bluuebunny/crossref_metadata_2025_split huggingface dataset:
Geotechnical Design for Open Pit Coal Mining in Proximity to Electrical Power Lines: Risks, Mitigation, and Regulatory Compliance
Authors: Zvarivadza T. , Ng’andu S. , Zindi L. , Mohutsiwa M. , Masethe R. T. , Adoko A. C. , Onifade M. , Chikande T. , Moyo S. , Firoozi A. A. 
Published: August 2024

ABSTRACT:
Open pit coal mining near electrical power lines presents distinct geotechnical challenges and regulatory demands, particularly under Section 17.6 of South Africa's Mine Health and Safety Act. This section requires a minimum 100 m buffer between mines and structures such as power lines unless deemed safe at closer distances. To balance safety with economic considerations, a detailed geotechnical risk assessment was performed to reduce this distance without compromising safety. This practical study is pivotal in optimising coal extraction while ensuring the integrity and safety of nearby power lines through well-considered geotechnical design. Employing empirical methods based on geological and geotechnical data, the study proposes a suitable geotechnical design, incorporating slope stability, ground control, and real-time monitoring to evaluate risks. This approach not only ensures compliance with regulatory standards but also enhances economic feasibility by increasing the minable coal resources. The findings highlight the critical role of comprehensive geotechnical design in allowing mining operations to coexist safely with essential power infrastructure. This research provides valuable insights for engineers, regulators, and industry stakeholders, establishing a framework for responsible mining in complex geotechnical environments. The recommendations from this study also guide future mining projects facing similar challenges, promoting sustainable and compliant mining practices.

1. INTRODUCTION
The extraction of coal through open pit mining is a cornerstone of the global energy landscape, supplying an indispensable resource for power generation (Moloi and Zvarivadza, 2016; Woodworth, 2017; Pouresmaieli et al. 2023). However, when such mining operations occur in close proximity to electrical power lines, a unique set of geotechnical challenges emerges, requiring meticulous attention to safety, regulatory compliance, and economic feasibility. This paper delves into the intricate interplay of these factors, focusing on the geotechnical design considerations that underpin the successful and responsible extraction of coal resources in challenging geological settings near critical power infrastructure.
The slope stability evaluation and design in this study pertain to an open pit mining project in close proximity to power lines. The objective is to find appropriate slope parameters such that the mine is stable, and the pit edge is not close enough to the power lines to cause the instability of the powerlines. This is in fulfilment of the Mine Health and Safety Act requirements as stipulated below:
Assessing the Variability in Direct Shear Testing Interpretation for Sets of Natural Fractures
Authors: Franco M. A. , Potter J. , Meyer B. 
Published: August 2024

ABSTRACT:
A direct shear test is a standard geotechnical laboratory test used to estimate the shear strength of rock fractures. This paper builds on previous work conducted by the authors to assess the extent of variation in shear strength parameters resulting from different approaches to interpreting direct shear test data. This interpretation involves selecting shear stresses from a shear stress versus shear displacement plot and utilizing them in the Mohr-Coulomb constitutive model to calculate friction angle and cohesion. The authors navigate through a series of direct shear results on fractures in the same rock type. Furthermore, a Python script was developed to automate the interpretation process, offering analysts an alternative tool. A variation up to 22.9 degrees in friction angle was observed and the effects of area and dilation corrections were analyzed.

1. INTRODUCTION
Direct shear tests (DST) are geotechnical tests designed to assess the shear strength and deformation properties of soils and rock discontinuities (MacDonald et. al. 2023). This test can be conducted either in a controlled laboratory setting using core specimens or in the field under in-situ conditions (Sanei et al. 2015).
A DST involves placing a core sample containing a plane of interest, referred to as a ‘discontinuity,’ onto a shear holder. The top part is displaced in relation to the bottom by applying a force parallel to the discontinuity (shear force) while maintaining a constant force perpendicular to the discontinuity (normal force). The resulting shear forces and corresponding shear displacements are measured and recorded. These forces are converted to stresses by dividing by the surface contact area, resulting in a shear stress vs. shear displacement trace (ASTM 2016). The test is generally performed three to five times on the same or similar samples with increasing applied normal loads. Figure 1 shows direct shear traces of a quartz monzonite fracture. The resulting data allows the interpreter to determine normal and shear stiffness, peak and residual shear strengths, and dilation angles (MacDonald et al. 2023).
Application of Novel Structural Finite Elements Implemented Within Combined Finite-Discrete Element Methods
Authors: Padilla A. , Lei Z. , Munjiza A. , Rougier E. , Knight E. E. 
Published: August 2024

ABSTRACT:
Simulating the structural response of concrete and reinforced concrete structures to blast loading conditions is a challenging task, as it requires modeling the fracture and fragmentation processes in this composite material with reasonable computational efficiency for large scale simulations. To address this problem, novel shell formulations have been incorporated within Los Alamos National Laboratory's implementation of the combined finite-discrete element method, called HOSS (Hybrid Optimization Software Suite). In this numerical study, these new finite element formulations are utilized for modeling thin concrete and metal linings for applications in building construction. Both unreinforced and reinforced concrete can be modeled with this method which opens the door for addressing many practical applications.

1. INTRODUCTION
Since its inception, the combined finite discrete element method (FDEM) has become a tool of choice to address a variety of problems involving fracture and fragmentation processes in solids. FDEM combines the strengths of the finite element method (FEM) and the discrete element method (DEM). The key advantage of FDEM is the utilization of finite strain-based deformability combined with suitable constitutive material laws which are then merged with discrete element based transient dynamics, contact detection, contact interaction solutions, and objective discrete crack initiation and crack propagation solutions (Munjiza, 2004). The comparison of DEM and FEM with a schematic visualization of FDEM is shown in Fig. 1.
In FDEM, the solid bodies are modeled as a collection of deformable particles that are bonded with each other (Rougier et al., 2014), Fig. 1. These solid bodies (called discrete elements) are discretized into finite elements where their finite displacements and rotations are assumed a priori (Munjiza, 2004; Munjiza et al., 2011, 2015). The bonding is numerically represented with cohesion points along the boundaries of the deformable particles (Rougier et al., 2014). The cohesion of these bonds is a combination of normal cohesion and tangential cohesion. When an FDEM model experiences fracture, failure, or fragmentation and the material is exposed to high enough levels of stress, these bonds become increasingly strained until they reach their ultimate strengths and eventually break resulting in the adjacent finite elements to also become unbonded (Rougier et al., 2014). The single discrete element domains are transformed into interacting domains upon which discretized contact solutions can be used for both contact detection and contact interaction (Knight et al., 2020).
Crack Initiation (CI) Thresholds from Acoustic Emission and Stress-Strain Data: A Comparison of Values Measured for Rocks from Montana and Idaho
Authors: Humphreys M. C. , Link C. , Berry S. M. , MacLaughlin M. M. 
Published: August 2024

ABSTRACT:
Rock mechanics researchers have defined crack initiation (CI) and crack damage (CD) thresholds as the points at which microcracks begin to propagate and coalesce under increasing stress levels. CI and CD correspond to cracking events and can be identified using Acoustic Emissions (AE). AE monitoring is a passive, nondestructive testing method which records the elastic energy released during loading. In this study, CI is determined using the Cumulative Acoustic Emissions Hits (CAEH) method (Zhao et al, 2015), which involves graphing cumulative counts vs. axial stress, implemented as a MATLAB® v7 module. The CAEH method was designed to make the determination of CI less subjective. Augmenting previous studies by others, this study involves using unconfined compression tests in conjunction with AE monitoring to identify CI and CD thresholds for specimens of several different rock types from Montana and Idaho. The unconfined compression tests were performed on a TerraTek load frame using strain rate control, and the AE data were collected and recorded using a Mistras' Express-8 AE system and AEwin Express-8 software. CI values determined from the stress-strain curves ranged between 34% to 60% of the UCS for all but 2 of the specimens. The CAEH CI values were generally higher than the stress-strain CI values, and were sensitive to the selection of the initial point. Data from two AE sensors mounted on the same specimen yielded surprisingly different CI values.

1. INTRODUCTION
As compressive stress increases in rock, cracks initiate and coalesce, leading to nonlinear behavior and eventually to failure. Stress and strain data from a traditional unconfined compression test on rock provide values of yield stress and unconfined compressive (peak) strength (UCS) as the specimen is loaded past the point of linear elastic behavior. Rock mechanics researchers have also defined crack initiation (CI) and crack damage (CD) thresholds as the stress levels at which microcracks begin to propagate and coalesce under increasing compressive stress, originally associated with the point of departure from linear on axial stress vs. lateral strain (for CI) and on axial stress vs. axial strain (for CD) plots (Ghazvinian et al., 2012, referring to work by Brace et al., 1966, Bieniawski, 1967, and Lajtai & Lajtai, 1974). Identifying CI and CD can be valuable for understanding the behavior of rock under load, so efforts have been made to associate them with more definitive observable points on the stress-strain data plot. Due to the subjectivity involved in selecting some of these points combined with large variations in behavior observed in rocks with drastically different porosity values, this process is not necessarily a straightforward one.
Methodology Development to Incorporate Anisotropy in Slope Stability Analysis at Los Bronces Mine®
Authors: Córdova M. , Vallejos J. 
Published: August 2024

ABSTRACT:
The rock mass strength depends on a combination of non-persistent discontinuities and blocks of rock mass. Currently, the representation of the strength for slope stability analysis includes the joints sets (structural domains) with preferential orientations that generate unfavorable stability conditions. For the limit equilibrium stability analysis of slopes the strength of the anisotropic rock mass is estimated by means of an anisotropic rosette and the respective rock bridge percentage. This work focusses on providing guidelines for Los Bronces Mine to estimate the directional resistance according to the structural domain and slope design. First, it is created a discrete fractures network (DFN) using a robust structural database that represents the probabilistic distribution of each joints characteristic, i.e., orientation, persistence and intensity. Once the DFN has been established, it is possible to characterize the structural condition of the rock mass and estimate the equivalent structure that controls the slope failure. This process is carried out through two-dimensional continuous numerical modeling with explicit structures and the obtained indicators of slope stability. Next, the results of the numerical model are compared with a two-dimensional limit equilibrium analysis, allowing to establish the characterization of the anisotropy rosette and the rock bridge percentage.

1. INTRODUCTION
it is important that when studying rock mass geomechanical behavior in slopes, its characterization includes the effect of discontinuities and their possible effects on stability at both the inter-ramp and global scales in an open-pit mine.
Structural domains play a significant role in this study, representing in some way the strength of the rock mass, whose preferential orientations promote the formation of instabilities. The orientations of the discontinuities create a kind of network that translates into a final rupture surface, where rock bridges define an equivalent structure or possible instability mechanism.
The final rupture surface includes both discontinuities and rock bridges, allowing the definition of an equivalent structure (Fig. 1). Generally, to estimate the shear strength of these equivalent structures (which conditions slope stability), a stepped path simulation is developed considering the properties of structures oriented sub-parallel to the slope (unfavorable).
Enabling Geomechanical Insights from Drilling Data: Automated and Data-Driven Proxy Mechanical Earth Modeling
Authors: Jeong C. , Lin S. , Reyes A. , Sharma V. , Wendt A. S. 
Published: August 2024

ABSTRACT:
The energy industry has acknowledged the intricate relationship between mechanical drilling and subsurface geomechanical parameters. However, establishing an accurate connection between these parameters remains technically challenging. Constructing a mechanical earth model (MEM) and utilizing it to predict or monitor mud weight window (MWW) boundaries currently necessitates log data acquisition, processing, and significant expertise in data interpretation, modeling, and correlation identification. To simplify MEM and MWW construction and reduce reliance on log data, an automated and drilling data-driven workflow is proposed. This involves a systematic exploration of the relationship between mechanical specific energy (MSE) and unconfined compressive strength (UCS) to identify the most relevant MSE to UCS model(s). The workflow includes data segmentation for scaling and fine-tuning related parameters such as well inclination, hole conditions, and geological formations, change point detection for transition patterns, and integrative machine learning for optimal correlation modeling. The resulting correlation model(s) can then be utilized for well planning and real-time MWW monitoring, offering a significant advantage in scenarios where LWD or wireline data acquisition is limited.

1. INTRODUCTION
The energy sector has acknowledged the intricate connection between mechanical data obtained during drilling and the geomechanical conditions of the subsurface. This acknowledgment is supported by empirical and physical correlations that explain how subsurface formations react to the drilling process. These correlations have been pivotal in recent decades, leading to the development of effective workflows for deducing rock properties
Mechanical specific energy (MSE) is defined as the amount of energy required to destroy a unit volume of rock and was proposed by Teale (1965) for the rotating drilling systems in the mining industry. MSE measures provide a quantification of the total energy input into drilling divided by the volume of rock destroyed over a given timeframe. This approach was defined in the following formulations (Eq. (1) to (4)).
(equation)
(equation)
(equation)
(equation)
where WOB = weight on bit, RPM = rotational speed, AreaB = borehole area, DB = bit diameter, ROP = rate of penetration, and T = torque.
After Rabia (1985) applied the concept of specific energy for bit selection, various studies were performed to broaden its applicability. Pessier and Fear (1992) sought to quantify drilling problems, and Graves et al. (2002) summarized and tested multiple published MSE equations to enhance drilling methods. In a pilot study, Dupriest and Koederitz (2005) reported that the average rate of penetration (ROP) increased by 133% for six rigs when using MSE surveillance.
Tensile Strength of Serpentinized Harzburgite
Authors: Asem Pouyan , Bažant Zdenek P. , Matter Juerg , Labuz Joseph F. 
Published: August 2024

ABSTRACT:
Ultramafic rocks play an active role in geologic processes including the carbon cycle and serpentinization reactions. Many of these processes accompany mineral transformations that result in volume increase of the product phase (e.g. serpentinization, carbonation). Accommodation of changes in volume is often associated with formation of fracture surfaces as new minerals form. Thus, fracture properties such as tensile strength or fracture toughness are of interest in analyses of volumetric deformation during mineral replacement. Cores extracted from Oman ophiolite were used to measure the tensile strength of the ultramafic matrix. A specimen of serpentinized harzburgite was machined with one notch and used for a three-point bending test within a closed-loop, servo-hydraulic system with crack opening displacement (COD) as the feedback signal to achieve controlled fracture. Acoustic emission (AE) was used to provide additional details on the nature of crack propagation.

1. INTRODUCTION
Coleman (1977) and Evans (2004) argue that an increase in volume during serpentinization of peridotites can be explained by immobility of Mg or Si (i.e. similar MgO/SiO2 ratios between protolith and serpentine equivalents) and formation of brucite. Field evidence of kernel structures (O'Hanley 1992; Evans 2004) is also in favor of volume increase during hydration processes. Hess (1955) suggested hydration of peridotites below the Mohorovicic (Moho) boundary can cause ocean floor rise, where the volume increase is equal to the volume of water added. The reaction describing the formation of serpentine minerals in closed system (constant composition) can be written to conserve Si and Mg as:
(equation)
The reaction in Equation (1), however, requires (i) continuous circulation of hydrothermal fluid in the rock mass, and (ii) access to fresh minerals enabling dissolution and precipitation to move forward. Potential clogging of the fracture network through vein formation, therefore, can stop the processes of serpentinization or carbonation if the hydrothermal fluids carry dissolved inorganic carbon resulting in dihedral angles greater than 60 degrees (Watson and Brenan 1987).
Accommodation of changes in volume is often associated with formation of new fracture surfaces as new minerals form. Thus, fracture properties such as tensile strength or fracture toughness are of interest in analyzing of consequences of volumetric deformation during mineral replacement processes. We designed a suite of experiments to investigate tensile strength of a harzburgite, where evidence for present day serpentinization and volume change has been documented (Evans 2004).

2. THEORY
Formation of fracture surfaces in the matrix surrounding the ultramafic mineral undergoing serpentinization or carbonation and hence volume increase requires local stresses to equal the tensile strength of the matrix. The nominal strength, i.e. nominal stress at peak load, of geometrically similar specimens can be defined as (Bazant and Planas 1998):
(equation)
Study on Adsorption Characteristics of Micro-Nano Proppants in Fractures and Related Numerical Simulation
Authors: Lu C. , Zhu Q. Y. , Li Y. , Luo C. , Liu T. B. 
Published: August 2024

ABSTRACT:
In hydraulic fracturing, micro-nano proppants can easily enter microfractures for support and have strong adsorption properties, so it's very important to explore their adsorption in micro-fracture support. By analyzing the forces of the proppant in fractures, a mathematical model of the microscopic interaction energy between the objects of action was established to calculate the microscopic interaction energy level of hydrophobic micro-nano proppant and water molecules, and then reveal the adsorption process of micro-nano proppant on fracture wall and the competitive adsorption mechanism between the fluid (water). Finally, FLUENT-EDEM was used for numerical simulation verification. The forces of micro-nano proppant in microfractures mainly include fluid drag force, settling force, van der Waals force, electrostatic force and hydrophobic resistance. The competitive adsorption process with water can be divided into three processes: closing to the hydration shell, breaking through the hydration shell and being adsorbed on the wall. To overcome the resistance to break through the hydration shell mainly depends on electrostatic attraction, and being firmly adsorbed on the fracture wall depends on hydrogen bonding. The above research can provide theoretical guidance for the design of micro and nano proppants and the application of effective microfracture support technology.

1. MICRO-NANO PROPPANT
At present, many reservoirs, especially the dense unconventional reservoirs, the fracture size formed after fracturing is very small, even up to the micron, nanometer level. Conventional proppant particle sizes are unable to enter induced and naturally occurring microfractures, so the microfractures close, reducing the conductivity of the reservoir fracture network and inhibiting its extension and expansion. To achieve effective fracture support, micro-nano proppants can be used.
Micro and nano proppants were first defined by Bose (2015) in sizes ranging from 100 nm to 1mm. Guo et al. (2022) defined it as less than 140 mesh proppant, while most defined it as less than 100 mesh proppant (Calvin et al. 2017; Danso et al. 2021). Micro-nano proppants are usually SiO2, small in size and light in weight. Scholars (Khanna et al. 2013; Keshavarz et al. 2014; Dahl et al. 2015; Li et al. 2020) have proved through experiments that micro-nano proppants can enter micro-fractures for effective support. Dahl et al. (2015) used ESEM microscopy to capture microproppant clusters or aggregates adhering to shale fracture surfaces, forming partial monolayers. This shows that micro-nano proppants have adsorption properties during migration in fractures, so it is of great significance to study the adsorption properties of micro-nano proppants for their application in oilfield.