bluuebunny/crossref_metadata_2025 huggingface dataset:
DEM Modeling of 3D Kinematics in Rock Slope Failure
Authors: Keissar Y. , Brown I. R. , Gardner M. H. , Sitar N.
Published: August 2024

We compare solutions obtained using 3D Limit-Equilibrium (LE) and the 3D Discrete Element Method (DEM) analyses of rock slope stability and runout to illustrate the importance of kinematics in modeling of rock slides. While 3D LE methods provide a measure of the factor of safety against failure, the failure surface is assumed, and the rock mass is typically represented by vertical columns in the analysis. Thus, the kinematic response of the rock mass is artificially constrained, and the quality of the analysis heavily depends on an accurate capture of the potential failure surface and the failure mechanism. In contrast, a specific mode of failure is not assumed in DEM, since natural discontinuities, joints, shears, and fractures, as observed in the field can be used to create a more realistic representation of the rock mass such that failure can occur along any of the discontinuities. We use a case of rock slope failure in an existing mine to illustrate the difference between 3D LE and 3D DEM analysis results. We also show that with an increasing number of rock blocks in the model (tighter spacing of the joints), the rock mass is less stable. This has implications for rock slope stability evaluations, as rock that is more fractured will be less kinematically constrained and require more mechanical strength to remain stable. Additionally, during rock slide initiation, the rock within the sliding mass may fracture and disintegrate, such that it becomes less constrained as it deforms. The outcome is a progressive rock slope failure and accelerating displacements as the rock blocks within the sliding mass become more fractured.

1 INTRODUCTION

In fractured rock masses, slope failure occurs along pre-existing discontinuities, such as joints and fractures. The interaction between the discontinuities and the geometry of the slope plays an important role in the displacement of the blocky rock mass, both for failure initiation and runout. While 3D DEM methods have been available for some time, their utility for routine analyses has been limited due to their high computational demands and lengthy execution times in serial code implementations. However, the implementation of DEM in a modern HPC (High-Performance Computing) environment opens opportunities for efficient and affordable, full-scale analyses of failure initiation and runout.
Microscopic Defect Dynamics During a Brittle-To-Ductile Transition
Authors: Pec Matej , O’Ghaffari Hoagy , Mok Ulrich , Chang Hilary , Evans Brian , Bernabe Yves , Mittal Tushar , Cross Andrew
Published: August 2024

The strength of the lithosphere is limited by pressure-dependent, "brittle" deformation of the upper crust and temperature- and strain-rate-dependent "ductile" deformation in the lower crust and upper mantle. From a simplified mechanistic point of view, intersection of these two strength envelopes can be used to estimate the depth of a region known as the brittle-to-ductile transition (BDT) where rocks deform by semi-brittle flow. This BDT is key for estimating the integrated strength of tectonic plates, constraining the earthquake cycle, and utilizing deep geothermal resources. The BDT region is associated with changes in 1) dominant deformation mechanisms, 2) strain localization, and 3) fault stability; however, the transitions in all three attributes are influenced by many parameters, including lithology, grain size, porosity, the presence and migration of pore fluids, the loading conditions, metamorphic reactions, and the geometric complexities of geologic formations and faults. Thus, the transitions in deformation mechanisms, failure mode, and stability do not typically occur simultaneously, resulting in complex behavior that is poorly understood.

In this talk, we show that the crossing of a BDT in marble during deformation experiments in the laboratory is accompanied by systematic increase in the frequency of acoustic emissions suggesting a profound change in the mean size and propagation velocity of the active defects. We further identify dominant classes of emitted waveforms using unsupervised learning methods and show that their relative activity systematically changes as the rocks cross the brittle–ductile transition. As pressure increases, long-period signals are suppressed, and short-period signals become dominant. At higher pressures, signals frequently come in avalanche-like patterns. We propose that these classes of waveforms correlate with individual dominant defect types, that is cracks, twins and dislocation avalanches. Complex mixed-mode events indicate that interactions between the defects are common over the whole explored pressure range (0.1 - 250 MPa), in agreement with postmortem microstructural observations. To corroborate these interpretations, we performed deformation experiments on large calcite single crystals recording acoustic emissions and imaging the propagating sources with a high-speed camera. We discuss our results in the framework of a new micro-mechanical model and link the onset of the BDT to stress states at which tensile cracking around spherical cavities ceases to be possible. Our measurements provide unique, real-time data of microscale dynamics over a broad range of pressures and aid in the development of micromechanical models for semi-brittle deformation.
Numerical Simulation of Long-Term Stability of Irregular Underground Salt Caverns Under Alternating Loads
Authors: Chang Zhi , Xia Yan , Dai Kun, , Liu Tianen , Zhang Qi , Ban Fansheng
Published: August 2024

The proportion of green energy, such as photovoltaic and wind power, in power generation is increasing year by year. However, green energy often exhibits significant periodic fluctuations. Therefore, it is imperative to construct a large number of compressed air energy storage facilities to meet the daily demand for peak power regulation. Utilizing the dissolved cavity of salt rock layers to build underground salt cavern energy storage presents an economical and reliable solution due to the low permeability and self-repairing properties of salt rock. Nevertheless, most salt rock layers in China contain mudstone interlayers, which pose challenges in accurately controlling the shape of salt caverns during the water injection process within the dissolved cavity. This often results in irregularities, unevenness, and large curvatures near the mudstone interlayer within the cavity shape. Such irregularities on the inner wall of cavities pose a significant threat to long-term stability as they are prone to stress concentration and collapse. The present study establishes a sophisticated three-dimensional geometric model based on the geometry and geological conditions of underground salt caverns in the Hengyang area. Utilizing COMSOL, a numerical simulation is conducted to investigate the long-term creep stability of irregularly shaped salt caverns over a period of 30 years. The impact of salt cavern geometry on long-term stability is quantitatively assessed through key parameters such as volume shrinkage rate, plastic deformation, and stress concentration areas.

1. INTRODUCTION

With the approaching of the carbon emissions peak date, the proportion of green energy such as photovoltaic and wind power in power generation is increasing year by year (Pan et al., 2023; Van-Tien et al., 2022). However, green energy usually has a large cyclical fluctuation (Mahdieh et al., 2023; Jean-Paul et al., 2013), and at the same time, the electricity consumption in the population gathering area itself has a daily cyclical fluctuation, so it is urgent to build a large number of compressed air energy storage to meet the daily demand for power peak regulation (Liu, X. et al., 2023). Therefore, the establishment of underground salt cavern energy storage is an economical and reliable scheme for power peak regulation (Chen et al., 2024).
Evolution of Seismicity at Malmberget Mine
Authors: Jonsson K. , Dineva S.
Published: August 2024

The Malmberget iron ore mine owned by LKAB (Sweden) is one of the largest iron underground mines in the world. At present 10 orebodies are being mined, with seismicity being a known issue for several of them. The seismic system consists of 143 geophones, of which 36% are triaxial. They are a mix of 4.5 and 14 Hz geophones installed underground and in crown pillars. On the ground surface five 1 Hz geophones have been installed to estimate seismic source parameters. The mine seismic system records on average 440 events monthly with ML > 0. The largest seismic event recorded until the end of 2023 is with ML 2.9. The study was carried out in order to identify some trends in seismicity as the mining goes deeper and to find a correlation with some main controlling parameters – volume and depth of the production in order to obtain information for future seismic hazard and risk analysis. Another purpose of the study was to identify trends and behaviors for different orebodies (mining areas). The seismicity correlates strongly with the production depth, but there are differences between the orebodies.

1. INTRODUCTION

The Malmberget iron ore mine owned by LKAB (Sweden) is one of the largest iron underground mines in the world. Mining in the area started by the official records in the mid-18th century, but in a small scale. The railroad was finished in the 1890s, which meant an upswing in the mining activities. Already in 1914 underground mining dominated the production. The Malmberget underground mine consists of about 20 orebodies, of which 11 are mined at present (December 2023), covering a surface area of about 4 × 8 km. The orebodies vary in size, shape and dip in addition to having different rock mechanics issues related to geology and extraction sequence. Some orebodies have been mined by surface mining, while mining in others started some distance below the ground surface, leaving a crown pillar. At present the mine uses the sublevel caving mining method.
Influence of Monitoring Time on Rockfall Magnitude-Frequency Uncertainty
Authors: Phillips C. , Walton G.
Published: August 2024

Rockfall along mountainous roadways poses a hazard to transportation infrastructure, commercial traffic, and the public. Lidar scanning and photogrammetry are powerful tools to create high-resolution point cloud models of rock slopes and quantify change, facilitating rockfall volume estimation. The empirical magnitude-cumulative frequency (MCF) distribution of rockfall defines the number of rockfalls of various sizes that occur for a certain study area over a given period of time. The time required for the MCF curve fit parameters to stabilize varies for different slopes depending on source area size and rockfall frequency. Four Colorado rock slopes with remote-sensing-based rockfall inventories were studied to determine the typical length of monitoring necessary to produce an MCF power law that accurately reflects long-term slope rockfall activity. Bootstrapped confidence intervals on the MCF fit parameters were used to quantify the power law variability for each slope over time (as additional monitoring periods are added) and with the sequential addition of rockfalls to the database. The results of this research include guidelines for minimum rock slope monitoring time and database size to accurately constrain the rockfall magnitude-frequency relationship.

1. INTRODUCTION

Empirical distribution fitting is commonly used to model natural, difficult to predict phenomena in the geosciences. Many natural processes follow an empirical power-law to describe the relative frequency of their size or energy over a certain range, including earthquakes, forest fires, landslides, rockfall, and volcanic eruptions (Corral & González, 2019). In rockfall hazard analysis, an inverse relationship of decreasing rockfall frequency with increasing size has been consistently observed from rockfall records (Benjamin et al., 2020; Guerin et al., 2020). A power law model fit to this magnitude-frequency distribution is commonly used to predict the exceedance probability of a given rockfall volume (Dussauge-Pessier et al., 2002; Graber & Santi, 2022; Hungr et al., 1999; Janeras et al., 2023). Use of this model as a predictive tool is dependent on the accuracy and completeness of the rockfall inventory used to define the power law.
Approximation of Stress near Tunnel Intersections in Deep Burst-Prone Mines for Support Selection and Rockburst Hazard Assessment
Authors: Rigby A. , Malovichko D. A. , Kaiser P. K.
Published: August 2024

Assessing the depth of rock fracturing around tunnels is of critical importance for the design of ground support systems in strainbursting ground. Considering the heterogeneity of the rock, explicit modelling of stress-fracturing around tunnels at such a massive scale is a numerically demanding task. Previously, a semi-empirical approach to evaluate the extreme depth of failure based on elastic modelling has been suggested. It can be adopted at a mine scale by performing explicit modelling of large excavations (stopes, caves, chambers, etc) and then approximating anticipated conditions at tunnel locations using elastic approximations to obtain the local stress level. This implicit approach to incorporating tunnels into the stress model ignores interactions between tunnels, which can result in the underestimation of stress when tunnels are in close proximity, such as near intersections. To investigate this, we have explicitly modelled the stress distribution around tunnels near intersections with various configurations and loading conditions. Using these results, we present an approach to estimating stress magnifications near intersections that does not require explicit numerical modelling. A mine-scale example of an extraction level at a schematic block-caving mined is used to demonstrate the implications in the context of deformation-based support design and rockburst hazard assesment.

1 INTRODUCTION

The design and selection of support in stress-fractured and strainbursting ground is informed by the displacement demand anticipated prior to a strainburst and both the displacement and energy demand during a strainburst (Kaiser and Moss, 2022). The pre-burst displacement demand depends on the depth of damage dpre that has accumulated since support installation and the rockmass bulking factor (BF). Similarly, the displacement and energy demands imposed during a strainburst can be related to the depth of strainbursting dSB. For rockburst hazard assessment (RBHA; Kaiser and Moss, 2022; Malovichko, 2023) in strainbursting ground, it is essential to obtain these demands and to asses their variability, which allows for estimation of the probability of exceedance of design thresholds.
Anelastic Strain Recovery as a Measure of in Situ Stresses at FORGE
Authors: Ingraham M. D. , Ghassemi A.
Published: August 2024

Anelastic strain recovery, the process of measuring the time dependent recovered strain after a core is cut at depth was utilized to make a measure of the in-situ properties stresses at depth at the FORGE (Frontier Observatory for Research in Geothermal Energy) site in Milford Utah. Core was collected from a region of well 16B at approximately 4860-4870 ft. Core was instrumented with strain gages within 10 hours of the core being cut. The relaxation of the cores was measured for approximately one month, and the results analyzed, which showed that the principal stresses were slightly off vertical, and magnitudes are close to equal.

1. INTRODUCTION

Strain measurements on recovered core hold their root in the formation of the rocks themselves. As rocks are formed and stressed with burial, the grains deform and are locked in place either through cementation or through the compression of their neighbors. When cores are removed from depth the stresses are released and the strain begins to recover.

This recovered strain is measured and inverted in order to determine the principal strains, which are then converted to principal stresses though determination of the elastic modulus and application of Hooke's Law.

This technique has been applied to samples from the Utah FORGE (Frontier Observatory for Research in Geothermal Energy) site to help constrain the in-situ stress measurements at the site. The core was obtained from the 16B(78)-32 well at the site from the first core run taken above the kickoff point just below 5000 ft (core samples are from between 4865 and 4870 ft). The core is a relatively clean granitoid as shown in Fig. 1. The core was obtained on May 9th, 2023, and was instrumented within approximately 10 hours of the core being cut.

2. BACKGROUND

There are a number of ways in which in situ stresses can be determined such as hydraulic methods, i.e. fracture testing, acoustic methods, i.e. seismic waveform analysis, and core methods such as anelastic strain recovery (ASR), or overcoring.
Influence of Buttressing and Lateral Confinement on a Large Block Prior to Rockfall
Authors: Longar E. , Walton G.
Published: August 2024

Rockfalls are a source of danger for infrastructure near rock slopes containing potentially unstable blocks. Rockfalls can cause property damage, road blockages, and harm to people. Literature studies that monitor rock slopes have helped to demonstrate connections between rockfalls and the precursors that indicate potential instability. After identifying these precursors in potentially unstable blocks, measures can be taken to stabilize or remove the blocks to mitigate the risk to infrastructure near the slope. This study aims to evaluate the influences of buttressing effects and lateral confinement from nearby rocks on block stability through numerical modeling of a 76 m3 rockfall. Prior to the rockfall, a series of smaller rocks near the large block were displaced in association with loosening of the large block. To create the model, the topography of the block and surrounding area was digitized using photogrammetry. The rockfall process itself was simulated using the distinct element method, such that the rockmass is modeled as an assemblage of distinct blocks with boundary interactions between each block to account for the discontinuous nature of the rockmass. We used the model to evaluate trends in displacements of the block of interest with and without the presence of the surrounding smaller rocks.

1. INTRODUCTION

Rockfalls are a common hazard in mountainous areas, particularly along roadways adjacent to steep rock cuts (Copons and Vilaplana, 2008, Abellan et. al., 2010). Efforts have been put into place to monitor dangerous rock slopes, including by using LiDAR and photogrammetry to track slope change over time (Abellan et. al., 2013; Kromer et. al., 2015; Lim et al., 2005). Photogrammetry has been used as a tool to detect rockfall activity in both natural slopes (Graber and Santi, 2023) and cut slopes (Walton et. al., 2023).

One possible end-use of such monitoring data is for forecasting of future rock falls that can be mitigated before they occur. However, forecasting of rockfall events is only possible if rockfall precursors are understood (Kromer et. al., 2018, Royan et. al., 2015).

One potential precursor is the occurrence of small rockfalls before a larger failure. Monitoring of precursory rockfalls has been studied as a potential method of spatial and temporal prediction of rockfalls (Rosser et. al., 2007, Royan et. al., 2015).
Numerical Analysis of Induced Mechanism of Rockbursts in Tunnels
Authors: Deng J. , Gong Y. , Li S.
Published: August 2024

Rockburst is a sudden and violent failure characterized by the breaking up and expulsion of rock from its surroundings. Tunnel rockbursts pose a significant threat to the safety of excavation operations, leading to property damage and tunneler casualties. Buckling has been identified as one of the primary mechanisms causing rockbursts. Furthermore, it has been observed that rockburst can be induced by a seismic event or ambient blasting when stress waves reach the free surface of the underground opening. This paper aims to study numerically the induced mechanism of tunnel rockbursts based on the dynamic buckling of rectangular thin plates. When a rock stress wave travels toward a tunnel sidewall, it decomposes into horizontal and vertical components. The horizontal stress propagates to and reflects from the free surface, creating a rectangular thin plate of rock on the surface. The vertical stress activates parametric resonance in the rectangular thin plate, leading to the induction of a tunnel rockburst. An example of tunnel sidewall rockbursts from the Jinping II project is presented to parametrically study the effect of stress wave amplitude and frequency, static and dynamic components. Based on the mechanism analysis, measures are proposed to alleviate the hazard of tunnel rockbursts.

1. INTRODUCTION

Horizontal extended underground structures can be categorized based on the purpose of the completed structure into two types: (i) Tunnels: Extended, flat, or only slightly sloping underground cavities with excavated cross-sections exceeding 20 m2. Primarily designed for road or rail transport, each tunnel features two openings to the surface. However, in some hydropower projects such as Jinping I and II in China, there are tunnels that have only one opening to the surface due to harsh conditions. (ii) Adits, drifts, or galleries: Extended underground cavities, either horizontal or sloping at angles less than 25° to the horizontal, with relatively small diameters. These structures accommodate pipes or cables, provide access, and serve as auxiliary structures during the construction phase or for permanent use. Often, they have only one opening to the surface (Maidl et al, 2013). The present paper is concerned with rockbursts in either tunnels, adits, drifts, or galleries.
A 3D Continuum-Based Voronoi Tessellated Model (VTM) for Hard Rocks
Authors: Hamediazad F. , Bahrani N. , Moallemi S. , Yacoub T.
Published: August 2024

In conventional continuum numerical models, rock is typically simulated as a homogeneous material. However, these models fail to capture pre-peak tensile damage in hard rocks under compressive loading. The Discrete Fracture Network (DFN) is widely used to generate various types of rock heterogeneities at different scales. Among these, the Voronoi structure has been successfully implemented in discontinuum models to replicate the failure process of hard rocks. More recently this method has been effectively applied in 2D continuum models; however, its suitability for simulating hard rock failure in 3D continuum models has not been investigated. This paper aims to address this research gap by presenting the development of the first 3D Voronoi Tessellated Model (VTM) using the finite element program, RS3. The central objective of this study was to replicate the failure process of hard brittle rocks under unconfined compression. For this purpose, the micro-properties of a previously calibrated VTM constructed using the 2D finite element program RS2 were utilized in the RS3-VTM. The results indicate that the stress-strain curve and the peak strength of the RS3-VTM are comparable to those of the RS2-VTM. Furthermore, the simulation results demonstrate that the RS3-VTM captures the anticipated failure mode of hard rocks in laboratory unconfined compression tests.

1. INTRODUCTION

Experimental and numerical studies have indicated that, at low confinement, the failure process of brittle rocks involves the generation of localized tensile stresses due to grain-scale heterogeneities. These induced tensile stresses can lead to the initiation and propagation of tensile cracks before reaching peak stress, even when the rock medium is under an overall compressive stress field. To realistically simulate this process using numerical modeling, an explicit representation of the grain-like structure of rocks is required. Discrete Fracture Network (DFN) models are commonly used to generate various types of geological structures at different scales. Among them, the Voronoi structure has been extensively employed to replicate grain-scale heterogeneities (i.e., grains and grain boundaries) in brittle rocks.
Tackling Data-Limited Rock Mechanics Models
Authors: Maleki H.
Published: August 2024

Rock mechanics models are "data-limited," i.e., one seldom knows enough about a rock mass to use computational models unambiguously. Statistical methods, however, are capable of being applied where there are good data but a limited understanding of certain natural phenomena, such as the creep of rock salt or coal burst mechanics. To demonstrate the use of statistical-analytical techniques in rock mechanics problems, two case studies are used. The first study involves a historic examination of a nuclear waste repository in rock salt, where mathematical models are built using excavation convergence data to identify significant variables and estimate future deformation and stability. The second case study focuses on ongoing analysis of coal burst mechanics and associated factors. Over the last three decades, a hybrid statistical-analytical methodology has been applied for identifying significant factors affecting coal burst. The final model utilizes data from 30 case studies from Utah, Colorado, Kentucky, and other Eastern U.S. mines providing predictive capability for the entire United States coal fields.

1. INTRODUCTION

There are two methods used by engineers and researchers as tools to help predict conditions in the future: statistical and computational. Starfield and Cundall (1988) identify rock mechanics models as "data-limited," that is, one seldom knows enough about a rock mass to use computational models unambiguously. Statistical methods, on the other hand, are uniquely capable of being applied where there are good data but a limited understanding of certain natural phenomena, such as the creep of rock salt or elevated risk domains associated with the violent failure of strata commonly referred to as coal bumps or bursts. Rock bursts and coal bumps are defined as sudden, violent failure that occur near mine entries that are of such a magnitude that they expel large amount of rock and/or coal into an excavation, restricting safe and efficient access to the working area (Maleki and White 1997). Gradual failure and spalling is common in coal mine environment and is considered not problematic but controlled through proper mine orientation and application of support as needed. Important to these real-world statistical evaluations are (1) having sufficient number of data collected consistently and (2) incorporation of analytical calculations for quantifying geologic, mining and particularly geotechnical variables. By combining the strength of the statistical and analytical models, an improved "hybrid" model is created and utilized. Powerful examples of the use of statistical techniques to evaluate stability and performance using significant field investigations are given by Parson and Dahl (1971), Maleki and White (1997), Maleki and Owen (2001), Maleki et al. (2001), Maleki et al. (2023), and Maleki (2023).
Tool Development and Field Test of the Stress Measurement Method with Dual Bit Coring Applicable to Geothermal Fields
Authors: Ito T. , Kaneko K. , Sasaki M. , Ogawa K. , Yokoyama T. , Funato A. , Tezuka K.
Published: August 2024

The Dual Bit Coring (DBC) is the method to record the in-situ stress state into cross-sectional shapes of a boring core. The magnitudes and orientations of the in-situ stresses in a plane perpendicular to the borehole can be estimated from the measured core diameters upon the principle with which the core expand radially in an elastic manner as it is relieved from the in-situ stresses. We developed a downhole assembly to realize DBC which contains small and large diameter bits. A core sample is cut out in three stages with changing those two bits. We developed another downhole tool to detect the core orientation. They are designed to operate in temperatures more than 200 °C at depths of a few km considering application to geothermal fields. We simulated the three-stage coring by numerical simulations and confirmed the core to have cross sections of an expanded-elliptical shape and a circular shape prior to expansion in the lower and middle sections, respectively. We tested the tools in field tests and estimated the in-situ stress state successfully.

1. INTRODUCTION

Rock core samples obtained by drilling have slightly elliptical cross-sections instead of circular ones, when the in-situ stress state is anisotropic (Funato and Ito, 2017). Such elliptical shapes arise as the core expand radially in an elastic manner when it is relieved from the in-situ stress. The amount of expansion is proportional to the stress magnitude. The core expands most and least in the orientations of the maximum and minimum stresses, respectively, that act along the plane that is perpendicular to the drill hole, resulting in the elliptical cross-section.

We applied the phenomenon of core expansion to measure the in-situ stress state. To do this, we proposed a novel coring method referred to as Dual Bit Coring (DBC) that results in a single core that has two signature transverse cross-sections: the first has an elliptical shape resulting from core expansion and the second records the initial circular shape prior to expansion. Then the amount of expansion can be estimated as the difference between the cross-sections prior and posterior to expansion, and the stress magnitudes and orientations can be estimated from the circumferential distribution of the core expansion.
Impact of Cold Fluid Injection on Hydraulic Fracture Propagation
Authors: Rueda J. , Mejía C. , Firme P. , Roehl D. , Rossi D. , Henriques F. , Sousa E. , Chaves R.
Published: August 2024

Hydraulic fracturing is widely employed to enhance permeability and well-reservoir connectivity, increasing fluid flow and heat transfer in oil/gas/geothermal reservoirs. Analytical and numerical solutions have been developed for predicting the hydraulic fracture propagation. However, most solutions neglect the thermal effects within the porous medium and in the fracture development, even though these effects strongly affect the properties of the rock formation and the injected fluid. This work studies the effects of cold fluid injection on induced hydraulic fracture propagation. To this end, a fully coupled thermo-hydro-mechanical (THM) finite element model was adopted. The model simulated fracture propagation using interface elements with a thermo-pore-cohesive zone model (TPCZM). The presented model is verified against related analytical and numerical solutions. Moreover, the work investigates the influence of cold fluid injection under leak-off-dominated regimes. The numerical results show that injection period, heat transfer, and initial stresses significantly impact the fluid leak-off, pore pressure evolution and fracture geometry growth. Finally, the study adds valuable insight to a better understanding of the complex hydraulic fracturing process considering thermal, hydraulic, and mechanical coupled behaviors.

1. INTRODUCTION

The hydraulic fracturing technique is widely employed to enhance permeability and well-reservoir connectivity, increasing fluid flow and heat transfer in oil/gas/geothermal reservoirs (Barbier, 2002; O'Sullivan et al., 2001). Other applications include rock-burst control and cave inducement in deep mining (Board et al., 1992; Jeffrey & Mills, 2000; Van As & Jeffrey, 2000), waste disposal in shale (de Laguna, 1966; Maloney & Yoxtheimer, 2012), and assessment of in situ stresses (Desroches, 1995). Modeling efforts on hydraulic fracturing have attracted numerous research contributions in the last decades (Green & Sneddon, 1950; Khristianovic & Zheltov, 1955; Nordgren, 1972; Perkins & Kern, 1961; Sneddon, 1946). Simplified analytical solutions based on KGD, PKN, or penny-shaped geometries have been presented to predict fluid pressure evolution, opening, size, and profile of the fracture (Adachi & Detournay, 2002, 2008; Bunger et al., 2005; Detournay, 2016; Dontsov, 2016, 2017; Garagash et al., 2011; Savitski & Detournay, 2002). These models are excellent approaches for studying hydraulic fracture evolution in different regimes of propagation (Adachi & Detournay, 2008; Rueda Cordero et al., 2020). However, analytical solutions consider a basic description of rock properties and infinite elastic homogenous media (Adachi & Detournay, 2008). Furthermore, these solutions neglect the thermo-hydro-mechanical (THM) effects within the permeable porous medium.
Geomechanics Finite Element Modelling for Nuclear Waste Storage
Authors: Mohamad-Hussein A. , Ni Q. , Haas M. , De Gennaro V. , Subbiah S. K. , Rodriguez-Herrera A.
Published: August 2024

Nuclear energy represents one of the key energy sources that will make it possible to achieve net-zero carbon emissions. Safe and efficient management are crucial requirements when dealing with radioactive waste. Once a geological repository is selected, the development of site involves various stages. Site characterisation represents one of the early phases. It includes performing geological, hydrogeological, and other studies to understand the site's suitability for nuclear waste storage. This paper is devoted to modelling the radioactive waste disposal into a geological repository. A comprehensive geomechanics finite element modelling approach is adopted to address the challenges arising from nuclear waste storage.

A unified finite element model has been constructed for the shaft, gallery, and storage cavities. Finite element modelling has been performed to simulate the excavation of the various underground structures within the host rock formation. Hydromechanical simulations were conducted for excavating the various cavities. The installation of the radioactive waste containers is simulated. The behaviour is investigated by simulating the impact of thermal heating on the surrounding formations.

This work serves as a critical step towards achieving the safe containment isolation of radioactive materials and reducing environmental risk as we move towards a future powered by clean, sustainable energy sources and commitment to net-zero emissions.

1. INTRODUCTION

As one of the least greenhouse gas emitting energy sources, nuclear energy has been shown to be essential for delivering low-carbon sustainable energy transitions (Gibb 1999). However, it is also widely acknowledged that safe disposal of spent nuclear fuel (nuclear waste) can present significant social, environmental, and technical challenges (Themann and Brunnengräber 2021; Christiansson 2014). The concept of nuclear waste storage is to isolate radioactive material from humans and the environment for sufficiently long time periods. Therefore, storing such waste in deep impermeable geological formations is considered a viable option (McKinley et al. 2007). Regardless of the choice of rock type, the general design of the storage solution requires placing the nuclear waste container in a chamber created in a geological formation. However, high-level radioactive waste with associated heating and cooling processes over long period of time causes complex changes to the surrounding rocks. Their nature and performance can change according to the internal and external conditions and ultimately could affect the integrity of the storage chamber (Jia et al. 2006; Teng et al. 2021; Plúa et al. 2021). To achieve the engineering safety of the storage chamber, it is necessary to carefully investigate and manage the risks associated.
Mode I Fracture Behavior of Lightweight Concrete Made of Mine-Tailings-Based Aggregates
Authors: Asadizadeh M. , Hedayat A. , Tunstall L. , Taboada Neira M. , Vega González J. A. , Verá Alvarado J. W.
Published: August 2024

The exploration of mode I fracture behavior in lightweight concrete (LW-concrete) made from mine-tailings-based aggregates holds great significance in the realm of construction materials. This research is vital, as it offers crucial insights into the structural integrity of the material and its suitability for diverse applications. The utilization of mine tailings (MTs), abundant in aluminum oxide and silicon dioxide, and their transformation into lightweight aggregates (LWAs) signifies an environmentally responsible approach to address the environmental impact of MTs while reducing disposal costs. This study explored the fracture behavior of LW-concrete composed of mine-tailings-based aggregates, particularly under mode I loading. This aspect necessitates a comprehensive examination of this innovative material. Mode I fracture tests were performed on three-point bending beam specimens to better understand the fracture behavior. Using alkali-activation and palletization techniques, LWAs were produced using a blend of 30 wt.% fly ash type F and 70 wt.% MTs. The concrete mix incorporated a combination of coarse LWAs and natural, normal-weight fine aggregates. Specialized molds were employed for the direct casting of notched beam specimens, which were subsequently subjected to three-point bending tests after the curing process. The study revealed a mode I fracture toughness of 434.88 kNm^1/2, a crack tip opening displacement (CTOD) of 90.28 μm, and the characteristics of the fracture process zone (FPZ) measuring 2.88 mm, with comprehensive analysis conducted using Digital Image Correlation (DIC).

1. INTRODUCTION

Natural aggregates find widespread applications in civil engineering and construction industry. They hold significant importance in the manufacturing of concrete (Guo et al., 2020), building roads (Ryms et al., 2015), surfacing asphalt (Qian et al., 2013), and other related applications. However, since natural resources are scarce and their utilization may have adverse environmental effects (Tabsh & Abdelfatah, 2009), there is an increasing interest in manufacturing lightweight aggregates (LWAs) utilizing waste materials like mine tailings (MTs) (M. Asadizadeh et al., 2023b, 2023a; Mostafa Asadizadeh et al., 2023, 2024; Yliniemi et al., 2017).
Assessing Pillar Stability in Underground Stone Mines: Impact of Geological Structures and Stress Variations in the Appalachian Region
Authors: Elibol A. , Tuncay D. , Agioutantis Z.
Published: August 2024

Roughly 29% of fatalities in underground stone mines have been associated with roof and pillar collapses from the beginning of 2002. The S-pillar software can assess how a significant joint set intersecting a pillar impacts the pillar's stability, but the approach doesn't account for the relative positioning of geological structures concerning the pillars or in cases where multiple joint sets intersect a single pillar. This study delves into the Northern and Central Appalachian region's horizontal stress variations and their influence on the stability of underground limestone mine pillars by investigating their effect on the reduction of the load-bearing capacity of pillars and the potential increase of the risk of pillar failure. Discontinuity sets extracted from point clouds acquired by Light Detection and Ranging (LiDAR) sensor and the stress data obtained from the World Stress Map are investigated in conjunction with the region's geological history. The maximum horizontal stresses in the Northern and Central Appalachian regions align along the NE-SW direction, contributing to the formation of folds, faults, and discontinuities in the region. These geological phenomena are attributed to the Alleghenian orogeny, representing a pivotal moment in the region's geological history. The research goes beyond the factors such as overburden load and terrain configuration and analyzes the historical geological events that have shaped the area. Expanding analysis of pillar systems to examine varying topographies, geometries and modeling the discontinuities in the area, and adjusting geological information will enhance mine safety considerations. These collapses have occurred in geologically weak zones where a high frequency of discontinuities exists, resulting from a distinctive stress distribution. The paper will present possible correlations between stress distribution, tectonic processes, the Appalachian orogeny, and the geological discontinuities within the pillars and their overall integrity since a significant amount of pillar collapses associated with pillar stability issues have occurred within the Central and Northern Appalachian orogeny.

1. INTRODUCTION

Mining operations, particularly in underground stone mines, face significant challenges in ensuring the stability and safety of miners and pillars. A concerning statistic reveals that approximately 29% of fatalities in these mines result from roof and pillar collapses since 2002 (Centers for Disease Control and Prevention. (n.d.)).
Analyzing the Effect of Bolt Spacing on Coal Rib Stability Through Numerical Simulation
Authors: Xue Y. , Mohamed K. M.
Published: August 2024

Rib falls pose a major safety risk in underground coal mines, and there is currently no standardized approach for rib support design in the U.S. coal mines. To tackle this issue, a standalone application, Design of Rib Support (DORS), was developed for rib stability assessment and rib support design under development load. The last step of the rib support design in DORS was to calculate the bolt spacing from the recommended rib support density, bolt grade and number of bolts. Notably, the change of bolt grade and the number of bolts significantly affects bolt spacing, but it remains unclear how varying bolt spacing impacts the supported rib factor of safety (RibFOS). In this study, numerical simulations were conducted to analyze the influence of bolt spacing on coal rib stability. Initially, plane-strain 3DEC models were used to estimate the RibFOS of unsupported solid coal ribs, serving as a baseline for rib stability evaluation. Subsequently, 3D models were conducted for supported solid coal pillar ribs. A parametric study was conducted to investigate the influence of bolt spacing on the supported RibFOS under different conditions, such as varying overburden depths and bolt lengths. The simulation results show a general trend of reduced supported RibFOS with the increase in bolt spacing, and the trend can be further affected by varying conditions. The variation of supported RibFOS with bolt spacing can be quantified by normalizing the supported RibFOS to its values with a bolt spacing of 0.3 m. Finally, when the rib support density was maintained by varying bolt grade and bolt spacing, the influence of bolt spacing can still be observed in the results. Thus, it is essential to consider this bolt spacing effect in rib support design.

1. INTRODUCTION

Coal pillars are intentionally retained during mining to support overlying rock strata and prevent mine roof collapse and play a crucial role in maintaining the structural integrity of underground coal mines. When coal is extracted from a seam, the overburden load and/or abutment load tend to transfer and redistribute to the remaining pillars, leading to excessive pillar load. Coal ribs are the walls of coal pillars with free surfaces. Without rib support, the coal mass has low or no confinement, leading to lower strength and less constraint for deformation. The occurrence of rib falls presents severe safety risks, encompassing injuries, fatalities, and equipment damage. According to the Mine Safety and Health Administration (MSHA), statistics during the 10-year period between 2010 and 2019, rib-fall accidents contributed to 45.2% of the ground-fall fatalities (Rashed et al. 2022). Thus, rib falls pose a major safety hazard in U.S. underground coal mines.
Concept Feasibility and Predicted Behavior of Mining a Rock Tower with Drill-And-Blast Undermining Using Dynamic Three-Dimensional Discontinuum Numerical Models
Authors: Abousleiman R. , Contreras C. I. , Cremeens J. , Worsey T. , Rouse N.
Published: August 2024

The safety and efficacy of a proposed novel mining method - felling a mineralized rock tower away from an adjacent river and towards an existing open pit using a wedge-shaped "key-cut" blast pattern and post-split hinge – was analyzed by integrating site-specific and site-adjacent data to develop a into a dynamic three-dimensional discrete element method numerical model. These data included historic laboratory testing and geomechanical core logging from the adjacent open pit, Lidar scans and geomechanical spot mapping of the rock tower, local signature blast seismic data, and proposed blast-pattern. Static and dynamic model stages were run to assess the pre-blast, syn-blast, and post-blast deformation of the mineralized rock tower. Model sensitivities to mesh size, dynamic time-step, block size, and joint strength were assessed. Ultimately, model results indicated that the proposed mining method would likely result in 97 percent retention of the blasted material within the existing open-pit, and only 3 percent of material would be cast towards the adjacent river.

1. INTRODUCTION

The Dragon's Tooth rock tower is located near the base of an existing open pit at Mine A along the bank of a perennial river (Figure 1). The rock tower extends 50 meters (m) vertically above the open pit bottom and ranges in diameter from approximately 20 m at the crown to approximately 40 m at its basal contact with the adjacent open pit. The Dragon's Tooth and underlying material contain gold ore but were not mined with the completion of the open pit due to limited safe access for conventional open-pit mining equipment.

Successful mining of the Dragon's Tooth depends on limiting the casting and sliding of large blocks (i.e., blocks that require re-blasting) towards the river and the volume of fill required for access. This will afford more ore recovery and avoid blocking the river for a prolonged period. Mine A contacted Dyno Consult (DC) to develop a method to safely collapse the mineralized tower away from the river. DC developed a wedge-shaped "key-cut" blast pattern (Figure 2) and post-split hinge to topple the rock tower towards the open pit. The safety and efficacy of the proposed method was assessed using numerical models.