attempts to integrate different rock mass characterisation models, numerical modelling and stope performance data to assist in improving the overall excavation design process. The key philosophy behind design optimisation is the continual reduction in uncertainty in collected data, analysis and design methods used with a view to improving the overall reliability of the design. A stope span design optimisation approach is proposed which attempts to ensure that the appropriate methodologies in data collection, data analysis, rock mass model formulation and stope design are utilised at relevant project stages in order to minimise uncertainty and maximise design reliability. The design optimisation approach recognises that the appropriateness of a particular design methodology is highly dependant on the availability of an appropriate rock mass model, which is in turn dependant on the availability of quality rock mass data. With respect to the design of spans in open stope mining, the key aims of the proposed integrated approach are to; • Assess the suitability of data for analysis • If data is unsuitable, assess the most appropriate data collection strategy • Assess the most appropriate approach to rock mass modelling • Assess the most appropriate design methodologies • Assess the reliability of the design criteria and quantify the potential economic impact of the design on the projectOptimisation of the design process also requires integration of state-of-the-art techniques in data collection, analysis, modelling and engineering analysis and design at the appropriate stage of project development. During development of this thesis a number of improvements have been proposed in key areas in the rock engineering design process which can be incorporated into the integrated approach, including; • A rock mass data model has been developed that assists in facilitating the ongoing rock mass characterisation process. The data model is capable of integrating rock mass data from various sources, which promotes sharing of data and avoids duplication of data collection efforts. The data model is able to query rock mass data, define relationships between data types, apply bias corrections, and perform basic analysis for use in subsequent detailed analysis and rock mass modelling. • An implicit based approach to spatial rock mass and deterministic discontinuity modelling can be employed to improve understanding of the spatial variability of rock mass parameters, inter-relationships between rock mass characteristics on their role in design. For example, understanding the influence of large-scale structures on rock mass characteristics and excavation performance. • Improved scale independent geometrical assessments of stope performance have been proposed that maximise the use of stope performance data. • An integrated back analysis framework has been presented that is able to account for structural complexity, scale and features that cannot be directly incorporated into linear elastic numerical modelling codes. • With regard to linear elastic back analyses, an number of improvements have been proposed, as well as a suggested method to assess appropriateness of continuum models based on discontinuity intensity and critical span

Advances in Condition Monitoring, Optimization and Control for Complex Industrial Processes

The book documents 25 papers collected from the Special Issue “Advances in Condition Monitoring, Optimization and Control for Complex Industrial Processes”, highlighting recent research trends in complex industrial processes. The book aims to stimulate the research field and be of benefit to readers from both academic institutes and industrial sectors

Microstructure, Geometry and Hydrogeology of the fracture network of the Boda Claystone Formation

This dissertation extensively examines the brittle structural elements of the Boda Claystone Formation (BCF), which could serve as a host formation for high-level radioactive waste in Hungary. Despite the formation's low porosity and permeability, which give its retentive features, it is crucial to assess the tectonic setting of the rock body to comprehend the timing and magnitude of faults and folds. The idea behind the research is that each successive phase of the study examines the problem at an increasing scale, from microstructural observations to models of the fracture network based on more than one borehole. The main goals of this study were to identify the geometry and hydrogeological properties of the fracture network of the Boda Claystone Formation as well as the investigation of the spatial extensibility of the properties of the fracture network. The BAF–2 well was regarded as a base well in this study because it explores the maximum thickness of the formation (917 m) with almost 100% core recovery and offers unique opportunity to evaluate its brittle structural elements. In addition, the analysis of the BAF–4 well was also done to investigate the extensibility of the properties of the fracture system. The petrographic description of the sigmoidal veins in the shear zones was carried out on thin sections. The volume and density changes of the shear zones were analysed based on the geometry of the sigmoidal veins, using the isocon method and micro-computed tomography. The geometry of the fracture network was investigated using the discrete fracture network modelling method, while its hydrological properties were characterised using the flow zone indicator. This indicator designates hydraulic flow units based on porosity and permeability. The relationship between the fracture network and well log data was investigated using multiple linear regression analysis. Based on petrographic observations, the sigmoidal veins in the BCF can be interpreted as "pennant" veins whose formation was caused by conjugate Riedel fractures. Despite the formation of sigmoidal veins, a 5-8% volume loss occurred in the shear zones. Based on fracture network modelling, five fracture network geometries can be distinguished in the BAF-2 well. In some models, the fracture network forms a communicating system along the entire length of the borehole, while in other cases it breaks down into subsystems that do not communicate with each other at depths of 100, 400, or 700 meters. The fracture system can be divided into seven hydraulic units, the boundaries of which coincide with the boundaries designated by fracture network modelling. In the upper 100 meters of the borehole, the hydrological properties of the rock were affected by weathering. Based on the properties of the fracture network, the rock column of the well can be divided into two very distinct blocks with a border at a depth of 400 m. The hydrological properties of the formation at 700 meters were determined by the by fine-grained sandstone layers. Based on multiple linear regression analysis, the fracture density of the BCF can be estimated based on density and resistance well log data. Fracture density can also be estimated in boreholes without acoustic borehole televiewer data using the regression equation

Tracing back the source of contamination

From the time a contaminant is detected in an observation well, the question of where and when the contaminant was introduced in the aquifer needs an answer. Many techniques have been proposed to answer this question, but virtually all of them assume that the aquifer and its dynamics are perfectly known. This work discusses a new approach for the simultaneous identification of the contaminant source location and the spatial variability of hydraulic conductivity in an aquifer which has been validated on synthetic and laboratory experiments and which is in the process of being validated on a real aquifer